Practical Engineering

I think both wheel drawings are wrong, the back wheels need to be 1/8" smaller than drawing, so finished diameter 10.1/4" and the front wheels need to be 3/8" bigger than drawing, so finished diameter 9.1/2" diameter. These dimension have been scaled from a drawing showing full size dimensions. After measuring my model with the wheels in place the new dimensions ensure the chassis on my model will have the correct ride height and the chassis will be parallel.

The drawing dimensions are as follows:

The rear wheels at 3' 5" = 41" divide by 4 = 10.1/4" The current rim diameter is 8.3/8"
The front wheels at 3' 2" = 38" divide by 4 = 9.1/2" The current rim diameter is 7.5/8"

A friend Dan Coates has drawn the tyres to the new dimension so the company chosen can vulcanise and machine the profile of the tyres. Drawings are below but please check dimensions on your own model before using these drawings.

 3" Foden wheels and tyres. The tyres were vulcanised and machined by Reliant Rubber

Completed wheels with tyres.

Rear wheels

Front Wheels