Melting the brakes....?

[Trumpettom001]

I've just moved onto a road bike, and part of my ride is a mile long, VERY weavy downhill section - and braking is a must.... How hot do you have to get a tyre before it blows off the rim? i've always has discs on bikes in the past, and never worried about stripping them or anything? happened to anyone?

 

[Gerry Attrick]

Blimey, how long is a piece of string? I have heard of this with pro riders descending Mt. Ventoux and the like, but for the average joe I can't imagine a problem Put it this way, I have braked hard and long from a 52mph blind downhill in Leicestershire, along with several other riders. I never gave a tyre blow out a thought. (Maybe if I had I would have stuck to 15mph!).

 

[psmiffy]

I blew a tyre out due to overheating on a long steep descent in NZ - When I went to take the tyre off the rim was hot enough to burn my fingers -at least 5 - 10 minutes after the blow out - I had cantilever brakes and quite a lot of weight - never suffered the problem since changing over to Vs and subsequently HS33s (and I suspect that the fact I am aware that it could happen) which are effective enough that I can take speed off quickly by cadence braking

 

[RedBike]

Never heard of anyone in the UK suffering from exploding tyres due to heat. I often drag a brake on the fixie down some long steep hills and i've never had any issues.
You will wear out your pads / rim quickly though

 

[psmiffy]

I think its a matter of how long it is steep for plus a bit of air temperture thrown in - long descent in the UK is not that long by the standards of a lot of other places

 

[PaulB]

It happened to me last year but not in Britain. It was a very long and very twisty-turney descent down from the Troodos mountains in Cyprus and it was a hot day. The constant braking in the heat melted the inner tube which blew up. I had to chuck the water I had in my bottle over the wheel to cool it down before I could touch it!

 

[Philip Whiteman]

It happened to me coming off Hardnott. The brakes started to hiss as the rubber blocks started to melt from the friction against the rims. This was despite pulsing the brakes.

They samething happened last year coming down The Burway off the Long Mynd.

Both incidents occured in hot weather.

 

[psmiffy]

One of the things I have found that is a dead giver away on a long hairpin descent when it is raining is the steam rising from the rims

 

[jimboalee]

It happened to me down Fish Hill during an Audax in 1996??. A 160km from Earlswood Village Hall via Banbury, Stow on the Wold and Broadway. Anyone else remember that day. Middle of June and blistering hot.
Was that organised by The Beacon, Philip? It wasn't Solihull.

It was 34 C in the shade and I held the bike back down the hill on the rear brake while slurping from my bottle in my right hand.

Chucked the bottle, hit the grass verge and landed safely on the turfs.

Walked back to get the bottle while the rear rim cooled down.

Diverted to a car parts shop who sold BSOs in Evesham to restock my spare tube.

 

[Amanda P]

Cheddar Gorge, June 1985, I think. (Does this date me? I was a teenager at the time!) Just as well I had a spare tube because the one that was in there had a split six inches long along a moulding mark. Rims were too hot to touch.

I've never had it happen since, despite some long descents on hot days in South Africa on small wheels (less aluminium in a Moulton rim to absorb the heat). I think knowing it can happen is enough to ward it off. Stop and look at the view for a bit while the rims cool. Then carry on.

 

[jimboalee]

Cheddar Gorge, June 1985, I think. (Does this date me? I was a teenager at the time!) Just as well I had a spare tube because the one that was in there had a split six inches long along a moulding mark. Rims were too hot to touch.

I've never had it happen since, despite some long descents on hot days in South Africa on small wheels (less aluminium in a Moulton rim to absorb the heat). I think knowing it can happen is enough to ward it off. Stop and look at the view for a bit while the rims cool. Then carry on.

Sorry to be pedantic.

Braking on a descent requires energy to overcome the force of gravity. That energy becomes heat generated by the friction between blocks and rim.

The Moulton rims will have less mass, so only a slightly smaller amount of energy ( because the rider is by far the largest body of mass on the vehicle) will be dissipated by less mass = more calories per gram = hotter.

 

[Philip Whiteman]

It happened to me down Fish Hill during an Audax in 1996??. A 160km from Earlswood Village Hall via Banbury, Stow on the Wold and Broadway. Anyone else remember that day. Middle of June and blistering hot.
Was that organised by The Beacon, Philip? It wasn't Solihull.

It was 34 C in the shade and I held the bike back down the hill on the rear brake while slurping from my bottle in my right hand.

Might have been Alan Partridge's Audax for Redditch. I had a similar problem around three years ago with heat - though it was not the descent but having to gasp for air on a steep ascent in temps of 30 Celsius.