Hello. I'm F55 mcs owner and planned to upgrade JCW brake kit, so I have to upgrade 17" alloy wheels also. Is 17" 7.5J ET35 (eg. Sparco Pro Corsa) is suitable for my case? Or should I find offset range ET38 to ET40? Thanks.

 

ET35 is spot on

 

It's really about the spoke shape and clearance not so much the offset. As you need the spokes to come around the caliper. The only way to know is to find a JCW owner that has the wheels you want, or test fit the wheel on the brakes yourself.

When you are ready for the brakes let us know
https://www.waymotorworks.com/john-c...-cooper-s.html

 

Upgrade on rear for the GP3 I developed several tweaks among them upgrade on the the rear

It need 2 rotors drilled 280 mm ( 260mm Std.) due to the drills the rotor weights the same.
It uses the orignal caliper need new brackets and new brake pads

 

Here is the write up I did on the JCW brakes - https://myredmini.com/team-dynamics-brembo-brakes/