Tubeless versus Tubes
whole story (?), and then some...
INCLUDING tire tread performance, tread life, and various other things you may not have thought of.
© Copyright, 2014, R. Fleischer
section54, subsection 6
This article will discuss
in depth: Rim shapes (and BMW rim shapes); using tubes (or not) on tube-type rims; tubeless
operation; repairs; arguments for and against using tubes with
rims designed for tubes. Other articles on this website have further information on
these subjects, such as http://bmwmotorcycletech.info/section5.htm and http://bmwmotorcycletech.info/tirerepair.htm
Here is a link to an article that has enough math (but enough photos too), from a Goldwinger (Honda Wings have somewhat unique rims) to spin your head, for the nerdy amongst us. Fine if you want to scan the article, but do see the second part of the article....and then REPEAT that look-see.
That article has extensive vector and other diagrams, which may bore you....but, also has some conclusions about contact size and pressures/forces, that may well astonish you. When you read it, keep in mind what REALLY happens when you are cornering..............and....THINK....about the effects of you changing, say, a tire size....from, example, from a 90/90 to a 100/90; or, 3.25-90 x 19 to 3.50-90 x 19, or similar change from 4.00" to 120 metric, etc.
That is, think about what REALLY happens when you go to a larger size tires (larger width and/or profile change). You may be very interested.
The below article will present data, discussion, & arguments, for tube/tubeless tires and tube/tubeless rims.
Some of the concepts/discussion really WILL require YOU to, perhaps, read one paragraph, and then THINK and PONDER about what is being said. It is UNlikely that readers will be able to just read this article straightaway-through, and gain the information I wish YOU to have.
There are folks (including some that I highly respect) that say you must ""never"" run any sort of tire without a tube on wheel rims that were not designed to be run as tubeless. I am personally not 'that much' against the practice. What I believe is not the pertinent thing...what IS pertinent is that YOU gain a full and complete understanding of all aspects & be able to make your own decisions.
I will try to inform you herein with UNbiased information. There ARE a lot of misconceptions, wrong-thinking, failure to be open-minded enough to see the whole picture, etc.
There are also real reasons to do what the manufacturer of tires, tubes, rims, and motorcycles too!....said to do...which, generally, are to not use rims designed to be used with tubes, as tubeless.
There are also things not at all widely known. Keep in mind that manufacturer's are not at all interested in long-winded information, like in this article you are reading. Such verbose information would tend to cause them a lot of labor in further explaining things, as there are always people who 'need to contact the manufacturer' to make specific points, commentary, or have the makers provide additional information, etc. Thus, manufacturers make simple easy to understand statements...do this, or, don't do that. Their company lawyers would agree with that attitude.
Motorcyclists & sidecar/trike drivers do all sorts of non-standard things. Car tires, wide rims, change of rim diameters, LOTS OF "ETC.".
If it was really so vastly UNsafe to run tubeless tires withOUT tubes on motorcycle wheels, how come sidecar rigs, which produce SIDE FORCES that can be EXTREME (2 wheelers do NOT have anything even close to those forces), do not have lots of accidents with blown tires, tires coming off rims, etc....?
Sidecarists sometimes, depending on the situation and equipment, install tires in the 'wrong direction'. Ever notice that NOWADAYS many tires are marked on the sidewall as to what usage is (rotational direction), but SOME tires are marked for one direction OR THE OTHER, depending on if used as a front, or a rear.
THINK!!! These are only two of the many variable uses.
This hardly means that 'anything goes'!!
Did you know that some have raced Airheads on paved tracks, at high speeds, using BMW Snowflake wheels that were specified for tubes only? Did you know that arguments that tires greatly expand in diameter at high speeds and thus will be likely to have the tire tread move to the center of NON-safety rims, and loose all air very suddenly, is FALSE? In fact, tires expand in width at speed/temperature, and that is not any factor in a tire moving to the center of the rim. Did you know that the primary method by which a tire 'becomes unglued from the rim' is from a massive bending of the rim from the tire hitting a large object in the road? Did you know that THAT can happen with tubeless....or tube...type tires/rims/etc...?
There are plenty of reasons folks will proffer about why they want, or would want, to NOT use tubes on rims 'designed for tubes'.....besides the thin-round-steel-spoked types (unlike BMW GS rims)...which WILL leak air unless sealed at the spokes (spoke sealing is also done by some):
(1) Easier on-road tire repair. I think THAT is the PRIME REASON.
(2) Possibly reduced weight, which means slightly better handling and mileage.
(3) No need to carry a spare inner-tube(s).
(4) Possibly deeper tread on some tires, as tubeless tires can run cooler, so tread MAY be made deeper SOMETIMES
(5) Without a tube, the tire temperature is less, and the tire tread may last longer.
(6) Tubeless tires MAY loose air from simple punctures much more slowly, whereas a tube with a puncture MAY be similar, it usually leaks faster and thus HAS
TO BE FIXED by a patch, which typically means wheel and tire removal.
Not all that often do such folks also say that they know that tubeless tires with a seriously bad puncture should be REPLACED, not repaired (or, repaired only very temporarily, and ridden at low speeds, until they can obtain a NEW tire).
I think it reasonable for me to state that I have mixed feelings about all these things. While many have done tubeless tires without tubes on tube type rims quite successfully and safely for many decades & hundreds of thousands of miles, back, ever so long ago now, I put on huge mileages every year, and I never THOUGHT about tubeless tires for my motorcycles. ONE reason was that when I started riding there were no such things as tubeless tires. That means that the inner walls of the tires were not officially fully sealed to prevent air loss. The truth probably is something like SOME tires really were sealed rather well on the inside, and COULD have been used (perhaps) as tubeless......but we never thought of it....or, if we did think about it, no one I knew had tried it.
Tubeless tires are NOT a recent development, at least not for CARS. Although invented and patented decades earlier, it was ~1955 that tubeless tires became mostly standard on automobiles. Before that time, tires required a separate inner tube which failed (besides punctures) because of incorrect tire fit, friction between the tire wall and inner tube generating excess heat. Tubeless tire technology does away with the need for an inner tube, and it is, REALLY!... accepted by the various manufacturer's, that tubeless tires INCREASE safety (at least on rims designed for them, as the manufacturer's don't want to discuss it further). ONE of the reasons is that a simple puncture releases air more slowly, than a tube (usually).
If a tubeless tire (no tube installed) gets a small puncture, air escapes only through the puncture hole, leading to a slow and typically gentle deflation. The actual point of DEflation where YOU feel something may be wrong, will vary. This is due to the various types of tire construction, sidewall stiffness, your speed and loading, etc.
Conversely, an inner tube could potentially burst like a balloon, leading to a more rapid deflation of the tire which could result in sudden loss of control of the vehicle. That was one argument some gave, not considering the exact circumstances....which, for that, would PROBABLY be the tire coming off the rim or partially, perhaps due to a large rim bending. Another argument was that in most instances a punctured tube, used inside a tire mounted to a tube-type rim, will almost always leak faster. That would need some explanation, and further details about rim shapes. I'll get into a lot of these things further on in this article.
NOTE!....A burst-balloon effect could not happen if the tube remains inside the tire and is not bulged out from under the tire bead. The idea here that if a tube is punctured, it typically leaks slowly, just about the same or somewhat faster, than a tubeless tire puncture.
Please read the next paragraph over and over, until you FULLY picture it in your mind and FULLY understand what is being said by me:
If the tire bead becomes disconnected from the rim's bead area, and the tire bead moves inwards, then the tube might bulge out, perhaps the rim or even the tire bead itself would cut it, causing a very fast deflation, from such a ballooning effect. It is THIS idea that needs to be fully gotten into, and I will attempt that in this article, because THIS IDEA is the PRIME argument area. NOTE that the tube could bulge out from the tread from a seriously damaged rim or from enough DEflation to allow the tire bead to move inwards (assuming no ridge in the rim construction that prevents this...or MIGHT prevent this...).
The SAME fast exiting of the air pressure in a tubeless tire, is also possible, somewhat or more or less depending on the rim; and, of course, any rim damage. Thus, manufacturer's sought ways of keeping the tire bead in contact with the rim area, even for rather extreme instances of the rim seriously bending from such as a large pothole, or the tire hitting an object in the road. While tire beads and rim shapes have changed, with improvements for bend rim problems, they still strongly exist, because there is no common method in use, nor has ever been promoted, to keep any type of tire 100% in contact with the sidewall area of the rim, no matter what the problem. It is more likely, if it ever happens that the tire becomes disassociated to the rim, in THESE circumstances:
1. Cars: Rim is VERY seriously bent or cracked/damaged, perhaps the rim is even totally broken into pieces due to impact. The rim damage, and escape of air from the tire, is not likely to be any problem for loss of control....the accident has already caused that loss of control, more or less.
2. Motorcycles: Rims are lighter, easier to bend from road debris, rarely crack badly, but it is possible. Compared to cars, loss of control in an actual collision accident may be total loss of control (impact with another vehicle, striking a deer, etc.). However, hitting debris in the road can cause loss of control or momentary loss of control, or hardly any such; but the bending of the rim might be enough to let all the air out quickly from a TUBELESS usage, or, tube might bulge or be cut from the rim, and air escape that way.....ETC.
Concern over loss of air from a simple puncture, and then loss of control following, would, in my estimation, be rare if very sudden and complete, as almost always there is an indication of mushiness and weaving that considerably precedes any complete loss of air.
Manufacturers tried rims with various angles to the bead area. They also put bumps in the rim so that the tire would not likely be able to move into the center area of the rim. They also tried different rim shapes in the center of the rim. NOTE that there are TWO general and common types of 'bumps' to prevent the tire bead from moving into the center of the rim, and ONLY the type with a bump or ridge just a bit inside of the mounted tire's bead area, will work to help keep the tire attached to the rim bead area. That type of rim is generally known as a Safety Rim. Bumps or ridge positioning do NOT prevent the tire from becoming disassociated with the rim bead area, thus, even with a tubeless-designed rim, it is possible, on a flat, to have the tire lose are quite rapidly, perhaps less likely (no statistics found by me). Many have argued that the rim bumps or ridges prevent fast loss of air on a tubeless tire, and that is obviously not so, but they can be 'helpful'.
Thus, my conclusion is that many who say disasters are about to come on one who uses tubeless tires without tubes on a tube-type rim, are not, or may not be, thoroughly thinking things through. The tire manufacturer's will all say, in their literature, not to do this. If I manufactured tires, I, too, would tell people NOT to use tubeless tires as tubeless on tube type rims. BUT....really....just what IS the REAL safety difference?
My personal conclusion, and I want to make it very clear that this is NOT ADVICE: using a tire without a tube on rims that are not designated for such use, is probably somewhat less safe. How much less I do not really know. It is very difficult to find real data.
This is from a 1979 R45. Snowflake. Note the
center drop and its curve, note the lack of any
bead holding bumps. This is NOT what has
been generically called a "safety rim". This is a WM.
Below is a 19" front Snowflake wheel, basically the
same as the above wheel in design.
Flat bottom type of rim, similar to above wheels,
except for the flat bottom area, and that there is
knurling for the tire bead!
This next group is safety bead/ridges styles:
Flat bottom. Same basic rim design as the R100GS, see photos above.
These 3 above photos are Morris Mag's, rear wheel, for Airheads
1. Except for later model Airheads that came from the BMW factory WITH tubeless tires (BMW phased-in the tubeless rims, generally from 1985, but phasing-in was not generally completed for several years, and it depended on which model), all others came with tubes. Those models, using early-style rims (that is, pre-tubeless) have an industry standard type of rim shape/contour called WM-2 (same as WM2). This is a particular shape of primarily the inside area of the rim tire bead wall; although there can be differences in the dished center areas of the rim. The WM shape does not have the 5 degree angle increase of the tubeless rims of the bottom area and side area, that the tire bead rests against. The WM-2 shape has a contour in the middle; and, angles outward from the middle, and where the tire bead contacts, that is and was for use with tubes; note that the WM is also made with a non-straight shoulder! THAT is what has caused a LOT of confusion over rim safety if you go tubeless. Some BMW rims have 'safety rims'...which help to keep the tire onto the rim and not allow the tire to move towards the interior/insides. Another commonly used rim shape for use with tubes is the CP contour, which was also used in some later BMW models. This shape has a more pronounced drop center, and the horizontal part that the bead ending fits has a 4 degree slope.... that slope is OPPOSITE the TUBELESS rim shape!! Yes, that is correct, the angular part goes in the other direction!
At this point, I will stop descriptions, and place some photos here, to allow you to see what I am describing.
The 5° drop angle on CP is sometimes 4°. All the above rims are identified as TUBE TYPE, but are also OK for use
with tubeless-rated tires, IF USED WITH TUBES. NOTE! There is a rim shape called MT. It is for tube or
tubeless use, depending on what the manufacturer of the vehicle says. The appearance of the rim is the same as the
TL-H2, below, withOUT the bump!
NOTES: There are many types of rims. One popular one called an MT is nearly identical to the WM-non straight shoulder type.
The CP type, see above and also below to right, has a reverse taper seat. This type is/was,
as far as I know, used only on some BMW's, Moto-Guzzi's, and Laverda's.
Note the HUMP on the TL-H2. Be sure to read 3. below.
REPEATING!: There is a rim shape called MT. It is for tube or tubeless use, depending on what the manufacturer
of the vehicle says. The appearance of the rim is the same as the TL-H2, below, withOUT the bump!
I can provide the engineering book from such as Metzeler, showing this!
SPECIAL NOTE!....in the TL-H2 sketch, above, the BUMP in the rim is generically shown. The actual bump or ridge might be just barely inwards of the tire bead when the tire is mounted and sealed to the rim; or; that bump could be as shown in the sketch, where the purpose is to prevent the tire, which might have disassociated with the rim, from moving inwards to the well area. A compromise is usually made, and some rims even have had both bumps/ridges, or combinations. If a tire moves to the center of the rim, the loss of air will always be very rapid....on any type tire not containing a tube. Note also, how 'easy' it would be for a tire using the TL (not TL-H2) to move into the center area.
Especially not how the CP type rim will help keep the tire association with the rim. If you think about these sketches, and think about what REALLY might happen under several circumstances of using and not using tubes, you just might get the idea that a CP rim WITH bumps or ridges, might be near-ideal.
For the NERDY: Metzeler says that if you use a TL-H2 rim, with a tube, it must be a Metzeler tube. They did not specify why. I think it due to the higher safety of a natural rubber tube, and the Metzeler tube design at the core.
2. BOTH the CP and the WM series are for use with tubes. They are also OK with most tires that are marked tubeless; the WM with tubes. Tubeless tires have a bead, etc., that is reverse compatible with CP and WM series rims. That does not mean it is officially, or unofficially, OK to run tubeless marked tires on these rims without tubes. MANY DO and HAVE, safely. YOU ARE ON YOUR OWN if you do so. Those words do NOT mean that such use is inherently vastly unsafe; just that my lawyer would insist I say that.
The flat portion of the tubeLESS rim just inside the bead is also usually a bit wider (depending on the particular tubeless rim design), its ANGLE not being parallel to the tarmac, as the WM is (and CP opposite to tubeless types). You can't see that, above sketches.
3. There are rim shapes, such as MT and MTH2, that are usually specified for tubeless tires without tubes in them. These types of rim shapes WERE used on some Airheads, such as the R80GS (NOT G/S); R80R; R100R. The R80GS had both these types depending on the year. The R80 and R80RT from 1985 (the year BMW went to the 'not serviceable except to replace them' type of front wheel bearings); late R65, R100RS and R100RT...all phased into production between 1985 and 1987, had the MT-2 version of these rims. BMW's later wire-spoke wheels had a new, clever BMW design, in how the spokes were fitted, so that the spokes were outside the air cavity. This enabled tubeless tires to be fitted to a wire wheel, which otherwise would leak air at the interface of spoke and rim.
The MT and MTH2 rims are different from the WM and CP. The more-or less horizontal part of the rim that meets the sidewall of the bead is angled slightly (5 degrees). On the MT, which is specifically designed to allow the use of tubeless tires without tubes (but CAN be used with tubes), the horizontal part of the rim is 5 degrees UPWARD, tending to hold the tubeless tire onto the rim at the shoulder (side). The MTH2 not only has that 5 degrees, but there is a BUMP in the rim shape, upwards, just before the drop center area. That bump tends to keep the tire bead from dropping into the center of the rim. That bump has two very practical functions, one is to help in putting air into the tire when it is being installed or when flat and the sidewalls are not contacting the rim all-around enough, and the other function is to help DEcrease the possibility of very fast air loss upon a VERY serious bump....like hitting a rock or riding into a VERY deep pothole.
The MTH2 rim is often used on OFF-ROAD motorcycles, where the rider may, under some circumstances, use a vastly lower than normal tire pressure. That is why GS bikes use them.
OK...now that you have plowed through and read all that (and likely gotten confused)......below is the easier (?) to understand information...on what you need to know.
Part II, the rest of the information:
these things are MY personal interpretations/ideas; read & do
what you want at YOUR RISK, NOT MINE:
1. Often in life, folks simply accept various rules, ideas, statements, specifications, etc., without THINKING things through. What I will discuss in this paragraph is one of those situations, or, at least partly.
You are told, by BMW, by tire makers, and by many others, that you MUST use tubes on the Airhead wheels that came with the bike that were designed to use tubes.
If you were to use a tubeless-rated tire, and add a tube, THE RULE/ADVICE, where available, is/was that you should REDUCE the speed rating of the tire by one step. This RULE/ADVICE does not mean much, regarding safety, to Airhead owners, who are UNlikely to be riding at the maximum speed the tire is rated for reduced one notch, anyway! The reason given for the reduction in speed rating is that the use of tubes causes the tire to heat up more due to the flexing and tire to tube combination flexing. That much IS TRUE. Just heat increase alone will reduce tread life, as the tire tread moves into an area of hotter tire-to-road interface temperature. Again, this is true. BUT: This is very unlikely to be any sort of real problem, at least for normal road-going motorcycle tires on Airheads, even to speeds towards 120MPH, and maybe considerably more. Some of this information used to be, and maybe still is, found in SOME tire manufacturer's literature.
There is another point to consider. Tires are designed, in the rubber compound, sidewalls, and tread depth, belts, etc, so that from zero to the rated speed, they deliver a certain friction and angular, ETC., performance. If you cause the tire to be hotter than it was rated for, at any speed, performance of some sort MIGHT suffer. I say MIGHT, because, at any reasonable speed, it is my belief that the effect is QUITE MINIMAL....providing that the tire pressure is reasonable. By this I mean that if normal pressures (range of pressures) are used, you are very unlikely, again in my opinion, to have any sort of handling problems. I base my conclusion on theory, manufacturer's engineering manuals, and on road testing. Yes, I actually did testing on two very different tire types (brands, models...) with huge pressure differences....on the same tarmac area, both with and without tubes. I also have testing, and others' reports, on extremely hot tarmac and heavily loaded bikes, at higher speeds, on road tires and off-road tires. The tests could be thought of as extreme, very hard on the tire treads, and in one instance the treads were so heavily loaded by gear and passenger, in such hot weather and extremely hot tarmac, that the tread literally began melting away.
Another point is that tire manufacturer's control the depth of the tread on new tires for a reason. All other things being the same (belts, sidewalls, tire compounds, etc.) for any one type of tire, the depth of the tread greatly influences the tire tread temperature, due to flexing/squirming effects, etc.
For the SAME tire make/model, it is often advantageous, for tire tread life, to purchase a lower speed rating in that tire model (if available), get a deeper and longer lasting tread! That can work out well, particularly if your speeds and loads are moderate.
>>>> If you stop here and THINK/PONDER some, would it not be 'reasonable' to 'ASSUME', that with a regular tube-use-specified tire, run withOUT a tube, you might well have a INCREASE in tread life, because the tread is less hot, as there is no tube friction, ETC....? Well, that is probably going to be correct...and, yes, it was so.
BUT, I speculated that a tire in such usage MIGHT not be in its 'best performance' heat range, as originally designed. I tried to find out, during testing, and I even did various pressure setting changes. I was UNable to prove that the tires had ANY degrading (or hardly much improvement either) of HANDLING performance by removing the tube. I also note here that the optimum pressures hardly changed much. This was on various types of surfaces, speeds, tightness of turns, and on some wet areas too.
I have to admit that I did not expect this....I EXPECTED more change than I found. What I DID find was that the tires were just a bit more slippery feeling on very cold roads in very cold weather (this I expected), and that measured tire wear was REDUCED (THAT I also expected).
2. HINT: NEVER fail to use
tire talc when installing a tube; rub it all
over the tube and inside of the tire with your hands....this allows the tube to
move about a bit, avoiding excessive friction against the tire;
and also helps the tube, upon installation, to avoid any folding.
3. Almost all tires marked tubeless, are OK for use WITH tubes at a reduced maximum speed; per the manufacturer's. Exceptions MAY exist in trying to use RADIAL tires. As a general rule, I suggest you do not use old-style radial tires on your Airhead. You generally will not find old-style radials that fit your Airhead anyway. If you do try a radial tire, approach handling with slowly increasing steps of aggressiveness and speed, until you know what the tire and motorcycle will do. I suggest you adjust the steering head bearings carefully, for just a trace of weaving at maybe 25 mph, before doing radial tire testing. This is a good adjustment for any tires on an Airhead. There are now 'radial' tires specifically made to work with old bikes like the Airheads. You might be interested in trying them, preliminary reports are GOOD, but tire pressures seem to be a bit more critical, IN MY opinion.
4A. Tires marked tubeless are supposed to be specially made to ensure they hold air for long periods of time. This is typically done by a special coating on the inside of the tire. Talk of special bead areas, etc., are WAY exaggerated.
Tires not-so-marked (for tubeless) MAY loose air if not use with tubes, as the TIRES could be porous in one area or another. I have seen tubeless tires hold air for a long time on tube-type rims; and have seen others that would not hold it long. Mostly what I have seen is that the loss is quite slow, and weekly topping-up is adequate; pressure loss not usually being much more than normal when using 'natural rubber' tubes. Tire pressures are supposed to be checked before every day's ride, right?!
There have been a FEW ""reports"" that SOME snowflake wheels are porous and leak air. Maybe. I have not seen this, and I know of no serious air losses; but, see #7 below. SOME folks have used the snowflake cast wheels with tubeless tires, and installed a tire sealant; and had good success in greatly slowing any air loss and have had the sealant work well for them with punctures. MANY have had hardly any air loss over time. Some types of tubes, whether used with tubeless rated tires or tube-type rated tires, WILL lose pressure slowly, compared to the 'plastic' type tubes...but the tubes said to be 'natural rubber' are probably much less likely to be ripped from a puncture.
4B. Purposeful off-road tires are, in the majority, meant for use with tubes, and most of these tires do not have any interior sealing coating. These tires may be used at times as low as 5 or 8 pounds of pressure. Avid off-road riders typically have other methods in keeping tires on the rim, besides special rim bumps, when using very low pressures.
5. Tube Mounting NUTS:
When installing a tube (tubeless or tube type rims), normally do NOT leave the mounting nut against the rim.
There reasons NOT to screw the tube valve stem nut to the OUTSIDE of the rim, although that is done, although loosely,
DURING INSTALLATION OF THE TUBE, TO MAKE THINGS EASIER:
(A). The tube could fail to release air from between the tube and inside of the tire....which it is SUPPOSED TO DO normally
in use & the tube could chaff, & fail early. This is particularly so if you did not rub the tube & tire insides with tire talc.
(B). Leaving the nut against the rim defeats the safety of allowing the tube to be able to move slightly, upon a flat occurring.
Run the nut up against the cap, or throw it away, or put it in your tool tray....Some tubes are sold with that nut, and the
purpose is TO HELP DURING INSTALLATION OF THE TUBE/TIRE. Restating this: Using the nut against the rim
does not allow for tube movement if one has a leak, and then the tire rotates on the rim some.
(C). 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 & a BMW bulletin on these facts!
(D). BMW has had several bulletins out on these valve nuts, and one SI gave an additional reason to have it up against the cap,
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, and I will, was that this comes from very low inflation
AND over-inflation during seating of the tire.
(E) For TUBELESS TIRES being used on TUBE TYPE RIMS, the rim hole is 8 mm. If you do not wish to enlarge the rim hole for a
standard pull-in type of stem, then there is a special valve stem that is available, even from BMW, that seals at the inside of the
rim by means of an O-ring built into a recess of the stem unit. The stem area of the rim, inside, must be machined flat for this to work well.
***There are those, often sidecarists, who seal the stem with rubber doughnuts or by other means. Sidecarists do lots of things that some may consider wrong (or, otherwise unwise). See #10 below.
6. The VERY SAFEST thing to do, considering big bumps/potholes/objects in the road, is to use the wheel as BMW intended. Because of the mixture of the wheels BMW has used, and the way wheels bend or crack in serious 'hits', no hard and fast rules that fit all situations is possible. If you are willing to understand that a fast air release is possible on a flat (occurring, perhaps, from with a rim-bending size bump or pothole) (same from tubeless safety rims too!), and don't mind that...then, it is your choice, with that knowledge...to use a tube or not. NOTE, however, that VERY SAFEST, might, or might not be, nearly the same thing as how you intend to otherwise do things. In other words, if very safest is 100%, it might well be that using no tube is hardly very much less safe, maybe 99% in practical use. This is only an example, I have NO idea about the %; and in every incidence of type of problem.
Since rims vary in angle of the bottom and sides, and some have the protective internal bumps to prevent the tire from moving INwards, ETC., you need to THINK about things, if considering not only NON-standard use, but, yes, in STANDARD use. For one example here, if you have a very serious rim bending situation (truly nasty pothole or some object in the roadway you ride into),...AND... if you bend the rim enough with ANY type of rim, .....a tubeless tire may loose air, very fast. But, if you had ANY type of rim, WITH A TUBE, you COULD have the SAME situation occur, if the tube managed to get pinched and the rim then cut it. Thus, it is NOT AT ALL clear if, ALWAYS, tubed tires are safer than non-tubed tires, or not so, no matter what type of rim is being used.
My tentative conclusion is that tubeless tires are of some advantage, OVER-ALL, due to less heat build-up without tubes, easier installation, easier flat repairs, etc. There are disadvantages, primarily that if a puncture is really large and truly awful, the tubeless tire used as tubeless, needs replacement, not repair.
7A. It IS possible for the snowflake tube type wheels to be converted to use tires as tubeless without using tubes. Some very few snowflakes have been reported to be porous, but that is fairly rare, most will hold air OK. For the porous ones, they can be very thoroughly cleaned and a lacquer applied to the inner surface.
One conversion method involves enlarging the stem hole, and possibly spot facing the inside of the rim slightly. That allows small tire 'rubber tubeless stems' to be fitted, instead of trying to use larger types. There is also a metal stem that is available with a rubber O-ring that can be fitted, into the existing hole size (spot facing inside MAY be needed). See #11.
For these various options, do consider the amount of spot-facing, or flush machining, that, if excessive, might weaken the rim. I have NOT seen that, so far.
There are also those who have used a stem from an old tire tube, with appropriate rubber pieces (often cut from the same tube) to seal the stem to the snowflake wheel. This works OK.
7B. The conversion to tubeless has been done many times and I have heard, SECOND-HAND, of only ONE problem, over the years. However, so, yes, while practice is NOT as safe theoretically as using tubes, problems do seem to be very rare. Folks have done considerable racing with tubeless converted snowflakes. So far, except for that one instance, I have been unable to trace down any problems...most seem to be passed-on old-wives tales! This does NOT! mean that there have been no problems....just none I know about. I probably would have heard of at least some of them though, after so many years of being on the Airheads LIST, consulting dealers, independents, etc.
8. HINT: As tires rotate at very high speed, the forces involved can sometimes tend to OPEN the valve stem core, and valve stem cores are manufactured both short and long, and also as short 'with a red band'. The red band valve core is designed to not have a high speed problem. The problem generally occurs at speeds well above what you can attain on a stock Airhead anyway; but, there have been instances of weak valve stem core units that leaked air. A short valve core, and a quality cap that seals, is OK. The short or long core, with no air-sealing cap, is not good as you may loose air very slowly. ALWAYS use a CAP on the stem, of the type that seals against air loss. My preference is the metal type cap with an internal rubber seal, whether or not it has the tip tit that will unscrew valve cores.
9. HINT: When a snowflake (or other wheel, WM or CP) is used without a tube, you MIGHT have problems trying to get it to hold air during a tire change or tire repair, if the tire bead does not stay in full, all-around contact with the rim. That is why tire folks use a BAND (or rope!) around the rim of a tubeless tire, to squeeze the tire to the sidewall....and this is one goodly reason I don't recommend carrying those high pressure steel CO2 mini-bottles that are in some tire repair kits. I have seen folks tie a couple of pants-belts together to help hold the tire beads to the rim, while pumping up the tire. I vastly prefer a piston/cylinder operated, or battery operated pump....UNlimited air (but not necessarily unlimited volume!), as the pressure supplied is typically not very big. One of the 'secrets' about getting tires (tubeless or tubes) to seal fully all-around the rim, is to remove the valve core and use a compressor with a large tank of high pressure air; large internal diameter hose;....together with lots of properly thinned commercial tire lubricant. It REALLY helps to remove the teat in the air chuck, to enable an even faster flow rate; and to do the work with tire and wheel hot from being in the sun. Use of lots of real tire lubricant on the beads, and lots of air volume, helps seat the tire.....otherwise, very high pressures inside the tire/tube might be needed, which could be very dangerous. I remove the tip core of my compressor tire chuck, to allow the air to flow as fast as possible. I even have a larger inside diameter hose. My compressor tank is only 5 or 6 gallons, at 125 PSI.
10. Sidecar folks sometimes use rear tires on the front of the tug, with the directional arrow, if there is one, reversed.
11. It is possible to seal the tube stem via rubber and metal washers and exterior nut to the rim to hold air better should the tire/tube be punctured. That must be offset with the knowledge that if the tire rotates any on the rim, it could carry the tube along with that movement and rip the stem out of the tube. This is as opposed to not having the nut at the rim, and the tire might be able to rotate a bit on the rim and the tube stem NOT be damaged irreversibly. The tube nut really is, normally, just for help in installing the tube/tire, then it is NOT to be used....or; it can be put up against the valve CAP, NOT against the rim. Doing otherwise should be done with knowledge, which is one reason this article talks about it. Some have, as noted previously, purposely gone tubeless and used a valve stem assembly cut from a tube...with added rubber inside and outside the rim, with a curved tube washer.
12. Tube type and tubeless type rims vary at the valve stem hole. Generally, the tubeless rim has a 11.5 mm rim hole. Tube type is 8 mm. When installing a tube into a tubeless rim, care must be taken about squeezing the tube if using the typical tube nut, and a special nut is available. This comes right from the old Metzeler engineering handbook. Also in that handbook, is this fact: The valve must not be used with a nut to try to make an airtight seal. Air trapped between tire and tube must escape through the valve hole, otherwise there is a risk of tube chaffing. This is the only place I really mention this, but, frankly, you are unlikely to have a problem, if the tube is talc'd. IMO.
In case any of this is confusing, remember that some folks want to install a tubeless tire withOUT a tube, and some have tubeless rims and want to install a tube, and all sorts of variations on these themes. I'm trying to cover them all, so read carefully.
I think MOST of those reading this article are interested in installing a tubeless rated (sometimes a tube rated) tire withOUT USING A TUBE. Thus, paying attention to the types of valve stems and their installation, is important!
BMW sells a chrome-looking 7 mm valve stem, 36-32-1-452-748 with a rubber O-ring, that will fit most tube-type snowflake holes, with a bit of modification to the rim. That part was for the 1985+ rims with 8 mm hole and proper fit at the inside. There are similar, or exactly the same, various valve stems, available from tire distributors, etc. If you install such a valve stem, it works well with the snowflake wheels, just install carefully, and with knowledge.
13. Snowbum has, on two of his Alaskan adventures, installed tubes WITH rubber washers and
14. The snowflake tube-type wheels will handle major rim denting and still hold air, if tubes are installed as they were designed to be. HOWEVER, there have been numerous reports of very serious rim bending, with NO problems with tubeless tires, without tubes!
Thus, considering everything I have mentioned so far in this article, there is NO clear-cut 100% answer, in MY opinion, on whether or not....it is safe, or safe enough, or not safe, to remove the tubes from tube-type snowflake wheels.
In December, 2004, there was an inquiry to the Airheads LIST about using radial tires. Below is my reply, edited here, which may clarify some things:
You can mount any tire that fits, onto your snowflake wheels. That does NOT mean that you SHOULD. We've had a lot of threads over the years on putting tubeless tires on the snowflakes, the pros and cons. I have posted about it many times. There is information in a specific article on my website. I even have posted about why not to have the TUBE valve stem 'nut' against the rim. Many don't listen, or don't heed the advice; or, believe I am wrong. There are advantages.....and disadvantages.....to tubeless tires.
Tubes can be repaired (replacement is better), and you can almost always re-use the tire. For simple punctures, a tire used as tubeless is much easier to repair when on the road, as opposed to removing a wheel, removing a tube, repairing or replacing the tube, etc. Some types of punctures on tubeless tires without tubes in them are not always repairable (even with INternal patches that are done in a shop). Plugged holes in tubeless-use may or may not hold up, and EXternal plugs are very iffy at speed. The internal ones (or external mushroom types if not ridden-on too far or too fast or too heavily loaded) are better. It is advisable to NOT drive at speed using a plugged tire, until the tire can be INternally patched; even then I don't or won't drive at extremely high speeds. This advice also applies to mushroom plugs. The convenience of tubeless tire repairs is very appealing. The CO2 containers are a PIA....I recommend engine pumps....or a $10 Walmart pump, etc....see my tire repairs article.
Side note: WalMart, and others, sell small 12 volt electric pumps cheaply, these are in a small plastic case, I purchased one for myself, it even
has a gauge; a photo is in the tire repairs article. The innards of the various versions are removable, and then the pumps are even smaller. They might fit in the tool tray on your bike, together with other tools, a test light and a small multimeter.
There are a number of types of radial motorcycle tires on the market. I expect more. Generally speaking they are not made in sizes that fit your Airhead; with some exceptions, and even some appearing in and since 2013 that are made specifically to replace bias ply tires on older vehicles. Radial tires...again, in general.....have some peculiar characteristics that could make them handle strangely on Airheads. You might love them. The ones specifically designed to replace bias tires are an exception to the comments about handling strangely. YOU ARE ON YOUR OWN.
Radials, like other tubeless tires, will fit the rims, probably seal to them
OK (rims CLEAN AND smooth) as far as holding air under NORMAL conditions, but may come
off the bead/rim area under conditions of a major pothole,
or other rim-bending type of force (and, perhaps, the rim
need-not bend, for the problem with a radial tire). This may NOT apply to the new ones designed for motorcycles and to replace bias ply tires.
1. SOME manufacturer's tubeless tires and tube-tires have slightly
different beads, but I have been TOTALLY unable to get DEFINITIVE information,
and my personal inspection has not shown enough difference to make it more
than a minor mention. The flat portion of the tubeLESS rim just inside the bead
is usually a bit wider (depending on the particular tubeless rim design), and I have previously noted the angle differences. I do NOT think this any major thing.
2. When any tire containing a tube gets a bump big enough to damage the rim severely, you may well retain air with a tube, and less likely to without a tube. This does depend on the type of rim construction, and where any 'safety bumps or ridges' are located....and, the shape of the drop center or curved center of the rims. There is also the rare event of a tube bulging out from underneath the tire bead, being cut by the rim.
As a general rule, I usually advise against any tubeless tire withOUT tubes on tube-type snowflake wheels. I think that such use is VERY SLIGHTLY LESS SAFE, OVERALL, all things and conditions considered, than WITH tubes. How much less safe? Well, maybe very little, overall, in practical use. You are totally on your own in this regard.
NOTE!...this is an OFFICIAL DISCLAIMER!:::
.....I am NOT advising that it is, in ANY way, safe...or not... that you run tubeless tires withOUT tubes (and especially radial tires, without tubes....OR WITH TUBES)....on your tube-type snowflake wheels! You are on your own in doing modifications...I am NOT responsible, and I am not advocating changes to the wheels, nor using tubeless tires without tubes on wheels BMW did not intend that for. This is a legal disclaimer!!!
06/19/2004: updated and released to Internet
09/01/2004: final update
12/05/2004: ADD section containing the reply from the Airlist
06/02/2006: editing for clarity only
08/10/2007: Remove a paragraph on the BMW threaded valve stem, add #10.
10/15/2007: Revise entire article for clarity
12/06/2009: check entire article. No major changes. Some clarifications and emphasis only.
05/20/2010: Check article; minor typos fixed.
10/14/2012: Add QR code, add language button, update Google Ad-Sense code
07/04/2014: A bit of updating, mostly to clarify and condense.
04/16/2015: Added sketches, added comments, updated article ONLY for clarity purposes.
06/01/2015: Add more notes, more information, more conclusions/speculations, add the Honda link, etc.
Requested rim photos on Airheads List. Will do same for Airheads Beemer Facebook page.
06/14/2015: Final release with rim photos, updated commentary, etc.
06/17/2015: Add 3 Morris Mag photos
07/05/2015: Add R100R photo
© Copyright, 2014, R. Fleischer
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