I assume its a rule they can't go with different rims of any sort in NASCAR, like one with a more aerodynamic look to it. I see some guys have black colored rims and some chrome, but with no obvious advantage.

Steel wheels only - 15" X 10". No aero aids or other add-ons. There are at least 2 suppliers with approved products on the market. Chrome plating is not permitted. Michael Waltrip Racing's cars appear to have chrome wheels ... they're powder-coated - not plated.

Thanks for answering.

A little bit of additional info on wheels. As Speed Freak already mentioned wheels have to be steel, the size is actually 15 X 9.5 and we also mandate a 4.5 inch backspacing. The minimum weight is 27 lbs. (that weight is for an uncoated wheel with no valve steam hardware attached.) The coating mentioned is a heat coating now being used on the inside of the wheel by most teams to control heat build up in the wheel particularly near the bead. Prior to 2006 NASCAR certified wheels for use in competition; however since 2006 SFI has come out with a certification standard for steel stock car wheels which is SFI 35.1. Since that time NASCAR has required any wheels being used that were manufactured after Jan of 2006 be SFI 35.1 certified and they must display that label. As a team you can still run wheels that do not display the SFI 35.1 label as long as they were purchased before 2006 and NASCAR inspected them prior to use. That inspection is normally an annual inspection at the start of the year. The average life span of a wheel is 5 years and that time frame is reflected in the SFI 35.1 rating. All wheels must also be equipped with two valve stem holes. The car number also has to be visible in 1 ¼ inch letters on the outside and the inside of the wheel. As already mentioned no chrome wheels are allowed the rules actually say no electroplated wheels allowed, so chrome, nickel, and zinc would all be examples of wheel coatings that would be unacceptable. Today all the wheels are powder coated. Currently three manufactures are producing wheels which meet NASCAR’s rule requirements: Bassett, Aero, and Circle.

The rules don’t actually say that you can’t run something with a slightly different aero look; they only say you have to run wheels from an approved manufacture, but NASCAR will make you run the wheels in the same configuration that the manufacture and NASCAR intended them to be in. If you could actually look at pictures of all three manufactures’ wheels you would find that they all differ in appearance. The rules are restrictive on wheels so the teams concentrate on small things that give them an edge during a pit stop. To many tire carriers and changers the size, number and configuration of the D cut outs in the wheel are important. The D cut out is what forms the spoke in the wheel. The Bassett and Aero wheels only have 8 cut outs while a Circle wheel has 10. This cut out is what the tire carrier places his fingers thru when placing a wheel on the hub for the changer, and it is what the tire changer grabs when pulling a tire off the hub. Some guys swear by Circle wheels because they have more cutouts they are easier to grab and the carrier can position them more accurately because he or she has more options for hand position. Other changers like Bassett wheels because the D cut out is almost an oval shape so they can more comfortably get their fingers thru the holes because the holes are a bit bigger that the ones on a Circle or Aero wheel. Well this is probably way more than you wanted to know, but I hope it helped to further answer your question about wheels.