Breaking force

[philvantwo]

Cloudy here mick f, will it still work. Oh, not got any white bin bags.

[Mick F]

When you have a white bag, and a black one, both to hand, as well as a thermometer, as well as some sunshine ..............

Have a go.

[CJ]

When you have a white bag, and a black one, both to hand, as well as a thermometer, as well as some sunshine ..............

Better than that: I have a spare silver-anodised rim, and a black one. I just put them both outside in the sun. Both got warm and the black one was a little warmer, but still pleastly warm rather than uncomfortably hot, so maybe 50° rather than 40°, so no big deal.

On the other hand, black surfaces are not only better at absorming radiant heat, they are also better at emitting it. So when a black item is much hotter than its surroundings, it cools faster than a silver one. That limits how much hotter a black rim can get than a silver one, when both are illuminated by a VERY hot thing, but are 93 million miles away from it and surrounded by a lot of stuff that's much cooler!

Of course Cornwall IS a bit closer to the sun than Derbyshire

I think it's more likely that better brakes allow one to brake harder and later, so one can approach the steepest parts of a hill a bit faster. So during the approach stage more energy goes into moving air out the way and none into heating aluminium. That happens only on the difficult and dangerous sections of each descent and the better one's brakes the shorter are the sections that description applies to.

[Mick F]

Excellent reply CJ.

You are spot on methinks.
Crap brakes need more application, so get hotter.
Braking harder and more firmly, retards the bike better than softer brakes that need longer to apply the retardation.

Black rims are a red herring.

[foxyrider]

Black rims are a red herring.

surely that should be black herring?

[Mick F]

Nicely put!