That’s where I found the time to cool interesting, being roughly twice as long as the time to heat up, which does suggest that even ‘proper’ technique will likely result in a rim which gets progressively warmer on a technical descent.

+1 fifeandy

Brake dragging is really not a good idea

The usual advice is the opposite to that – higher speeds mean more air cooling and more ‘free’ braking due to wind resistance.
Dragging results in more heat build up in the wheel and less ability to cool it.

But how much cooling do you want and need? It’s all about managing peak temperatures with carbon. Above a certain temperature the glue is affected and therefore rim life is. Below that threshold the glue is fine, so as long as you manage your rim temps then you can drag your brake as long as you like. Mechanical wearing of the rim then becomes the issue that determines rim life just as with alloy rims.

At any given applied brake force a certain amount of energy is imparted into the rim. The temperature that ‘builds up’ depends on how well you can cool the rim. At relatively light braking forces the temperature is quite cool and constant i.e. it doesn’t build up and continue to increase. At very heavy braking forces you might not be able to cool quickly enough so rim temps might very well continue to rise and build up.

The aerodynamic braking effect is marginal. In the same way as you need more and more power to get to higher speeds because drag increases to the square of speed, when it comes to braking the same effect applies – the drag reduces to the square of speed, so aerodynamic drag as an aid to braking is not very effective other than at very high speeds. As soon as you slow down the drag effect drops off very very quickly.

Old rules may not apply. You might need to choose between descending more slowly and carefully to manage rim temps and preserve rim life, or descending quickly and brake harder, but eat up rim life more quickly.

But it’s all academic. For the majority of us who are not hitting the Alpine descents week in week out, I suspect it’s not an issue unless you’re routinely a really heavy braker. And for those of us who do hit the Alpine descents how many of us are really hitting them like a Pro? I don’t, I’m like an old woman.

And for those of us who do hit the Alpine descents how many of us are really hitting them like a Pro?

purely anecdotal, but a bloke who works for a locally-based team told me they delammed 6 front Campag Boras during the Pyreneen stages of the TdF two or three years back. Obviously being tubulars they didn’t result in any spectacular failures but it’s interesting that the riders *probably* aren’t your average brake dragger unused to 80+km/h descending.

And for those of us who do hit the Alpine descents how many of us are really hitting them like a Pro? I don’t, I’m like an old woman.

But that means you’re braking far more, and you have clinchers, and you don’t have the full width of the road to use, and you have to worry about what’s around corners etc etc.

The “pros are fine” point is a really daft one IMO!

so aerodynamic drag as an aid to braking is not very effective other than at very high speeds

[quote]I don’t, I’m like an old woman.[/quote]Clearly you don’t descend fast enough – at typical alpine descending speeds getting out of your tuck and sitting up (still on the drops) to take the wind slows you significantly.

And for those of us who do hit the Alpine descents how many of us are really hitting them like a Pro?

Typically amateur riders will be harder on brakes than pros as they can hit the same straight line speeds comfortably enough but only have half the road to play with on the corners so have to slow more.

Someone stopping to avoid a bin lorry on a steep descent on Chinese rims IIRC.

That was me 8)
There’s half a dozen descents round here that would overheat rims.
In my time in Lbs’s I’ve seen failed rims (both clincher and tubs) from just about every manufacturer.

Mavic, Enve and Boyd respond to test, they agree with points made here – Alto do so well because it appears their rims generate lower friction, so yes, they don’t heat up as much, but they also don’t stop as well. They also say their rims would have stopped you so much earlier they’re effectively penalising better braking performance. Mavic just say they’re lying (paraphrasing).