spinconn

I am not mechanically gifted. I have nonetheless decided to attempt on my own to change my cassette and chain on my Shimano Claris 8 Speed (Giant Contend AR4). I have the tools I need but I am changing from the stock 11-34t cassette to a 12-25t. Am I correct in assuming I am going to have to adjust the rear drailleur due to the different spacing?

_ForceD_

As long as the replacement cassette is a Shimano Claris compatible 8 speed, the spacing should be the same. But that’s not saying that you won’t need to make adjustments. It’s been my experience that sometimes the design of different cassettes may cause them to fit onto the hub just bit closer in, or farther out. In that case, you’ll need to make adjustments to the limit screws and barrel adjuster. With the conversion to the cassette you mentioned…you may also want to look at chain length. If the barrel adjuster is at its max…you might need to make an adjustment at the cable clamp. — Dan

rollagain

Wouldn't that change also involve adjusting the B screw?

Ogsarg

What's the worst that can happen? Put on the cassette and see if it works. If not, look at it and see what's wrong and adjust accordingly. Don't know what or how to adjust, then ask here for more specific help.

If it all fails and you lose patience, toss it in the car and take it to the bike shop but if you figure it out, you'll have learned some things about how it all works and feel more confident the next time you want to do something.

spinconn

Thanks for the help, it got done, eventually, and the difference between the new and old cassettes is amazing. Tailor made for my kind of riding, a cheap part change that amounts to a major performance upgrade for me. However, it did cost me $16 to have my bike mechanic straighten out what I messed up trying to do it myself.