bert37

hello,

without thinking much about it, I swapped out the wheels on a recently purchased (used) bike in favor of existing wheels from an old bike (due to thinner and better tires).
Commuting the next day, the chain was constantly slipping while in a certain rear gear, and I realized that the cassette sizes may be different, although they are both 9-speed. Sure enough, according to the manufacturers' specs:
original cassette: SRAM, 11/32T 9spd
replacement cassette: SRAM PG-950, 9 Speed 12-26

I'm surprised that the shifting / slippage isn't actually much worse, since the cassettes appear to be quite different in sizes -- there's currently only slippage in a single rear gear (5th, I believe), and shifting is as smooth as I remember previously.

Is this slippage to be expected with the different cassette sizes? Would it be easy / cheap to have the derailler adjusted to work with the new cassette? (the reason I may avoid doing this is I expect to be swapping back to the other wheelset, occasionally) Is there potential for damage to the derailler or other components if I leave everything as-is, and just deal with the slippage?

thanks much..

Mondoman

When you write about cassette "sizes", you're thinking about the numbers of gear teeth; however, the main adjustments on the rear derailleur (L and H limit screws) instead concern the left/right position of the derailleur, and so would only be affected by changed *thickness* of the gears or spacers in the cassette, or a difference in the horizontal position of the cassette when comparing the two wheels.
In general, "9-speed" cassettes and hubs should have very similar measurements even between brands (see https://www.sheldonbrown.com/cribsheet-spacing.html). Since your setup in general still shifts well, my guess is that you need only a minor rear derailleur readjustment. There is another adjustment on the RD, the "B screw", which affects the closeness of the RD pulley to the cassette gears -- this will probably need to be adjusted to take into account that your current smallest cog (12 teeth) now has a bigger radius than your previous one (11 teeth). Check out the Park Tool website for nice maintenance task writeups, including RD adjustment.'

sch

A chain/cassette wear mismatch will also result in glitches, more pronounced on
some cogs than others. A check on chain wear might be helpful. Cassette wear
is a bit harder to discern.

adaminlc

If you repeatedly rode in the offending gear on the old bike it would explain the problem. Look at the cassette and look for uneven wear on cogs that are giving you trouble. Chains stretch over time this causes uneven wear, espcially on cogs that get the most use. Those two pieces will continue to work together for a while, but the cassette will be incompatible with any other chain. Finally the worn chain and cassette will start to slip. When the wear gets to that point, the whole set-up is a lost cause and needs to be replaced. Sheldon Brown has an article on this (https://sheldonbrown.com/chains.html) but a quick way to measure for stretch is to know that each link should be about 1 inch in length and that over twelve links (one foot) you should not see a cumulative stretch of over 1/8th of an inch. Remember that you will need to do this with the original cassette/chain setup for the most accurate results.

bert37

Thanks for the responses.

Mondoman - your explanation of the thickness / horizontal alignment of the cassette does make sense to me. Thanks for clearing up my confusion. I'll look into adjusting the B screw as needed.

Also, the gear that is slipping a lot *is* the most-often used gear on my old bike, so adaminlc, your suggestion makes sense also. I'll try to check for worn cassette cogs and/or stretched chain.


Thanks again, folks -- much appreciated.

kycycler

I suspect chain/cassette mismatch. A new chainshould take care of he problem,