18" tyres

[David_Hayward (RIP)]

I thought it might be found interested to know the War Department tyre sizes that they specified immediately pre-war, which dictated Canadian sizes of course:

9.00 x 13-inch tyre: 8-cwt GS Trucks
9.00 x 16-inch tyre: 15-cwt GS Trucks; 6-wheel Field Artillery Tractors; Field Gun Carriages; Field Artillery Trailers.
10.50 x 16-inch tyre: 30-cwt 4-wheeled lorry.
10.50 x 16-inch sand tyre: 15-cwt and 30-cwt vehicles for use in Egypt and other sand localities.
7.50 x 20-inch tyre: 30-cwt GS 6-wheeled lorry for load carrying purposes.
9.00 x 22-inch tyre: 3-ton lorry.
13.50 x 20-inch tyre: Medium Artillery Tractor; medium Gun Carriages; heavy trailers of various types.

The 18-inch tyre size [9.00 x 18] was suggested by Ford of Canada but it was non-WD standard. The WD were concerned that tyre sizes larger than 16" might cause the tyre to creep on its rim.