Bicycle Mechanics - Gear question
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12-09-03, 01:39 PM
Has anyone had a problem with the front crank in the small sprocket and the rear casette in the 2nd to the smallest sprocket and the chain catching on the little nobs on the inside of the large sprocket. It doesn't happen on the 3rd to smallest sprocket in back. I have Dura Ace comps. I've been told to avoid the smallest 2 sprcoekts in back when you are on the small front crank sprocket. Is there a way to alleviate the problem. Unconsiciously going to the 2nd spcoket will lock up the chain.
12-09-03, 03:01 PM
I've never had this problem and I ride 9-speed Dura-ace. I don't use that gear combo a lot, but when I do it works fine. My bike has pretty short chain stays, too.
Here are some things that could cause the problem you describe:
1. Your crank might be too far inboard causing excessive chain deflection when using that gear.
2. The chain could be too wide. 9-speed chains are much narrower than 6/7/8-speed.
3. Your chainring(s) may be bent.
You can try increasing the chain tension with the tension adjustment screw on the rear derailleur but if it always happens rather than sometimes happens, I doubt it will help.
Some bikes just won't allow you to use those gears because the chain line is too far in. You'd have to get a slightly wider bottom bracket spindle length to make it work which really isn't worth the trouble when you figure that gear is probably duplicated on the middle ring.
12-09-03, 04:58 PM
Thanks for the info. What does the tension screw do? I assume it increases and decreases the chain tension by moving the der around. Would a tighter tension possible decrease the problem?
If the clearance is really tight between the chain and the big ring and the chain tension is loose (which it is on those rings) then there can be a tendency for a bump or uneven pedaling to cause the chain to swing out and catch the big ring. If there's more tension in the chain it reduces this. If it always catches the big ring no matter what,then chain tension won't help that. I tend to run with as much tension as I can, especially on my mountain bike, because it reduces chain suck as well.
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