[Tony Smith]

Originally Posted by David Dunlop

It makes sense different weight classifications of CMPs would be geared differently in such a way as to make convoy movements of mixed vehicle fleets travel together at a consistent road speed.

Would you not also expect differing fuel consumption rates across the CMP weight classifications? If one did not also take that into consideration, planners would run the very real risk of vehicles running out of fuel randomly along the supply routes. It would be far better to ensure each differing weight classification carried enough fuel that all could expect attaining the same range when they all start out with full fuel tanks. Loaded weights and gear ratios would all play into fuel capacities, would they not?

David

Absolutely, and even within the class of 3 ton trucks, fuel usage would vary between Ford and Chev, and between say a 4x4 CMP and a 4x2 Standard truck with narrow tyres. The logistics planners would have a lot to consider when allocating fuel for a particular convoy from A to B.

But even though a 60cwt is in a lower gear and revving higher than a 30cwt, it will still be a more economical way of moving a 3 ton load than providing 2 30cwt trucks. A 60cwt revving at 2400rpm will be using about 60% more fuel than the 30cwt revving at 1600rpm, which is a saving really on moving 100% more load.

Originally Posted by Tony Smith

Note that within each brand of CMP, all weight trucks have identical engines (and power and torque figures), and identical gearboxes (with the same ratios).

..... And the 15cwt, 30cwt and 60cwt have all standardised on the same fuel capacity of 2x 12 Gal fuel tanks, with the FATs having 2x 20Gal.

With the additional consumption of the 60cwt travelling in convoy with smaller CMPs, the design brief should have considered the 20 Gal tanks to give an equivalent range between refills.