Are some road wheels too strong?

rjsterry

My run in with a pothole, which is going to cost me two new wheels, got me thinking. Both the front an rear wheels were still more or less true after taking a 20+mph blow onto the exposed edge of some ironwork/tarmac, however, the rims are un-repairable due to the dents caused by said pothole.

Looking at the damage in detail, it seems that the spokes and rim are so rigid that the only thing left to absorb the impact once the tyre has blown is the side wall of the rim buckling inwards. If the rim had been more springy, or a spoke had snapped, I wouldn't have been able to ride any further, but I could have had the whee repaired relatively cheaply.

These weren't even the most super-rigid set of wheels either - Shimano WH-R560s. Anyone think I'm on the right track or is my limited knowledge of structural engineering leading me astray? Any suggestions for more springy (but not too springy, I'm no MTBer) winter wheels

cjcp

You could buy wheels with a higher spoke count, so you don't need to tension the spokes as much e.g. 36h.

Thinking out loud here, but if you have "springy" rims, would this affect their wear thought braking? (I'm not sure what the hypothetical Martian reading all this talk of springy rims would think... )

UndercoverElephant

I think the thing is that if your tyres had had a decent pressure, they wouldn't have compressed enough for the edges of the hole to hit your rim at all.

My Rubino Pros have a minimum pressure of 100 PSI, but I keep them at about 130; Well below the maximum of 145. I crash over potholes almost all the time and I'm reasonably heavy too - my wheels have stayed true for the last 1500 miles.

rjsterry

UndercoverElephant wrote:

I think the thing is that if your tyres had had a decent pressure, they wouldn't have compressed enough for the edges of the hole to hit your rim at all.

My Rubino Pros have a minimum pressure of 100 PSI, but I keep them at about 130; Well below the maximum of 145. I crash over potholes almost all the time and I'm reasonably heavy too - my wheels have stayed true for the last 1500 miles.

Might have been the issue (I try to keep the pressure topped up to at least 115psi (I'm only 64kg, so much higher than that really loosens my teeth), but it could have dropped a bit, although, as I say, the impact burst the inner tube, so there was no longer any cushioning at all. Also, the wheels are still true, it's just the ripple in the rim that means I can't brake properly, and no amount of spoke adjustment will remove this.

UndercoverElephant

rjsterry wrote:

Might have been the issue (I try to keep the pressure topped up to at least 115psi (I'm only 64kg, so much higher than that really loosens my teeth), but it could have dropped a bit, although, as I say, the impact burst the inner tube, so there was no longer any cushioning at all. Also, the wheels are still true, it's just the ripple in the rim that means I can't brake properly, and no amount of spoke adjustment will remove this.

My thought was more that if the original puncture was caused by the tube compressing enough that it could pinch and actually blow, then perhaps this was the issue. If it was that low that it not only pinched the tyre, but also knacked the rim...

It's all hypothetical though, pure conjecture. Except to say that the only time I managed to puncture my tube on a pot-hole was when I'd used my hand pump. It claimed I'd got to 85 PSI, I suspect nearer 60.

rjsterry

UndercoverElephant wrote:

rjsterry wrote:

Might have been the issue (I try to keep the pressure topped up to at least 115psi (I'm only 64kg, so much higher than that really loosens my teeth), but it could have dropped a bit, although, as I say, the impact burst the inner tube, so there was no longer any cushioning at all. Also, the wheels are still true, it's just the ripple in the rim that means I can't brake properly, and no amount of spoke adjustment will remove this.

My thought was more that if the original puncture was caused by the tube compressing enough that it could pinch and actually blow, then perhaps this was the issue. If it was that low that it not only pinched the tyre, but also knacked the rim...

It's all hypothetical though, pure conjecture. Except to say that the only time I managed to puncture my tube on a pot-hole was when I'd used my hand pump. It claimed I'd got to 85 PSI, I suspect nearer 60.

Sadly, this is the most likely explanation, which kinda means it's my fault rather than TfL. Time to buy a track pump then; go and get another shovel full... :roll:

UndercoverElephant

Joe Blow FTW! 8)

AidanR

The narrower the tyre, the easier it is to get a pinch puncture. Get yourself some wider tyres, say 28c, and this will help. You won't have to run them at ridiculously high pressures, so they'll be more comfortable.

Also, how come you hit a pot hole in the first place? If you can't bunny hop, it's worth learning.

As for rims with a bit of give, this isn't really possible. If a rim was flexible enough to take a hit, it wouldn't have the compressive strength necessary to build a wheel in the first place. Rims are in compression, so must be rigid otherwise they would buckle. Any material with enough rigidity is either going to plastically deform, like aluminium, or suffer brittle failure, like carbon fibre. As for a spoke breaking, this is quite unlikely as they are in tension - a hit will actually lessen the tension in the spoke.

amnezia

I have the R560s on my commuter and have been surprised how well they've held together.

Sounds like your were quite unfortunate, must have been a mammoth pothole!

rjsterry

AidanR wrote:

The narrower the tyre, the easier it is to get a pinch puncture. Get yourself some wider tyres, say 28c, and this will help. You won't have to run them at ridiculously high pressures, so they'll be more comfortable.

Also, how come you hit a pot hole in the first place? If you can't bunny hop, it's worth learning.

As for rims with a bit of give, this isn't really possible. If a rim was flexible enough to take a hit, it wouldn't have the compressive strength necessary to build a wheel in the first place. Rims are in compression, so must be rigid otherwise they would buckle. Any material with enough rigidity is either going to plastically deform, like aluminium, or suffer brittle failure, like carbon fibre. As for a spoke breaking, this is quite unlikely as they are in tension - a hit will actually lessen the tension in the spoke.

Not sure I'd get 28c's under my brakes but have considered this since, and a) it was dark, b) I was doing 20+mph in a vehicle sandwich, so was concentrating on not piling into the back of the front taxi, or getting punted by the one tailgating behind. It's a pretty fast junction when the lights are green and everyone comes steaming off the bridge. I've managed to miss that same pothole every other night, but got caught this once. It's been there so long, you can see the start of it on Googlemaps Streetview.

Take your point about the rim being in compression more than bending stress. A springy rim would be a bit like riding on jelly.

AidanR

I think that counts as extenuating circumstances

I think 28s should fit all but the tightest frames - I don't think the brakes themselves should be a problem. That's not a guarantee though!

rjsterry

amnezia wrote:

I have the R560s on my commuter and have been surprised how well they've held together.

Sounds like your were quite unfortunate, must have been a mammoth pothole!

I know they're relatively cheap wheels, but they were my first proper upgrade for the bike, and I was really fond of them. They are generally bombproof, and as my OP says, they are still true and rideable, but the dented rims make them no good for braking. I think UE is right and if I'd had the tyres a bit harder, I'd probably be just nursing sore wrists and a few loose teeth.

il_principe

@rjsterry I have a pair of unwanted Shimano WH-R550 or (560's not sure which) yours if you want them for a token sum. Let me know and I'll dig them out. They came with my 06 Focus and have hardly been used as I upgraded them v quickly.

PBo

UndercoverElephant wrote:

Joe Blow FTW! 8)

sorry - having abbreviation amnesia.....FTW?

merkin

I struggle with the abbreviations too. :?
Just looked on acronymfinder. It means Free The Wookies. :shock:
Did you report the pothole?

PBo

UndercoverElephant wrote:

Joe Blow FTW! 8)

FTW??? abbreviation memory failure - help please!!

Oddjob62

PBo wrote:

UndercoverElephant wrote:

Joe Blow FTW! 8)

FTW??? abbreviation memory failure - help please!!

For The Win