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 Post subject: How worn is that rim?
PostPosted: Wed Mar 13, 2013 9:15 am 
retrobike rider / Gold Trader
retrobike rider / Gold Trader

Joined: Sat Jul 21, 2007 9:48 am
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Location: Bristle
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

Image


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PostPosted: Wed Mar 13, 2013 10:20 am 
retrobike rider
retrobike rider

Joined: Sun Sep 23, 2007 11:22 pm
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Location: Hove
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?


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PostPosted: Wed Mar 13, 2013 11:32 am 
Old School Grand Master

Joined: Tue Oct 09, 2007 1:55 pm
Posts: 8204
Location: New Forest, UK
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.


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PostPosted: Wed Mar 13, 2013 11:35 am 
retrobike rider / Gold Trader
retrobike rider / Gold Trader

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Location: Bristle
That rim is an EX721 so pretty burly to start with


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PostPosted: Wed Mar 13, 2013 11:44 am 
MacRetro rider
MacRetro rider

Joined: Fri Feb 09, 2007 4:16 pm
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Further reminding that I need to replace a rim on a rear wheel before I discover how thin it has become :shock:


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PostPosted: Wed Mar 13, 2013 1:51 pm 
retrobike rider
retrobike rider

Joined: Sun Sep 23, 2007 11:22 pm
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Location: Hove
cce wrote:
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.


Attachments:
2013 Mavic EX721 Disc.jpg
2013 Mavic EX721 Disc.jpg [ 71.1 KiB | Viewed 293 times ]
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PostPosted: Wed Mar 13, 2013 2:03 pm 
retrobike rider / Gold Trader
retrobike rider / Gold Trader

Joined: Sat Jul 21, 2007 9:48 am
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Location: Bristle
EX721 was intended as a rim-brake capable burly rim. I think it's basically a D521 replacement


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PostPosted: Wed Mar 13, 2013 4:00 pm 
retrobike rider
retrobike rider

Joined: Sun Sep 23, 2007 11:22 pm
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Location: Hove
cce wrote:
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.


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PostPosted: Wed Mar 13, 2013 4:02 pm 
retrobike rider / Gold Trader
retrobike rider / Gold Trader

Joined: Sat Jul 21, 2007 9:48 am
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Location: Bristle
As hamster suggests, I'd guess it's designed that way so it collapses without blowing the tyre off when worn


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PostPosted: Wed Mar 13, 2013 4:10 pm 
retrobike rider
retrobike rider

Joined: Sun Sep 23, 2007 11:22 pm
Posts: 7305
Location: Hove
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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