I've got 15s on my 182 Cup and changed my previous Mini Cooper S Works to 15s from 17s too. Both with 195/50x15 tyres.
The saving in unsprung weight can be considerable depending on what 15s you go for, and for every 1kg of unsprung weight you save, is equal to 4kg of sprung weight!
The handling of both cars felt lighter and more responsive after going to 15s and in both cases felt a bit more plush whilst not losing any directness in steering.
Good 195/50x15 tyres are less than half the price of 205/45x16 standard fit Michelins and even Michelin Pilot Exaltos in 195/50x15 are only £70!
Plus, I'm a big fan of smaller wheels on small cars, too be honest 16s on the Clio didn't look bad, but I always thought Minis looked a bit cartoony on 17s.
Usually if you look at the race version of a car it will show you he best size wheels for that car. Minis raced on 15s with Toyo 888s as a control tyre. Not too sure about phase 2 Clio race cars though.
I'm currently running Clio Williams Speddlines in black, although I want to get them powder coated white. They are 15x7 with a 60.1mm centre bore and an offset of et37 (or thereabouts) which gives me an extra 16mm of track front and rear.
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