Are 9 speed and 10 speed cassettes interchangeable?
 

I am going to purchase an Open Pro wheel with a PowerTap 2.4SL. I have two bikes that I want to use it on. The first bike is a Cervelo P2C and I count 9 rows of teeth so assume this is a nine speed. The other bike is a Motorbecane LeChamp. I count 10 rows of teeth so assume ten speed.

Is it possible to buy a 9 or 10 speed cassette and use it on both bikes? Or if I want to use the PowerTap on both bikes am I going to have to buy two cassettes?

The P2C is a Shimano Ultegra 12-25 and the Motobecane is Ultegra 6600 11-23T.

Also if I buy a Shimano CS-6500 9 speed from PerformanceBike would this be compatible with 9 speed Ultegra 12-25 on the P2C?

Thanks in advance for any help. I am confused how this works.

Nope.

To be able to interchange the wheel between the 2 bikes you will need the same shifting system on each bike. ie: you will need 10 spd on both or 9 spd on both. (assuming that BOTH are the same mfg like Shimano or SRAM or Campy) Then you can use the wheel with a matching cassette.


If there are any differences in # of gears or mfg then you can't swap the wheel without changing the cassette.

This really is genuine curiosity...

How in the world did someone convince you that you needed to spend the money on a PowerTap when you don't even know enough about cycling to know for sure whether something is a 9 speed?

Especially curious since you are listed as a senior member...

There is yet another solution.

Buy a right hand 10 speed shifter for the Cervelo. The rest of the components will work well enough with 10 speeds and don't need to be replaced. Then the OP would have two 10 speed bikes.