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BMW Motorcycles:

Tubeless versus Tubes ...the whole story (?), and then some
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 and against using tubes with rims designed for tubes.   Other articles on this website have further information on these subjects, such as catch.htm and section5.htm.

This article will present arguments for various sides of controversy involved with tube and tubeless tires and tube and tubeless rims. 
NOTE:  There are folks (that I highly respect) that say you must never run any sort of tire without a tube on these rims that were not designed to be run tubeless.   I am personally NOT AT ALL that much against the practice. I will try to inform you herein with unbiased information.

PART I...the rims....

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 and the early 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 bottom; although there can be differences in the dished center areas of the rim.  The WM2 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.  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.    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!!

2.  BOTH the CP and the WM 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 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.

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). 



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. 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 gotten confused......below is the easier (?) to understand information...on what you need to know.
Did you note that I have not included photos/sketches of these rim shapes?


Part II, the rest of the information:

Caution!.... SOME of these are MY personal interpretations/ideas; read and do what you want to, 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 supposed to use tubes on the Airhead wheels that came with the bike (and that were designed to use tubes).  If you were to use a tubeless-rated tire, and add a tube, THE RULE is/was that you should REDUCE the speed rating of the tire by one step.  This RULE really does not mean much to Airhead owners, who are UNlikely to be riding at the maximum speed the tire is rated for 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 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 treads (depth, belts, etc), to, over the zero to maximum rated speed, 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 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 some road testing I did.  Yes, I actually did testing on two very different tire types (brands, models...) with huge pressure differences....on the same tarmac area.   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!    In a few instances this might have an effect on handling at moderate to higher speeds, but I have not seen enough of this to warrant more than this maybe statement.  

2.  NEVER fail to use tire talc when installing a tube; rub it all over the tube and inside of the tire....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 folds.

3.  Almost all tires marked tubeless, are OK for use WITH tubes at a reduced maximum speed.   Exceptions MAY exist in trying to use RADIAL tires.  As a general rule, I suggest you do not use radial tires on your Airhead.     You generally will not find 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, actually. 

4.  Tires marked tubeless are 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 overblown.
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 slow, and weekly topping-up is adequate.  Note that tire pressures are supposed to be checked before every day's ride.  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. MANY have had hardly any air loss, comparable to the use of some 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 with 'natural rubber' can be said to be much less likely to be ripped from a puncture.

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.   When installing a tube (tubeless or tube type rims), do NOT normally leave the mounting nut against the rim.  You could have the tube fail to release air from between the tube and inside of the tire....which it is SUPPOSED to do normally in use...and the tube could chaff, and fail early.  This is particularly so if you did not rub the tube and tire insides with tire talc.   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 IN INSTALLING THE TUBE/TIRE. 

There reasons NOT to screw the tube valve stem nut to the OUTSIDE of the rim:
     (A).  No allowance for tube movement if one has a leak, and the tire rotates on the rim some.
     (B).  If the tube seals to the rim too well, it can trap air from tube to rim, and allow tube chafing.
            The purpose of the tube nut is to help DURING installation of the tube...and can be
            discarded...or run up to the cap...after the mounting is done.  These ARE NOT just my
            ideas!   I can quote from tire manufacturer's manuals...and a BMW bulletin...on these facts!
     (C).  BMW has had several bulletins out on these valve nuts, and one SI gave an additional reason to have it
            up against the cap, that was that improper inflation could cause the tube to be weakened at the valve stem
            and if the nut was at the rim, and not the cap, the stem could disastrously tear out, suddenly.  What BMW
            did not say, was that this comes from very low inflation AND overinflation during seating of the tire.


***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

6.  The 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 are 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), and don't mind that...then, it is your choice, with that knowledge...to not use a tube.

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 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.  There is also a metal stem with a rubber O-ring that can be fitted, into the existing hole size (spot facing inside MAY be needed).      See #11.  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, this practice is NOT as safe theoretically as using tubes.   This does NOT mean it is totally UNsafe.  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.  As tires rotate at 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 a great idea 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.  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....together with lots of properly thinned commercial tire lubricant.  It also 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.

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.

 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. 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.

13.   Snowbum has, on three 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 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.   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.  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 sells small 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.

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.   Radial tires...again, in general.....have some peculiar characteristics that could make them handle strangely on Airheads.  You might love them.   YOU ARE ON YOUR OWN.  They, 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).
 


ADDENDUM:

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 without a tube. 

As a general rule, I advise against any tubeless tire withOUT tubes on snowflakes, my feeling is that it is LESS SAFE, OVERALL, all things and conditions considered, than WITH tubes.  How much less safe?  Well, maybe very little.   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... to 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!!!

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.

 

Copyright, 2014, R. Fleischer

 

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