Thanks for the comments guys. So it has to be a 9 speed compatible hub? It wont work like I said getting a 9 speed cassette with a spacer on the WH-7800's?
7800 freehubs have a different spline pattern to regular Shimano ones, so you can only use 7800 cassettes which are 10 speed.
So you either need a different wheel or a 10 speed drivetrain.
@Scilly.Suffolk started
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Thanks for the comments guys. So it has to be a 9 speed compatible hub? It wont work like I said getting a 9 speed cassette with a spacer on the WH-7800's?