# Cracked rim for trainer use?



## BlaugranaMD (Apr 24, 2015)

Just a quick curiosity, we got an indoor trainer for the wife and I and I have a set of mavic ksyrium rims that have 2-3 thin eyelet cracks that are just hanging out in the garage. Would these be safe to mount a trainer tire onto and a cheap cassette to swap onto either of our bikes for trainer use to avoid wasting our road tires or having to change tires each time we use the trainer? I figure the rims and spokes are bearing less weight since the trainer mounts via the skewer. Or am I just over thinking this? Thanks!


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## brucew (Jun 3, 2006)

When rim cracks appear around the spokes, many times the wheel goes out-of-round. 

While not a safety matter, it would make adjusting the roller pressure and drag a bit of a pain. You'd feel surges as the rim became tighter and looser against the roller.


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## Lombard (May 8, 2014)

BlaugranaMD said:


> Just a quick curiosity, we got an indoor trainer for the wife and I and I have a set of mavic ksyrium rims that have 2-3 thin eyelet cracks that are just hanging out in the garage. Would these be safe to mount a trainer tire onto and a cheap cassette to swap onto either of our bikes for trainer use to avoid wasting our road tires or having to change tires each time we use the trainer? I figure the rims and spokes are bearing less weight since the trainer mounts via the skewer. Or am I just over thinking this? Thanks!


Wow! I've never heard of a problem like this with Mavic Ksyriums. These have a pretty good reputation. I had this same thing happen on Bontrager Race rims at 4,000 miles, but that is expected with those.

But i digress. Using these rims on a trainer? Well, for liability reasons, I don't want to say "yes", but in the worst case scenario if one of the rims collapses, I would guess the skewer attachment to the trainer would keep you from falling off the bike. In reality, since the loads and stresses on a trainer are far less than in the real world, catastrophic failure is unlikely. Most likely, as the cracks get larger, spokes will start breaking. But since this is a safety question, I would ask a pro at a bike shop that you trust.


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## Kerry Irons (Feb 25, 2002)

Lombard said:


> Wow! I've never heard of a problem like this with Mavic Ksyriums. These have a pretty good reputation. I had this same thing happen on Bontrager Race rims at 4,000 miles, but that is expected with those.
> 
> But i digress. Using these rims on a trainer? Well, for liability reasons, I don't want to say "yes", but in the worst case scenario if one of the rims collapses, I would guess the skewer attachment to the trainer would keep you from falling off the bike. In reality, since the loads and stresses on a trainer are far less than in the real world, catastrophic failure is unlikely. Most likely, as the cracks get larger, spokes will start breaking. But since this is a safety question, I would ask a pro at a bike shop that you trust.


A confusing reply. First, there have been lots of reports of MAVIC rims cracking, all across their product spectrum. Nobody really knows if this is because their rims are not that strong (relative to the spoke tension they use) or simply because there are a lot of MAVIC rims in use and therefore a lot of reports.

Second, as the rim cracks it REDUCES the tension on the spoke and in that respect reduces the likelihood of spoke breakage. This is counterbalanced by the increase in spoke flex as the tension is reduced which might cause breakage at the rim. Hard to really say if a rim crack has any influence at all on spoke breakage.


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## QuiQuaeQuod (Jan 24, 2003)

If you go for it, I suggest you check the wheel for true/round after a few rides, and then after a few more rides. If the wheel keeps its shape, you are likely fine. If it goes out of shape, you probably want to stop using it. If for no other reason than it will be a PITA to re-true it all the time.

The rim is unlikely to fail catastrophically early on in trainer use. I don't see how failure of the rim would be a danger... to anything other than the rim, hub, cassette, chain, chain/seatstays, paint, or legs from shrapnel. 

BTW, you can likely get a very cheap rear wheel (used/take off) from a LBS, and not have to worry about it at all. A heavy wheel isn't a problem on the trainer, just gives you a bit more of a work out when accelerating.


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## cdhbrad (Feb 18, 2003)

I have used stationary trainers for more than 30 years starting with the old Turbotrainers that relied solely on wind resistance. I now have a Kurt Kinetic. In all those years, I have never done anything special to the bike I was to use on the trainer including with the wheels and tires. I just put the bike on the trainer, secure the rear skewer, adjust the tension, and ride. 

That said, I don't think I would use a wheel on a trainer that was not road worthy, but what have you got to lose by trying the rear wheel? It isn't like you are going to crash if the wheel fails entirely. I'm curious though how you use one rear wheel on two bikes unless your wife and you ride the same size frame. If it would mean switching a single wheel between two bikes, that would be way to much work for me to deal with and I'd just leave it on one bike and either use your regular road wheel or pick up a cheap "trainer" wheel as others have suggested.


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## Lombard (May 8, 2014)

Kerry Irons said:


> Second, as the rim cracks it REDUCES the tension on the spoke and in that respect reduces the likelihood of spoke breakage. This is counterbalanced by the increase in spoke flex as the tension is reduced which might cause breakage at the rim. Hard to really say if a rim crack has any influence at all on spoke breakage.


If a rim crack causes a spoke to losen on one side, spokes will be tighter on the other side which could conceivably lead to breakage and.....more rim cracks. Not to mention as you say, flexing of the looser spoke will cause stresses at the nipple causing spoke breakage.


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## Marc (Jan 23, 2005)

Lombard said:


> If a rim crack causes a spoke to losen on one side, spokes will be tighter on the other side which could conceivably lead to breakage and.....more rim cracks.


That isn't how it works at all...I'd bow to Kerry on this one.


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## Gregory Taylor (Mar 29, 2002)

It will be fine. 

The only caveat is that if the wheel does fail, you might louse up the paint on the bike. I had a buddy who had a Ksyrium let go while riding - spoke popped at the rim - and it made a hell of a racket as it banged against the frame.

I might put a big piece of tape on the rim and write "TRAINER ONLY" on it just to remind you not to venture out on a potentially bum set of wheels.


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## robt57 (Jul 23, 2011)

Agree, risk of damage might/should be considered. Which is why my computrainer dedicated bike is a 1999 Allez and the rear wheel is a Race-x-lite Bonty with spoke bed cracking I would not ride out on the road or sell.. ever...


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## tlg (May 11, 2011)

Lombard said:


> Wow! I've never heard of a problem like this with Mavic Ksyriums.


Wow. It's a pretty widely known issue. Google mavic ksyrium rim crack. You'll have hours and hours of reading.




QuiQuaeQuod said:


> The rim is unlikely to fail catastrophically early on in trainer use. I don't see how failure of the rim would be a danger...


Unless you use rollers. Or one of these trainers that don't have a tension adjustment and rely on rider weight to keep the wheel on the roller.


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## Jay Strongbow (May 8, 2010)

I haven't read all these responses but it's hard to believe so much has been said about such a non-issue.

"2-3 thin eyelet cracks" is no problem at all on the trainer. Heck, it's not really a problem on the road for that matter, it's just an indication that a problem is on it's way.


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## Mcfarton (May 23, 2014)

i use a old cracked bontreger rim on my trainer. It has a dedicated trainer tire and a cheaper cassette. The wheel is slightly out of true so I just release the caliper and pedal. I check the rim every now and then, if it gets worse I will toss it. 
What could go wrong? 😨


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## Doug B (Sep 11, 2009)

You don't really care about weight or aerodynamics for a trainer wheel. Go buy a $30 rim from Nashbar or Performance and make a dedicated trainer wheel.


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## AndrwSwitch (May 28, 2009)

Kerry Irons said:


> Second, as the rim cracks it REDUCES the tension on the spoke and in that respect reduces the likelihood of spoke breakage. This is counterbalanced by the increase in spoke flex as the tension is reduced which might cause breakage at the rim. Hard to really say if a rim crack has any influence at all on spoke breakage.


I could see the spokes breaking sooner. I think the rim would share the load less well and the cyclical portion of the load on the spokes would be greater. So, more fatigue.

I wouldn't be too worried about using the wheel on a trainer that held the quick release skewer. I don't necessarily see myself in this situation, but I think that the wheel would start doing weird stuff before failing entirely. When it gets too annoying to use, throw it out.


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