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Primarily for BMW Airhead Motorcycles,
but may be of interest to all motorcyclists.
Tubeless versus Tubes.
IN DEPTH discussion. Tubeless on
Snowflake tube type rims; others??
© Copyright 2021, R. Fleischer
section 54, subsection 6
https://bmwmotorcycletech.info/section6.htm
This article will discuss in depth:
Rim shapes (including BMW rims). Using tubes (or not) on tube-type rims; tubeless operation; repairs; arguments for & against using tubes with rims designed for tubes and not for tubes. Tires designed for tubes. Tires designed as tubeless (and if used with tubes or not). Other articles on this website have further information on these subjects, and much more, such as:
https://bmwmotorcycletech.info/section5.htm
&
https://bmwmotorcycletech.info/TireRepair.htm
Make a pot of coffee ...you are going to need the caffeine to read all this next part; ...after which you will be reading the rest of MY article ...stopping, pondering, thinking....
First, a link to a nerdy article that has enough math (enough photos too), from a Goldwing'er (Honda Wings have somewhat unique rims) to spin your head, even for the nerdy amongst us. Fine if you want to quick-scan the article, but do see the second part of the article.
https://www.goldwingfacts.com/threads/design-differences-between-car-and-motorcycle-rim-tire.400426/
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. That article has some real jewels of information here and there, in-between the nerdiness. It is really worth the read. It is one article, followed by dozens of pages of commentary from others; look at them if you want to. Amongst the 'jewels' in the article are the definitive details on rim shapes and dimensions of such as motorcycle tire bead areas (thickness and shape too) versus car types; and, the facts about why friction (traction) is INDEPENDENT of contact area ....and why wider tires are used to obtain better WEAR from otherwise less-mileage stickier rubber compounds. 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 110 or 120 metric, etc. Think about what REALLY happens when you go to larger size tires (larger width and/or profile change). You may ...I hope so ...be very interested. Once primed (or mentally worn-out!), then it's time for the rest of my article, which starts just below here.
The article, below, will present data, discussion, & arguments, for tube/tubeless tires & tube/tubeless rims. Some of the concepts & discussion may require reading a paragraph, & then stopping to think. It is not likely that readers will be able to just read this entire article straight through, & gain the information I would like/hope you to absorb.
There are folks (including some that I highly respect otherwise) 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, and why you are reading this article (?), is that YOU gain a good understanding of all aspects & be able to make your own decisions.
I will try to inform you here with UNbiased information. There is a lot of wrong thinking, misconceptions, failure to be open-minded enough ....to see the whole picture.
There are 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. BUT ....there are things not at all widely known. Keep in mind that manufacturer's are not at all interested in long-winded 'explanations-information", like in this article you are reading. Such verbose information would tend to cause them a lot of labor in further explaining things, as there are always people who 'need to contact the manufacturer' to make specific points, commentary; or, have the makers provide additional information, etc. Thus, manufacturers tend to make simple, easy to understand statements, ...do this; or, don't do that. Their company lawyers are probably the ones that promote that attitude ...and company policies.
Motorcyclists (& especially sidecar/trike drivers) do all sorts of non-standard things. Car tires, wide rims, change of rim diameters, lots of "etc". If it was really so vastly unsafe to run tubeless tires without tubes on tube-type motorcycle wheels, why do sidecar rigs, which produce side forces that can be extreme (2 wheelers do NOT have anything even close to those forces) do NOT have lots of accidents with blown tires, tires coming off rims, etc.? Sidecarists, sometimes, depending on situation & equipment, may even install tires in the 'wrong direction'. Now-a-days many tires are marked on the sidewall as to what usage is (rotational direction), but many tires are marked for one direction ...and some are marked for both directions, depending on if used as a front, or a rear. These are only some of the many variable uses. Sidecar rigs have an exceptionally safe record.
I'll try to answer questions in this article ....and, I will strongly try to be non-biased in my provided information.
Of course, just because many folks use tires & rims in all sorts of non-standard ways hardly means that 'anything goes'.
There are levels of safety in just about everything. Typically, the lower levels of improvements are large jumps. With additional improvements, every slight bit additional means more and more effort, & one then might well question why one should go to huge lengths for a tiny improvement. The car manufacturer's, and the motorcycle manufacturers all well know this. Vehicles are compromises in nearly every area. Ultimately, the safest tire/rim usage is TO NOT RIDE AT ALL! I am not being facetious here. Just what are the chance that your particular decision about modifying your motorcycle rim or tire/tube usage will result in an accident; or, result some other situation, versus not having done the modification? What are the REAL facts?
Did you know that some have raced Airheads on paved tracks, at quite 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.
Tubes vs Tubeless, from several viewpoints:
Before getting into usage/rims/etc., you may want to come back later and review the following article, https://bmwmotorcycletech.info/section5.htm. One specific point is that tubeless tires, all else remaining the same, can be safer, in some respects, than tubed tires, due to less heat buildup, AND, tubeless tires allow the tire manufacturer to use a softer better griping rubber compound (which may last longer too!) ...and there are other good reasons too. Tubeless tires are also nearly always easier to repair flats on. The wheels can be lighter with the tires mounted without tubes and this alone improves handling. All is not necessarily better. This article is primarily about mixing up tubed tires, tubeless tires, various rim shapes, etc., but it is only fair to mention these other things.
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. Having it move outwards is possible, if unlikely. If you think about it, what about safety bumps or ridges in automotive wheels? ...don't those tires get exposed to side-forces that try to force the bead off or inwards, compared to 2-wheeler's that hardly have much 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. If the rim had been converted to tubeless use, would the tire have lost pressure? How fast? No loss? It is entirely possible that if the tire/rim in the photo did NOT have a tube, it may or may not loose air, but certainly would have if the bent area was deep enough. 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 similarly cause the tire to loose air very quickly. A valid argument can be made for situations where there IS a tube, & a puncture or otherwise a 'flat' causes the tube to be squeezed outwards some, and then sliced open by the rim itself. That will result in a fast exit of air. Loss of air, how & how fast, is the PRIME ARGUMENT for or 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. BTW, one of the arguments (well, 'discussiions') is ...or should be .... what the owner feels/thinks about repairing a tubeless flat versus a tube type flat; AND, perhaps, is that owner willing to trade off what probably is a very tiny amount of safety, for a fair amount of convenience.
TUBELESS-TUBED:
(1) Easier on-road tire repair. The prime reason usually given, if asked. Other reasons include that tubeless tires MAY loose air from simple punctures more slowly (reasons for such thinking are almost never explained). With tubes, flats have to be fixed by a patch, or, a new tube, all of which is all more labor intensive & means wheel & tire removal from the wheel, or, at least one side is demounted.
(2) Possibly reduced weight of tubeless, which could mean better handling & mileage.
(3) No need to carry a spare inner-tube(s); repair kits can be simpler, take up less room. Those can be true. However, there are other factors, not the least of which is if the tubeless tire deflates and moves inwards some ...you may have trouble getting it back to full bead contact so you can inflate it; and, a bend rim may mean you need to install a tube to get riding again.
(4) Possibly deeper tread on some tires, as tubeless tires can run cooler, so tread might be made deeper. Without a tube, the tire temperature is less, & the tire tread may last longer; or, a better rubber compound could be used. Note that these arguments in are not necessarily true as all tires are designed to be run between certain temperature limits, otherwise the rubber does not perform as desired. Still, without a tube, the tire manufacturer probably can produce a better handling longer lasting tire.
(5) A tubeless tire can be ruined by some types of punctures; $$$ replacement; while a tube type might need only patching of the inner tube or a simple innertube replacement. Seldom do folks say that they know that tubeless tires with a seriously bad puncture must be replace, not repaired; or, repaired only temporarily, & then ridden at low speeds, until they can obtain a new tire. Sometimes they do know, & ignore these things. Thus, under some circumstances, a tubeless tire can be costlier, and/or require slow speeds, etc.
(6) Carrying a tube needs to be considered and not in place of patching equipment, and vice- versa.
(7) Spare tubes take up on-bike storage room.
(8) In the boonies, tubes allow you to reduce the tire pressure greatly, when needed. If you run as tubeless, and depending on what type of rim, you may well not be able to run quite as low pressures.
(9) What type of tires are used by BMW on their G/S and GS bikes that are sold for on/off road use? 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!
(10) Many folks do ride on TUBE type tires withOUT tubes, even on tube type rims. Tube type tires are supposed to not have the rubber pressure sealing layer inside. (Sidecarists are more likely to do this, but it is hardly all that popular to do so).
(11) Many folks do ride on TUBELESS type tires WITH tubes, on tube type rims.
(11) YOUR arguments, here:______________________________________________.
I have mixed feelings about things I have mentioned so far in this article. Riding safely, without incidents, on tubeless tires without tubes on tube type rims (probably the situation most cited in the various arguments) has been probably done for millions of miles. MY CONCLUSION, AFTER STUDYING WHAT INFORMATION IS AVAILABLE, WHICH IS NOT MUCH ...IS THAT IT IS LESS SAFE. That hardly means it is totally unsafe or even largely ...not even moderately. I think it appears to be SLIGHTLY less safe.
What IS the percentage or some other statistic, however possibly presented ...of "UNsafe"...?? It is my belief that 'less safe' is far safer, over-all, than many will say or even believe. It is your choice, anyway .
It is only reasonable to point out that motorcycling is a more dangerous thing to do, than to use many other forms of transportation. Humans like to do certain things that are fun, yet dangerous. Perhaps the better statement might be what is YOUR level of safety? Do you wear All The Gear All The Time (ATGATT)?? ALWAYS? ...100.000%? Wear easy to abrade-through-to-your-skin common jeans? Always wear proper boots? Armor padding? Leather is safer than nylon products like Cordura ...what about YOU?
What is more dangerous, not wearing ATGATT, or running tubeless on tube-type snowflake wheels? Is it really fair to ask that question at all? Would this argument/question be better if I put it in other terms? What are the statistics between rides or miles, and incidents/accidents, even severity ....due to not riding as ATGATT ...versus ...tubeless use on tube type rims (or, any other combination), for any problem at all? Is riding on tubeless tires as tubeless, on tube-type rims, more dangerous? Less dangerous? ...than exceeding the posted speed limit? Riding on a wet road? Riding on gravel? Riding on half-worn+ tires? Drinking? Slightly low tire pressure because you did not check the pressure? Not wearing gloves on a hot day? I could make a very long list. What about the REAL statistics about riding on tubeless tires without tubes on tube type rims ...versus using tubes? NO ONE, NO COMPANY, to my knowledge, has any meaningful statistics. I have heard of ONE accident ...and the details are NOT clear.
Am I promoting use of tubeless tires on tube type rims? NO. I am just trying to get you to actually think, and not blindly accept someone's (or some company's) statements.
........why the heck should YOU pay attention to MY writing? :__________________.
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. Probably some tires were sealed enough on the inside ...& might have been useable as tubeless ...but we never thought of it ...well ...no one I personally knew had discussed nor tried it; and one of the reasons was that flats were repaired by installing patches on the TUBES, and all riders knew how to repair their tubes, and just about 100% did so. BUT ...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 which let tube movement be abraded by rust/scale, etc. There are still plenty of cars and trucks with tube type tires being driven with tubes, with the same old problems.
Tubeless tire technology does away with the need for an inner tube & it is well-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 that too much further). A reason is that a simple puncture typically releases air more slowly than with a tube, mostly due to valve sealing fitment (adding sealing rubber at the tube type valve stem is a special argument and discussion). Another reason is it could be CHEAPER, with no tube required. That also means less labor to install the tube and 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. Manufacturer's are also using increasingly lower profile tires, and getting away with it (usually such tires produced a hard jarring ride), due to accumulating changes in suspensions, public acceptance, lighter cars, and other things.
Public Demand was not overwhelmingly FOR tubeless tires, which may surprise you, until you think about it. The reason it was so little desired by the public, hype & advertising aside, is that cars carry spare tires & few drivers actually repair a tire themselves with a punctured tube. They install the spare tire/wheel, and at the next convenient "Gasoline and Service Station" or "tire store" would very commonly have the puncture repaired. This is still the norm, whether old style tubed tires or more modern tubeless tires.
If a tubeless tire (no tube installed) gets a small puncture, the air typically escapes only through the puncture in the innertube, and then via the rim's assorted typically tiny places....almost always the process leads to a slow & typically gentle deflation. That puncture hole tends to remain small due to the surrounding rubber tending to somewhat fill-in the puncture. For a tube puncture, the release of air can be faster, but does not have to be. 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, tube (if any) construction, your speed & riding technique at the time, etc. Neither tubeless nor tubed type of tires, with or without tubes, will usually burst like balloons, in fact that is exceedingly rare. Tires also almost never come off the rims on motorcycles....no matter what type of rim (designed for tube use, or tubeless use). Do not forget that the majority of today's motorcycle tires are designed (otherwise, usually are tube type for off-road use, due to low pressures often used in soft stuff) to be used as TUBELESS, but are allowed to be use as TUBE type (BUT, TYPICALLY, THE SPEED RATING OF THE TIRE IS TO BE REGARDED AS BEING ONE-STEP lower).
Here are some various statements, arguments, whatever:
If a tire did come off the rim on a motorcycle, even partially, it was going to be due to a large rim bend allowing the inner tube to protrude & be badly gashed/slit by the rim, causing a very fast deflation; or, in the case of a tubeless tire, the tire disassociated with the rim and the air leak was very fast. For a tube type, a full deflation, or nearly-so, could allow the tire to rotate on the rim, and because of tube-to-tire friction, carry the tube along with that rotation, and snap the valve stem off the tube, allowing a fast deflation that way, even if the tire was still fully on the rim, and the tube was not being cut by the rim edge. Valve stems were specified to NOT to be solidly tied to the rim by a nut, so as to allow the tube to slightly rotate with the tire rotating on the rim without tearing out the valve. A burst-balloon effect could not happen if the tube remained inside the tire & was not bulged out from under the tire bead. With CARS, drivers tended to be oblivious to a slow to moderately fast deflation, until the car handled terribly bad ...by which time the tire might, or might not, have been ruined by running flat. Some would drive until the wheel rim was sparking on the surface. Motorcyclists are much more sensitive to changes in handling, and are unlikely to continue to ride if the pressure in the tire/tube goes down by even half.
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 somewhat deeply in this article, with photos/sketches, because of its importance to the topics in this article.
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 & 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, and would have NO safety ridges or bumps. Suppose this was a tubeless tire, and on a tubeless or tube type rim. Have you EVER seen anything written about how impacts may cause tire movements outwards, or inwards, in any real detail, or do they 'just say' that safety ridges/bumps are to prevent the tire bead from moving inwards. Many think it is obvious that the air pressure inside the tire (or tube) is what keeps the tire bead in contact with the wheel rim bead area (which is NOT all that true, once the tire is seated ...which YOU know about if you have ever seated a tire, then totally deflated it, the tire is USUALLY unlikely to come free of the rim bead area. ...but what happens if you just get a flat tire, no rim bending impact is involved. What does the tire do?...does it move inwards? Does it stay in contact with the rim? Can you think this through? I'm going to get into things in a lot of depth in this article.
Again, I caution you to THINK, and not blindly accept what may be old-wives-tales and/or misinformation ...even from bike manufacturer's, and tire and equipment manufacturer's!
Fast exiting of the air pressure in a tubeless tire more or less can depend on the rim design & 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 (besides screws through the bead), to keep any type of tire 100% in contact with the sidewall area of the rim, no matter what problem occurs.
Cars: Rim is VERY seriously bent or cracked/damaged. 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.
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 even modest sized 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' arise 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 rare for a rider to lose control and have an accident because of a pressure leak.
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. It is not the same thing for the edge of the rim to be moved/bent, as in the earlier photo, and an angular or side impact, which bends areas inwards. That is a very rare, indeed, type of bent rim. A considerable amount of bending is needed to cause the tire to come off the rim; and much more common is what you see in the photo, above. If the bending in the photo was enough, the air in a tubeless tire releases VERY quickly. If a tube was inside, it might get pushed out by the air pressure, as sort of a bubble, and then the continuing rotation of the wheel might (may not) cut the tube, and air would release fast. If you are thinking this through, you just might get the idea that tubeless tires are NOT all that much safer, perhaps not at all, or even as safe, as a tube type, for impacts with objects in the road. You might just be getting the idea that tubeless tires may have some advantages in many areas, but not all.
It is MY belief that the biggest advantage of tubeless tires for motorcyclists is the relative ease of repairing common simple punctures, where the tire has NOT moved inwards which makes it difficult to get a good air seal when trying to inflate after the repair. In second place is, arguably, advantages of lighter weight, potentially better handling, etc.
Since one 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! They did not want the tire rotating on the rim, tearing up the tube.
here 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 towards the rim center of the mounted tire's bead is functional for this. The thickness of the tire bead is important, and few seem to know that CAR tire beads are considerably wider, and do not fit motorcycle safety wheels well. Safety beads, bumps, and ridges, all will work to help keep the tire attached TOWARDS the rim bead area. These types of rims are generally known as Safety Rims. 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 have been 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, may not be thoroughly thinking things through. The tire manufacturer's will all say, in their literature, to NOT 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, and, in what specific area(s)?
My personal conclusions, & 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 less safe". How much less safe, over-all, I do not really know. It is very difficult to find real data. It would appear, TO ME, that the lessened safety is very small. 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? Tube rim? Tubeless 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 these, & maybe some other questions, may be of help.
How many times have you heard these words:
1. "...we all know"
2. "...it has been proven over & over"
3. "...the more lights you can add to a
motorcycle"
"...use of reflective clothing"
"...bright paint colors"
".. bright reflective colors on a helmet",
....ETC......."....all reduce accident rates."
UNfortunately, such 'common knowledge' is NOT NECESSARILY NOR ALWAYS TRUE. Fixation effects have been studied; as has blending effects. Taller and wider illumination works well, ...more lights in a small area can be worse. I know, you don't believe me. The initial reports, done by the military/government, are in here, besides personal testing which is on-going:
https://bmwmotorcycletech.info/recog-safety.htm
But, my point: ....is there a limit or some point on some sort of plotted accidents curve, that shows how much of anything 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 attention-getting reflective color on your helmet? Not having ...and how many ...extra rear lights? What about a headlight modulator? We do not know... OR, DO WE? Have you ever thought about finding out what really works?
RIMS:
Enough photos, etc., to make your head swim....
WM style rim 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".
Below is a 19" front Snowflake wheel, basically the same design as the above wheel.
Flat bottom type of rim, similar to above wheels, except for the flat bottom area, & 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? It is true that forces are trying to rotate the tire with regards to the rim, and if it does rotate, maybe due to a flat .....maybe rip the tire valve off the inner tube, releasing air faster? What is YOUR idea about the knurling? What about flat bottom versus curved bottom?
This next group of photographs is of safety bead/ridges styles:
Note the lack of any knurling. Tubes are not used, so no need for knurling to avoid tire movement on the rim, which would 'take along' the tube, and rip the tube valve out of the tube. If you are really thinking here, you probably just asked yourself a question. Quite a lot of literature says it is OK to install a tube ...but this rim does NOT have knurling to help prevent the tire from rotating on the rim, pulling a tube along with it and ripping out the tube stem. Take a close look at the rim bead area angle & compare to the rims, above, with no ridges. BMW was more concerned about the tire bead moving inwards (?), than outwards (?), rotating(?). You are often told that you can add a tube to a tubeless tire; think about what that means with this rim. Think also about how the tube is being stretched to fill the tire, and the rim and tire bead shapes, no matter what type of rim.
The next two photos are of a black powder-coated 1988 R100RS wheel, clearly showing the two safety ridges.
Yes, below photo is of BMW's famous spoked wheel where the spokes are outside the tire area. Notice that the bottom area in the middle has rather squarely abrupt sides and a flat bottom ...and ...especially notice that the bottom dropped area is hardly wide-enough for TWO sidewalls to drop into at the same time. That may or may not be really pertinent, after all, your next thought, as a thinking-type-person, should be: "Well, that's just how it worked out for this particular rim WIDTH....what about a rim for a wider tire, which will still have the same thickness of tire bead.....". Maybe? Maybe not?
Flat bottom. Same basic rim design as the R100GS, see photos above.
These 3 below photos are Morris Mag's, rear wheel, for Airheads. See any safety ridges? Nope, I don't either.
1. Except for late 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 one of the industry standards type of rim shape/contour, the BMW version is 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.
Some BMW rims are 'safety rims' ...which helps to not allow the tire to move towards the interior or 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! Think, maybe, that the CP is safer with tubeless tires without tubes, than the WM styles? 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. Which one(s) ...if any ...are safer (against a flattening tire's bead moving into the center ...making it easier (??) for the tire rim (??) to cut the tube?? 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 and 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? Heck, I am >>>how can a TL-H2 shape without any bump/ridge area be OK for tubes and tubeless? How, indeed! The CP type has a reverse taper seat. See the above sketch, and the tiny sketch somewhat below the next sketch. 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, just below. Be sure to read 3. below. I can provide the engineering book information, 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 center-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 bead using the TL (not TL-H2) to move into the center area. Below 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 associated with the rim. If you think about all these sketches, & think about what might happen under several assorted circumstances of using & not using tubes, you might get the idea that a CP rim with bumps or ridges, might be near-ideal. How about a TL-H2 with both bumps & ridges? 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 when conforming to several angles at such as the transition areas of the inside of the rim; and maybe the particular Metzeler design slightly up from the valve stem on the 'sidewall' of the tube; & maybe even the Metzeler tube design at the core. Probably a good suggestion by Metzeler ....yet totally forgotten, well, paid no attention-to, by probably nearly 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. The flat portion of the tubeless rim, just inside the bead area of the rim, 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. Time to 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 released 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? 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 upwards, 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. A few of you may be using car rims with motorcycle tires, or motorcycle rims with small car tires. This is done by some sidecarists, and sometimes with 16" wheels on Harley Davidsons, and I know of other instances. There is a difference between all these things that is not commonly known. Motorcycle tires have a THINNER bead area, where the tire fits between the edge of the side (where it meets the horizontal, before the safety ridge). If you think about this you will understand that if you use a car tire on a motorcycle rim, the safety ridge is fairly ineffective, as the tire bead will ride over it. If the motorcycle tire is used on the tire rim, the motorcycle tire's bead can move back and forth a bit. Now that you have plowed through this article up to this point, and likely gotten confused (less so if you look at the photos while reading the text); ...below is the easier (?) to understand information ...on what you need to know. The REST of the information: Caution: 1. Often in life, folks simply accept various rules, ideas, statements, specifications, etc., without thinking things through. You have already, herein, read about some of my ideas, & manufacturer-published information (which may, & 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 sort of possibly determinable value (a mathematical number, or some sort of specific statement of fact, or?) of higher safety in doing so in some circumstances. I think this is a fair statement, that all could agree on. 2. If you were to use a tubeless-rated tire & add a tube, the common, & manufacturer-published rule and advice, where available, is/was that you should reduce the speed rating of the tire by "one step". That, alone, does not mean much, regarding safety, at least to Airhead owners, who are not likely to be riding even close to the maximum speed the tire is rated for, even reduced one step. Not hardly ever said or published anywhere, is that this advice for tire speed ratings IS FOR SUSTAINED speeds. ALSO not mentioned is that with heavy loads, and quite hot weather, on quite hot black tarmac, the tires may be overloaded ...if not by the weight specification, then by the bad effects on the rubber compound. This is true for any tire. Heavy loads and high speeds require INcreased tire pressure. The reason given for the reduction in speed rating is that the use of tubes causes the tire to heat up more than without tubes, due to the flexing & tire to tube combination flexing. That much is true. Just heat increase alone will reduce tread life, and reduce safety if quite hot. This is very unlikely to be any sort of problem, at least for normal road-going motorcycle tires on Airheads, even to speeds somewhat over 100 MPH, assuming proper tire pressures. Some of this information used to be, & usually still is, found in some tire manufacturer's literature. Manufacturer's nearly always equip their motorcycles with tires rated for considerably higher speeds than the motorcycle can attain. This can be thought of in many ways, including a larger safety factor. Note what I said earlier about extremely hot weather, quite hot black asphalt (tarmac), overloading, etc. In one instance I know about, the treads were so heavily loaded by gear & passenger, in such extremely hot weather & extremely hot tarmac, that the tread literally began melting away! I have earlier mentioned tire rubber reversion. 3. Tire manufacturer's design and specify the depth of the tread for various 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 friction/flexing/squirming effects, etc. For the same model tire it is often advantageous for you ...for improved tire tread life, ...to purchase a lower speed rating in that tire model (if available), & thus get a deeper & longer lasting tread. That can work out well, particularly if your speeds, aggressiveness, and loads, are moderate. It is also true, generally, that a wider tire will give more miles before the tire wears out. 4. If you stop here & think and ponder some, would it not be 'reasonable' to 'assume', that with a tube-type tire, but you are running it without a tube, you might well expect to have a increase in tread life, because the tread is less hot, as there is no tube friction & extra flexing friction, etc....? Yes, it is so. Manufacturer's, not wishing to get overly-involved, do not mention this. They also don't like to discuss the sealing of the tube-type tire, when used without a tube. But, there is more to this: I speculated that a tire in such use might not be in its 'best performance' heat range, as originally designed; that is, the tire would be running too cold for optimum performance. I tried to find out during testing, & I even did various pressure setting changes. I was unable to prove there was any degradation ...nor, hardly any improvement either ...in handling performance, ...by removing the tube. Optimum pressures did not seem to change very much either; about 3 psi was the very worst; even getting that much change required aggressive riding. This was on various types of surfaces, speeds, tightness of turns, etc. I did extra testing ...and...yes, tire mileage seems to be extended. 5. 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 will likely not find old-style radials that fit your Airhead though. 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 usually a good adjustment value for any tire on an Airhead. 6. There are now 'classic radial' tires specifically made to work with older bikes like the Airheads. You may be interested in trying them, preliminary reports are very good, but tire pressures seem to be a bit more critical, in my preliminary opinion. I may be wrong. 7. Never fail to use tire talc when installing a tube; rub it all over the tube & inside the tire with your hands. This allows the tube to move about a bit, expand a bit, etc., avoiding excessive friction against the tire; & also helps the tube, upon installation, avoid any folding. Don't use baby powder or home type talcum powder. 8. 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 (rubber of some type?) on the inside of the tire. Late model Airheads use tubeless rated rims, and no inner tubes, and do usually seal well, for weeks at a time. 9. Talk of special tire bead areas, are, IMO, over-exaggerated. It is my belief that different bead sealing areas are partly a misunderstanding about car beads versus motorcycle beads, which have different widths, as I outlined earlier. Tires not marked tubeless tubeless may slowly lose air if not used with tubes, as they could be porous in tread or sidewall, or bead. Rarely they lose pressure rapidly. I have seen tubeless and tube-type tires hold air for a long time on cast tube-type rims; and on spoke rims that the spokes and spoke nipples are sealed at. I am talking about just a few psi per week or three weeks. In every instance (except one porous rim), it was due to lack of a "tubeless coating" on the inside of the tire, or, poor cleaning of the rim bead area before fitting the tire. Weekly topping-up is adequate; pressure loss not usually being much more, could even be the same, as the normal amount found if using 'natural rubber' tubes, which quite normally leak faster than other types of tubes. Natural rubber tubes, which are really just a higher percentage of natural rubber in their construction, whether used with tubeless rated tires or tube-type rated tires, will lose pressure slowly, normally; 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. There are 'thick' inner tubes available, supposedly less likely to be punctured or ripped, and supposedly natural rubber (maybe, or maybe higher %), but these have drawbacks, such as heat buildup and weight. As you saw from my photos section, well above, some rims have a knurling or other deep marks, in the bead flat area (as opposed to the angled side of the inside of the rim ...but I have seen it there too). Since this helps keep the tire from rotating on the rim if a serious flat occurs, I am in favor of that method of rim construction, very particularly
so for when using tubes. 10. Tire pressures are supposed to be checked before every day's ride. 11. 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 long periods of time. I don't suggest adding such sealants (Slime, etc.) unless you are willing to deal with the mess, at the next tire change, or, with tubes, at the next tube or other repair. Some very few snowflake wheels may be slightly porous. You can clean and seal the insides with a coating. Purposeful off-road tires are, in the majority, meant for use with tubes, many of these tires do not have any interior sealing coating, although some do and it seems you are never given that information by the manufacturer, or anyone else. 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 such very low pressures. Some use special foam "snakes", mousse, etc., instead of tubes. 12. Tube Mounting nuts: (a). The tube could fail to release air from between the tube & inside of the tire; via the valve stem clearance to the rim ...which it is supposed to do. If the nut is tightened to the rim and the tube seals to the rim too well, it can trap air from tube to rim, & allow tube chafing, and thus the tube could fail. (b). Leaving the nut against the rim defeats the safety of allowing the tube to be able to move slightly, upon a flat occurring. This is worse if you failed to rub the tube and tire insides with tire talc. (c). Run the nut up against the cap, or throw it away, or put it in your tool tray. Many tubes are sold with that nut, & the purpose is to help during installation of the tube into the tire. It is better & easier, to use a special tool for inserting the valve into the rim hole. https://bmwmotorcycletech.info/TireRepair.htm (d.) Using the nut against the rim prevents any tube movement if one has a flat. The tire might rotate on the rim slightly, or more, ripping the valve completely out of the tube, causing a fast air loss. Remember the photos of the knurled tire rims, much earlier here? BMW has Service Information bulletins on not tightening the nut to the rim. I have tire manufacturer's manuals & BMW bulletins on this. BMW has at least two Service Bulletins (SI's) on the valve nuts. One SI gave an additional reason to have it up against the cap: improper inflation could cause the tube to be weakened at the valve stem & if the nut was at the rim, the stem could suddenly & disastrously tear out. What BMW did not say, & I will, was that this can also come from very low inflation ....and can even be caused by over-inflation during seating of the tire.
Some of these things are MY personal interpretations & ideas; read & do what you want, AT YOUR RISK, NOT MINE:
When installing a tube (nearly any type of rim), normally do not leave the mounting nut (whether knurled or hex type) against the rim. There are 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 that job a bit easier. So, why the advice to not leave the outside nut against the rim?
13. If you use a tube type rim without a tube, then you have a decision to make. The stock tube-type rim hole is 8 mm. If you do not wish to enlarge the rim hole for a standard pull-in-place type of rubberized tubeless stem, then there is a special valve stem that is available ...even from BMW! ...that seals at the inside of the rim by means of an O-ring built into a recess of the stem unit. The stem area of the rim, inside, must be machined reasonably flat for this to work well; although I have seen folks seal with a bit of rubber or thin O-ring added. Some clever (?) folks have used the stem from an old tube (maybe removing a bit of the rubber on the metal stem), cut from the tube, and maybe a piece of tube rubber, and one of the nuts, inside, to make a valve stem that seals when used with an unmodified rim hole ...that is, no need to enlarge the diameter of the hole, and no need to have any flat area for the described metal special stem to seal. I have seen this done where it works rather well. 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, unwise, ...or at least strange).
14. Since rims vary in angle of the bottom & sides, & some have protective internal bumps or ridges to prevent the tire from moving inwards, etc., you should think about things, if considering not only non-standard use, but in standard use. For an example, if you have a very serious rim bending situation, such as a 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 a similar lose-air-fast situation occur, if the tube was pinched or pushed-out and the rim then cut it. If using a rim for a non-standard purpose, some thinking is advisable about what you want to do, safety, etc.
15. One conversion method, as noted, involves enlarging the stem hole, & possibly spot facing the inside of the rim slightly so the mounting area for the stem is relatively flat & 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 (even from BMW) with a rubber O-ring that can be fitted, into the existing hole size (spot facing inside as needed, to give a flattish area).
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 as using tubes, problems do seem to be extremely rare. Folks have even done considerable racing with tubeless converted snowflakes. So far, except for the one instance, reported by OAK, and details not provided, 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, plus consulting dealers, independents, etc.
16. HINT: When you are at quite high speeds, the tires obviously are also rotating at a good rate. 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 (no matter the rim diameter) anyway; but, there have been instances of weak or damaged valve stem core units that leaked air. A short valve core with a quality cap that seals, is OK and I recommend it. 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.
17. MORE HINTS: When a BMW Snowflake wheel (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 sometimes use a band around the outside circumference of tubeless tires to squeeze the tire to the sidewall. This is just one of several reasons why I don't recommend carrying high pressure steel CO2 mini-or-medium metal pressure bottles that are in some tire repair kits. Of course, if touring and not in your garage with your compressor and tank, you have little choice, you must use those CO2 bottles; or, my recommendation ...a small low volume output Chinese type electrical compressor. I have seen folks tie a couple of pants-belts together to help hold the tire beads to the rim, while trying to pressurize the tire.It can be real fun to get a tubeless tire to re-seal to the rim, when touring. Luckily, the tire will tend to go flat from a puncture without coming unstuck to the rim, but NOT always. Usually, even if unstuck, the problem is minor on a used tire.
Another problem is getting any tire to seal CONCENTRICALLY, that is, totally onto the rim, with the concentrically molded tire line (on both sides of the tire) to be equidistant from the tire rim, all-around. That is, the tire is fully onto the rim, concentrically and evenly, side-to-side. In your home garage, some 'secrets' about getting tires (tubeless or tubed) to seal fully all-around the rim, is as follows:
Besides a very clean and smooth rim, remove the valve core & use a compressor with a decent sized tank of high pressure air and a large internal diameter hose; ...together with lots of properly thinned commercial tire lubricant. It helps considerably to remove the teat in the air chuck, to enable an even faster flow rate (use the compressor valve); & to do the work with tire & wheel hot from being in the sun. Using lots of air volume flow helps seat the tire ...otherwise, the bead tends to get friction-trapped. Very high pressures inside the tire/tube might be then be needed, which can be very dangerous. In many instances the fast flow will do far better than trying dangerously high pressures into the tube/tire. I remove the tip core of my compressor tire chuck, to allow the air to flow as fast as possible. I have a larger inside diameter hose. My compressor tank is ~8 gallons, filled to 125 PSI, but smaller tanks, say 2 gallons absolute minimum, can work OK. The higher the pressure in the tank (as allowable by tank safety factor), and the larger the tank, the better the result. A 175 psi commercial shop's compressor was wonderful, when I had one, before I sold my BMW business.
18. Sidecar folks sometimes use rear tires on the front of the tug, with the directional arrow, if there is one, reversed. Some modern front tires are actually marked for use in both directions.
19. It is possible to seal the tube stem via rubber & metal washers & 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 & rip the stem out of the tube. This is as opposed to not having the nut at the rim, & the tire might be able to rotate a bit on the rim & the tube stem not be damaged. The tube nut is normally just for help in installing the tube/tire, then it is NOT used ...or; it can be put up against the valve cap, not against the rim. Whatever YOU do should be done with knowledge, which is one of the reasons this article talks about the various methods.
Some have, as noted previously, purposely gone tubeless & used a valve stem assembly cut from a tube ...with added rubber inside and outside the rim, with a curved tube washer. That installation avoids spot-face machining on the inside of the rim, and can work OK. Others have used an inside curved metal piece, such as comes with some tubes.
20. Tube type & tubeless type rims vary at the valve stem hole. Generally, the tubeless rims with the standard small auto type stem has a 11.5 mm rim hole. The BMW Snowflake rim is rounded where the inner tube stem came through. The hole for inner tubes is 8 mm. These things are why many do not machine the inside of the wheel for a flattened area for the special metal valve stem.
When installing a tube into a tubeless rim, care must be taken about squeezing the tube if using the typical tube nut, & 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 hardly the only place I discuss tube chaffing from an airtight stem installation when using an inner tube. Actually, you are unlikely to have a problem, if the tube is well hand-talc'd. IMO. Always a chance, even if talc'd.
In case any of this is confusing, remember that some folks want to install a tubeless tire withOUT a tube on a tube-type rim, and some have tubeless rims and want to install a tube, and all sorts of variations on these themes. I'm trying to cover them all, so read carefully.
I think most reading this article are interested in installing a tubeless rated (sometimes tube-rated) tire without using a tube, probably in snowflake wheels designed for use with tubes. Thus, paying attention to the types of valve stems and their installation, is important!
I've mentioned this before. BMW sells a chrome-looking 7 mm valve stem, 36-32-1-452-748 with a rubber O-ring that is fitted into a machined groove in that metal stem base. That stem will fit most tube-type snowflake holes, with a bit of modification to the inside rim. The part was actually 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, or can, with the snowflake wheels, just install carefully, and with knowledge.
21. Snowbum has, on two of his Alaskan adventures, installed tubes WITH rubber washers and a cup washer.
22. The snowflake tube-type wheels will handle major rim denting & still hold air, if tubes are installed as they were designed to be. However, there have been numerous reports on these rims of very serious rim bending, with NO problems with tubeless tires WITHOUT tubes.
CONCLUSIONS, COMMENTS:
Considering everything in this entire article, THERE IS PROBABLY 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. Many other conditions, combinations, etc., have been discussed, from which you can determine if what you want to do is safe, not safe, in-between-safe, ....and a lot of details have been discussed. I hope the rims discussion was informative.
Some manufacturer's tubeless tires & tube-tires have slightly different beads, but I have been unable to get definitive information, & my personal inspection has not shown enough difference to make it more than a 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 a major item.
When any tire/wheel gets a bump big enough to damage the rim quite severely, you may well retain air with a tube, & perhaps somewhat less likely to without a tube. On the other hand, the tube may bulge out from the rim some, and the rim might cut it during the riding.
NOTE!...this is an OFFICIAL LEGAL DISCLAIMER!:© copyright 2021, R. Fleischer
Last check/edit: Thursday, April 08, 2021