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I have an old racer (1994 Specialized Epic Allez - lugged carbon) that's in pretty good shape. I brought it to an LBS that's got a pretty good reputation and that I've used before, to change the chain and look at the front crankset as it was making a weird noise.

When I come to pick it up they have changed the whole crankset, chainwheels and all. I used to have a 34-50 (or so - I can't remember the details), and now the larger wheel is definitely bigger (52?). In theory I don't mind, as I was missing a higher gear for the flats.

But there's one problem... My chain is not long enough to use the largest chainring in front while on the largest cog at the back. I know that it's not 'the done thing' to use diagonal gears like that, but I did get into that combination by mistake yesterday, and was rather shocked when everything just got stuck.

My question is the following:

Is this a dangerous combination? Will I at some time by mistake get into the 'wrong' gear and by stamping on the pedals ruin the derailleur?

Or should I simply learn never to use that combination of gears? And instead be happy that I now have an even higher gear for those nice long slightly downhill stretches?

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You should simply learn not to use that LBS again. Just go over there for a last time and ask them to add 2 or 4 chain links on your chain. –  cherouvim Jun 5 at 8:59
    
Hmmm.... Yes, that's one option. But then I would have to find another shop that I could trust. What I like with this place is that they (or at least one guy) seem very knowledgeable. And they're reasonably local (or at least close to where I work). But this has really ruined my faith in them. I'm tempted to give them at least one more chance though. –  Popup Jun 5 at 9:11
    
It sounds to me like they changed the chain first, or did not change it at all. Take the bike back and have them extend (or replace) the chain. –  Daniel R Hicks Jun 5 at 11:14
    
The chain is definitely changed. (Or maybe just cleaned...) But I can easily check that - the old chain was pretty worn. (It had done about 2.5kkm and had accumulated about a 1% stretch.) –  Popup Jun 5 at 11:28

1 Answer 1

up vote 3 down vote accepted

As suggested in the comment above, I would take it back and ask them to add a few more links. It's totally negligent of your LBS to fit a chain that cannot accommodate every combination of gears, however silly. There's always a chance you can fumble a shift and end up locking the drivetrain, as you've already experienced. This is definitely dangerous - if the pedals suddenly lock up and surprise you, you could crash. Another possibility is that if you keep pedalling, the rear mech will be pulled into the spokes, trashing both mech and wheel.

There is also an outside chance that with the new, larger chainring, you have exceeded the take-up capacity of the derailleur - meaning that adding links will result in a slightly slack chain in certain other combinations of gears. This is less of a problem, but bear in mind your chain may jump off if you run the small ring with a small sprocket on a bumpy road.

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Thanks! It's a pretty old, but good, derailleur. A Shimano 105. (I think it came with the bike in 1994.) I was told by a friend that it does not have enough take-up capacity to accommodate three platters in front, something which would be great on the hills around here (I live within cycling distance of four HC climbs.) So that's something I'll have to look at. –  Popup Jun 5 at 11:10
    
I went back to the shop, and they were very apologetic. They added a link to the chain, and everything is tickety-boo. –  Popup Jun 6 at 11:15
    
I love a happy ending :) –  headeronly Jun 6 at 11:21

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