15s are a good compromise.

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17s look awful IMHO.

get 195/50/15s all round.

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that way you keep the same rolling radius as stock.

Wider tyres will just make it tramline all over the place and will not improve performance.

215s are way too wide.

It'll be the most boring, tramlining drive you'll ever have.

go for F1s

(road work, not good for track).

Or SO3s for both.

you will get more mechanical grip with wider tyres yes.

But you will lose the progressiveness of the handling if you go really low profile.
