This is a RC wheel I've designed for my Land Rover Defender but it is a great wheel for any other car. It is 1.9" standar size, but has a positive offset of 3mm to get narrower axle look. It uses standar 12mm hex.
This wheel has been tested with stock Axial SCX10 and stock Vaterra Ascender knuckles. If you use different knuckles be sure they have similar design, or due to possitive offset the wheel could hit them.
You will need five 1.6mm screws to get the final scale look (I use 1.6x8).
NOTE: It has no hub cap, but a good option to get a great scale look are some Junfac hubs (as shown in photos): http://www.junfac.com/shop/index.php?main_page=product_info&products_id=492