Tire recommendations/tests, wheels,
spacers, nitrogen, tire wear, hydroplaning, ETC! ...MOSTLY for BMW Airhead Motorcycles.
PLUS things you never knew about tires;....etc!
© Copyright, 2014, R. Fleischer
article #54, section 5
It is difficult
to maintain a list of recommended tires, due to
changes in what is available, and what I have ridden and tested. This article
is kept as up-to-date as I reasonably can. As I get older, I am doing less testing, and less
vigorous testing, but my normal testing is...or was.. often considerably more vigorous than that of many riders. I will clearly state when I have less experience or no experience on a particular tire. In the past I have I not often included other's remarks about tires I have not personally ridden ridden on & tested. Beginning Spring of 2014, I now have a few people, whose tire testing mirrors mine close enough. I will be including their input now and then.
I list a number of discontinued tires, on purpose.
>>>A lot of information on Tires, wheels, ETC.... is located in:
MORE information is in other sub-sections of main listing #54. Don't miss them!
1. Some types of tires do not work well on Airhead
motorcycles. Radial tires are
not recommended. Radial tires do not generally come in Airhead sizes; particularly the twin shock
Airheads. For the
Classic K-bikes, radials seem to work OK, generally anyway. Sometimes they
2. LOW profile tires may not work well, & many simply don't properly fit Airheads. Generally a "90" profile works best on all but the last Airheads. SOME 80 profile tires will work on earlier model bikes. The frame & suspension were designed by BMW to work hand in hand with certain tires, and for that reason, BMW used to issue bulletins with names and models of tires that BMW had TESTED and APPROVED; that has not been done for Airheads for many years.
Many if not mostly all, of those tires from the seventies, eighties and nineties, are no longer available, except perhaps for a few, including the classic Continental RB2 and K112, for which the front unfortunately follows rain grooves. Rain groove-following is a problem with all straight ribbed front tires. There are tires made now that have only one center rib, it is usually wider than the old narrower grooves....and these new types are better on rain grooves. Tires withOUT these of any sort generally do not follow rain grooves. Some folks are bothered by the feel of the bike when the tires track rain grooves, others are not. Bridge gratings are another instance....and can cause goodly pucker factor.
I have personally ridden on quite a few modern tires, besides the old old tires, and find few that do not work reasonably well. 'Work' here, to me, means good road handling, predictability of handling in various situations, indication to the rider of what the tires are doing AND GOING TO DO; as well as comfort, load carrying, traction in cold/wet/dry and not unreasonably different in handling between wet and dry. The thing usually discussed, MILEAGE (tire wear), is NOT the most important characteristic for most riders! ...although for some folks, who put on large mileages, mileage CAN be of prime importance...so I do get into recommended tires for mileage.
I like to test tires in a variety of situations, from mild to very aggressive riding, and I like to test them on asphalt and concrete paved roads as well as gravel and hard-pack, and occasionally rather soft stuff. My testing is, perhaps, unusual. I have available to me very specific roads and places near my home, that I CONSISTENTLY use for testing that offer a wide variety of surfaces and conditions. I test in below freezing temperatures, as well as hot summers. When a favorite road or section of same, that I use for testing, is repaired or re-paved, I take one of my personal bikes out on it, to see if any changes show up. I have made a point of trying to ride when it rains.
3. NOTE that 'classical' BMW handling
is had GENERALLY & LIKELY ONLY with the original type of tires in original
sizes. This is particularly so with the older models that had 3.25
x 19 front tires and 4.00 x 18 rear tires. The only tire (that I
NOW KNOW OF) that has the
classical ribbed front, and matching rear, with exactly correct sidewall
stiffness, ETC....that will duplicate the 'original
ride' ...is the Continental's, mentioned above, the RB2 front
and K112 rear tires. Some Metzelers will have such handling if still in production, but I have not seen them in many years in the USA. In order for a full classic experience ride, do use the same types that were designed to work together as a set.
It is possible that some ChengShin tires will also exhibit the classic feel. Bridgestone has the Accolade tires, front is ribbed, but I do not have any experience with them.
NOTE: Some tire sizes are getting harder to find in INCH sizes. While a number of the old sizes, such as 3.25-19 are available from several manufacturer's, some are not very common. An example is the 3.25-18 used on the R45 and R65. Try: http://www.durotire.com/
........and click on CLASSIC (or similar word).
Not many ride on original type of ribbed front types. They do tend to follow rain grooves, contrary to what is said in some Clymer's publications. Still, you MAY want to try a set, as they DO deliver that classic ride and handling that the bike was designed-for; and ...note here, that these tires generally work best at the originally recommended by BMW tire pressures (label was under the seat, see your owners manual too), or slightly higher (typically by 2 psi front, 3 psi rear). I recommend that if you run these classic tires that you inflate to the TWO-UP and/or high speed pressures shown in the Owners Booklet. These tires give reasonably good mileage before they wear out. If you have a modified suspension, the classic ride and handling will be modified.
4. MANY 'modern' tires require considerably higher pressures than stated on the tag under the seat or in the owner's manual or in some tire manufacturer's literature. Failure to inflate to these higher values will give you lousy handling; the tires will feel like they are rolling off the rim, etc.
5. THE TIRE PRESSURE LISTED ON A TIRE SIDEWALL IS NOT THE RECOMMENDED TIRE PRESSURE. IT IS A MAXIMUM TIRE PRESSURE, BASED ON WHATEVER STANDARDS THE MANUFACTURER USES FOR THE CARCASS CONSTRUCTION. I treat tire pressures a bit more in-depth in article 54, sub-section 12: TireRepair.htm in a section 4 near the bottom of that article.
6. NOTE: When the rear tire 'squares-off', & some do this rather faster than others (dual-compound tires are better at not squaring off fast), handling can be poor in curves, particularly fast changing twisties. INstability (wobbles) can be very apparent with a squared rear tire. See: instability.htm
|I will no longer be doing the extremely aggressive two-wheeler tire testing that I used to do. As I enter my late seventies, I have decided to 'cool down' my testing aggressiveness. While I have not dropped a bike, I would heal slower if I had an accident, and age eventually has effects. Another problem is that I am not as strong as I used to be; don't weigh but 148, and have trouble horsing a 2-wheeler around aggressively (especially in deeper sand and dirt). MY idea of aggressively is close to race aggressiveness, nearly dirt-riding style on pavement.
I originally had set a date of age 80 to stop doing all serious testing; and, to stop riding 2-wheels entirely. That would have been late 2017.
I may even hold to this :-).
As it is, in January of 2014, I disposed of the last of my 2-wheelers.
Testing on 2-wheelers has not stopped, however, and has lately be done on borrowed bikes. :-)
I still have fast reflexes and excellent eyesight. I am blessed in living in an area that has a variety of terrain, including all sorts of types of twisties in mountain passes. I even have some deep sand areas (that were set aside for motorcycles), approximately 3 miles from my home. My paved-road testing area gets rain, snow and ice. In the past I have tested tires extensively on 2-wheelers as well as some on sidecar rigs, not just my bikes and rigs either.
So.... I am still, for awhile, doing some aggressive testing, using other folks' bikes for the 2-wheelers. My past testing nearly always included deliberately sliding the tires (yes, front and/or rear, depending on the situation), and braking performance on wet (and sometimes icy and snowy) roads. I also will continue to test road tires OFF ROAD, in moderate to hard-pack dirt, gravel, and sand (likely even if I quit street riding on 2 wheels).
MUCH of what I hear and read about tires seems to be based on nothing but thin air, or ...the owner has purchased them and WISHES they tested as he says they do. I realize this is cynical, but it is the truth.
In general, about 1/3rd of the tires I have in this article have been tested for MILEAGE by me; otherwise, it is reported by at least several others. I may note which is by whom.
Tires by brand and description of performance:
Avon: I am not a fan of the Avon AM26 Roadriders in
moderate to deep rain and don't
like the AM20/AM21 either; the Avon Roadriders DO, reportedly, seem to get very good
mileage! Some have reported the opposite. I am not surprised!
I have done NO testing. here have been what I consider too many reports of tire cracking
on Roadrider tires, even in the tread area, however, there are no reports of actual tire
Dual-sport riders: the Avon Gripster AM24 has been around for a LONG TIME, a WELL-
proven tire, it is a fairly good street tire, if a bit noisy, stick WELL in cornering, quite
stable for a tire this aggressive, and not bad in rain either. Work pretty good in off-road
gravel and hard pack, fair/poor in mud, & are, perhaps, a bit rough/hard feeling. I suggest
using about 31 psi front and 35 psi rear for all-around use.
These are possibly not quite as good as the Michelin Anakee for street and dirt.
The Continental TKC 80 is better than the AM24 off-road.
Avon's Distanzia AM43/AM44 tire is much more of a street tire, decent in the rain, only
fair off-road, but fine for the street rider who ventures off the road on occasions.
This is the Avon Distanzia (front)
NEITHER of these two Avon tires would be my choice for a bit deeper or rougher
off-road dual-sport work.
Both the Gripster and the Distanzia are primarily paved road tires, with modest to
good off-road capability, the Distanzia having the edge for the street & life, at maybe
1/3rd more cost. The Gripster is a quite decent tire for the person who is primarily a
paved-road-rider, yet ventures off the road now and then, who may even be a bit
aggressive off-road. This AM24 is a darn-good all-around tire, and works well in
anything but mud (keep in mind only VERY aggressive tires work in mud).
Bridgestone: S-11 Spitfires (tested: 110 rear, 90 and 100 front). ONE of my favorite ROAD tires,
all things considered. I first tried these quite a number of years ago on a SWB R75/5, and
really liked them. Very predictable handling in all conditions, although like any road tire
they are not for deeper soft stuff. Decent mileage & good grip on pavement. A
dual-tread-compound construction is part of how they get the performance. Use the
90-90 or 100-90 front if using 19 inch (pre-1977 bikes need a wider fender mount for the
wider 100-90 tire, 46-61-1-234-907, this is common to all brands). Use 110/90-18 rear.
There is also a 120/90-18 rear (not generally recommended by me for twin shock models,
especially the rear drum brake twin rear shock models). S-11 tires are also available
in sizes to fit the much later Airheads and also K bikes. Highly recommended
by me for many years now. Hard to beat the over-all mileage and performance for the $.
I really like these tires on Airheads and K bikes. Because of my extensive experience
with these, I use them as comparo's.
My 1984 R100RT got 10,600 miles on the last REAR S-11 tire, and the bike is driven at
goodly highway speeds, not babied. The tire still showed tread that was usable, but it
was down to about 1/16" or so. A good tire for all paved roads, and decent in rain, and
quite OK for those that ride relatively aggressively. Cheaper than many tires. For
those that do mostly highway riding the S-11 tires are quite good because the
dual- compound rear tire does not tend to flat-square quickly, although, like all tires, it will,
eventually. Squared-off rear tires can lead to high speed weaving and other instabilities,
even dangerous types. Again, note that this happens with ALL rear tires.
NOTE: The Michelin Pilot Activ, available in INCH sizes, may be competitive to the S-11
and maybe BT45 for performance, if not price. I may have more to say about the Pilot
Activ later....so see below for Michelin.
BT-45: Another Bridgestone dual-compound tire. Probably a bit better than the above
S-11 in WET conditions, and maybe in all conditions, but at a large $ increase. I do NOT
think them worth the substantial extra cost. HOWEVER, you might. These tires perform
well under all road conditions.
Bridgestone has the Accolade tires, front is ribbed, but I do not have any experience with them.
Cheng Shin: Chinese-made, the brand used to have a bad reputation for problems. That is NOT
SO now. These are good tires delivering OK performance, at a low price.
The 906 model is quite similar to the Metzeler Laser ME33, and it matches well with the
907. Decent tire in both wet and dry. I have not tested many Cheng Shin tires.
Continental: Old TK 16, TK17, NOT recommended. Especially 120 size, which is much too wide
for ANY dual-shock airhead.
Continental TKH23 front and RKH24 rear are long life tires, available in 3.25H-19 front
and 120/90H-18 rear. I cannot remember if that rear can be fit, it might have the too-wide
fit problem as the TK17. BUT, they make this tire in a 4.00-18 rear...and it DOES fit.
Otherwise, decent tires, reasonably priced.
The TKC 80 is truly for dual-sport use and is decent-enough on pavement, even in rather
aggressive riding, although feels a bit squirrely to me. Limited sizes available...several in
17" for rear and 19 and 21 for front. More sizes might be available as time goes on.
This tire grips OK on pavement, on gravel, dirt, even reasonable on mud!!! It is a much
better choice for those going off-road more often....yet retains good performance on the
street, wet or not, even OK on snow! One of my favorite all-around dual-sport tires. It
corners good and has a relatively LONG LIFE, contrary to naysayers.
It is also fairly quiet, and inspires confidence in how it FEELS. Really good tire. I think
MOST riders, no matter the model of BMW, will like this tire, even if you are a street rider,
and you do half your riding truly off-road. If you want all-around performance in a tire that
will be capable of any surface, even a bit of mud, this IS THE ONE. Original equipment
on some BMW models. Drawback: expensive.
This is the Continental TKC80
If you like the TKC80, you might also want to try the TrailAttack. You also may want
to look at what I say about the Kenda K784. I have NO experience on the TrailAttack, and
RB2/K112 (also TK22): Original types used on the OLD airheads as ORIGINAL equipment.
I have not ridden on any in many years; I always disliked the way they followed rain
grooves...but they do...or at least did....offer the classic BMW soft ride, last pretty good,
and used with original 'high-speeds, two-up' tire pressure settings, are good. See
beginning of this article about pressures.
Owners of early airheads that came with the 3.25-19 front and 4.00-18 rear tires as stock
sizes should try a set of these Continental tires.
((Note: I don't purchase Continental tires myself due to how they treated my shop when
they had a bad batch of tires, many decades ago. But, I do NOT in the slightest want to
discourage YOU from trying these tires, as you may very well love them)). For the
Classic Ride feel & handling, I DO recommend these Continental RB2 & K112 tires. If you
intend to ride on classic type tires, I also suggest you try the classic old Metzeler tires
like the ME11, etc. BMW offered Metzelers in the old models/sizes, besides Continental's.
This is the Continental RB2 (front)
Classic Attack: This is a new type tire from Continental. Continental says that they
specifically designed this tire, A RADIAL 0° type, to enhance and sharpen the handling of
older classic bikes which were originally designed for bias-ply tires. I have not yet tested
these tires. From a look at the tread pattern, I think the tires will NOT track rain grooves,
and should feel FINE. The tire is supposedly fairly high mileage and excellent grip and
fast break-in. Reports welcomed.
The tire is available only in metric sizes, as far as I know. The 100/90R19 57V TL size is a
front tire, and is expensive, although discounts are available. That tire, like all of that size,
will possibly not fit earliest Airheads without the proper later fender brace,
46-61-1-234-907 from the 1977-1980 /7 series. Probably will need the later fender too.
The tire, last time I checked, was made in only 3 sizes, the other two sizes are
110/90R18 61V TL and 120/90R18 5 65V TL, these two are designed for rear use. NOTE
the load rating on these tires, compare to your previous and other tires. Note also the
"TL". These tires are V rated and if used with tubes, you should reduce the speed rating
by one step. That's FINE for Airheads. Some riders who have tried these LOVE THEM.
Continental Attack Classic Radial: NO personal testing information yet.
Dunlop: Vintage K70 front,
3.25H-19; K70 rear, 4.00H18/.
Somewhat similar in some respects: Dunlop F11 front 100/90H-19; use it with a K627 rear
110-90H-18. Reasonably OK, obsolete now.
K491-Elite II: This is a Premium tire, premium priced and a VERY long lasting VERY high
mileage tire. Pretty fair wet handling too for such a long lasting tire, and good on rain
grooves and reasonable IN RAIN. Get the 90-19 front (some 100-90) and 110/90-18
rear. The oversize 120/90 rear should also fit the early eighties Airheads. Tire has
probably been discontinued.
TrailMax Dual-Sport: can't recommend these; pretty lousy off-road.
D606: This is a good mixed use tire, for tarmac AND off-road. It is priced in the lower
area, and is good on road and off-road....with an emphasis for off-road. My limited
testing found some high speed instability, but I did not have time to test pressure
changes nor loading in that regard.
Good performance for the cost. I think the Michelin T63 is better.
GOOD TIRE...and you may MIGHT like it over the Conti TKC80.
Kenda: K784 Big Block. So-so on pavement, pretty damned good off-road, even quite good
in mud. Wears relatively fast...to be expected for good off-road and even mud type tire.
Maxxis: C6011 is good, not sure if it is available in the 18 inch now. See Cheng Shin comments.
Metzeler: (see Continental, RB2/K112, for comments regardin gthe Metzeler ME11)
ME33 Laser: both standard & the low profile metric. I recommend the 3.25 or 3.50
front. If you have gone to an oversize rear, use the oversize front. This tire will follow
some types of rain grooves, but NOT as badly as a ribbed front tire. You can use this
front tire with many other rear types. Decent in the rain, good dry grip (WAY beyond your
bike's capabilities). For mileage, you can expect lower to mid values. Some tendency,
sometimes, to cupping. The ME33 tread design was unique when introduced, and has
been copied by others. It has a lighter faster turning 'feel', and almost always can be used
with just about any rear tire design. There was a K compound version that was, well,
good enough to race on!
Lasertec: I do not like this tire for the average
rider. It is twitchy, and gives an unstable
feeling. Hard aggressive riders might want to try it, but I pushed the tire pretty hard, and
still don't like it. This tire does NOT feel like the ME33 to me, either. I cannot recommend
this tire due to one particular problem: They tend to follow rain grooves....likely due to its
single circumference groove (or multiple wiggle type) groove(s) in the center of the tire.
ME55: An old favorite for some, was also available in 120 size for the rear. I never liked
this tire, although it gave a good compromise on handling and mileage.
ME88: Front and rear versions. Good mileage tire, pretty good handling too; one of my
old favorites for use front and rear, and also works well as a rear, with ME 33 Laser front,
for more aggressive paved road riders. Discontinued...booo hooo.
ME880: NO personal tests yet.
Tourance: OK on the street, not so good on gravel and hard-pack dirt. The Michelin
Anakee is probably better all-around, by a bit, wet and dry, for dual-sport.
Enduro tires: Metzeler
has a selection of these tube type tires to fit older airheads.
Enduro 3 (Sahara or Sahara 3) is a good one for mixed on-off road. It is premium
priced, however. Watch the WIDTH....Enduro tires may be MUCH wider than their size
might lead you to believe, and thus may not fit on twin-shock models, due to clearance
problems. Nearly every motorcycle tire manufacturer has its own enduro tires.
Metzeler MCE Karoo: These are good GS type tires for off-road, fairly decent on
pavement. I suggest you don't mix other types on the same bike. For pavement
use, especially if the weather is cold, let them warm up before getting aggressive with
them. Many might equate these tires with the Continental TKC80, I think them only
somewhat similar. There is now a Karoo 3...no information nor testing by me, yet.
Macadam 50 & 50e. 100/90-19 & 3.25-19 front; 110/90 & 120/90 & 4.00 all in 18 inch rear.
Some really liked these. I don't have enough miles on them to say much.
The Pilot Activ replaces the Macadam. The Pilot Activ SEEMS, in LIMITED testing by me,
to be better for wet streets, handles better, reports say longer life, and that it may be
comparable to the Bridgestone BT45. In 2013 I installed a rear Pilot Activ 4.00H18
on the REAR of my R100RT, and did mild testing. The front was still a 3/4 worn
Bridgestone S-11. I intended to later install a front 3.25 H19 Pilot Activ, & do testing all
over again. However, I sold the bike in January of 2014, but I expect the very experienced
new owner will install the Pilot Activ rear tire immediately.....and I may ride the bike myself
in the future. I will say that the REAR Pilot Activ worked nicely with the very different
tread profile on the front worn Bridgestone, and with different pressures too.
Previous tests on someone else's bike, with BOTH tires being Pilot Activ's, were not
extensive enough for me to say much more at this time. I had a miserable time trying to
mount the Pilot Activ 4.00H18 to the 84 R100RT rear snowflake wheel. One side went to
the rim bead area OK, the other VERY difficult. Because of this, I modified my air
equipment AGAIN, and then it went on OK. I added the new information to my
tire repair article. This tire is very stiff in the sidewalls, even the tread. Do not be
discouraged by these remarks. This tire has a very well-made bead edge, which should
offer better sealing on a tubeless rim than others...but a tubeless rim and a tube type
rim do NOT have the same shape for the bead area...the angle is 9° different, for
instance. For those who use a tube type rim AS tubeless, I think this tire will do better
than many others in the instance of an air leak or flat. This is speculation on my part.
Such usage is not recommended by many. There IS an article on this website,
section6.htm, about such usage. CLICK
***NOTE: I used standard Michelin Butyl tire tubes for my testing.
The Anakee 3 is different from the Anakee 2. The 3 is for mixed on
road, and seems pretty good all-around until you get into mud, where it's poor. Emphasis
is on pavement riding. EXPENSIVE. May be difficult to mount? Competition for these
tires are the Continental Trail Attack, the Avon Distanzia, and Metzeler's Tourance.
T-63: For more aggressive off-road riders, handle decently on dry pavement (not
too bad on wet roads either), and probably one of the best buys for mixed use (dual-
sport, with a fair amount of emphasis towards off-road). The T63 is a truly good tire.
It is also less expensive than much of its competition. This tire has a moderately
aggressive enduro tread, so unless you do off-roading, don't get it. This is NOT the
tire for quite heavy loads, quite high speeds, coupled with very hot asphalt.
NOTE: I have ridden only about 40 miles on a bike equipped with these, but someone
I trust has also reported to me about them, and we have the same opinion. GOOD tire.
While the tread looks pretty aggressive, the tire is somewhat milder than it looks.
Pilot Road 2: Seem to be excellent on Classic K-bikes...very limited experience here.
Pirelli: Scorpion: cannot recommend for
GS....but have few miles on them. Some reports
say they exhibit wobbling if mixed with other tires, but I have no definitive information.
Sport Demon: reportedly will change handling for the worse AFTER some miles
are on them. NO personal experience.
Shinko: NO PERSONAL aggressive testing yet. One report from someone whose riding skills are
very good, and can ride hard enough to test tires reasonably well, likes these, &
compares them to vastly more expensive tires.
This is the "everything else" section of this longish article:
1. Some folks have trouble understanding tires sizes. On metric tires the first number is the width in mm on a nominal width rim, the second number is the aspect ratio of the sidewall to tire height. Metric sizes and inch sizes are not exact equivalents. GENERALLY speaking a 3.25 inch size as originally specified can be substituted by a 90 metric (often coded as MJ); a 3.50" by a 100 metric (MM); a 3.75 or 4.00 by a 110 metric (MN or MP); and a 4.25 or 4.50 by a 120 (or MR).
There WILL BE handling differences if you do not use the
originally specified tires. Those that have heavy loads ...may well
want ONE size oversize tires. It may well behoove you to look into the load carrying
capability of your proposed new tires...usually molded/printed on the sidewall. SOMEtimes a larger tire is rated for a LOWER!! load.
Using a stock rear tire, let us say 4.00-18, with a substantially oversize front tire, is not the best combination, as the bike
will PROBABLY have a tendency to fall into turns a bit; but I have NOT found
that at all excessive if not going to big.
As I noted; sometimes an oversize tire will have LESS load
capacity, and you MAY have to look at the manufacturer's technical date to
find this out.
***SOMEtimes an oversize tire will have LESS contact patch on the ground....due to the round profile! Do NOT willy-nilly increase tire sizes!***
IN GENERAL: OK for a 3.25 front to be 3.50 or 90/90 or 100/90; and, OK for a 4.00 rear to be 110 or 120. There is a 4.10 size that MIGHT work, but I have NO DATA, NO EXPERIENCE. I also have very limited information on using 80 profile tires....Aspect ratios of 80% will NOT always work on early Airheads. It is often a matter of the sidewall characteristics not just other fitment problems. Most of the early Airheads came with inch size tires: 3.25 x 19 inch front tire and 4.00 x 18 inch rear tire. For some time FEW tires were made in those sizes, but availability has improved, surprisingly! In general, these old sizes were in what, today, is called a 90 profile, but are not-so-marked. Some were closer to an 80 series. NOTE that the old Airheads did not come with enduro tires, and I mention this because most enduro tires in 4.00 x 18 will be VASTLY wider than a 4.00 x 18 paved road type of tire. An enduro tire may well NOT fit on twin shock Airheads, not enough room between tire and driveshaft housing. This is particularly so on those before 1981. These can have a wider right side of rear wheel spacer installed, and BMW even sells such, but that may not help enough. For the front tire, which came as a 3.25 x 19 (and in some cases, like the 18" on the R65), you can usually go to 3.50 x 19 or metric 100/90, but you might have to use a later seventies fender mount. More much later in this article on that. A 90/90 or even 100/90 on the front, and a 110/90 on the rear is very common on Airheads. In some instances SOME 120 will fit the rear; BUT, sometimes (pre-1981 for instance) one has to get the wider 10.7 mm spacer for the right side of the rear hub...BMW part number 36-31-2-301-737. That spacer change has been needed sometimes for 110, but not often, but more often for 120. Stock was 9.2 mm, and was 36-31-4-038-142. The spacers are VERY easy to install, and do NOT affect bearing preload. A few 120 rear tires fit rather tightly on drum brake models; that is, the wheel with tire mounted to it is a bit difficult to install, and at least deflating it is needed. NOTE: BMW uses 'top hat spacers', or call them brimmed spacers, at various places in the bikes. You will find them at the swing arm sides, and the wheels. One top hat spacer under part number 36-31-230-322, was originally an exceptionally WIDE hat type, and this spacer has been sometimes used to space the rear wheel to the left even more. That spacer is 12.9 mm wide, and the hat is nearly 32 mm in diameter.
The part number used by BMW for some of the top hat spacers at the swing arm bearings is different than the almost exactly the same 9.2 mm part used at the wheel bearings. They are usable however!
BMW modified the REAR WIRE SPOKED wheels for extra clearance, and this was done in the /5 days, as well as the ST and G/S days, and it was done by offsetting the spokes; details elsewhere's on this site. While many think that the ST and G/S 3 mm offset change came when the REAR wheel went to a 2.50 from a 1.85 size, this is not so, it was later on after that change.
2. The rear fender can be modified,
hardly shows, makes tire changes easier. CLICK for a photo. In general,
120-18 rear tires on twin-shock airheads are not recommended by me, but also not
recommended against.... although I certainly have had a lot of them on my
various R100RT bikes.
3. The BMW tube-type snowflake wheels are "WM2" in rim SHAPE, and other articles of mine treat the use of tubeless tires withOUT tubes. Click here for that link, section6.htm. It is almost always OK to install a tubeless tire WITH tube into a tubeless wheel...but mentally reduce the speed rating by one grade, due to heat buildup with a tube.
4. Try not to purchase tires more than THREE years old, date codes are on the sidewall, showing week of the year and the year.
5. The maximum inflation pressure shown on the sidewall is for normal use, not for inflation to seat a bead (which is higher, just how much higher is subject to safety concerns). For installing tires I don't go over 60 psi, try to stay at 50 psi, and use lots of REAL tire lube. Generally the manufacturers will allow up to 50% over the sidewall printing for mounting....be cautious, if a rim explodes you MIGHT be seriously injured. THE secrets to seating a tire are to have the rim bead area CLEAN and SMOOTH, use LOTS of the RIGHT type of lube (REAL tire lube) and have the tire and wheel (and tube if used ) truly hot from being in the sun! ...AND!!!!....TO REMOVE THE VALVE CORE ....AND ALSO REMOVE THE TIP IN THE HOSE CHUCK. USE A 125+ PSI 3 GALLON+ TANK ON THE COMPRESSOR and large inner bore size fittings and hose. ALL THIS SO THE INRUSH OF AIR IS FAST. YES, the SPEED of the air inflation is a BIG secret! Even so, an occasional tire will prove to be difficult.
6. NEW tires are VERY slippery!.....allow 20-50 miles to scrub them off. I ALSO prefer to first thoroughly brush the tires with a fairly strong detergent and hot water mixture, and then flush the area, before first riding on them. I use a stiff bristled old-fashioned floor scrubbing brush.
7. Continuous speed rating is marked on the tire, usually as part of the number/letters of the tire size. Tires with deeper tread, sometimes they wear longer, sometimes they do not, from the same manufacturer, are generally rated lower in speed, and usually are the better buy for touring. If you do not ride at warp speeds, an H rated tire may be a much better buy than a V rated, as an example. MAY is the word here. Sometimes the only difference is TREAD depth....the higher rated tire having a LESS deep tread. This is not universally so. Another way of stating this, a bit differently, is that a higher rated tire is NOT necessarily a better tire...for YOU!
Here is a chart of what the letters mean (remember, if you install a
tube in a tire marked tubeless, reduce a grade):
Letter Km/hr mph
B 50 31
C 60 37
D 65 40
E 70 44
F 80 50
G 90 56
H 210 130
J 100 62
K 110 68
L 120 75
M 130 81
N 140 87
P 150 93
Q 160 100
R 170 106
S 180 112
T 190 118
U 200 124
V 240+ 149 note that some V or VR tires may be rated for OVER 149 mph
W 270 168
Y 300 186
note that there is a Z and ZR rated group, they also are over 149 mph like the V/VR
(A) Sometimes sidecar folks will use a tire designed for rear use, on the front. If you do so,
& the tire has a directional arrow, REVERSE the tire, so the direction arrow is in the 'wrong'
direction of travel.
(B) For sidecarists, 16 inch rims CAN be used for passenger car tires OR motorcycle tires (if rim
width is proper). Do NOT generally use or try to install, a 15 inch m/c tire on a 15 inch car
rim, nor 15 inch car tire on a 15 inch motorcycle rated rim. You MAY be able to use a 15"
car tire if the motorcycle rim is skimmed on a lathe or the car tire is a quite small one.
PLEASE HEED THESE WARNINGS!!
15 inch car tires and 15 inch motorcycle rims are NOT the same diameter!!! 16 and 17
inch seems OK. If you insist on putting a 15" car tire onto a 15" motorcycle wheel, the smallest
tires may work OK, the larger ones are definitely dangerous to mount.... YOU CAN HAVE A
CATASTROPHIC FAILURE! NOTE that some sidecar manufacturer's use 15" rims, and those
are usually actually made for small car tires.
9. There ARE reasons to NOT
screw the tube
valve stem nut
to the OUTSIDE of the rim:
(A). No allowance for tube movement if one has a leak, and the tire rotates on the rim some.
(B). If the tube seals to the rim too well, it can trap air from tube to rim, and allow tube chafing.
The purpose of the tube nut is to help DURING installation of the tube...and can be
discarded...or run up to the cap...after the mounting is done. These ARE NOT just my
ideas! I can quote from tire manufacturer's manuals...and a BMW bulletin...on these facts!
(C). BMW has had at least two bulletins out on these valve nuts, and one SI gave an additional
reason to have it up against the cap, that was that improper inflation could cause the tube
to be weakened at the valve stem and if the nut was at the rim, and not the cap, the stem
could disastrously tear out, suddenly. What BMW did not say, was that this comes from
very low inflation AND overinflation during seating of the tire.
10. Inflation is usually in psi (pounds per square inch), but some tires have it in BARS. Bar means BARometric pressure, one bar is atmospheric pressure, about 15 psi. NOTE!! ...manufacturer's like Metzeler used to have in their technical books, information that during mounting, the maximum inflation pressure (DO use plenty of tire lube!!) was 150% of the tire sidewall printed value. Manufacturer's are getting lawsuit conscious....and many now say not to exceed the sidewall printed value, or 20% or some such. Because 150% can be interpreted by some to be 150% on top of the original pressure, some manufacturer's changed wording to say 50% increase over maximum sidewall-printed pressure. You are on your own. I do not go over 50 psi unless I am forced to, and it is very rare indeed that I go to 60 on a motorcycle type tire. This is NOT an OK for YOU to do that! An exploding rim can kill you. Seating of modern stiff tires onto the rim is usually THE problem seen. USE LOTS OF LUBE, on a smoothly cleaned bead area of the rim and have the tube and tire hot from being in sunlight. MIND the hints I gave, on having things hot in the sun and using a modified chuck and no valve in the valve stem, and lots of lubricant.....this really really does work well.
There is an old "Rule of Thumb" that after a considerable number of miles, the cold temperature pressure in a tire should have risen to about 8% higher now that the tire is hot. That is generally true, but not all types of tires seem to conform, particularly some belted and radial types. Still, it can be a useful idea. Where this idea came from is actually the manufacturers of tires. If the pressure is too low, the tire will flex more, creating more heat, and if pressure is too high, the tire will not heat enough. Tires require the correct pressure for handling and life, etc. Sometimes when I relate this, someone will ask about tire temperature. Road tires are designed to run at ~130°C at the contact point. That is VERY HOT. That was NOT a typo, it IS degrees Centigrade. That contact point cools off VERY rapidly when you come to a stop, so you can pretty much forget about trying to measure it.
Many TIRE manufacturer's used to tell you the REAL tire pressure to use or try with their tires. Lawyers probably got involved, and most literature now just shows the motorcycle manufacturer's recommendation......which may be too low for Airheads (generally BMW recommendations are pretty much correct on the single sided rear end Airheads and usually any Airhead from 1986)...and NOT correct, seriously not, for modern tires on pre-1986.
BMW had the recommended tire pressure on a label someplace under the seat; and, in the owner's manual. Some later BMW literature upped some of the old pressures to SOLO 32-34 psi, both front and rear. That pressure is LIKELY NOT correct for YOU and YOUR riding, tires, conditions. I have found almost NO tires that should have 32 psi in the rear! Modern tires require higher pressures. 38-42 rear, 33-36 front.
11. Motorcycle tires have had for some time a LOAD index coding, something like 81H. The tires may eventually get the standard car tire coding of alphabet letters for wear and heat. If you pack heavily, perhaps you weigh a lot, and you have a passenger.....pay attention to the manufacturer's published information on loading allowed. SPEED rating is downgraded by one grade if a tube is used in a tubeless-rated tire. TL means tubeless....does NOT mean you MUST run it tubeless. - means bias ply; R means radial; B means bias belted.
12. Airheads came with a number of different rim WIDTHS and TWO GENERAL SHAPES. BMW used the WM2 rim SHAPE up until they installed tubeless tires, not officially OK with tubeless tires withOUT tubes. Many arguments abound about this subject. The WM2 rim does NOT have the 5 degree increased angle of the flat area inside and the side area...all of which the tire bead rest against. You are ON YOUR OWN if you fit without a tube, in a snowflake wheel designed for tubes. Rim width and tire size fitted must be within a range of values in order to not only fit into the fender/brace/etc; and swing arm on the twin shock models.....BUT...if a tire is too wide for the rim, the tire will tend to roll in turns, making for lousy handling. EVERY tire manufacturer has a recommended range of rim sizes for each model and size of tire. Those recommendations ARE correct. Early /5 rims were 1.85" on front AND rear. Later /5 bikes had 2.15" rear rims. The 1.85" front rim was carried along right up to 1984 on most models. The R80G/S had the narrow 1.85 front rim, and early ones the 2.15 rear, then came a 2.50 rear. Of course, those G/S also had a 21" front wheel. Some of the bikes came with a 2.75" rear rim...this was on the 1978-84 RS, R100S; and 79-84 RT with disc brake rears; the drum brake rear bikes in these groups were generally 2.50". With the Monolever and Paralever bikes, things changed with the rims again, with a new rim design, for tubeless tires withOUT tubes, etc.
13. Some have a hard time getting a pressure gauge onto the valve stems of the snowflake rims. There is a 90 degree stem adapter available from BMW, I don't recommend its permanent use though. FRANKLY I don't use them at any time. 71-11-1-239-258. Any of the stock type, 45 or 90 degree head, pressure gauges are fine....just check their calibration once in awhile. BMW also has a steel, chromed, straight valve stem, for use with tubeless (and for snowflake conversions, but this is NOT officially approved), it is about $4 from BMW...and is available elsewhere's cheaper. The BMW number is 36-32-1-452-748...and this part is vastly nicer than a typical small car or yard vehicle all rubber stem.
14. Most flats/punctures are on rear tires. MANY can be avoided....by simply putting a LONG mudflap onto the FRONT fender, the closer to the ground the better. Nice looking ones are available. You have to drill some holes, use screws, washers, nuts. What this flap HELPS to do (theory anyway) is to deflect road garbage being thrown backwards into the path of the rear tire. Hence, the type that hangs down the furthest is desirable.
15. Tire dating:
Tire sidewalls have a lot of information. One area shows the manufacturing DATE....on earlier tires, prior to year 2000, there were THREE digits... first two digits meaning the WEEK of the year, and a third digit for the year. In the 1990's, there was a small triangle to identify that it was made in the 1990's. Sometime during the 2000 year all manufacturer's changed to the 4 digit system, the first two digits being the WEEK of the year, and the last two digits being the YEAR. There is additional coding you may be interested in. There will be something like the following:
DOT ENYO VLK 1704. What you MAY be interested in is the two letters after DOT, in this example, EN. These can be looked up at http://www.harriger.com to find out what factory they were made in. I have PURPOSELY not listed the exact URL for the specific PAGE in that website, as INTERNAL links do not properly relate to outside full URL's.
Thus, if the tire code was 455, you know the tire was manufactured in the 45th week of a year ending in 5 (but it had to be 1995, if the triangle preceded). The reason only three digits was originally used was that the bureaucrats thought that tires would not likely be in service for over 10 years.
is a longer DOT code in use now. The DOT coding begins by some
letters and numbers. The first two letters identify the factory.
The list is at:
www.harriger.com/tiremakers.htm. The last 4 digits are
the week and year, as above.
NOTE that while DOT regulations mandate information on both sides of the sidewalls, you may have to look in two places and two sides for the ENTIRE identification numbers/letters. The original reason this was done was, supposedly, to reduce problems with the manufacturing and mould interference.
16. Recommended and NOT
recommended tire vendors:
a. NOT recommended: MAW (www.mawonline.com, Motorcycle Accessory Warehouse).
: Discount motorcycle tire and accessories.
b. OK; but pay
attention to shipping charges, sometimes if you buy TWO
tires shipping is
free. Pay attention to date codes.
Motorcycle Superstore, Medford, Oregon. Cheaper if order is over $89, free shipping.
SW mototires (no shipping if buying two)
Generally, BikeBandit has decent prices and decent cost for shipping. AMA members get
10% additional discount.
c. Don't forget to do a thorough Internet search; and, do NOT forget about your local
independent and even your BMW dealership.
17. Nitrogen: There is a lot of BAD information, or just plain hype, on the use of nitrogen in any type of tire for road (and off-road) use. The facts are, that while there ARE benefits, use of nitrogen to fill tires is NOT practical for anything but pure racing. On the plus side, molecules of nitrogen are larger than average air molecules. These larger molecules do NOT pass through the rubber used in tires and tubes as easily as common air molecules. Thus, pressure loss over time is lower. On a practical basis, the slower loss is NOT a BIG difference. A plus factor for nitrogen is that it is less prone to accumulate water vapor, and, is DRY when installed into the tire, not so 'outside air' from your compressor nor a gas station. Water vapor in common compressed air in tires can lead to rather wild fluctuations in pressure as the tire heats up, and cools down. Obviously, this is minimized by using clean, dry, air. Nitrogen is, due to its lack of extra affinity for water vapor, a safer, more stable tire pressure, which can be somewhat important for very high speed driving (much more so at racing speeds). The final good point about nitrogen is that it does not contain oxygen, which tends to degrade rubber compounds over long periods of time.
The PROBLEM with nitrogen is cost, not easily available, and if you top off the tire with even a very slight amount of compressed air, especially if the air is not dead dry...the advantage of the nitrogen is LOST.
****There are instances wherein someone uses a tube-rated tire without a tube. This happens on sidecar rigs when using tube-type tires withOUT tubes on snowflake and other wheels; this is usually done because of not wanting to use a tube. In some instances this is done with various motorcycle tires, but also done with two special sidecar type tires.... and, there are only TWO types of these square-profile sidecar tires available, as far as I know. One in 18" and one in 19", and not from the same manufacturer! (19"=Avon Triple Duty; 18"=Metzeler Block K). I have tried nitrogen in these tires in these situations, and it appears that tire pressure decrease is SLOWER.
Another usage is a tubeless tire used on tube-rated rims. While that brings up a whole story in itself, and has its own article on this website: section6.htm, I have done some preliminary testing, and leakage does seem slightly less with nitrogen. The bottom line, of course, is that almost none of you are going to buy or lease nitrogen tanks for use at home!
18. TIRE WEAR: The reasons for various "strange" tire wear....and why one side of a front motorcycle tire wears so much faster than the other side...and why downshifting for braking instead of using the brakes (downshifting for braking lowers tire mileage); and a LOT more, is in this article, which is decent enough that I never wrote such a complete article myself:
The only thing that is NOT well-explained, is why some two people with identical makes, models, and years of motorcycle, with the same make and model and pressure in their tires, and the same riding habits and styles....will, or can, have such different tire wear. I'm not going to get into that, HERE.
There are several types. It does NOT have to be on water! The TWO types of hydroplaning that YOU are likely to be concerned about are called (1) Dynamic Hydroplaning; and (2) Viscous Hydroplaning. Both occur on wet roads, although the viscous type might be said to ALSO occur on ice. You are unlikely to be much concerned with the other two types of hydroplaning, except maybe you might have a passing interest in the fact that if the brakes are used hard enough to STOP a wheel from rotating (and you are still moving), you MIGHT heat up the rubber at the contact point to where the rubber REVERTS to its PRE-cured condition, and then it just plain slides, like on ice.
Dynamic hydroplaning occurs when the water in front of the tire can not be moved away from the contact surface fast enough. The actual science deals with the water pressure 'being rolled up'. That pressure is opposing the pressure the tire places on the wet surface (the weight of the motorcycle normally on that tire contact with the surface). Various things have an effect on just when hydroplaning will occur. Effects from: softness and other factors of the rubber compound; road surface; tire profile; type of rubber; tread depth. All those things would seem to be 'common sense'; and, yes, they are; but not to the degree you may think. NASA did a LOT of testing, and their testing has since been re-proven by common motorcycle and car tire manufacturers, and the results are that a major variable in dynamic hydroplaning is from the PRESSURE in the tire. The depth of the road surface water NEED NOT be very much at all.
Hydroplaning CAN occur with quite deep tire treads ...at a speed, in miles per hour, as low as 9.9 times the square root of the pressure in PSI. The figure for nautical miles per hour is 8.6, usually what is seen in various publications (and not mentioned that it is nautical, and ALSO note that this is "STATIC speed"...and no explanation). If you are MOVING, the speed is LOWER! These points are almost never in any articles about hydroplaning! Once hydroplaning starts, it can remain for MUCH lower speeds. You are in danger of loosing control, from JUST hydroplaning, on a wet road, even with really good and deep tire treads, at speeds as low as 45 mph if inflated to 27 psi; and 56 mph if inflated to 42 psi. If standing water is fairly thick, these speeds are much reduced, although some say there is no difference...the REASON is that they are talking about CAR tires, or reciting from literature meaning CAR tires.
In any case, note that hydroplaning speed rises ...a good thing...as pressures RISE. This is exactly backwards to what some riders believe. They think that in rain, they should LOWER the pressures. Well, in one way, they are correct!...the bike will feel more jittery, less planted, with higher pressures (assuming here that the higher pressures are higher than the recommended pressures). Since the front tire is almost always the critical tire, and almost always has the lowest pressure, beware of excessive speed in the wet!.....you may loose control without using the brakes, and much more likely if using the brakes (even gently). I am well aware that most of you probably think if you LOWERED the tire pressure, it would either grip better on wet roads, or be less likely to hydroplane. Keep in mind that hydroplaning is just one factor, and you can easily loose control due to insufficient tread depth, high water level, oil on the road or floating on the water, wind from the side, and a host of other factors. What all means is that you can loose control at a VERY much lower speed than that for JUST the published hydroplaning speeds.
"Viscous hydroplaning" is the type, at least on your motorcycle, that you might encounter if the road was rather smooth and the tire getting rather bald. This can occur at very low speeds and VERY low amounts of water on the road.
If you are hydroplaning, it will be like riding on ice. It is my opinion that on modern motorcycle tires if your tread depth is at least 3 or 4 mm, then the MAIN influence on the speed at which hydroplaning will occur, is the tire pressure and the thickness of the water on the road. If you never ride in the rain, you won't likely worry about hydroplaning. It is also true that there are very soft special rubber RAIN TIRES available for racing. They have special treads, and a lot more, and are NOT part of my discussion, beyond this mention.
For common ordinary street tires for your motorcycle, some are better than others in the rain (or, just mildly wet roads). The manufacturer's literature MAY...or may not.... be helpful in this regard. I can say the same for anecdotal 'evidence'....that is, can you believe what fellow riders say about a tire? If a LOT of your fellow riders have run the SAME tire, and nearly the same pressures, and they live in really rainy areas...well, I'd take THEIR word about the best street tires for rain....over the manufacturer's claims, or from someone who rides gently once in a great while on damp roads.
GENERALLY speaking, the LONGEST wearing street tires are the worst for rain. BUT, this is not universally so. Some premium long-lasting street tires are quite good when it is raining.
20. Tire sizes; rear swingarm clearance, ETC. Much of this information is also posted elsewhere's in this website. It is shown here on purpose....and expanded upon a bit.
The original tire sizes for all the early Airheads was 3.25 x 19 front, and 4.00 x 18 rear. A FEW manufacturer's still make those size tires. Avon, for instance. Continental still manufactures the old RB2/K112 front/rear tires. I am not sure about the Metzeler 11, etc. MODERN tires need higher pressures than the OLD Metzeler and Continental tires that the bikes came with.
For those wanting to go to modern metric sized
rubber, the 90-90/19 will fit all the 19 inch front wheels, and the 100-90/19 will fit the
models front if the fender support brace is changed to the later
wider type. The later wider fender brace you would want is the
1977-1980 used on the /7 bikes.
The BMW part number is 46-61-1-234-907.
For the 110 or 120 size rear tire, problems will be with the wheel/swingarm/discbrake stay area. Most often, the 110 size fits withOUT any spacer changes. Either the 110 or the 120 will do for the rear. You MIGHT have to go to the slightly wider right side top hat spacer, which is 36-31-2-301-737. NOTE THAT EVEN SOME 4.00 rear tires are quite wide (especially Enduro types)! If your rear tire is touching either the swing arm or the brake stay at high speeds, then you almost surely will have to use the wider spacer. That TOPHAT spacer I am speaking about is located in the RIGHT side of the rear wheel of twin shock absorber bikes, and is easily removed and changed. The wider spacer may not be needed on 1981 and later, but I HAVE seen it required.
There is a VERY MUCH wider spacer available too, see earlier in
The stock spacer is 9.2 mm wide, the 36-31-2-301-737 is 10.7 mm wide. On some bikes, with some tires (Continental TK17 in 110 was the worst I have personally tried, other than enduro tires in 4.00), the tire will rub the swing arm at high speeds (~85+), the spacer was a must....unless you liked the rubber smell, etc. Usually most 110 tires fit without needing the spacer, say on an early eighties RS/RT. On some rear disc brake bikes with the rear tire being a 120, I have had to ADDITIONALLY put a spacer on the left, a common very large washer called a Fender Washer, available at most hardware stores. Strangely (or not) that has mostly been when using an EARLIER snowflake wheel. These snowflakes can LOOK the same, but are NOT. That spacer moves over the brake stay very slightly...avoiding any possibility of tire rubbing at speed. The swing arms vary a bit, even in the 1980-1984 era, another reason for sometimes needing the spacer(s). When you change the right side tophat spacer to the longer (wider) one from BMW, that does move the wheel-spline-engagement very slightly to the left....by about 1.5 mm, which is a small amount. There are naysayers that think the wear on the rear splines will be such that you cannot go back, and that is not really so over the long run, nor does the tiny shortening of the spline engagement have any large bad effect on spline life. Changing the tophat spacer does NOT affect bearing preload.
The snowflake rear wheels on the RS and RT are slightly wider in rim width than the drum brake models. The disc brake snowflakes are 2.75" rim width (measured at the official point for tire contacting the rim); and the drum brake snowflake rims are 2.5". This slight 1/4" difference also makes the RS/RT disc braked bikes rear tires a bit wider...and puts a bit more rubber on the road too.
Don't forget that the under-seat and owner's booklet values for tire pressure are TOO LOW for modern tires. Try about 33-34 psi front and 38-42 psi rear.
21. Bridgestone tubes are of good
This section was added to try to explain
things often poorly understood...if at all...about such as tire profiles, sizes,
differences in construction, warming-up effects, differences between road,
track, and racing tires, etc. Some of this information came from
Harriet Ridley, a moto-writer in U.K., but the information has been added-to, deleted, subtracted-from, edited, etc., ...by me. So, if you see some familiar wording or sentences, they might be attributed to Harriet:
Some of what you read below is very basic. READ IT ALL!
Tires work with your motorcycle to determine how hard you can brake, how fast you can accelerate and how much you can lean and how well they keep you from loosing control. The tire and how you use it which includes inflation amount, determines how far you can travel before they wear out and let's face it, tires aren't cheap. There's no optimum tire for every situation. Each tire is a complex trade-off between grip, longevity and handling.... and R&D is poured into finding the perfect compromise for a given situation. With three aspects responsible for a tire's characteristics - compound, carcass and profile; besides, of course, inflation pressure and road conditions including surface and temperatures; - there's a lot for engineer's to work with.
If a tire were made from pure rubber it would wear EXTREMELY quick and would never take the required weight. Instead, the 'rubber' (often a synthetic equivalent) is mixed with carbon black to make it tough and resilient, then baked at high temperatures and mixed with what could be dozens of chemicals and even silica/sand. Varying quantities and types of these determine the compound's softness and its optimum operating temperature and its wear.
The tire grips by pushing itself against the surface so the softer the compound, the more it will grip. The softer compound will also be more abraded by the road and wear faster, as well as generate more heat by flexing more.
Regardless of compound, there's a temperature at which tires operate best for the purpose they were specifically designed for. Unless a tire reaches its optimum temperature the compound won't soften enough to provide the intended grip - hence the use of the silica in road compounds to ensure a certain level of grip in cold, damp conditions and why it is important to warm up your tires carefully. Silica can also INcrease tire tread life. There is also a temperature at which all tires will overheat. After construction a tire is cured in an oven at a certain temperature for everything to stick together. If your tire goes over that same temperature for too long, it will de-cure; at first it squirms and loses traction as it breaks down chemically, then it delaminates as it breaks down physically. So each tire is carefully tailored to suit its intended purpose.
Track-orientated tires: The compound is designed for plenty of grip at constant, high temperatures reached by the extreme pace maintained on a track: hard acceleration, hard braking and high corner speeds. Because it is designed to live at high temperatures the race compound will also take longer to reach its peak. If you use these tires on the road and even if you ride quite hard, you'll be forced to slow down for traffic and stops, etc., and every time you do so the tires will cool off and take a long time afterwards to even approach their required temperature again. Keep this up and the tires will wear fast and shed rubber through cold tearing; so they may look like they're being used hard, but in fact they're disintegrating from misuse.
Heat cycles: Each time a tire goes from hot to cold it's re-curing itself to become harder, as chemical oils used in the tread to maintain compound are released (hence, in some cases, the blue color you sometimes see on a tire's tread after hard use). While this is minimal on a road tire, it becomes more extreme on race compounds. Specialized race tires are designed to go through only one heat cycle before compound deteriorates, while track-focused tires are a lot more sensitive to heat cycles than their road equivalent. Hence tire warmers not only bring tires up to their required temperature, they also maintain a constant temperature between races or sessions to minimize heat cycles. ROAD tires are designed for all the heat cycles you might need.
CARCASS: The carcass gives the tire its required strength (it's more resilient on a road tire, and how much the carcass lets the compound flex affects heat generation) and its rounded shape. But because the tire's contact patch is flat the tire has to compress and distort where it meets the ground. This shape-changing means some of the rubber has to slide across the road to achieve the new shape, causing wear, while the constant flexing of compound and carcass at this point generates heat.
The old-style cross-ply tires used many layers of plies molded at an angle to give the tire strength. But the sheer amount of material used made them heavy and generate a lot of heat, so harder compounds had to be used to maintain the right temperature.
As bikes became faster, lighter and more agile, tires had to follow suit. Bias-belted tires appeared as a step on the path to radial heaven, and they're still in use on big heavy bikes where sidewall stiffness is more important. But radials broke new ground thanks to clever layering of fabric. A radial tire is not only lighter and more responsive, it also runs cooler as the tire distorts more easily, a special type of distortion and angle that seems to be opposite than flexing increasing heat that I have previously described (and with running tubes). Running cooler means you can use a softer tread for better grip with no increase in wear. The shape of the carcass's crown radius also dictates the way a tire handles, which together with the sidewall determines profile.
PROFILE: On a 120/70-17 front tire, 17 is the diameter of the wheel rim in inches; 120 is the width of the tire in millimeters, and 70 is the percentage height of the sidewall against the tire's width - so the sidewall is 84 mm tall. The higher the sidewall, the more slower steering but good stability. Lowering the sidewall by 10mm to a 120/60-17 the tire acquires a steeper profile - it is more 'triangulated'. The results are quicker steering and more grip when leaned over, but anywhere in-between straight line and transition from upright to lean angle is less stable. The carcass's crown radius also shapes the profile.
The sidewall also acts as suspension for the tire and comes in varying degrees of stiffness: a big heavy touring tire needs the thick bead filler found in the sidewall of touring tires for added strength and stability. By reducing the height of the sidewall, the tire is less capable of absorbing surface irregularities and tends to hop when cranked over, causing the bike to understeer. A race chassis with high quality suspension copes well with a quick-steering 120/60 or a racing slick's more radical profile and flexible sidewall, but fit racing slicks to a road chassis and the bike becomes un-settled. As a result road bikes and Superstock racers would generally opt for the more suitable 120/70 front tire.
Rear tire size also affects performance: a 180 section will steer quicker, while a 190 will last longer by coping better with power battering.
A road tire will greatly outperform a race tire in terms of acceleration, cornering speed, braking, durability and stability over the course of a road trip.
RADIAL TIRES: A tire's compound (tread) is molded onto the carcass. On a radial tire the carcass is typically made of two plies with strands usually of steel or aramid (that's Kevlar): the first is a radial ply that runs at 90° to the tire's rotation (folded under the steel bead), while the second runs in the direction of the tire's rotation to minimize expansion at speed. The top two plies are cross-plies (with usually Nylon strands) placed at an angle to add strength.
The bead that you'll find on all types of tires holds the tire to the wheel rim with a 'rubber' bead filler to strengthen the sidewall.
• Low pressures cause tires to move around and
generate heat, while high pressures will reduce the contact patch and the
tire will struggle to warm up. GENERALLY go with the manufacturer's
recommendations for road pressures, but if you're using your tires on a
racetrack lower them a few psi depending on track temperature and pace.
Always check your pressures from cold (cool to baby bottle temperature). NOTE that many manufacturers, due to
lawyers and thread of lawsuits, will simply repeat the motorcycle
manufacturer's recommendations for street riding tire pressures; which can
be WAY wrong for YOUR tires and riding. WAY WRONG!
Typically and generally, the real tire pressures you should use for street riding will be HIGHER than the manufacturer says. This is especially so for such as early Airheads, which used the old soft and ribbed tires, like the Continental RB2/K112. For modern tires, pressures under 30 or slightly over 30, will be QUITE WRONG for best handling...and life too! You will probably find that your bike that was specified for those tires, say 4.00-18 rear and 3.25-19 front, should be run at 33-36 front, 38-42 rear, depending on speed and loading.
• New tires need careful scrubbing in to get rid of the slippery mould release agent used at the end of the production process. Some say up to 200 miles. MY experience is that 50 miles is more than good enough, but if you scrub the tire after it is mounted and inflated, with soap and water, then flush it off, you can go far less. Just be particularly careful during initial 20 miles, and be sure your break-in miles include some steeper turns....head into them gently until the tires are scrubbed in!
• A slick's uninterrupted compound (or tread) optimizes dry grip, but it's unable to clear standing water and debris. Hence a pattern is molded into a road tire's tread. A tread pattern also generates heat by flexing ('block movement') and is usually no more than 5mm deep to prevent weave and excessive heat build-up; but some tires are up to 7 or 8 mm for a road tire. Mind what I have said about depth and tire rating (V, H, S...) much earlier in this article, and tire mileage.
• Race tires are available in different compounds and mix-matching can provide an ideal compromise between grip and longevity. A softer tread is used on the front for better grip while the rear gets a harder compound to cope with the power battering. The front is also sometimes fitted with a flatter, more stable profile while the rear can be more triangular for quick steering. But manufacturers do all the work for you on road tires so don't mix-match on them, unless you know what you are doing.
• Specialized race tires get different compounds on either side of the same tire, so where a track has a predominance of right-hand corners the compound will be harder on the right but softer on the left. Similarly, Bridgestone's dual-compound road tires get softer edges for good corner grip with a harder middle to reduce tires squaring off with the accumulating non-cornering miles.
01/28/2004: initial 'dated' upload after final revisions.
02/03/2004: expand information on handling and tire size uses slightly
02/09/2004: add #14
09/01/2004: Update article, with better clarifications and stem part number, etc.
04/03/2005: changes in emphasis throughout, and add some hyperlinks and add #15
04/20/2005: Add tire make and model description information in more depth
05/13/2005: minor updates, primarily on the top hat spacers.
08/07/2005: add comments on karoo and scorpion and info on Discount m/c tire and acc.
08/13/2005: update section 4
09/24/2006: add 17
12/15/2009: revise and add more tire model information
05/12/2010: Revise for clarity, combine some areas, add more information to what is now 23.
05/31/2010: Add 24.
12/22/2010: #25 finally added/updated.
12/23/2010: updated tire recommendations
03/14/2011: add #26
06/20/2011: Finally got around to updating my recommendations for dual-sport tires
06/28/2011: Add more information on tire flexing, contact temperature, use with tubes
08/04/2011: Correct my math on hydroplaning, add a bit more to that info too; combine into one place.
04/25/2012: Update tire information slightly, clarify minor things here and there
06/17/2012: add Bridgestone tubes; and, update vendors
07/11/2012: Minor updates on Roadrider tires and add 28
10/14/2012: Add QR code, add language button, update Google Ad-Sense code, minor other stuff such
as updating URL in #24. Language button removed later, as had scripting problems with it.
01/22/2013: Updated article to give more information, in depth, on tire types and uses, its own section.
04/23 & 24 /2013: Minor updating, tire pressure reference, etc. Edit to reduce SOME duplication and
improve clarity.....here and there.
09/20/2013: Add Conti-Attack listing and info.
10/07/2013: Add tire photos, and a few comments here and there
04/08/2014: Update the entire article. Fix typos, add information, fix numbering system, etc.
04/23/2014: Update various places. a bit more 09/25/2014
© Copyright, 2014, R. Fleischer
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