Wheel diameter question

[Hanno Spoelstra]

Originally posted by Stellan Bojerud
This picture is interesting. To the left we see the five spoke (front)wheels we have been discussing. To the right a later type. The brakes were on the back wheels (right on photo).

The gun is the original m/34 owned by Bofors and used for trials and demonstrations. From the beginning this carriage had four five-spoke wheels.

My guess it that they put up new back wheels because 1) the brakes had been damaged or 2) brakes had been improved.

Stellan, attached goes a picture of a Canadian 20-cwt GS Trailer chassis, which was uprated from 15-cwt by (besides some other details) fitting 20 x 6 Standard Commercial Disk five spoke five stud wheels with 4.5" offset, fitted with 7.00x20 pneumatic type tires. Their part no. is F/81T-1015, denoting they were supplied through (but not necessarily manufactured by) Ford Canada.
Why I am posting it here is because the 20-cwt trailer had drum brakes, so I see no reason why the five-spoke wheels had to be changed for the eight-spoke wheels on the m/34 Bofors gun. Could it have something to do with offset?

Hanno