Thorn Cycles Forum
Technical => Wheels, Tyres and Brakes => Topic started by: geocycle on August 06, 2008, 02:32:49 pm
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Can anyone remind me what the wear indicator on Sun CR18 rims looks like? I can't see any sign of anything on mine and I don't know whether something appears to show wear or disappears. If the latter then I probably need new rims! They've done 5500 miles.
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Depends how old it is I think, my last set had a small circular indentation which disappears as the rim wears down to the recommended minimum. This is very hard to see/find with all the muck and brake pad marks on the rim, so you probably have to give the rims a thorough clean to find it, if its there. Older versions didn't have any wear indicators though, as far as I know. Try giving SJSC a call and asking them when the wear indicators were introduced to see if your rims are likely to have them or not.
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Thanks for that. I now recall seeing those when new. As they've now disappeared I must be in the 'red zone'. Although the mileage is not great (5500 miles) I've done a lot of these off tarmac including a 5m stretch on cinders on my commute so I am not surprised they are wearing. The rear rim is also slightly bowed. I'm probably going to shift to the tungsten carbide rims.
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If you've done 5000 miles on them I would change them ASAP. We had one fail dramatically at about that mileage or probably less last year. We were on holiday in the western Isles and it was on a Rohloff hub so I ended up having to dismantle the front wheel, rebuild the rear wheel with the rim from the front wheel, then we were able to buy a cheap new front wheel at the nearest bike shop. The shop were unable, or unwilling to rebuild the rear wheel for us. One good reason for using the same rims front and rear on a Rohloff bike, you know you can swap them over and use the same spokes, if you have to!
I surprised myself by being able to do the rebuild well enough for us to continue and complete our holiday!
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Got the new tungsten carbide rims on the bike. So far so good with no squeal on the back and minimal on the front, I must have got lucky. I don't suppose anyone knows what the two drilled 2mm holes are on the top of the rim at the point rim joins are for? I guess they are part of the manufacturing process (there is also one on the inside). Looks to me as though they need filling with something before I start riding through deep water....
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This topic has shaken me a little. I scurried off to see if the indicators are visible on my own CR18 rims and surprse, surprise, they are not. I would guess the mileage on these would be in the order of 8,000 (13,000KM). So...I will replace these rims, but what has me worried is that I have 2 other bikes that have done many more miles in the years that I have had them, and the rims on these (Mavic Open Pro and Matrix Singletrack) aren't blessed with wear indicators. I suppose I should replace these too, but before I spend the money I've been saving for an Audax MK3 on half a dozen rims, can someone offer any advice on how thick a rim should be and whether it's possible to check the thickness with a micrometer or something similar?
Cheers,
pj
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Here is a link to an article from CTC by chris Juden :
http://www.ctc.org.uk/resources/Magazine/20011163.pdf
Also if you go to this next link and scroll down there is another
answer from Chris Juden and a photo of a dentists tool that can do
the job.
http://www.ctc.org.uk/DesktopDefault.aspx?TabID=3827
I think I have seen them advertised for sale at some bike shop website
also but cannot remember where.
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Hi Rualexander,
Many thanks for the information, which should see me on the straight and narrow. (and, possbly, on new rims)
Cheers,
pj
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I think the rim wear indicator is likely to be a bit conservative so probably no need to panic. That said, the rear rim had bowed and was showing clear signs of needing replacing even though it may well have done another few thousand miles. However, building a rohloff wheel is beyond me and I wanted to let SJS deal with it, so I was happy to err on the side of caution and get it replaced when I could plan to be without the bike rather than following a breakdown situation. I hope the new tungsten carbide rims will last longer.
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My rear CR18 cracked after about 7000 miles. It was very dished an the wear indicator was gone.
Basically it crushed under the force of my brakes. I just felt a thump-thump-thump when I was braking and pulled over to check what it was. Whoops. Slow ride home using only front brake.
It could be catastrophic on the front if the brake pad got stuck in the rim.
Carbide for me next time as well. What is their life-expectancy?
GEOCYCLE, please keep us posted on how the rims are going and which ones you got.
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Hi Fred,
So far I am very pleased with the carbide rims. I went for the rigida grizzly with eyelets. As I posted in a parallel thread I think they offer comparable dry weather braking performance to the CR18s using the swissstop blue pads (rather than the avid rim wranglers that come with the ultimate brakes). I wouldn't say they were any better in the dry but they do not lose as much performance in the wet. I've not had any problems of squealing after the first couple of rides. Obviously, I can't comment on longevity after only a few hundred miles. The 1.5 inch marathons sit very nicely on them and were easily fitted. The rims are slightly wider than the CR18s and I had to lose some spacers between the brakeshoe and the caliper. Any weight difference to the CR18s is neglible. My only very minor quibble is two drilled holes were left unfilled at the point the rim was joined which looked as if they could let water into the wheel so I got the silicone sealant out and all is now well.
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has anyone noticed rim wear caused by braking on dirty rims?
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not really but be sure to check brake blocks after each ride , more likely to get grit embedded in the rubber not great for rims. ::)
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Thanks for resurrecting this old thread... it really took me back! Since I went to carbide I have NEVER cleaned the rim or brake blocks. The front rim is still the same one with 20,000+ miles on it, the rear was replaced this year (mainly because the hub was with SJS for other reasons), oh and I'm on the second pair of blocks!
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Carbide it is then!
One thing I've noticed though is that in the rain, rims get dirty. Not to mention dirt roads in the country side, seems really abrasive.
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Carbide it is then!
One thing I've noticed though is that in the rain, rims get dirty. Not to mention dirt roads in the country side, seems really abrasive.
Yes, I am a strong advocate. I should point that the current Thorn recommendation in the mega brochure is to have a none carbide on the front as some folk have experienced serious braking issues when the rims are worn in excessive wet conditions. I've been lucky in that respect and never had a problem.
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Some people say you have to replace spokes when you put on a new rim. But if you have not had any spoke breakage and no other obvious reason to replace spokes, I prefer to reuse the old spokes if you get a new identical rim. You can tape the new rim to the old rim getting the valve stem in the same place. Then shift one spoke at a time from the old rim to the new one.
The time savings to avoid lacing up new spokes and cost savings of spokes may make buying the same brand and model of rim worth it if you are unsure what you really want.
If you try this with an old freewheel wheel, it is best to loosen up the freewheel first just in case something goes wrong and you find you need to replace any spokes on the drive side.
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cheers!
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Here is a link to an article from CTC by chris Juden :
http://www.ctc.org.uk/resources/Magazine/20011163.pdf
Also if you go to this next link and scroll down there is another
answer from Chris Juden and a photo of a dentists tool that can do
the job.
http://www.ctc.org.uk/DesktopDefault.aspx?TabID=3827
I have the actual CTC magazine with the article in it and the critical rim thickness quoted by Chris is 0.5 to 0.7mm.
Mike