Why is alloy better for braking than steel?

[Davidc]

It is the coefficient of friction that will be the important bit I think.

So long as teh rim is 'grippy' and not 'slippy' then the brakes will be better.

I changed the steel rims on my folder for aluminium BMX rims last week, one plain and one black painted. The chrome steel had little 'friction dots' on the surface and I could feel and hear them rubbing on the blocks. All in all the dots were proabably only 10% of the surface so 90% was still slippery.

The BMX rims were a lot better, especially when I used a power sander on the surface to take the grime off one and the black paint off the other.
The black paint was more slippery then the chrome steel.

It's the coefficient of friction in the presence of water that's of interest. Steel and chrome plated steel were fine in the dry, the problem was the lubricating properties of water.

As I said above I was told by sommeone who at least should have known the answer that it's just the surface properties of the materials involved and you can't do much except change materials (= use alloy rims). Your experience suggests that painted rims aren't the answer either!

The steel rims I used in the 60s to early 80s had a sort of criss cross engraved pattern to supposedly improve friction, and that used to make a buzzing noise. Even less useful than a chocolate teapot.

 

[tyred]

I've recently discovered that Fibrax still do leather faced brake pads.