Hi

The rear wheel on my racing bike has a Shimano 8 speed cassette with 25/12 teeth (largest/smallest sprockets). The two outer sprockets are separate from the rest of the cassette which I think is standard on this sort of cassette. The freehub measures about 35/36mm from where it enters the wheel to the end of the ribs which run along its length.

I recently removed the cassette and reinstalled it. When I tightened the lockring I noticed that the outer sprockets had a few millimetres room to move from side to side. I also have a hybrid bike with an 8 speed cassette and so I put that onto the racer where it fitted nice and snugly. I put the two cassettes side by side and the hybrid is about 1-2mm longer from outer to inner sprocket.

So my question is why is there room for the sprockets on the 25/12 cassettes to wobble from side to side. Presumably it can't be a design feature as it would make shifting difficult. I can think of a couple of explanations:

1) The shop fitted the wrong cassette. Possible but my understanding is that a 35mm hub is standard size for an 8 speed.
2) I mislaid a part, perhaps a spacer, when I removed the cassette?

Is there a way I can test these ideas, and are there any other possibilities. I’d be really grateful for thoughts/ideas here. I’m finding it a bit of a headscratcher

Thanks

Chris