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Primarily for BMW Airhead Motorcycles, but may be of interest to all motorcyclists!

Tubeless versus Tubes ...the whole story (?), and then some...
INCLUDING tire tread performance, tread life, & various other things you may not have thought of;
particularly for those contemplating using the tube-type BMW Snowflake wheel as tube-less.
Copyright, 2014, R. Fleischer

section54, subsection 6
section6.htm

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 & against using tubes with
rims designed for tubes.   Other articles on this website have further information on these
subjects, and much more, such as:
http://bmwmotorcycletech.info/section5.htm  &  http://bmwmotorcycletech.info/tirerepair.htm

 


Here is a link to an article that has enough math (but enough photos too), from a Goldwing'er
(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.

http://www.goldwingfacts.com/forums/10-reference-faq-forum/400426-design-differences-between-car-motorcycle-rim-tire.html
That article has extensive vector & other diagrams, which may bore you....but, also has some
conclusions about contact size & pressures/forces, that may well astonish you.
  As you read
keep in mind what REALLY happens when you are cornering...&...THINK...about the effects
if you change a tire size...from, example, a 90/90 to a 100/90; or, 3.25-90 x 19 to 3.50-90 x 19;
or, from 4.00" to 120 metric, etc.  Think about what REALLY happens when you go to 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 &
tube/tubeless rims. 
Some of the concepts/discussion may require reading one paragraph, & then stopping
to think.  It is UNlikely that readers will be able to just read this article straightaway
through, & gain the information I would like you to absorb.


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 & 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 wrong
thinking, misconceptions, failure to be open-minded enough to see the whole picture.   

There are also real reasons to do what the manufacturer of tires, tubes, rims, &
motorcycles too!...say to do...which, generally, are to not use rims designed to be
used with tubes, as tubeless. 

There are 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, they 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.".   I am not going to get deeply about
these folks usages....but WILL make a few statements. If it was really so vastly NOT safe
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....?       I'll try to answer some of these types of questions in this article.
Sidecarists sometimes, depending on the situation & 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?  SOME have BOTH directions,
depending on usage!
THINK!!!   These are only two of the many variable uses. 

That MANY use tires & rims in all sorts of non-standard ways hardly means
that 'anything goes'!

There are levels of safety.  In many things in life, the lower stages of improvements are
large jumps.  As things improve, every slight improvement takes a lot of effort, and one
might then question why one should go to such huge lengths.  

Ultimately, the safest tire/rim usage is to NOT RIDE AT ALL.  I am not being facetious
here.  Just what is the chance that your particular decision about modifying your
motorcycle rim or tire/tube usage will result in an accident, versus not having done
the modification?   What are the REAL facts?

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 & thus will be likely to
have the tire tread move to the center of NON-safety rims, & loose all air very suddenly,
is FALSE?  In fact, tires mostly expand in width at speed/temperature, & that is typically
not any factor in a tire moving to the center of the rim. 
 


Tube vs Tubeless, from several viewpoints:

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.  THAT can happen
with tubeless....or tube...type tires/rims/etc.  The 'safety' bump in a 'safety wheel/rim',
as used with tubeless rims, does not prevent air loss from a bent rim.  It does 'help'
prevent a very fast air loss that would occur if the tire became un-beaded, &
conditions & the rim were such that the tire bead would otherwise have moved to
the center.   Then, if you think about it, why the lack of such safety bumps or ridges
in automotive tires.....don't those tires get exposed to SIDE FORCES that 'should' try
to force the bead off or inwards, compared to 2-wheeler's that hardly have much in
side-forces, comparatively?  What about radial tires on motorcycles, where the tread
can move sideways even more?

Below photo is of a BMW Snowflake wheel which is designed to be used with a tube. 
A tube was installed, the rider ran over a brick, which bent the rim. The tube held air;
the rider returned home safely.  It is questionable if the rim had been converted to
tubeless use, if the tire pressure would have remained usable,,,,or would have
decreased; if so, whether that would have been fast or slow.     There is no
question in MY mind that IF the bent area was severe-enough, the air would have
disappeared from the tire VERY rapidly in a no-tube situation. If the rim was already
of the tubeless type with no tube, a severe bend could also cause the tire to loose
air very quickly.  
A valid argument can be, and IS, made for situations where there IS a tube, & a puncture
or otherwise a 'flat' causes the tube to be sliced open by the rim itself.  That will also
result in a fast exit of air. 
These are some of the various things to think about. Loss of air, how & how fast, are
probably amongst, or ARE, the PRIME arguments for/against using a tube-type rim as
tube-less (AND EVEN WITH TUBES!!).  Yes there are general arguments about which
is better, tube or tubeless,
even on rims being used as designed.  


Reasons offered by those who want tubeless tires: 
(1) Easier on-road tire repair. I think THAT is the PRIME REASON.  Tubeless tires MAY
      loose air from simple punctures much more slowly.   With tubes, a puncture MAY
      be similar, but they usually leak faster from a puncture; thus HAVE TO BE FIXED by
      a patch, which typically means wheel & tire removal.
(2) Possibly reduced weight, which means slightly better handling & 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 might
      be made deeper.
(5) Without a tube, the tire temperature is less, & the tire tread may last longer; or, a
      better rubber compound could be used.

Seldom do folks say that they know that tubeless tires with a seriously bad puncture
must be REPLACED, NOT repaired (or, repaired only very temporarily, & ridden at low
speeds, until they can obtain a NEW tire).  OFTEN they know, & ignore these things.

I think it reasonable for me to state that I have mixed feelings about many of the things
mentioned so far in this article.   
While many have ridden on tubeless tires without
tubes on tube type rims quite successfully & safely for many decades & hundreds of
thousands of miles,
MY CONCLUSION IS THAT IT IS LESS SAFE. That hardly means it
is totally UNsafe!   It is my belief that 'less safe' is far safer, over-all, than many will
say or believe.  It is all going to be your choice anyway. 


It is only reasonable to point out that motorcycling, in itself, is a more dangerous
thing to do, than to use many other forms of transportation.   Humans like to do
certain things that are fun/dangerous.   Perhaps the better statement might be: 
What is YOUR level of safety?   Do you wear All The Gear All The Time (ATGATT)??  
If not, what is more dangerous, not wearing ATGATT, or running tubeless on
snowflake wheels?   OR, is it really fair to submit that question at all?     Would this
argument/question be better if I put it in other terms?


When I started riding there were no such things as tubeless tires for motorcycles.
That means that the inner walls of the tires were not officially sealed to prevent air
loss.  The truth probably is something like SOME tires really were sealed OK on the
inside & might have been useable 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
& 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) now & then because of incorrect tire fit, friction between the tire
wall and inner tube generating excess heat, rusted rims, etc.
Tubeless tire technology
does away with the need for an inner tube & 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 this further).   A reason is that
a simple puncture typically releases air more slowly than with a tube, mostly due to
the valve fitment (adding sealing rubber at the tube type valve stem is an entirely
special argument and discussion).  Another reason is, of course, that it could be
CHEAPER, with no tube required,,,,,that also means less labor to install the tire. 
Another reason is longer tire life would be possible (less heat build-up), so one
could design for longer life.....or higher performance with some additional life.
To a MUCH LESSER extent was Public demand.  The reason it was so little
desired by the public, hype & advertising aside, is that cars carry spare tires & FEW
drivers will, themselves, actually repair a tire with a punctured tube.
 

Let's get back to exclusively motorcycles:

If a tubeless tire (no tube installed) gets a small puncture, air escapes only through
the puncture hole, leading to a slow & 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 & riding technique
at the time, etc.

While 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 motorcycle,
that was not very likely.  An 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), was allowing the inner tube to protrude
& be gashed/slit by the rim, badly, for a fast DEflation.   Arguments in favor of
tubeless tires was that situation, and another was that a punctured tube, used
inside a tire mounted to a tube-type rim, will almost always leak faster...but no proof
of that idea was furnished.  It also depends on the type and sealing of the valve stem. 
A burst-balloon effect could not happen if the tube remains inside the tire
and is not bulged out from under the tire bead.
 

Tubeless rim & tube type rims usually have different ANGLES of  bead area metal....
but not necessarily what you might think.  I will get into that a fair amount in this
article, with photos/sketches too.

The 'safety bead' or safety-bumps in a tubeless rim are supposed to prevent the tire bead
from moving into the rim's center.   Go back, and see the photo at the beginning of this
article.  The tire hit an object in the road, which way did the rim bend?...did the tire go into
the rim?   Remember, this wheel was designed to be used WITH tubes.  Suppose this
was a tubeless tire, and on a tubeless or tube type rim.  Can you think this through?
I'm going to get into things in a lot of depth in this article.

Tube-type usage is VERY common for DIRT BIKES, the PRIMARY reason for which is
that they may sometimes be used at quite low pressures. 

What type of tires are used on BMW's bikes that are sold for on and off road use, such
as the G/S and GS?  What is different about the rims?....and I don't mean just the later
GS rims that have the spokes outside of the normal 'in rim' area.   THINK!!!
 


Fast exiting of the air pressure in a tubeless tire more or less can depend on the
rim design & any rim damage.  Manufacturer's have sought ways of keeping the
tire bead in contact with the rim area, even for rather extreme instances of the
rim being seriously bent from such as a large pothole, or the tire hitting an
object in the road.  While tire beads & rim shapes have changed, with improvements
for bent rim problems, there is no common method in use, nor has one ever been
widely sold nor promoted, to keep any type of tire 100% in contact with the sidewall
area of the rim, no matter what problem occurs.    

Discussions:

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, & 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, think of them as less strong, easier to bend from
road debris, rarely crack badly, but possible.   Compared to cars, loss of control in
an actual collision accident may be instant from such as impact with another
vehicle, striking a deer, etc..  Hitting debris in the road can cause loss of control or
momentary loss of control, or none such; but the bending of the rim might be
enough to let all the air out quickly from a TUBELESS OR TUBE TYPE usage, since
in a tube situation the rim could slice the tube; and tubeless, the rim can be bent
enough to cause air loss.  

MOST motorcycle 'flat tires' come from a modest to slow loss of air from a simple
puncture.  Loss of control, would, in my estimation, be rarer, as almost always
there is an indication of mushiness & a weaving feeling that considerably precedes
any complete loss of air.  It is fairly rare for a rider to lose control.

Manufacturers have tried rims with various angles to the bead area.  Some also
put bumps in the rim insides so that the tire would not likely be able to move into
the center area of the rim.  That does not help matters if the rim bends towards
the hub enough to let air escape between tire bead and rim bead.


Since another possible movement of the tire is towards the center of the rim,
manufacturer's also tried different rim shapes in the center of the rim.  Dirt bike
riders from long ago, using very low pressures at times, actually had various
means of locking the tire bead to the rim...INCLUDING!!....CLAMPS & SCREWS!

NOTE that there are TWO general & common types of 'bumps' to prevent the tire
bead from moving into the center of the rim, & 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 TOWARDS the rim bead area.  That type of rim is generally known as a
Safety Rim.  Bumps or ridges do NOT totally prevent (as some think) the tire from
becoming disassociated with the rim bead area, thus, even with a tubeless
designed rim, it is possible, on having a puncture or rim damage, to have the tire
lose air 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, & that
is obviously not so, but they can be 'helpful'.   

My conclusion is that many who say disasters are about to come upon those who
use 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?  
THERE IS SOME...but just how much?
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 somewhat
less safe.  
How much less, over-all, I do not really know.   It is very difficult to find real
data.  BTW...in your riding career, how many times have you hit something in the road
large enough to cause a fast loss of air from a bent rim?  What about any of you reading
this that have been using tubeless tires without tubes on tube-type rims?
What about tubeless tires on tubeless type rims?

Answers to questions like those, & maybe some other questions, MIGHT give some direction as
to what any safety change REALLY means.

THINK!    We all know, and it has been proven over and over, that more lights added to a
motorcycle, & use of reflective clothing & certain bright colors on a helmet, ETC.......all seem to
reduce accident rates.   But, is there a limit or some point on some accidents curve, that shows
how much gives how much better protection?   
Would using tubeless tires on tube-type
rims, without the use of tubes.....be as less safe as, perhaps, not having the brightest
color on your helmet?   Not having ...and how many....extra rear lights?    What about
a headlight modulator?

WE DO NOT KNOW...      OR, DO WE?

I hope I have presented some ideas for thought.   I am not promoting the use of no tubes in
tubeless tires on tube-type rims, but I sure would like there to be a REAL discussion, or at least
some sort of thinking, about safety depths.

 


RIMS: 

This is from a 1979 R45.  Snowflake.  Note the
center drop & 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, & that there is
knurling for the tire bead!  What do YOU think those
knurled areas really are for or really do?  Keep the
tire from rotating as the inner tube looses enough
air, & forces are trying to rotate the tire, and maybe
rip the tire valve off the inner tube, releasing air
faster?   What is YOUR idea about the knurling???

 


This next group is of safety bead/ridges styles:
Note the lack of any knurling.  Maybe tubes are
not used...eh?
Take a close look at the rim bead area ANGLE,
and compare to the rims, above, with no ridges.
You MIGHT get the idea that BMW was more
concerned about the tire bead moving INwards,
than outwards...EH?!?


 

 

 

 
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, & 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 & side area, that the tire bead rests against.  The WM-2
shape has a contour in the middle; & angles outward from the middle, & 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.  
I think THAT style is safer than the WM, regarding tire movement off the bead.

Some BMW rims have 'safety rims'...which helps to 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; the horizontal part that the bead ending fits has a noticeable slope.... that slope is
OPPOSITE  the TUBELESS rim shape!!  Yes, that is correct, the angular part goes in the
other direction!

    
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. 

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!
AND....is nearly identical to the WM non-straight shoulder type. It is more like the TL shape! 
NOTE the 5 angle is OPPOSITE the CP, yet the CP is FOR tubes, and the TL-H2 can be for BOTH
tubes and tubeless.   Are you confused?  

The CP type, see above and also the lower, below, sketch, 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.
I can provide the engineering book from such as Metzeler, showing this MT situation.

   
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 & 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, & some rims even have had both
bumps & ridges.  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.


 
Above is another sketch, showing WM, a version of the MT/TL, & a
version of the CP.
Especially note how the CP type rim will help keep the tire association
with the rim.   If you think about all these sketches, & think about what
REALLY might happen under several circumstances of using & 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; the particular design slightly up from
the valve stem on the 'sidewall' of the TUBE; & the Metzeler tube design at
the core.  Probably a good suggestion by Metzeler....yet totally forgotten
by probably everyone.



2.  BOTH the CP & 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 &
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 (& CP opposite to tubeless
types). 
You can't see that, in the 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.   NOW, put on your thinking cap!   Those later
wire-spoke wheels with the spokes outside the air cavity were designed
specifically for TUBELESS tires.  Take a look at the R100GS photo, well
above.   THINK about the SHAPE of inside the rim, and you might get some
funny ideas?  EH?   You think that maybe the rim is safer ONLY when a tire
MIGHT try to move its bead to the CENTER?  Wouldn't air be release very
fast if the tire moved off the bead, INwards, in a very small amount of
movement?   If that is so with a TUBELESS tire, why could a Snowflake,
designed for TUBES, and the rim being so similar EXCEPT for the INNER
RIDGE,  be so much less safe, even dangerous, as some say?   HUH?
You may be getting the idea that old-wives tales and MISCONCEPTIONS
are rampant, EH? Wait until you read the next paragraph, in RED!


As you have seen previously, the MT & MTH2 rims are different from the WM &
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/ridge 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 & 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.  
Has ANYONE ever said anything to you; or,
have you EVER read anything, about the bump or ridge
REALLY being there to help hold the tire to the rim
so you CAN MORE EASILY inflate a tubeless tire?

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. 


OK...now that you have plowed through & read all that (and likely gotten confused)......
below is the easier (?) to understand information...on what you need to know.


 



The rest of the information:
 

Caution:     SOME of 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.  You have already seen some of my ideas, and manufacturer-published
information (which may, and does, vary with such blind acceptance). 

    You are told, by BMW, by tire makers, & by many others, that you MUST use tubes on the
    Airhead wheels that came with the bike that were designed to use tubes.  I say:  Let us simply
    accept, that there is SOME value of higher safety in doing so; in SOME circumstances.  I
    think this is a fair statement.

If you were to use a tubeless-rated tire & add a tube, THE COMMON, and manufacturer-published
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 anywhere's hardly even close to the maximum speed the tire is rated for,
even reduced one notch!  The Airheads are not capable.  NOT HARDLY EVEN is spelled-out
that this advice for tire speed ratings are for SUSTAINED speeds.
 

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 & 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. 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 somewhat over 100 MPH. Some of this
information used to be, & usually still is, found in SOME tire manufacturer's literature.

FURTHER, manufacturer's equip their motorcycles with tires rated for considerably higher speeds
than the motorcycle can obtain!   

More Snowbum thoughts:
Tires are designed, in the rubber compound, sidewalls, tread depth, belts, etc, so that from zero to
the rated speed, they deliver a certain friction & 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 or
other problems.  I base my conclusion on theory, manufacturer's engineering manuals, & 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 & without tubes.  I also have testing, &
others' reports, on extremely hot tarmac very 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, & in one
instance the treads were so heavily loaded by gear & passenger, in such hot weather & extremely
hot tarmac, that the tread literally began melting away.    

Tire manufacturer's design the depth of the tread for several reasons.  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 & longer lasting tread!  That can work out well, particularly if your
speeds, aggressivness, and loads are moderate. 


If you stop here & 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 and extra flexing friction, ETC....?   
Yes, it is so. Manufacturer's, not wishing to get overly-involved, do not mention this.

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, & 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 did not seem to
change very much (about 3 psi was the very worst; even getting that much change required QUITE
aggressive riding).   This was on various types of surfaces, speeds, tightness of turns, etc.

I have to admit that I did not expect these results to be exactly as I found.

2.  HINT:  NEVER fail to use tire talc when installing a tube; rub it all over the tube & 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 SOME 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 an old-style radial tire, approach handling with slowly
increasing steps of aggressiveness & 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....preliminary.... opinion.


4.  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 marked tubeless MAY SLOWLY loose air if not used with tubes,
as they could be porous in tread or sidewall, or bead.  I have seen tubeless AND tube-type tires hold air
for a long time on CAST tube-type rims (no experience on tubeless GS wheels).  Occasionally I have
seen tube type tires that would very slowly leak air, when used on tube-type rims, such as BMW tube-type
Snowflake wheels.  I am talking about just a FEW psi per week. In every instance, it was due to lack of a
"tubeless coating" on the inside of  the tire.  In most circumstances these were OLD STYLE SIDECAR
RATED TIRES.  Mostly what I have seen is that the loss is quite slow.   Weekly topping-up is adequate;
pressure loss not usually being too much more than normal found if using 'natural rubber' tubes, which
quite normally leak faster than other types of tubes. 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.

Tire pressures are supposed to be checked before every day's ride, right? 

There are plenty of other tires that are not supposed to be used as tubeless, yet still being made,
particularly for off-road use, and sometimes used as tubeless.

SOME folks have used the snowflake cast wheels with tubeless tires, & installed a tire sealant; & had
good success in slowing any air loss & have even had the sealant work well for them with punctures.
MANY have had hardly any air loss over time. 

Purposeful off-road tires are, in the majority, meant for use with tubes, many of these tires do not have
any interior sealing coating, MANY DO! 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/clamps, 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. 
That is done, although somewhat loosely, DURING INSTALLATION OF THE TUBE, TO
MAKE THINGS EASIER.

   
 (A).  The tube could fail to release air from between the tube & inside of the tire....which it is
              SUPPOSED TO DO normally in use. 

     (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, & the purpose is TO HELP DURING
              INSTALLATION OF THE TUBE INTO THE TIRE.  Using the nut against the rim
              does not allow for even slight tube movement if one has a flat; then the tire
              CAN rotate on the rim some, and rip the valve completely out of the tube, causing
              a FAST air loss!

    
(C).  If the tube seals to the rim too well, it can trap air from tube to rim, and allow tube chafing. 
             The tube could chaff, & fail early.  This is particularly so if you did not rub the tube & tire
              insides with tire talc.

     (D).  I can quote from tire manufacturer's manuals & a BMW bulletin on these facts! BMW
             has had Service Bulletins (SI's) on these valve nuts.  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 & if the nut was at the rim, & not the cap, the stem could suddenly &
             disastrously tear out.  What BMW did not say, & I will, was that this can come from very low
             inflation AND over-inflation during seating of the tire.

     
(E).  TUBELESS TIRES are, as you have seen in this article, sometimes used on TUBE TYPE
              RIMS.  The stock tube-type rim hole is 8 mm.  If you do not wish to enlarge the rim hole
              for a standard pull-in type of tubeless stem, 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.

     (F).  
There are those, often sidecarists, who seal the tube-type stem with rubber
              doughnuts or by other means.   Sidecarists do lots of things that some may
              consider wrong (or, otherwise unwise, or at least strange).  


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.

Since rims vary in angle of the bottom & sides, & some have the protective internal bumps to prevent
the tire from moving INwards, ETC., you should THINK about things, if considering not only
NON-standard use, but maybe in STANDARD use.  For an 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 loose-air-fast situation occur, if the
tube was pinched or pushed-out and the rim then cut it. 

7.  It IS possible for 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 & a lacquer applied to the
inner surface.
   see 4, above.

One conversion method involves enlarging the stem hole, & possibly spot facing the inside of the rim
slightly so the mounting area for the stem is relatively flat and possibly thinner.  That allows small tire
'rubber tubeless stems' to be fitted, instead of trying to use larger types.  As noted previously, 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. See prior comments too.
For these various options, do consider the amount of spot-facing, or flush machining, that, if
excessive, might weaken the rim. 

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 CAN work OK!

The conversion to tubeless has been done many times & I have heard, SECOND-HAND, of only ONE
problem over the years.   While practice is NOT as safe theoretically & probably practically too,
as using tubes, problems do seem to be very rare.   Folks have done considerable racing with tubeless
converted snowflakes. 
So far, except for the 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, & valve stem cores are manufactured both short & long, & 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 an Airhead anyway; but, there have been instances
of weak valve stem core units that leaked air.   A short valve core with 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 from
high speed rotation or just a poor seal.  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 MAY use a BAND (or rope!) around the rim
of a tubeless tire, to squeeze the tire to the sidewall....and this is JUST ONE of several goodly reasons
I don't recommend carrying 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.    One of the 'secrets' about getting tires (tubeless or tubes) to seal fully all-around
the rim, is to remove the valve core & 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; & to do the work with tire & wheel hot from being in the sun.
   Use of lots of real tire
lubricant on the beads, & lots of air volume flow helps seat the tire.....otherwise, very high pressures
inside the tire/tube might be needed, which can 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, but smaller tanks can work well.

10.   Sidecar folks sometimes use rear tires on the front of the tug, with the directional arrow, if there is
one, reversed. SOME modern tires are marked for use in both directions, depending on if used for a
front, or a rear tire.


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 many 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 a
cup washer. 

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 PROBABLY
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.


ADDENDUM/Clarifications:

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 occasional event
of a tube bulging out from underneath the tire bead, being cut by the rim.

 


CONCLUSION:

As a general rule, I usually advise against any tubeless tire withOUT tubes on tube-type
snowflake wheels. I think that such use is 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....on your tube-type BMW 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.
I am simply trying to inform you of how things work as best I understand them, what
others have done, and the caveats...as I know them.            This is a legal disclaimer!!!


Revisions:
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
remove language button in 2013, due to javascripting problems.
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
10/09/2015:  Revise most of article to try to improve clarity.
12/21/2015:  Additional revisions for clarity; update meta-code; justify left and reduce width

 

Copyright, 2014, R. Fleischer

 

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