Bicycle Mechanics - Chain skip

What would cause my chain to skip under hard pedalling? I just installed a new SRAM chain on my 12 speed road bike, but when pedalling hard, the chain skips a tooth on the last 2 small cogs. Al the others are OK. Could the chain be the wrong one for the bike?
Thanks,
Rich

More likely the cogs are worn.

is the new chain the same length as the old one> i had to take out an extra link on my SRAM

Originally posted by Coaster
What would cause my chain to skip under hard pedaling? Thanks,
Rich

Bottom bracket deflection due to hard pedaling? (I take it this was not a problem prior to the new chain...) :confused:

This was not a problem with the old chain. I sized the new chain according to the old, but when I installed it, found that the rear derrailleur spring was not loaded enough, so I took out a few more links. This allowed a good range of chain tension between the largest and smallest cogs. Now it skips. The old cogs do not look worn, but maybe I'm not looking at them correctly.
Does this help?
Thanks,
Rich

The cogs have worn to the shape of the old chain. Get a new freewheel or put the old chain back on.

Better also make sure the chain is long enough for the big/big combo,just in case.

first and easiest thing to do is check your rear derailleur adjustment. I had the same problem after installing a new chain. Drove me crazy, but went away after a good tune-up :)

Thanks for the replies. If I do replace the freewheel and install one of a different size, isn't there a way of checking what length of chain is needed?
Thanks,
Rich

Thanks for the replies. If I do replace the freewheel and install one of a different size, isn't there a way of checking what length of chain is needed?

Yup! We just recently thrashed that one to pieces in the forum. Search back through the group and you'll find it covered in detail.

I think I read some where you make the chain long enough to go large to large then add one link.:confused: but check before you take my advice

This exact same thing was happening to me about a year ago.

I had a drive train overhaul done. Didn't fix it.
I installed a new chain. Didn't fix it.
I replaced the rear cassette. Didn't fix it.
Finally I replaced the chainring I used most. No more slippage.

The only time I noticed the slippage was when I was really pedalling hard. When I compared the new chainring with the old one, there was definitely wear, but it was not as pronounced as I would have expected, but the concave section between the teeth was definitely asymetric, with wear on the trailing edge that pulled the chain around. For me this occurred with about 8,000 miles on the chainring.

Trekaholic

Here's an in-depth study regarding chain/cassette wear.





http://www.sheldonbrown.com/chains.html