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Help!Is My rim rupturing?

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Help!Is My rim rupturing?

Old 03-17-11, 09:38 AM
  #1  
trek330
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Help!Is My rim rupturing?

I have a Cannondale F700 mtb with sun CR17A 26 inch wheels.Suddenly my brakes caught my wheels without squeezing them.Got home,Took the wheel off,put it on the truing stand at one point on the rim its spread out at equal distances so that both calipers touch equally on opposite sides of the rim.Other than that the wheel is true.I did not hit a significant bump!This is not a dent rather a rupture.How did it happen?I checked my spoke tension and it is way low across the board Some thing like 50kgf and less.Some spokes up to 80.The spokes are 1.8 gauge.Should I try to bend it back and then properly tension the wheel or is it shot?By the way the tire didn't flatten out or lose any air.Thanks in advance for any help.What is proper drive side tension for that wheel.32 spokes.
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Old 03-17-11, 09:51 AM
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Using rim brakes will eventually remove enough material from the rim to the point where it can collapse like that. Using a wide tire highly inflated on a narrow rim will bring it about faster. The rim is lifed out.
You may try to find a new one identical to what you have, and simply transfer it over. Or try find another one with the same ERD + drilling and transfer that. Or use the opportunity to buy yourself a new wheel.
Rule-of-thumb driveside tension is 110 kg or thereabouts.
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Old 03-17-11, 10:24 AM
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I'd guess that this is an older and often used bike. Maybe one that you ride in all weather or muddy conditions. If the braking tracks on the rims are well worn and coved in hollow then you just found out how thick the rim side walls are. As dabac says, rims used for braking as well as mounting tires are a consumable commodity. It's time to buy a new rim and swap it over.

If the spoke nipples are all still fairly free turning and if you can find a rim with the same ERD it's a pretty easy job to slack off the spokes and tape the new rim to the old and then just move all the spokes over. Then just tension and true as if it were a new build.
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Old 03-17-11, 10:26 AM
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I can't tell from your post if it's simple wobble touching either shoe at various times as it spins, which can be re-aligned by working the spokes (up to a point).

Of if it's touching both shoes at the same time because it's spread wider there. This is not repairable and is the result of brake shoe wear to the point that the rim can no longer resist the tire pressure spreading it open.
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Old 03-17-11, 11:26 AM
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Using the Bikepedia - I`ve confirmed that the Cannondale F700 has been marketed from 1996 thru 2002 so its likely that this is a situation where the rims have seen enough use as braking surfaces to wear through them. Just one of those things.

And the notion that it might be due to wide tires on narrow rims is just an urban legend. Rims are pretty dumb. They don`t know what size of tire is on them - just how much PSI they have to deal with. The following is a direct quote from the Schwalbe Tire website and is nothing new.

Quote:"Since 2006 the combination of extra wide tires and narrow 17c and 19c rims is officially approved by ETRTO. This just caught up with reality, because this combination has already been an everyday occurance in MTBs and Balloonbikes for many years and has not caused any problems.

Often the use of a wider rim is useful because it brings additional stability to the tire, The tire pressure can be reduced slightly before the stability becomes `spongy`." End-quote.

And as per the Schwalbe tire/rim chart, 17c rims are approved for tires up to 62mm. Since the OP is running a mtb bike its a safe bet the rims are at least 25mm with a 19mm internal dimension and tire size would only be limited by frame clearance.
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Old 03-17-11, 01:10 PM
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Originally Posted by Burton View Post
And as per the Schwalbe tire/rim chart, 17c rims are approved for tires up to 62mm. Since the OP is running a mtb bike its a safe bet the rims are at least 25mm with a 19mm internal dimension and tire size would only be limited by frame clearance.
CR17A are 23.5mm wide, actually.
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Old 03-17-11, 01:20 PM
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One of my Sun Zero Degree Lite rims failed in this fashion after pretty low mileage. It's put me right off Sun rims now.

My shoddy troubleshooting techniques made the actual discovery of what was going wrong take much longer than it should have. I took wheel out, removed the tire, checked for dents (A-OK), checked for true (good enough for government work) and put everything back together.

Next ride - Uggh it's still dragging in that spot! This time I actually inspected the rim with the inflated tire still installed - A-Ha! Followed by a mourning period, which I'm still working through. I really need to get another rim on that wheel and recycle the old one so I can have some closure
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Old 03-17-11, 01:35 PM
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Take the tire and rim tape off the rim and check for cracking on the inner layer. Probably going from spoke hole to spoke hole. bk
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Old 03-17-11, 02:14 PM
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Check my thread 'Re-use Old Spokes' for details of the 'transfer' procedure. This is indicated when the spokes and hub are in excellent condition and when the new rim ERD matches the old. I didn't know about the spoke/hub transfer procedure when I posted and was amazed at how cool it is. I went from 1989 Ritchey Vantage rims to current Mavic 317s. I did not know the ERD of the old rims but the old and new looked so similar in that respect that I went ahead with it. I'm not a wheel builder but was able to do the swap and get the wheels dished and good enough to ride, although I did take them into the LBS for a pro truing. The guy at the shop spun the front wheel and said he didn't think it needed anything, which made me feel pretty good! I had them do it anyway, and am very satisfied with the results.
I never have thought about the effect of brake wear on rims, never having ridden a single bike long enough to experience it. I think you were fortunate to have stopped riding it when you did, or you may have eaten some road the next time it seized. Now I understand why the disc brake has become commonplace even on Wal Mart bikes.
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Old 03-17-11, 04:48 PM
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Brake pads harden with age and many are too hard when new. Replacing the pads with softer pads like Koolstop salmon pads can help with rim life.
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Old 03-17-11, 05:22 PM
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Thanks All for your feedback!I'll go with the consensus and bury that rim.Al1943 I just did just that!I replaced the pads witrh koolstops and was in seventh heaven with my brakes!! I got the adjustment right on and it was great...till now.I'm going to get a new rim and spokes and do it myself.I built my road bikes wheels-first build,and it was a huge success.I have all this a equipment I'm glad I'll get a chance to use it again.I'm gonna change the spokes too.They don't look to hot and I mentioned the poor tensioning all around so Might as well start new.Anyone recommend a good strong, AFFORDABLE 26 inch MTB rim.This one was 32 holes is there a 36 hole option?Why were the spokes 1.8?Wouldn't 2 gauge be stronger?Im 200+ lbs.Again thanks for all your valuable help!!
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Old 03-17-11, 07:07 PM
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If you're going to use the same hub you need to stick with a rim that has the same drilling as the hub. So stick with 32 spokes.

The spokes are MORE than strong enough to hold up 200'ish lbs of rider provided the wheel is built with proper tensioning and stress relieving and close to equal tension in all the spokes. Barring an impact related failure the most common spoke failure mode by far is to fatigue from being too LOOSE. When not tight enough to stay tight all the way around the rotation the load cycles too much and too close to zero tension and that is hard on the spoke due to flexing. If it's tight enough to stay decently tight then it's not an issue and the wheels will last darn near forever... or until you wear out the braking face...
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Old 03-17-11, 08:26 PM
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Originally Posted by bkaapcke View Post
Take the tire and rim tape off the rim and check for cracking on the inner layer. Probably going from spoke hole to spoke hole. bk
I had the same issue as the OP and couldn't figure out what happened until I removed the rim tape and found that the rim had cracked.
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Old 03-17-11, 08:36 PM
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Originally Posted by trek330 View Post
Al1943 I just did just that!I replaced the pads witrh koolstops and was in seventh heaven with my brakes!! I got the adjustment right on and it was great...till now.
Good, the softer pads should help the new rim with slower rim wear.
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Old 03-18-11, 03:46 AM
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Originally Posted by trek330 View Post
.Anyone recommend a good strong, AFFORDABLE 26 inch MTB rim.
I've been very pleased with Ritchey Girder OCR. Chainreactioncycles.com had them at a ridiculous low price a few weeks ago.

Originally Posted by trek330 View Post
This one was 32 holes is there a 36 hole option?
Not for all makes & models, but sure. It'd require a new hub though - at which point all financial sense usually goes out the window WRT building a new wheel from scratch by yourself. Not that money is the only influencing factor on how to do things...

Originally Posted by trek330 View Post
Why were the spokes 1.8? Wouldn't 2 gauge be stronger?
Depends on what you mean by stronger.
(all other things being equal) A wheel built with a thicker gauge will be stiffer, which is good if your mode of failure is a sudden collapse due to a brief overload, like coming off a curb, landing a jump etc.
But if your mode of failure is spokes breaking one by one, then a thinner gauge will be more durable. Spokes break by fatigue mainly, and the main driver for that is if the spokes go slack. A thinner spoke will be stretchier, so less likely to go slack and less likely to fatigue.
Given the assymmetry of rear wheels with external gears the combo of 1.5 mm spokes on the non-drive side and 1.8 on the drive side is often very good for durability.
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Old 03-18-11, 06:48 AM
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Thanks Dabac for your input.I checked out that site and their shipping costs are more than the rims!!I decided to go with a Sun Rhyno Lite and ordered it from Niagara delivered for $35.00.It seems to be an upgrade from the Sun CR18 which is the replacement for the CR17.Afer looking again at the spokes they look allright and I'm keeping them for the meantime to save money.the ERDs of this and the CR18 is the same and i don't kmow what the !7'sERD are.Hopingthe same.I"m mostly a roadbiker and just came back from a wonderful 54 miler,the first I did since Nov.when I had a heart episode and the winter started coming in.This bike I use mostly for walking the dogs and getting around in the winter,Though I have started exploring trail riding and I love it.I'll update when the new rim is mounted.
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Old 03-18-11, 08:41 AM
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Originally Posted by LesterOfPuppets View Post
One of my Sun Zero Degree Lite rims failed in this fashion after pretty low mileage. It's put me right off Sun rims now.
Machined sidewalls?
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Old 03-18-11, 09:01 AM
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Originally Posted by trek330 View Post
Thanks All for your feedback!I'll go with the consensus and bury that rim.Al1943 I just did just that!I replaced the pads witrh koolstops and was in seventh heaven with my brakes!! I got the adjustment right on and it was great...till now.I'm going to get a new rim and spokes and do it myself.I built my road bikes wheels-first build,and it was a huge success.I have all this a equipment I'm glad I'll get a chance to use it again.I'm gonna change the spokes too.They don't look to hot and I mentioned the poor tensioning all around so Might as well start new.Anyone recommend a good strong, AFFORDABLE 26 inch MTB rim.This one was 32 holes is there a 36 hole option?Why were the spokes 1.8?Wouldn't 2 gauge be stronger?Im 200+ lbs.Again thanks for all your valuable help!!
If you are using a rim with the same ERD as the old one you can reuse the spokes. As long as they are not kinked they will outlast many rims.
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Old 03-18-11, 09:34 AM
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Originally Posted by JohnDThompson View Post
Machined sidewalls?
It says"ABT: Advanced Brake Track, rim sidewalls are brushed for improved braking performance" Hope that's good.
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Old 03-18-11, 11:14 AM
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They won't be brushed. "ABT" is machined sidewalls.
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Old 03-18-11, 02:02 PM
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Originally Posted by BCRider View Post
They won't be brushed. "ABT" is machined sidewalls.
Is that good?
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Old 03-18-11, 02:11 PM
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Originally Posted by trek330 View Post
Is that good?
Not always. Machining removes material from the sidewall, decreasing its longevity.

Nobody used machined rims until a decade or so ago and we managed just fine.
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Old 03-18-11, 02:24 PM
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Yes, mine that failed young were machined.
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Old 03-19-11, 03:11 AM
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Originally Posted by LesterOfPuppets View Post
CR17A are 23.5mm wide, actually.
Thats a surprise but I`ll take your word for it Lester.

I`d have expected something that size on some road bikes, but even touring rigs I`d have thought a wider rim would be standard - more-so mtb bikes.
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Old 03-19-11, 08:17 AM
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Originally Posted by Burton View Post
Thats a surprise but I`ll take your word for it Lester.

I`d have expected something that size on some road bikes, but even touring rigs I`d have thought a wider rim would be standard - more-so mtb bikes.
The replacements,the cr18's are 22.5mm!!My new one I ordered will be 27.5mm.Y'all think that will ease mounting and removing the tire?Which brings me to this appendix to this thread.I indeed removed the tire and indeed right at the point of widening,only visible from the inside was this ugly fissure or crack extending between the spoke holes.I'm running 1.75 inch tires presently.Will the 27.5 width of the new rim accomadate them?
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