As you know I am no expert on CMPs, but there are 240 needles in a FV 623 hub reduction planet gear assembly. . . . . . . . . . .

Thinking from just an engineering/application standpoint, it seems sensible, given the tyre load ratings of the day and to afford better off-road mobility when towing even a relatively light Bofors gun, to use a much larger tyre/wheel combination which affords enhanced load capacity and a better footprint grip with increased rolling radius.

Personally, if I were designing the vehicle with what they had then, this would be the choice together with an increased diff ratio to regain the original speed capability or even lower it further to account for the trailed load.

In the case of artillery or LAA tractors wouldn't the application be largely static? Even such pieces as a Bofors gun would likely be set up for days in one location before moving forwards a few miles now and again. Even in one day, ± brew-up stops, you could do a fair distance at 10mph. Of course perhaps we should see the vehicle-mounted Bofors guns as a "rapid-reaction" arrangement.

It seems to me that 20mph was largely adequate for all WWII applications and convoy speeds were probably much less than this, perhaps even half. I don't think today's army would convoy much faster even now, and for convoy I don't mean just a couple of MKs, a DAF and one Landy going down the motorway.

We hear little of the Italian WWII MVs, these are often epitomised by smallish vehicles with grossly "oversized" wheels/tyres, they look awkward but may well have excellent mobility.

We don't know what typical previous civvy applications may have done with mix 'n match parts encouraged by the very availability of compatible spares like diffs. I know Brian K has towed his Bofors hundreds of miles behind his LAA CMP and reports the going very slow relative to modern traffic but generally 20mph is quite possible if you give the old flathead V8 some stick - wouldn't do for Ballard however. . . . . . . . . .

The Ford diesel conversion was little better except for reduced gear changing but brought a crippling penalty in noise; as you know it now has a French "big-bore" V8 which is a noticeable improvement but all largely superseded now with a suitable artic carrying rig. He could likely tell you more and the exact diff that is currently fitted.

I note from Ballard's B&W tape of the British haulage industry of the 50s and 60s that the vehicles even then were rigidly classified as 20 and 30 mph trucks; the 30mph types being used for local distribution/collection and the larger 20mph types for movement between national depots. Crikey, even as a kid I can remember larger trucks all having 20mph rear plates.

Interesting stuff indeed.

R.