The use of pre-shaped car bodies, machined wheels or axles acquired from the Internet or other sources is NOT allowed.

Racecars may weigh no more than 5 ounces (total) as determined on the official scales during check-in.

The car shall roll on the wheels from the kit. The wheels shall turn about the axle nails from the kit. The axle nails shall be firmly affixed to the wood of the car body. The Cub may cut new axle slots (or drill new axle holes) in the original block from the kit. The original axle-to-axle spacing of 4.40" (±0.125" (1/8")) must, however, be maintained. It must be obvious to the judges that the original groove spacing, wheels, and the nails from the kit are being used.
Axle nails must be mounted parallel to the track surface. Tilted or canted axles that cause the car to run on the edge of the wheels are not allowed. Wheels must run flat on the track surface. At least three wheels must be in contact with the track surface at all times as the car rolls.

Cars may be no longer than 7.00 inches with a maximum width of 2.75 (2¾) inches and a maximum height of 4.00 inches as determined by the official gages during the Registration and Inspection process. Underside clearance of at least 0.375 (3/8) inches and inside wheel to wheel clearance of at least 1.75 (1¾) inches is required to allow the car to clear the racetrack's center guide-strip. Adequate clearance is the responsibility of the racecar builder. IMPORTANT NOTE: Wood blocks supplied in the official kits are often slightly longer than 7.00 inches to allow for final shaping and sanding. Be sure to check the final dimensions of your car carefully. Do not assume that the dimensions of the block supplied in the kit will automatically be legal.

Weight may be added to the car and will be considered part of the car for purposes of all measurements. "Weight" is considered to be any material on the car that is not provided in the kit. All weight must be securely fastened to the car, e.g. by permanent glue, nails or screws, but not by "sticky substances", e.g. tape, or tack spray. Weights shall be passive, i.e. non-movable, non-magnetic, non-electric, non-sticky, etc.

Wheel treatment (hub and tread smoothing and polishing) may not result in substantial removal of mass or in reducing the wheel width or diameter from the original kit wheels. Some of the original "tread marks" on the wheel face must remain intact, i.e. apparent to the inspector. (Tread marks are the small zigzag lines visible at the very outer edges of the wheel when it is viewed parallel to the axle line.) Wheels may not be machined or sanded to a beveled condition. At least 80% of the original wheel width must contact with the track surface, and the portion of the wheel surface that contacts the track must remain parallel to the axle.  The hub through which the axle nail passes cannot be shortened. The area between the hub and contact surface of the wheel cannot be drilled or otherwise opened.