How worn is that rim?

cce

Retrobike Rider
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There's less life in it than you think. I showed this to some people and some of them would have ridden it before I cut it open

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That's very interesting Keir. I always assumed the thickness of the wall was constant, but with that rim the bit you couldn't see was a lot thinner than the lower (outer) bit. I make the lower bit of a 517 1.7mm thick when new, so I use a straight-edge to estimate how concave the brake surface is, then deduct that from 1.7mm. On this evidence, that method is going to over-estimate how much life the rim might have left. What kind of rim is that?
 
I assume that Mavic designed it like that so the rim would crush first rather than blow the tyre off. It looks like a safer failure mode.
 
Further reminding that I need to replace a rim on a rear wheel before I discover how thin it has become :shock:
 
cce":j7rcjq12 said:
That rim is an EX721 so pretty burly to start with
I wonder whether they make disc rims differently though? I must say I didn't know you could use an EX721 with rim brakes, but it does have quite deep flat sides and it says UB Control, so obviously you can.
 

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EX721 was intended as a rim-brake capable burly rim. I think it's basically a D521 replacement
 
cce":7qbyk5o2 said:
EX721 was intended as a rim-brake capable burly rim. I think it's basically a D521 replacement
Yes, I had just assumed it was disc-only because most of the rims called Disc are disc-only. Is it just my old eyes, or do the walls look slightly thinner above the cross-brace than below it, even in this latest version? I'm not sure it's a good idea - if a rim is supposed to be burly, I'd like the bits I can't see to be as burly as the bits I can.
 
As hamster suggests, I'd guess it's designed that way so it collapses without blowing the tyre off when worn
 
I read that, but I'd rather it didn't collapse at all. Or even if it did, I'd like there to have been some way of knowing it was coming. That looks as though you were quite close to being taken by surprise, and it could have been nasty, even without the tyre blowing off. It would have failed under stress, which means most likely on a fast rocky downhill.
 
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