Would a hot wheel rim cause a puncture?

sonicred007

I recently did the C2C and for 76 miles (ish) I only had the front brake... coming down into Nentheads after much braking I got a blow out... it was dry and when I felt the rim during the replacement of the tube it was hot

Similarly it happened coming down into Stanhope from Rookhope... is it coincidence or was hot rims the cause - checking the tube now there is the usual damage evidence of a puncture

Would I need to watch out for this ordinarily with two brakes on steep descents?

I had the bike serviced before the trip so the set up should have been fine and close inspection at rest stops showed good, even contact between block and rim - plus there was plenty of brake block left

I know I was stupid to continue (buckled wheel meant I released the back brake to keep moving)

teagar

Check your rims arn't worn and maybe run a bit less pressure in your tyres.

Learning to decend fast and safely by using your breaks much less also helps.

Just came back from the Pyranees where we had a couple blow outs, and they were largely to do with worn rims.

sonicred007

like i said it was serviced incl cleaning up the rims so i was assuming this would be picked up

what is the basic advice or guidance on descending - especially with rear panniers... i obviously failed as i was down to one brake... but that aside where can i find advice for the future

frenchfighter

When coming down long ascents, your rim will expand due to the heat generated from the braking friction. Therefore, it may be worth letting a little air out of the tyres before descending. I tihnk this only really matters on a longish descent. I heard this from an ex-pro riding a sportive.

sonicred007

frenchfighter wrote:

When coming down long ascents, your rim will expand due to the heat generated from the braking friction. Therefore, it may be worth letting a little air out of the tyres before descending. I tihnk this only really matters on a longish descent. I heard this from an ex-pro riding a sportive.

I guess this would explain my punctures descending on just one brake

careful

I have known patches to lift after long descents with hard braking. On one club run many years ago 4 or 5 people all had to replace patches at the bottom of a particularly steep descent. All were on fixies with just one brake. Never known actual punctures - I suppose the increased pressure could do it.

balthazar

frenchfighter wrote:

When coming down long ascents, your rim will expand due to the heat generated from the braking friction. Therefore, it may be worth letting a little air out of the tyres before descending. I tihnk this only really matters on a longish descent. I heard this from an ex-pro riding a sportive.

That is good advice, except that it is not rim expansion that is the problem, rather rim heat from braking, increasing tyre pressure. That pressure exceeds the limit of the tyre/rim combination and blows the tyre off the rim.

Achieving this requires long descents with much braking. Solutions include riding with lower air pressure in your tyre, to accommodate the increase, and braking less.

Monty Dog

There was a recent discussion on this on La Marmotte, where riders descending from L'Alpe de Huez to the start suffered similar problems - many of them on deep rim carbon wheels with aluminium brake tracks. This is another reason why seasoned pros still prefer tubulars. Obviously having only one brake and having the extra weight of panniers compounded your problem.

sonicred007

I'm far from the pro league... so keeping two brakes and avoinding long descents should be easy enough to achieve