[Keeping up with Junior]

My wife has an older trainer bike with Shimano 105 8 speed and the right lever has died. She is currently upgrading the components on her main bike so in the box of bike parts I will have a spare Shimano Ultegra 9 speed lever. Can I simply install the 9 speed lever in place of the 8 speed lever and put a 9 speed cassette on the wheel?

1) I believe the 8 speed and 9 speed Shimano cassettes are interchangeable.
2) Will I be able to use the 8 speed rear derailer with the 9 speed cassette and shifter?

 

[daneil]

My wife has an older trainer bike with Shimano 105 8 speed and the right lever has died. She is currently upgrading the components on her main bike so in the box of bike parts I will have a spare Shimano Ultegra 9 speed lever. Can I simply install the 9 speed lever in place of the 8 speed lever and put a 9 speed cassette on the wheel?

1) I believe the 8 speed and 9 speed Shimano cassettes are interchangeable.
2) Will I be able to use the 8 speed rear derailer with the 9 speed cassette and shifter?

Yes and yes. Shimano 8 and 9 speed cassettes are interchangeable as long as you use the correct corresponding shifters. And the 8 speed derailleur will work fine with the new 9 speed system.

 

[Squidward]

You might need a new, narrower chain.