Help: blew out wheel (spokes) and need to understand why...

If you drop your chain between the cassette and the spokes it's almost certain that you'll at least nick the spokes and if it happens under load like climbing a hill it's not unusual to break spokes. So the broken spokes as a result of dropping your chain off the top of the cassette isn't unusual the question is what you or the shop could have done to avoid the chain drop in the first place.

- First you really should never be 'cross chained' with your chain riding on the big front chainring and the big rear cog at the same time. That's a bad idea for several reasons including chain and cog wear but it also puts the chain under a lot of tension and depending on how many links in your chain and your derailleur style (short cage, long cage, etc.) you can really stretch your derailleur spring to the limit of its range while cross chaining big to big. Drop down into your small front ring and that tension is released all at once and that alone could cause even a well adjusted rear derailleur to drop the chain into the spokes so shift down to the small front ring before you end up cross chained as it doesn't help the situation.

- But it's likely that your rear derailleur could use some adjustment to it's low gear limit screw. Hard to check now that the wheel is trashed but it seems likely that the rear derailleur travel wasn't limited correctly for the hub, cogs and cassette spacer(?) that you were running. Shops guard against this possibility on most new bikes by selling them with a plastic 'pie plate' whose only function is to keep the chain from dropping behind the cassette body and gouging your spokes but most racers and many recreational riders remove the pie plate as it's not strictly necessary as long as the rear derailleur is well adjusted and the chain is cut to the appropriate length. Again the cross chaining probably didn't help but we've all done it occasionally and don't generally drop our chains as a result.

So definitely pay attention to gearing and try to avoid cross chaining in the future, make sure you shift before you have high loads on the system and check the rear derailleur adjustment carefully to make sure the limits are properly set. If you're really worried about it you can always run a pie plate spoke protector but in general it's not necessary.

Good luck,
-Dave

That is extremely helpful. Thanks very much for the response.

Your wheel is probably not dead. If you have a standard lacing (and you probably do if your bike is more than 7 years old), you have only killed one quarter of the spokes, ie 7, 8 or 9 of them. Even if you bought new ones, this repair would cost no more than $18 in this country, if you do the work yourself. Add $30 for labour if you get a shop to do it. The undamaged spokes may not even need to be touched.

The last time I managed this feat myself, I had enough old spokes of the correct size lying around to allow me to make the repair.

I agree that the problem is probably a combination of cross-chaining and imperfect adjustment of the lower limit screw.

Quote:

I had a local bike shop tune my bike up to get it ready, and took her out for a spin on Sunday ...

FWIW. I would be a little miffed if I paid a shop to do some work on a bike and they subsequently delivered it in a state of adjustment which resulted in the chain coming off the largest (or, also the smallest) cog & into the spokes.

You SHOULD blame the bike shop ... while you should have probably shifted to an intermediate cog before downshifting to a smaller chainring, the chain should NOT have drifted off of the largest cog & into the spokes if they had correctly adjusted the stops on the rear derailleur.

• You paid for a service which the shop failed to deliver.
  

Consequently, I think the shop should re-spoke/rebuild your rear wheel OR replace it with a comparable wheel (which they probably have), accordingly, gratis ...

THEY should be thankful that your bike doesn't have some high-zoot wheels and that the repair-or-replacement won't set them back by too much.

I appreciate all of your replies. You all are very knowledgable and have helped me get informed about my equipment. The bike shop I used for this is a small, locally owned business. As such, I am hesitant to demand they take a hit on this, unless they choose to be jackasses about it. Part of figuring that out is obviously being as informed as possible so I can ask them enough tough questions to be sure they are not being dishonest. I guess I'm a lot more comfortable taking a hit on this if I am supporting a small business that does things honestly.

Quoted post said:

Originally Posted by alfeng [IMG]/img/forum/go_quote.gif[/IMG]

Quote:

I had a local bike shop tune my bike up to get it ready, and took her out for a spin on Sunday ...

FWIW. I would be a little miffed if I paid a shop to do some work on a bike and they subsequently delivered it in a state of adjustment which resulted in the chain coming off the largest (or, also the smallest) cog & into the spokes.

You SHOULD blame the bike shop ... while you should have probably shifted to an intermediate cog before downshifting to a smaller chainring, the chain should NOT have drifted off of the largest cog & into the spokes if they had correctly adjusted the stops on the rear derailleur.

• You paid for a service which the shop failed to deliver.
  

Consequently, I think the shop should re-spoke/rebuild your rear wheel OR replace it with a comparable wheel (which they probably have), accordingly, gratis ...

THEY should be thankful that your bike doesn't have some high-zoot wheels and that the repair-or-replacement won't set them back by too much.

A BIG PLUS 1

Do you understand what Alfeng is saying? This should be a no brainier, the LBS did the tuneup, thus they did it wrong, thus things broke due to their negligence, thus they owe you make it right-whether they rebuild it or replace it that's up to them, but they have to do one or the other.

Your point about them being a small company is lame, they did it-their responsible, unless you have an over abundance of cash and don't care you got screwed. And their not being honest if they make it right, so your going to support a dishonest business because it's local? You make no sense.

Bring your bike back to the shop that did the tune up. They are responsible for the damage and should fix it for you free of charge. Although the damage may appear to be fatal to you it is no big deal for them to fix this properly and still earn a profit from the original tune up charge. If you are concerned about supporting your small LBS dont be this is their part of the deal in earning your support.

One more bit of shifting advice:
I NEVER shift from my big ring to my small ring when in my largest rear cog. Instead, no matter what rear cog I am in, I shift down 2 cogs (harder gears) just before shifting the front to the small ring. This is all done in really quick succession and makes the gear change to the small ring not so drastic. If you stay in your biggest cog and switch to your little ring, you will find yourself suddenly in your very smallest (easiest) gear ratio, spinning like mad, and getting nowhere. Finally, when changing from big to small (or small to big) chainrings, do this slowly and deliberately by slowing my pedal stroke momentarily (for one revolution) until the chain is securely on the correct ring. If you put too much load prematurely, you can cause the chain to slip off the front down into the bottom bracket or between rings. I realize this wasn't your problem, but a slow and deliberate gear change might have helped in your situation of extreme cross chaining as well.

I agree with everyone that if the shop didn't adjust the derailleur correctly, they should rebuild your wheel. However, I think you were asking a lot of your equipment to handle that particular gear change with your chain crossed all the way over. My guess is that the shop will fix the wheel for free without your asking them to do that, but they will secretly know that user error was the major culprit.

froze is right, they will probably look after you because they'd hope to keep you as a customer in the future.

As I first understood it, the chain jumped off at the front, which could well happen on an extreme change - but seemingly it was at the back...

If that was so, then it should not have happened provided the rear mechanism and gear hanger was fitted straight and adjusted right, because any jockey cage movement due to sudden release of tension would have been in line with the bike.

My guess from long distance is that the rear mech or hanger was twisted, so that when the cage and mech swung back it had a sideways component. That could throw the chain, especially if the adjustment was at the edge of tolerance. Twisting out of true is a common thing and can happen when the bike falls on the chain side or during transport.

If that was the case, the shop should have spotted it and trued the mechanism / gear hanger. After the event it is always difficult to prove anything because the gear will probably be bent anyway now.

Skydog may have misused his equipment on that ride but it is built to take it on any reasonably modern bike. He should not be blamed for it - and on a similar subject - what did Schleck do to his chain exactly? Anyone know? [IMG]/img/vbsmilies/smilies/smile.gif[/IMG] Billcycle.

Quote:Originally Posted by Froze [IMG]/img/forum/go_quote.gif[/IMG]

Quoted post said:

Originally Posted by alfeng [IMG]/img/forum/go_quote.gif[/IMG]

Quote:

I had a local bike shop tune my bike up to get it ready, and took her out for a spin on Sunday ...

FWIW. I would be a little miffed if I paid a shop to do some work on a bike and they subsequently delivered it in a state of adjustment which resulted in the chain coming off the largest (or, also the smallest) cog & into the spokes.

You SHOULD blame the bike shop ... while you should have probably shifted to an intermediate cog before downshifting to a smaller chainring, the chain should NOT have drifted off of the largest cog & into the spokes if they had correctly adjusted the stops on the rear derailleur.

• You paid for a service which the shop failed to deliver.
  

Consequently, I think the shop should re-spoke/rebuild your rear wheel OR replace it with a comparable wheel (which they probably have), accordingly, gratis ...

THEY should be thankful that your bike doesn't have some high-zoot wheels and that the repair-or-replacement won't set them back by too much.

A BIG PLUS 1

Do you understand what Alfeng is saying? This should be a no brainier, the LBS did the tuneup, thus they did it wrong, thus things broke due to their negligence, thus they owe you make it right-whether they rebuild it or replace it that's up to them, but they have to do one or the other.

Your point about them being a small company is lame, they did it-their responsible, unless you have an over abundance of cash and don't care you got screwed. And their not being honest if they make it right, so your going to support a dishonest business because it's local? You make no sense.

You may actually be doing the shop a favor by returning it for them to fix. Maybe they have a young wrench who doesn't know the right way to adjust the RD, or maybe he doesn't realize that this adjustment is part of a tune up. Returning lets the shop's owner realize that he had a problem so that he can take the appropriate steps to correct it.