Hmm. That's an interesting one. I haven't seen anything, but one must assume that it moved the point of balance, which Wilson had worked out carefully on Mother, towards the rear. How much would the fuel and the petrol tank weigh? Enough to make a difference? On a hard surface, the Mk I to 3 rested on a flat section, about 17% of the overall length, twelve track plates IIRC. So the question is: was the shifting of the fuel tanks enough to alter the point of balance, and if so, what difference did it make? If it tilted the tank towards the rear, then some of the twelve plates on the flat bottom might lift clear of the ground, but the track run to the rear of them was rounded, albeit slightly.
Then again, would any effect be noticeable in a vehicle that was hardly sensitive?
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The fuel capacity was raised from 50 gallons in two tanks (Mark 1) to 70 gallons (Mark IV); I believe that in a single tank.
The other allied question was did the design change result from the removal of the steering tail which provided some additional balance.
In a rare example of my maths being correct, 70 gallons of petrol weigh just under four and a half hundredweight (222kg approx). Does that help?
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