What's your dune climbing technique?

[PeeBee]

If two vehicles of different weight but similar power availability and drive fitted with identical tyres attempt to cross a surface the tyre pressure at which point they will succeed or fail depends on the ground pressure exerted and is independant of the actual mass of the vehicle.
If a 3 ton Patrol fails at say 24 psi but gets thru at 18 psi then a 15 ton truck will fail at 24 but get thru at 18 psi also (all other things being equal)

ET, I am not sure you have this correct. Negating the internal pressure of the tyre, which in your example states the tyres and pressures are the same, if you raise the weight of the vehicle by 500% your unit pressure is raised on the sand also, ie if say the 3t vehicle running at 18psi, has at each wheel 100 sq inches of ground contact, so 400 sq inches across 4 wheels. 3000kg = 6600lbs/400=16.5lb/inch2 unit pressure. If the load carrying capacity of the sand is 18psi, then yes it would float across the top. Now, next vehicle, same tyres/pressure, 33000lbs/400= 82.5psi, hence it will sink if the load carry capacity of the ground is 18psi, this is assuming the actual footprint of both vehicles is the same. So mass/footprint = ground pressure, nothing to do with internal pressure.

What you need to achieve is a 'footprint pressure that is less than the resistive pressure of the ground'. What cannot be determined is what the footprint of the tyre would be at 18psi on a 3t v 15T vehicle and I think this is more the issue than the internal pressure. I admit that logically the tyres on the truck would bag out more than at 3T, at 18psi, but I think the principle lies in actual footprint pressure than internal pressure of the tyre.

In conclusion, if we put 20 tyres on the 15T truck the ground pressure would be equal to the 3T one, being 33000/2000inch2 = 16.5 psi ground pressure, assuming the footprint is the same. Does this make sense?