Kean Maygib 3'7" coach wheels

[grovenor-2685]

a new tyre being around 20mm thick, the minimum being something around 6-8mm

Those are very thin tyres, ours on DLR are a lot thicker although i don't have the dimensions in my head, i'll check tomorrow.
Regards

[Matthew]

I could quite definitely be wrong - the max and min are painted in the top of my tool box which is hiding in the depths of Bristol SPM.

[grovenor-2685]

Our wheels go from 740 mm dia new to 660 mm dia at scrapping which means we take 40 mm off the tyre thickness during it life. I don't have a figure to hand for the residual tyre thickness at scrapping but would estimate it as somewhere near 20 mm.
Generally, without tread brakes the diameter does not change significantly with actual wear, it is changed by turning to restore the profile and get rid of flats etc. When the flanges wear thin you need to take quite a bit off the diameter to get the flange profile back.
Regards