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Anybody had a tire blowout during a long descent?

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Anybody had a tire blowout during a long descent?

Old 12-02-10, 12:37 AM
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safariofthemind
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Anybody had a tire blowout during a long descent?

Raymond Bridge, author of the new Sierra Club's "Bike Touring: The Sierra Club Guide to Travel on Two Wheels" (2009) writes that a potential problem of rim brakes is that heating of the rims during long descents could cause a tire to overheat and blowout. This would of course, be catastrophic. He claims the reduced air volume of skinny road tires would heat up even faster than that of fat tires, making skinny tires a poor choice for hilly terrain.

Bridge goes on to point out that disc brakes don't have this problem and can be preferable in hilly landscapes.

I can't recall ever hearing about anyone having a tire blowout during a descent due to heat. I have heard of rim damage and other mechanical problems, or punctures or spoke breakage, but not blowouts caused by over heating.

Has anyone actually seen this happen? I mean, first hand as opposed to anecdotal accounts...
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Old 12-02-10, 01:43 AM
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Yes, sort of. Rear tire on our tandem. I was using poly rim tape instead of cotton. The tube developed so much pressure that it blew through the rim tape. Changed to cotton.

I don't think he's right about tire volume. More volume = more force on the rim, not less. That's the reason that rim manufacturers specify maximum tire pressure for each width of tire. As the tire gets wider, the maximum allowed pressure goes down quickly. I believe the mechanism is that the rim heat melts or softens the tire bead. When the bead won't stay behind the rim hook, the tube comes out and goes bang, just like it would with a beginner's tube trapped behind the bead.

This is a well-known problem with tandems, which almost always carry much more weight per brake than a loaded tourer. The prevention is don't let your pads fade. As long as your pads have good friction, you're probably OK. Tandems usually use one brake until it starts to smell, then use the other, etc. That way the rim gets really hot, which causes faster heat transfer into the atmosphere. If braking effectiveness really decreases, it's time to use both brakes to stop and let everything cool down, or better yet, do that before you start to lose your brakes. The other very effective technique is to let the bike run, but that only works on descents without hairpins, etc.

There is great debate over whether a disc brake really does better than a rim brake under such conditions. There's a lot more mass in a rim than in a disc. Disc brakes don't have that problem, instead they get even hotter, warp, and may burn their pads.

By "well-known," I don't mean common. It's very rare. It's just that it gets people's attention.

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Old 12-02-10, 04:35 AM
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I burnt my hands on the rim after a huge descent from the Picos de Europas. No tyre blowout even with a patched tube.
Ive had a downhill blowout due to sidewall damage. The tyre ripped open. 1st thing is to recognise that the bang is a blown tyre, then avoid the temptation to apply all brakes. I slowed myself with the good rear wheel and came to a safe stop without spilling.

Tandems are a completely different ball game when it comes to descending. They should have a rear hub drag brake to keep the speed in check. These are pretty resistant to over-heating and much better than disk brakes for this application.
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Old 12-02-10, 05:22 AM
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Not a dramatic blowout, but I've seen two flats on a 4000ft descent into Borrego Springs, CA on the HI-AYH Christmas ride. The first was on a tandem rear wheel where the rim was hot to touch. This was a few years ago. The rear tire went flat quickly, but I don't think there was loss of control.

Last December, I also had a flat on my front tire on that descent. The underlying cause was that the front tube pushed through the rim strip into sharp bits on the rim. Prior to this flat, the front tire had gone thousands of miles without a flat. The rim was warm, but I also believe the extra weight distribution of leaning forward onto the front tire contributed to extra pressure pushing the front tube. Again, the tire went flat quickly, but I didn't lose control as I wasn't going too fast (due to the extra braking).
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Old 12-02-10, 05:24 AM
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Only the once on a loaded tourer on a long steep twisty descent in New Zealand - soon learn
  1. to cadence brake
  2. not to grab the hot rim immediately that you have stopped
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Old 12-02-10, 05:54 AM
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We had a flat on the tandem descending from the Bolivian Andes to the Amazon basin. I was pretty far behind at the time so didn't see it happen - don't think it was a major blowout, but the tire went flat quickly as far as I know.

John tried to fix it, but commmented that it looked like the tube was melted. He patched it, but it didn't hold. He took it apart and patched it again. then again. Finally he threw the tube away.
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Old 12-02-10, 07:14 AM
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In the road bike world, it's a serious concern for people ride "sew ups," which are tires that have their tube sewn inside and then the whole thing is glued to a rim. Hot rims can melt the glue.

Best not to ride the brakes continually and instead to apply them intermittently.
Originally Posted by Carbonfiberboy View Post
I don't think he's right about tire volume. More volume = more force on the rim, not less. That's the reason that rim manufacturers specify maximum tire pressure for each width of tire. As the tire gets wider, the maximum allowed pressure goes down quickly. I believe the mechanism is that the rim heat melts or softens the tire bead. When the bead won't stay behind the rim hook, the tube comes out and goes bang, just like it would with a beginner's tube trapped behind the bead.
I don't understand what you're saying. If, for example, you had the same rim and different tire widths pumped up to the same pressure, the force acting on the rim doesn't change.

I think the point referenced in the OP with skinnier tires means that with a smaller volume of air, the heat from the rim has less to heat up than with a higher volume of air, thus the problem of increased pressure due to temperature increases is more dangerous on skinnier tires.

I'm also not sure what the tire bead has to do with tire pressures because stronger beads could easily be made to overcome any problem with heat. My guess is that larger tires have lower pressure capabilities because riders with bigger tires don't want or need high pressures. For example, in mountain biking, it's pretty common to run under 40 psi because higher pressures reduce the tire's ability to maintain contact in loose rocks, dirt, and sand. People riding touring rigs are similar with their needs in that they don't usually want the harsh ride of 100+ psi, and if they did, the tires would have to be much stronger and significantly more expensive and heavy, etc.

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Old 12-02-10, 07:52 AM
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I've never had a blowout on a descent, but I have seen one. During Ride the Rockies about ten years ago, there was a rest stop right near the bottom of Red Mountain Pass (very steep and twisty; lots of braking). There were a bunch of bikes parked on the side of the road while their riders were getting food or using the port-a-johns, and one of them had a tire blow while just lying on the ground.

Apparently, what happened was that the rim was heating because of the brakes, but the airflow over the tire was sufficient to cool it. When the airflow stopped (i.e. the bike stopped moving), the rim was still hot, more heat accumulated in the tire, and the tire blew.
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Old 12-02-10, 08:02 AM
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i never had a tire blow out but, but once i was following a bus down a steep hill. I had to break the whole time because the bus was going to slow, at near bottom my tube blew.... not a fun thing when your going 50km/h
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Old 12-02-10, 10:20 AM
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I've had flats, not blowouts. The tire when flat quickly or slowly and I slowed down to a stop and changed it. I knew a friend with an underbuilt wheel on his tandem and it folded in a turn. Most flats occur on the flats and not on descents. There's more crap on the flats and you spend more time there. I almost wiped out in a wet turn and when the sliding rear wheel hit dry pavement it tacoed and I had to stop as it was hitting the chainstays/brake pads. If you're braking so much that your overheated rims are affecting the integrity of the tire it's time to do something different, like not let your speed build up so much.
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Old 12-02-10, 10:56 AM
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Interesting. This has definitely made me decide on disc brakes for the machine being built for me by Naked Bicycles. I think mechanical Avid BB7's are sufficiently reliable and easy to repair and have been field tested long enough to be a good choice for Latin America touring.

Raymond seems to know his stuff. I'd read the older version of this book and this updated edition has some nice up to date information. The comments on using mountain bikes, off road touring and equipment choices have been particularly interesting.

You all may want to get a hold of a copy at your local library.

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Old 12-02-10, 11:07 AM
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Originally Posted by SBRDude View Post
In the road bike world, it's a serious concern for people ride "sew ups," which are tires that have their tube sewn inside and then the whole thing is glued to a rim. Hot rims can melt the glue.

Best not to ride the brakes continually and instead to apply them intermittently.
I don't understand what you're saying. If, for example, you had the same rim and different tire widths pumped up to the same pressure, the force acting on the rim doesn't change.

I think the point referenced in the OP with skinnier tires means that with a smaller volume of air, the heat from the rim has less to heat up than with a higher volume of air, thus the problem of increased pressure due to temperature increases is more dangerous on skinnier tires.

I'm also not sure what the tire bead has to do with tire pressures because stronger beads could easily be made to overcome any problem with heat. My guess is that larger tires have lower pressure capabilities because riders with bigger tires don't want or need high pressures. For example, in mountain biking, it's pretty common to run under 40 psi because higher pressures reduce the tire's ability to maintain contact in loose rocks, dirt, and sand. People riding touring rigs are similar with their needs in that they don't usually want the harsh ride of 100+ psi, and if they did, the tires would have to be much stronger and significantly more expensive and heavy, etc.
As I said, rim manufacturers quote different max tire pressures for different width tires, because large tires exert more force on the rim. That's the reason they do that. Tire pressures are measured in psi or bars. Such and such a force per unit area. If you increase the area by running a larger volume/larger cross section tire, you therefore increase the force, because you've increased the internal area of the tire. It's true that the greater volume of air in a larger tire will take longer to heat. However the force on the rim will also increase more quickly with temperature than in a smaller tire, plus it's the rim heat acting on the tire bead that seems to cause the blow, not just tire pressure itself. However, no one really knows for sure.

There is no relationship between tire pressure and tire weight. In fact, thinner tires often have higher recommended pressures. The problem is simply that rim heat softens the bead of the tire, you know, the part that sits behind the rim hook. When that softens, it comes unhooked. It's not a matter of strength. As far as anyone knows, folding tires and wire bead tires can both be made to blow off the rim.

One of the problems of these discussions is that the occurrance is so rare that there isn't much of a database, even if there were anyone keeping track of what blew on what rim and how.
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Old 12-02-10, 11:14 AM
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Originally Posted by LeeG View Post
I've had flats, not blowouts. The tire when flat quickly or slowly and I slowed down to a stop and changed it. I knew a friend with an underbuilt wheel on his tandem and it folded in a turn. Most flats occur on the flats and not on descents. There's more crap on the flats and you spend more time there. I almost wiped out in a wet turn and when the sliding rear wheel hit dry pavement it tacoed and I had to stop as it was hitting the chainstays/brake pads. If you're braking so much that your overheated rims are affecting the integrity of the tire it's time to do something different, like not let your speed build up so much.
Actually, your rims will heat less if you let the bike run as much as possible. For one thing, faster air flow cools the rims more quickly, and for another, wind resistance goes up as the square of the speed, so you'll reach terminal velocity pretty quickly and won't have to brake at all. The best technique on switchbacks seems to be to let the bike run between them, then brake down hard for the turn, then hope the rims cool some on the next run, etc. But that depends on the steepness of the road. On really steep descents there's nothing for it but to ride the brakes and stop frequently.
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Old 12-02-10, 12:07 PM
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Tandem schmamdem. If tandem crew was twice as heavy as a single rider, and on average it is usually less, then the single rider would only need to be ridding 1.44 times faster to generate the same kinetic energy as the tandem team. So if you go downhill at 20 on the tandem, the solo rider would need to be going about 29 to have the same energy. We have people here who claim to ride hills at 50. Of course if they are able to just run it out, that would be OK. But if you have to use your brakes at higher speeds, you will be generating a lot of heat.

We also have plenty of riders who weigh what a fit tandem team would. If one cycled a lot in the Rockies using the same tech as a tandem would make sense.
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Old 12-02-10, 01:13 PM
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Originally Posted by Peterpan1 View Post
Tandem schmamdem. If tandem crew was twice as heavy as a single rider, and on average it is usually less, then the single rider would only need to be ridding 1.44 times faster to generate the same kinetic energy as the tandem team. So if you go downhill at 20 on the tandem, the solo rider would need to be going about 29 to have the same energy. We have people here who claim to ride hills at 50. Of course if they are able to just run it out, that would be OK. But if you have to use your brakes at higher speeds, you will be generating a lot of heat.

We also have plenty of riders who weigh what a fit tandem team would. If one cycled a lot in the Rockies using the same tech as a tandem would make sense.
You make some good points. However, it's not so much the kinetic energy in the system as it is the potential energy. All the potential energy in the system has to be turned into heat somehow, either through atmospheric friction or brake friction. Our loaded tandem weighs about 390 lbs. There may be some touring singles out there at that weight, but I've never seen one. Most touring tandems are quite a bit heavier.

In any case, it's easy to get overexcited about this heating problem. Basically it's just common sense. Don't cook your brakes.

The real tire danger is sidewall blowouts. I've had several front tire sidewall blowouts, mostly on my single, but one on the tandem, all on right hand corners. I think it's right handers because it's harder to see shoulder debris in time to alter your line. The thing to do is straighten up the bike and get on the rear brake. Luckily, all my blowouts took place with no oncoming, otherwise I might not be telling about it.
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Old 12-02-10, 01:56 PM
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Originally Posted by Carbonfiberboy View Post
The real tire danger is sidewall blowouts. I've had several front tire sidewall blowouts, mostly on my single, but one on the tandem, all on right hand corners. I think it's right handers because it's harder to see shoulder debris in time to alter your line. The thing to do is straighten up the bike and get on the rear brake. Luckily, all my blowouts took place with no oncoming, otherwise I might not be telling about it.
Absolutely, the plain vanilla blowouts are scary stuff. Another reason not to go cheap on the tires and pay attention to debris. I know a lot of us like to hug the right edge of lanes despite knowing we sometimes ought to own the whole lane, especially when turning. It's hard to shake off that fear factor of some wacko blindly rolling over us.
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Old 12-02-10, 03:16 PM
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Originally Posted by Carbonfiberboy View Post
As I said, rim manufacturers quote different max tire pressures for different width tires, because large tires exert more force on the rim.
Do you have any examples of this? I've seen rim manufacturers quote a maximum pressure for a rim, but it has always been irrespective of the tire size...

However the force on the rim will also increase more quickly with temperature than in a smaller tire, plus it's the rim heat acting on the tire bead that seems to cause the blow, not just tire pressure itself.
If by "force" you mean "psi", then I'd have to disagree. The ideal gas law would seem to suggest that you have to put more heat into a high-volume tire to achieve the same pressure increase you'd see in a lower-volume tire. Or, to put it another way, if you put the same heat into a low-volume tire and a high-volume tire then the pressure in the low-volume tire will increase by a greater amount.
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Old 12-02-10, 03:28 PM
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I have had one puncture which may have been caused by heating of the rim. It may have caused the rubber around the valve to fail.

After this, I always pumped the brakes on a long descent. If I allowed the bike to speed downhill without braking, the brakes would have great difficulty in slowing the bike down enough for a corner. It helped keep the rims cool also. It may be that the rims will heat far greater if you do not keep your speed down. The energy of descent increased with the square of velocity so the faster you go, the energy quaduples in relation. This energy is then converted to heat on the rims as you brake severely for a corner. perhaps leading to a greater heat buildup than if you had kept your speed down and pumped the brakes.

I have now changed the front wheel to a disc brake. On my last tour, I descended a 15% gradient and found my disc brake to fade badly upon repeated use so once I stopped and let it cool, I had to pump this brake also and keep the speed down.
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Old 12-02-10, 05:32 PM
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Originally Posted by safariofthemind View Post
Interesting. This has definitely made me decide on disc brakes for the machine being built for me by Naked Bicycles. I think mechanical Avid BB7's are sufficiently reliable and easy to repair and have been field tested long enough to be a good choice for Latin America touring.

Raymond seems to know his stuff. I'd read the older version of this book and this updated edition has some nice up to date information. The comments on using mountain bikes, off road touring and equipment choices have been particularly interesting.

You all may want to get a hold of a copy at your local library.
After reading about this in some touring books, I decided to go disc on the front, at least. The MTB frame I built up for touring is not set up for disc, so I figure the rear V-brake/booster will be plenty (as stated, rear offers a lot less effective braking due to weight transfer, etc.).
I took the opportunity to raise the front a little by getting a 29er disc fork, which also slackens the steering a bit on my 26" frame. With Avid BB7 Road caliper and a 203mm rotor, it pulls down 'smartly'! Even when towing my two wheel trailer, I have plenty of 'stopping power', as long as I don't get crazy.
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Old 12-02-10, 06:07 PM
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Originally Posted by sstorkel View Post
Do you have any examples of this? I've seen rim manufacturers quote a maximum pressure for a rim, but it has always been irrespective of the tire size...
I got this information from a product bulletin that came with a rim for a wheel I was rebuilding. I think(?) it was a Velocity product. However, I can't find anything published on the web regarding tire pressures at all. I was quite surprised to see that I had been exceeding the manufacturers specs on these rims! The pressure differential w/r to tire size was considerable. IIRC it went from 130 lbs on 23c to 105 lbs. on 28c. Something like that. I didn't save the paper.

I kept on exceeding the rim specs, figuring they had a safety factor for rim wear, meaning I might have to replace the rim sooner than if I'd run a lower pressure. OTOH, I've never dented a rim, so that's good.

Multiplying it out, this looks like about the right pressure relationship.

Originally Posted by sstorkel View Post
If by "force" you mean "psi", then I'd have to disagree. The ideal gas law would seem to suggest that you have to put more heat into a high-volume tire to achieve the same pressure increase you'd see in a lower-volume tire. Or, to put it another way, if you put the same heat into a low-volume tire and a high-volume tire then the pressure in the low-volume tire will increase by a greater amount.
By "force" I don't mean psi. I mean the force on the tire bead. You could have a little fun and inform us all by calculating the change in tire bead force for different size tires using the same caloric heat input, and using as a starting point cold tire pressures that produce the same bead force. I could be wrong, but anecdotal experience says I'm not.

I'd be interested to see what you came up with.

My vague memory of it being a Velocity rim might have some validity. A while back, Velocity had problems with one of its rims exploding. I believe Velocity traced it to tourers who were running like 2" tires at 100 lbs. and just blowing the rims in half. So they might have a CYA interest in such a chart.

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Old 12-02-10, 10:11 PM
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Very nice rig indeed badamsjr! Looks perfect for some long xc touring as well road touring. Do tell... how has it done for you? Climbs and descends well? Brakes well in rain on descents?
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Old 12-02-10, 10:47 PM
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Originally Posted by Carbonfiberboy View Post

My vague memory of it being a Velocity rim might have some validity. A while back, Velocity had problems with one of its rims exploding. I believe Velocity traced it to tourers who were running like 2" tires at 100 lbs. and just blowing the rims in half. So they might have a CYA interest in such a chart.
Velocity seems to be having LOTS of problems! We started our tour with Velocity rims on the tandem - they split right down the middle. Velocity sent out new rims and arranged for a bike store to rebuild our wheels.

We made it 700 miles and they started splitting again. Velocity sent out more rims and arranged for a bike store to rebuild the wheels and they paid to put us up in a hotel while we waited.

then they split again. That time we decided we simply were not willing to deal with that and switched to Rhynolites.

We have some friends who are also touring on tandems - they have Velocity rims. They have only cycled less than 6000 mile so far and have split SEVEN rims! Velocity has been good about sending the rims out to Paraguay and Peru and whereever, but our friends are still sitting around for a month or more waiting for them to arrive.

I also know of another tourist who has had the same problem with Velocity rims.

I suspect they are building an inferior product.
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Old 12-02-10, 11:20 PM
  #23  
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Originally Posted by nancy sv View Post
Velocity seems to be having LOTS of problems! We started our tour with Velocity rims on the tandem - they split right down the middle. Velocity sent out new rims and arranged for a bike store to rebuild our wheels.

We made it 700 miles and they started splitting again. Velocity sent out more rims and arranged for a bike store to rebuild the wheels and they paid to put us up in a hotel while we waited.

then they split again. That time we decided we simply were not willing to deal with that and switched to Rhynolites.

We have some friends who are also touring on tandems - they have Velocity rims. They have only cycled less than 6000 mile so far and have split SEVEN rims! Velocity has been good about sending the rims out to Paraguay and Peru and whereever, but our friends are still sitting around for a month or more waiting for them to arrive.

I also know of another tourist who has had the same problem with Velocity rims.

I suspect they are building an inferior product.
Which rims? We run Aerohead and Deep V rims, never a problem with either other than wearing the brake track out on two Aeroheads. Touring, we weigh 390 all up and run 28c at 120 lbs.
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Old 12-03-10, 01:08 AM
  #24  
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Originally Posted by sstorkel View Post
Do you have any examples of this? I've seen rim manufacturers quote a maximum pressure for a rim, but it has always been irrespective of the tire size...
I have one. Recently I called Mavic to ask them if I would be ok with 700x50 Schwalbe Marathon XR tires on my A119 rims (Rocky Mountain Sherpa). They told me that it does depend on the tire size. I think the reason is that the larger tires at higher pressures will tend to spread the rim outward more (or something like that - I didn't write it down). So the biggest recommended tire for the A119 was 50mm (phew) and the highest recommended pressure for that size is 66 psi. Then for 44mm it's 76 psi, and for 40mm the max is 82 psi. So it definitely depends on the tire size for any given tire/rim combination.

I think many people who have rims splitting are maybe simply not aware of this (I wasn't until recently) and perhaps they are running larger tires at too high a pressure for the rim. This was also the opinion of Dwan Shepard at Co-Motion when I asked him why the Ribbon of Road guy had so many wheel failures on his way to Argentina - in Dwan's opinion he was running large tires at too high a pressure with a very heavy load.

In future I will always be checking with the rim manufacturer to see what the highest pressure is for a given tire size.

Neil
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Old 12-03-10, 03:24 AM
  #25  
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Originally Posted by Carbonfiberboy View Post
By "force" I don't mean psi. I mean the force on the tire bead. You could have a little fun and inform us all by calculating the change in tire bead force for different size tires using the same caloric heat input, and using as a starting point cold tire pressures that produce the same bead force.
PSI would seem to be the only force component likely to change with increases in temperature caused by braking. If you can think of another force that varies with temperature, please elaborate. Feel free to play around with the ideal gas law, too: pV=nRT where p is pressure, V is volume, and T is temperature.

Here's a start: p=nRT/V.

I could be wrong, but anecdotal experience says I'm not.
Aren't you the same guy who said, and I quote, "One of the problems of these discussions is that the occurrance is so rare that there isn't much of a database"? Kinda makes me wonder where all of this anecdotal evidence is coming from... Thin air, perhaps?

So they might have a CYA interest in such a chart.
If so, they didn't relate it to me when I e-mailed them while building my touring wheels using their Synergy OC rims. I got a range of suggested tire sizes, a maximum pressure, and a maximum spoke tension...
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