Tubeless versus Tubes
...the
whole story, and then some
©
Copyright, 2012, R. Fleischer
section54, subsection 6
section6.htm
This article will discuss in depth: 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.
This article will present arguments for both sides of this controversy. There are those 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 "all that much" against the practice. I will try to inform you herein with unbiased (I hope!) 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. This is a particular shape of primarily the inside area of the rim. The WM2
shape does not have the 5 degree angle increase of the
tubeless rims on the
bottom area and side area, that the tire bead rests against. The WM2 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.
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.
The flat portion of the tubeLESS rim just inside the bead
is usually a bit wider (depending on the particular tubeless rim design).
3. There are other rim shapes, such as MT and MTH2,
suitable
for use with or without tubes. These types of rim shapes WERE used on some
Airheads, such as the R80GS (NOT G/S); R80R; R100R. The R80GS has 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 part of the rim
that meets the sidewall of the
bead is nearly the same (in fact the part of ALL the rims mentioned in this
article are pretty much the same where they meet the side of the bead, except
that angle). 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.
***The CP and the WM2 do not have that MT 5 degree upwards slope;....rather, the angle is 4° DOWNward on the CP, and none on the WM.
This section reserved for sketch or photo of rim shapes
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.
Part II, the rest of the information:
Caution!....
these are MY personal interpretations; read and do what you want to, at YOUR
RISK, NOT MINE:
1. You are supposed to use tubes on the Airhead wheels that came with
and were designed to use tubes.
If you use a tubeless-rated tire, and add a tube, you should
REDUCE the speed rating of the tire by one step. Use of tubes
causes the tire to heat up more, reducing tread life, and that is
the primary reason for the speed rating change. This
information used to be, and maybe still is, found in some tire
manufacturer's literature. 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.
2. Almost all tires marked tubeless, are OK for use WITH tubes at a
reduced maximum speed.
SERIOUS exceptions MAY exist in trying to use RADIAL tires. DO
NOT! You generally
will not find radials that fit your Airhead anyway.
3. Tires marked tubeless are specially made to ensure they
hold air. Tires not so marked MAY loose air, as they 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, but mostly what I have seen is that the loss is slow,
and the usual weekly topping-up is adequate. There
have been a FEW reports that SOME snowflake wheels are porous and
leak air. Maybe. I know of no serious air losses
though.
Off-road tires are, in the majority, meant for use with tubes,
and many certainly do not have any interior sealing
coating. Those tires (well, tubes) may be used at times as
low as 5 or 8 pounds of pressure.
Some have used WM2 rims without tubes,
usually with only a veru slow leak, over maybe a week or two for maybe half
pressure (many times much less); but this is very unclear, not
enough reports have been given to me.
3. 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 will chaff, and fail early. This is particularly
so if you did not rub the tube and tire insides with tire talc. Using that nut against the rim defeats the safety of allowing the tube to
be able to move slightly, as the tire might, upon a flat occurring.
Run the nut up
against the cap, or throw it away, or put it in your tool tray....it is part of
some of the tubes you purchase STRICTLY
TO HELP IN INSTALLING THE TUBE.
***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 #9.
4. 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.
5. It IS possible for the snowflake tube type wheels to be converted to use tubeless
marked tires without using tubes. Some few snowflakes are porous, but that
is fairly rare, most will hold air OK. For the
porous ones (again, quite rare), 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)...but all these conversions need some thought, ahead
of doing the modifications. See #9.
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.
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, etc.
6. 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 sealing cap, is usually OK for us. 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.
7. 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. Restating:
In the
HOME or SHOP environment, a LARGE tank of high pressure air
really does HELP, as a large
VOLUME of air is available to help seal the tire to the rim. NOTE
that the best practice is to REMOVE the valve core when installing a
tire.....and this applies to both tube and tubeless tires, with or without
tubes. 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. Having the tire in the
sun, letting it heat up quite hot, is a big help too.
8. Sidecar folks sometimes use rear tires on the front of the tug, with
the directional arrow, if there is one, reversed.
9. 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 rip the stem out of the tube; 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, 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.
***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 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.
10. 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.
11. Snowbum has never converted his snowflake
rims. Snowbum WAS going to convert his Airhead sidecar tug's
snowflakes; never did, as he sold the rig before he got around to
modifying his rims and installing tubeless tires. Snowbum has,
on three of his Alaskan adventures, installed tubes WITH rubber washers and
a cup
washer.
12. The snowflake tube-type wheels will handle major rim denting
and still hold air, if tubes are installed as they were designed to be.
That being said, there have been numerous reports of very serious rim bending, with NO problems
with tubeless tires, without tubes.
Thus, there is NO clear-cut 100% answer, in MY opinion, on whether or not it is safe, or safe enough, 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 on 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. That is OK with me. There are advantages.....and disadvantages.....to tubeless tires. Tube-type tires with tubes develop more heat due to friction effects, but the tubes can be repaired (replacement is far better), and you can almost always re-use the tire. Not always repairable with some tubeless tires, 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) 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 is now selling
cheap small electric pumps in a small plastic case, I purchased one for myself, it even
has a gauge; a photo is in the tire repairs article.
Radial tires: 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 VERY iffy on
Airheads. You may find the handling dangerous. Or anything else.
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).
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).
When any tire containing a tube, gets a bump big enough
to damage the rim severely, you may well retain air with the tube, and less likely
without a tube. It's a mixed bag because the tube-type rims (WM2) are much more likely
for the tire bead loose integrity with the rim, thus
the tube is a help. There are definite reasons
that off-road bikes mostly use tubes.
NOTE that MANY, maybe the vast majority, of tubeLESS marked tires that fit the airhead snowflake WM2 rim,
are fine WITH tubes
installed...just mentally reduce the speed rating by one step, due to tube friction effects (be SURE
to install all tubes with tire talc on the tubes and inside the
tire walls). Tubeless tires have
basically the same or nearly the same bead area as tube only tires, the
primary difference is the inner sealing layer of the tire....but, again, there seem to be some exceptions, and I have been unable to get definitive,
KNOWLEDGEABLE answers....because
I have been unable to chat with the actual factory engineers, and the representatives seem to be....ah.....not so knowledgeable....or just
secretive (or, otherwise afraid to say anything).
The flat portion of the tubeLESS rim just inside the bead
is usually a bit wider (depending on the particular tubeless rim design).
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.
You are totally on your own in this regard. If
you noticed that I earlier mentioned that I was going to run tubeless on my sidecar rig,
keep in mind that I would be carefully selecting the tire, and NOT modifying the rim (special valve stem, sealed with O-rings,
would be used), and that I understand the tradeoffs....including my not doing warp 9
speeds. However, trying to be honest here, sidecar use puts
intense side-pressures on the tires, since the the motorcycle is
not leaning in curves (well, except for leaner-type sidecar
rigs....another story....), and as such, sidecaring is MUCH
harder on the tires, as far as rim sealing would be concerned.
Thus, PERHAPS, my cautions are excessive, for 2 wheel motorcycle
use.
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
© Copyright, 2012, R. Fleischer
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