Center caps

Not sure how to measure wheels for the center cap size. I have 4 Rays 57 extreme wheels but the center caps are calibre. I want to get the correct caps for the wheels. Can anyone tell me where to measure for the size. It may be simple to some of you, but i have never done this before. Any help will be appreciated. Thanks. Chris.

They push in from the outside, so measure the diameter of the wheel centre bore. If they are correctly sized for the MX5, it will be 54mm and change. Contact Rays for the correct caps. There are lots of cheap knock offs around.

Thanks for the info, Will get them measured today.