Carbon wheels in the Alps
- Thread starter gbs
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Yellow Saddle
Guru
- Location
- Loch side.
No, absolutely not. Carbon is a poor conductor of heat and won't channel heat away or dissipate it. However, in your previous post you said that you will be using disc brakes for your Alpine trip, which makes the issue moot.
However, brakes work like this. The heat is generated at the interface between the two friction materials, that being the disc or rim and, pads. The heat is generated in the softest of the two materials (lets stick to rubber brake pads for clarity) and transferred via conduction to the harder of the two materials which then dissipates it via radiation and conduction. Typically on a road bike, the aluminium brake track (aluminium is a good conductor), removes the heat from the pad, spreads it through the rest of the rim, into the nipples and spoke ends, where airflow removes the heat. Note that just about zero heat moves back through the brake pad into the brake caliper, since rubber is too good a heat insulator. It is therefore futile to add cooling fins to the back of rubber brake shoes.
Should you now replace that aluminium rim with a carbon one, the following happens. Heat is generated in the pad at the interface of rim and pad. However, the carbon rim cannot remove the heat from the pad, the pad overheats and melts - hence the need for non-melting pads on carbon rims. These pads are made from a material that doesn't melt but goes directly from solid to gas. This could be cork, aramid fibres or something like that. Howver, this compromises brake performance and a carbon rim doesn't stop as quickly as an aluminium one. It also abrades quickly, can delaminate from the heat etc.
You need good airflow to keep your brakes cool and good technique. Do not drag your brakes, rather as someone else suggested, use them alternatively and intermittently.
Which wheelsets are recommended? It doesn't matter, as long as they are aluminium. Also stay away from tubbies, the high heat softens the glue and the tubbie can slide on the rim and bunch up at the valve. Not nice.
Not all brake pads are created equal either. Some rubbers, including that used by Shimano, forms hard crystals when melting, which picks up aluminium from the rims. If you remove a black pad on a hard working bike you'll notice bits of alu stuck in the rubber. You'll also notice that the rim is scored. For your Alpine trip, consider Koolstop Salmon pads, these don't pick up aluminum and perform better than OEM stock.
However, brakes work like this. The heat is generated at the interface between the two friction materials, that being the disc or rim and, pads. The heat is generated in the softest of the two materials (lets stick to rubber brake pads for clarity) and transferred via conduction to the harder of the two materials which then dissipates it via radiation and conduction. Typically on a road bike, the aluminium brake track (aluminium is a good conductor), removes the heat from the pad, spreads it through the rest of the rim, into the nipples and spoke ends, where airflow removes the heat. Note that just about zero heat moves back through the brake pad into the brake caliper, since rubber is too good a heat insulator. It is therefore futile to add cooling fins to the back of rubber brake shoes.
Should you now replace that aluminium rim with a carbon one, the following happens. Heat is generated in the pad at the interface of rim and pad. However, the carbon rim cannot remove the heat from the pad, the pad overheats and melts - hence the need for non-melting pads on carbon rims. These pads are made from a material that doesn't melt but goes directly from solid to gas. This could be cork, aramid fibres or something like that. Howver, this compromises brake performance and a carbon rim doesn't stop as quickly as an aluminium one. It also abrades quickly, can delaminate from the heat etc.
You need good airflow to keep your brakes cool and good technique. Do not drag your brakes, rather as someone else suggested, use them alternatively and intermittently.
Which wheelsets are recommended? It doesn't matter, as long as they are aluminium. Also stay away from tubbies, the high heat softens the glue and the tubbie can slide on the rim and bunch up at the valve. Not nice.
Not all brake pads are created equal either. Some rubbers, including that used by Shimano, forms hard crystals when melting, which picks up aluminium from the rims. If you remove a black pad on a hard working bike you'll notice bits of alu stuck in the rubber. You'll also notice that the rim is scored. For your Alpine trip, consider Koolstop Salmon pads, these don't pick up aluminum and perform better than OEM stock.
Last edited:
Yellow Saddle
Guru
- Location
- Loch side.
Tubular tyres. Tubbie is a colloquialism from my part of the world, sorry.+1 for the above!
indeed koolstop salmon have a very good reputation although i haven't tried them yet
when you say tubbies, what exactly do you mean? when i google tubbie it just comes up with telle tubbies! do you mean, tubular cheels and tyres rather than clinchers?
Cheers Ed
young Ed
Veteran
Oh yes, I think I understand you now. Thankyou so much for explaining that old chappie! (read in most upper class voice whilst wearing top hat and a monocle!)
Cheers Ed
ayceejay
Guru
- Location
- Rural Quebec
I think the glue melting between tubular rims/tyres from too much braking heat comes from the same school as carbon frames dissolving in the rain. Tubs do come off the rim when they shouldn't but this is more likely to be due to poor fixing.
