Search BMW roundels on E-bay and they have a bunch if both sizes but the front ones on the 4s are 70mm, actually about 73 - the rear one is 80 mm.
http://www.ebay.com/itm/REAL-BLUE-CA...30783273585%26
not sure if the backs are the same - seems I put mine on with silicone 0
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2006 M COUPE - 380 total production, 1 of 40
Imola Red produced for NA , ESS 455 Supercharger, Speedhut Gauges, VPM CLS wheels, 19" Hancooks, Stromung Exhaust, Carbon fibre accessories and black and white badging,