Hi

Excellent start. You also need to allow for tyre deflection with cushion or pneumatic tyres. I haven't got actual data on typical deflection versus load for these forklift tyres but would suggest it is of the order of 10 mm per tonne.

The net effect on clearance with the drive tyres compressing and the steer tyres expanding is probably a reduction of 10 - 15 mm.

You might add a field on tyre type fitted and then at a minimum have a statement that when loaded the clearance may be reduced by 10-15 mm.