rim wear with V-Brakes

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thekelticfringe
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rim wear with V-Brakes

Postby thekelticfringe » 21 Nov 2009, 3:12pm

How do I assess rim wear? How much wear is too much? Thanks
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julk
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Re: rim wear with V-Brakes

Postby julk » 21 Nov 2009, 3:53pm

Some rims have a recessed line, mark or depression. These mark the safe limit of rim wear by braking.

If you had no wear limit marks then you should find a way to measure the rim sides thickness and see how much metal is left in order to decide when to replace them.

Alternatively, how far have they been ridden?
The rims on my bike are looking like they will do 5 or 6 thousand miles from new before needing replacement.

thekelticfringe
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Re: rim wear with V-Brakes

Postby thekelticfringe » 21 Nov 2009, 4:20pm

Thanks - I've seen wear guides (a groove all around the rim) but these rims don't have that. I reckon they may have been ridden only 1500 miles or so but they're pretty lightweight. I have done two sets of blocks since I've had them if that helps any. Running your fingers over the friction surface you can feel definite concavities.

How do they fail? What I mean is do they just get more flimsey so you're forever truing them and get more kinks/dings, or do I have to worry about some kind of catastrophic failure? :(
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rualexander
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Re: rim wear with V-Brakes

Postby rualexander » 21 Nov 2009, 4:38pm

Yes they can fail suddenly with a bang and with potential safety implications but you should be ok for a while yet i reckon, 1500 miles is not far. What type of rims are they?
You could try Chris Juden's suggested test of temporarily pumping the tyres up to 50% more than the rated pressure and if they survive that they should be good longer. His other method is to measure rim thickness and if there is still 1mm (I think)left, they are still ok.

thekelticfringe
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Re: rim wear with V-Brakes

Postby thekelticfringe » 21 Nov 2009, 5:25pm

So - I'm running quite wee tyres - carcase pressure rating is about 100psi. Maybe take it up to about 150psi? Sounds a lot! Think I'll wear safety goggles
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andrew_s
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Re: rim wear with V-Brakes

Postby andrew_s » 21 Nov 2009, 7:30pm

Some rims have internal wear markers, so you get a hole in the side of the rim when you pass the wear limit.
Other rims won't have any markers at all.

The way I check for wear on my older rims is to take the track pump and pump the tyre up substantially harder than I'd actually ride on - 160psi or so.
Leave it overnight, and if it doesn't blow up, and the sides don't get more concave than they were, the rim is still OK.
You can also get gauges that will reach round the rim hook to measure the thickness. Below 1mm is starting to get dodgy - the failed rims that I've measured have been at 0.6 to 0.7mm. You've got to take the tyre off to do the measuring.

Failure could be a short crack that makes your brake knock, or if you are unlucky the tyre will explode and you'll get bits of rim flailing about. If you are very unlucky, you are doing 40mph down a steep hill at the time.

rualexander
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Re: rim wear with V-Brakes

Postby rualexander » 21 Nov 2009, 8:55pm

Here are links to Chris Juden's information and tests for rim wear :

http://www.ctc.org.uk/resources/Magazine/20011163.pdf

http://www.ctc.org.uk/DesktopDefault.aspx?TabID=3827

Read your way through the second one as there are various interesting snippets all the way through

thekelticfringe
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Re: rim wear with V-Brakes

Postby thekelticfringe » 22 Nov 2009, 9:16am

Thanks - very helful. I'll have a look today - seems like something to keep an eye on. A collapsing wheel throwing thin shards of alli alloy around would not be an improvement to my commute. Actully, both wheels are disc capable, so maybe a word to Father X might be a good idea!
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thekelticfringe
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Re: rim wear with V-Brakes

Postby thekelticfringe » 22 Nov 2009, 2:07pm

andrew_s wrote:if you are unlucky the tyre will explode and you'll get bits of rim flailing about. If you are very unlucky, you are doing 40mph down a steep hill at the time.


PS - I do tend to be fairly unlucky :roll:
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james01
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Re: rim wear with V-Brakes

Postby james01 » 22 Nov 2009, 4:27pm

thekelticfringe wrote:So - I'm running quite wee tyres - carcase pressure rating is about 100psi. Maybe take it up to about 150psi? Sounds a lot! Think I'll wear safety goggles


...and ear-plugs. I did this test in my garage a few weeks ago and the rim burst like a gunshot. I was glad it happened there and not during a fast descent. :shock:

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CREPELLO
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Re: rim wear with V-Brakes

Postby CREPELLO » 22 Nov 2009, 5:09pm

Another quick and very unscientific way of assessing wear is to butt a steel rule up to the rim, edge on. I think rim design allows for at least 1mm of wear (could be more). The daylight showing between the rule and the rim can then be assessed, if you're confident in estimating measurements. Not ideal, but quick.

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fausto copy
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Re: rim wear with V-Brakes

Postby fausto copy » 22 Nov 2009, 9:32pm

Have a look at my "In the garage" posting in the On the road section for a photo of what an exploding rim looks like!

thekelticfringe
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Re: rim wear with V-Brakes

Postby thekelticfringe » 26 Nov 2009, 2:04pm

Just to say thanks for all the advice. I'll get a regular programme of checking, as it sounds like a hazard that is easy to avoid, but could be quite nasty!

FWIW I worked out that my commute alone is about 5K miles a year, ignoring any leisure/pleasure cycling. It's a fairly hilly route, involves short stretches of gravel/un-sealed surfaces, and concludes in the city so there is appreciable use of the brakes no matter how kamikaze I'm feeling, so that could mean new rims every year!!

Discs might be the solution, I think.
Pedal faster, I hear banjos!