"Why different sized road wheels?" Topic

Was painting a Valentine and got to wondering why the first and last road wheels are larger than the others ones. Same for the A9 and A10. Wheels of the same size would make logistics and maintenance/repair easier. Anyone know the reason?

I would imagine that the pressures and strains on the roadwheels would be greater on the first and last wheel.

True, but plenty of other designs managed without having larger road wheels on the first and last stations.

Might be to increase climbing height, larger wheels would not get hung up as easily trying to go up a stair step-type obstacle.

The Chieftain did a video on the A10, where he states the supposed idea was a larger bogie for surmounting obstacles, followed by smaller bogies to allow more of them to be fitted into the allotted length (thus giving more pressure relief points). The discussion of the suspension is at 7:18 although like all of the Chieftain's videos you'll enjoy the whole thing:

YouTube link

Thanks I will check it out. I guess once you have decided to put a big wheel on the front making the rear with the same layout is the sensible thing to do. It made the bogies interchangeable. Ie the right front would fit the left rear and ice versa.

I would guess that the rear wheels are as large as the front wheels, so that it has then same handling when in reverse gear.

It is a three wheel version of the Horstman suspension system introduced by Vickers in the 1930s. It is still used on Challengers now….

The single large wheel is a substitute for a double wheel bogey, which is then coupled to a traditional double bogey Horstman suspension (with two smaller wheels).

I assume the big wheel was to to keep the hull length down rather than having four double bogies.

The Valentine inherited the suspension from the A9 and A10 as it worked so well, but the Army were determined to go with Christie suspensions for its cruisers. Christie was dumped as a dead end and Horstman came back with Centurian and was retained for Chieftan.

Excellent explanation Martin, thank you.