Quick help on cassette choice

I’m interested in the Wahoo kickr core. My bike I would like to use is an old GT Tempest mtn bike I’ve used on occasion since I bought it in 95. It has Shimano shifters and I guess 21 gears as it’s 3 on the left and 7 on the right. The 7 on the right seems to correspond to the 7 sprockets on the rear wheel. I’d buy something newer but really I don’t plan to ride outside at all given the pain of having to haul the bike somewhere before riding (not practical if going to use this as a workout).

So, would I be correct to assume that I should just order with the 10-speed cassette and I’ll be good to go? There is obviously not a 7-speed cassette option that I see so…

Specs of my bike are here:

thks for any help.

No, no you should not.
10sp and 7sp chains and cassettes are significantly different widths, you can’t put a 7sp bike onto a trainer with a 10sp cassette and expect the chain to even sit on the teeth of the cassette.

I run an 8sp bike on an 8sp cassette on a Core currently and it’s fine, but I did have to get a couple of small spacers to get the fit correct.
I suspect you’d get away with the same with a 7sp cassette.


you don’t need a new cassette, assuming you already have a chainwhip and cassette lockring tool to remove the 7 speed cassette from the rear wheel of the bike.

You will need to order 4.5mm spacer because a 7sp cassetter is 4.5mm shorter than the 11sp freewheel.

Bikemonger 7 Speed Cassette Spacer 4 5mm


I was about to reply - but by now you’ve got your answer. :+1:

Welcome to the forum btw.



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Yeah. You can use the cassette from your current rear wheel (with an appropriate spacer). However, 7 speed cassettes are pretty cheap <$25, and leaving the one on your wheel will remove a significant impediment to an impromptu opportunity to ride outside should it or the inclination arise. You could take your trainer to a bike shop and they should be able to provide and install a cassette and the needed spacer. One small caveat. Going between the trainer and cassette might require a flew clicks on the rear derailleur cable adjuster to account for slightly different position between the two.


Fair point. I was recently able to pick up a Dura Ace Ti 10spd cassette used for only $50 to give an old wheel a new go.

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Ok, great info. Was hard to find 7 speed 11-28 cassette on Amazon but seems this one should work:

The cassette spacer is a bit confusing. I found the following but it’s 4.0 mm vs the one linked above that was 4.5mm. I assume this would work ok?

When I searched for 7-speed cassette spacers lots came up that were much thinner than 4.5 mm and the above was closest to it.

That’s because an 8sp hub is narrower than an 11sp one, you wouldn’t need as thick a spacer. Depending on the age of your rear wheel it may have an 8spd freewheel and already have a spacer fitted with the 7 sod cassette.