I’ve been having problems with the gears on my road bike and replaced cassette and chain. Also checked alignment of the hanger. After lots of fiddling I discovered that there is some lateral movement of the cassette although it is done up tightly on the freehub. Wheels are quite old, so do I just need some new bearings?

How much movement? Is it actually moving side to side, rather than having loose/worn bearings?

Yes, a small but noticebale movement when you hold the cassette and pull/push it. I spent ages trying to index the gears and this seemed like the only problem I could find. The cassette lockring is tight and there were similar issues with the old cassette, so I changed it.

Not sure how much this will relate but my brothers hope pro 4 hub has a small spacer behind the cassette. When I switched a different cassette onto it I didn’t use that spacer (as I’ve never had one before) and I noticed a small amount of play which affected the gears.

I don’t think I should need a spacer to fit a 10 speed sram cassette onto this, but happy to be corrected.

On 9s and below I’ve never found this to be an issue with indexing (nor the cassette or chain FWIW). New fangled 10/11 may be different, but I’d check cables.

A small amount of play in freehub body isn’t uncommon. I’d be starting off with the cables to be honest as that’s the most likely issue. Obviously if there’s loads of play in the body then it needs sorting but a little bit wont make much difference.