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In our kitchen its like being in a womb. Its more that super safe
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usually around the 145psi which is fine if you're running 100-120
The issue with carbon fibre rims is one of heat- whilst alluminium (being a metal) conducts heat very well, carbon fibre is essentially an insulator, and holds onto heat rather than conducting it away.
So, high, but within tolerence tyre pressure for a rim can turn into a pressure that is far too high for a rim that is starting to soften due to heat.
What happens I hear you ask?
Typically, our hero is descending a steep hill, on the brakes a lot, when the rim either deforms outward dramatically, sometimes locking the wheel, or simply spits the tyre off, both of these under brakes.
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usually around the 145psi which is fine if you're running 100-120
Thats for metal clincher rims, and even for metal rims it can be a fair bit lower than that. A decent chunk under what is pinted on your tyres
Carbon fibre isnt great under the sort of focused tension a rim bead undergos. So is likely worse.
The issue with carbon fibre rims is one of heat- whilst alluminium (being a metal) conducts heat very well, carbon fibre is essentially an insulator, and holds onto heat rather than conducting it away.
So, high, but within tolerence tyre pressure for a rim can turn into a pressure that is far too high for a rim that is starting to soften due to heat.
What happens I hear you ask?
Typically, our hero is descending a steep hill, on the brakes a lot, when the rim either deforms outward dramatically, sometimes locking the wheel, or simply spits the tyre off, both of these under brakes.
If the carbon is an insulator. How is it going to warm up properly?
Youre looking at hitting 180-200C throughout the bead to soften the epoxy.
The heat build up thing is purely a surface factor. Which might well ruin your braking. But it would take a lot of heat to soften the rim.
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Whatever it is, it doesn't sound super safe....
Cork brake pads should help fix the coooked braking surface thing. Still not going to be as good as alu though.
Quality carbon clinchers probably have the same max PSI as a alu ones. The point is that this is lower than most realise, and that they wont fail in the same manner as an alu rim.
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why don't race car brakes go squidgy when they get hot and when i say hot i mean red hot ...
600C even with CB's power he won't get rims warmed up to 600CInorganic carbon surface.
Not organic like the epoxy part of carbon fiber rims.Not much organic likes temps over 450C.
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Thats for metal clincher rims, and even for metal rims it can be a fair bit lower than that. A decent chunk under what is pinted on your tyres
Carbon fibre isnt great under the sort of focused tension a rim bead undergos. So is likely worse.
If the carbon is an insulator. How is it going to warm up properly?
Youre looking at hitting 180-200C throughout the bead to soften the epoxy.
The heat build up thing is purely a surface factor. Which might well ruin your braking. But it would take a lot of heat to soften the rim.
My post is ScobleKnowledge it is true, but plenty of anecdata out there about rims failing (deforming and/or spitting the tyre off) under high braking loads.
Some suggest that its' heat transfer into the air in the tyre, causing the pressure to rise in line with the heat- I don't have enough understanding of the matter to establish if that is credible.
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I bet loads of alu rims have done exactly the same.
Next time I do a long decent on my carbon clinchers I'm going to give the beads a quick squeeze.
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Is CB likely to do an alpine desent on his fixie?
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Why did Iain start this thread?
Fixed.
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Fixed Super Light Super Safe
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@ChainBreaker
usually around the 145psi which is fine if you're running 100-120