Quick help on cassette choice

Equipment
1

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.

2

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.

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3

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

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

Welcome to the forum btw.

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This.

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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.

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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.

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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.