[Eddie Grice]

I think most of us who race to the following CSCRA rules in the UK use 1/8" 5-40 threaded axles and "vintage" wheel hubs fitted with the below mentioned Ortmann tyres.
If you wish to follow this route I suggest you contact Phil Smith (scaleslotcars) who should be able to put together a package of axles, wheels, tyres and inserts for you.

" Grand Prix class GP3. 1950-1960 Grand Prix and Indy Cars
(Any car which competed in a Formula 1 race or any other event counting towards
the Drivers World Championship during this period).
• Motor orientation: Inline only*.
*Except that Vintage motors designed to be mounted as sidewinders can be used
provided that the motor and drive gears are covered by the body.
• Minimum ground clearance: 4mm.
• Track dimensions must be 1/24 scale within + or – 3mm and must not exceed a
maximum overall width of 66mm.
• Front wheels and tyres: Minimum diameter 27mm, minimum width 6mm.
• Rear wheels and tyres: Minimum diameter 29mm, maximum overall width 9mm.
Wheels must be a minimum of 17mm diameter to represent a 15 inch wheel, and can be
up to 19mm diameter to represent an 18 inch wheel.
All tyres must have a realistic aspect ratio. Square section tyres will not be accepted.
Recommended tyres for this class are: Ortmann 46a (Front) and 46 (Rear) but there are
other tyres in the Ortmann and other manufacturer’s ranges which would also be
suitable."