Larger tyre less torque?

Remember your engine is normally driving your wheels, not the opposite.
The vehicle's gearing hinges on the tyres. Gear ratios in the differentials, and in the gearbox and transfer case are selected to provide, adequate take-off torque at the wheels in the first gear high, and adequate cruising speed with suitably low revs, at 100km/h in fifth, while maintaining enough torque to nudge up a gentle incline. If you increase the diameter of your tyres, however there will be less torque at the wheels in every gear. Brakes are designed to operate on fixed rolling diameter. Increase the tyre diameter and the brakes are forced to work harder in and emergency stop. And even the vehicles Speedo will be affected.

Taller rubber lifts the lot, diffs included

But now, the good news! Taller tyres are far better at rolling over obstacles, and they also boost ground clearance. You will achieve an increase in ground clearance equivalent to half the increase in tyre diameter (i.e., the tyre radius), without having to touch a spring or a shocker. The best thing about this clearance is that even the axle tubes and diff housings get it. Compare that to lifting the suspension, the body goes up, but the diff and axles retain their original ground clearance.

Further, taller tyres not only boost ground clearance, but also approach, departure and ramp angles. Result? Fewer scrapes and graunches in really rough broken terrain. The downside of this clearance upgrade is that the centre of mass (a.k.a. the centre of gravity) goes higher. Result? More likelihood of a rollover seeing as how the vehicle is easier to tip over. ‘More likelihood' doesn't mean ‘ deadest dangerous' it's a question of degrees.

Kel

Torque is the force produced at standard distance from the centre of a shaft. If you measure the force at a radius greater than the standard measuring distance you will measure less force for the same torque figure. With your bigger tyres you will not change the torque produced but you will have less tractive effort.

PeterD

jolo
Your vehicle has a gear box , use it , the vehicle has no feelings , it's all in your mind , and yes you will notice a small difference , as for the 40mm , what's the law state about that, I read something along those line a few weeks ago,

.

In my opinion Cooper LT A/T tyres are great. I run them on my 2002 Pathy and this is my 2nd set after having done 90,000 ks on the first. I tow a 18' caravan and have just returned from a 12 month trip around OZ and never even had a flat. I do a fair amount of off road (not real hard stuff) and never had any problems.
The only gripe is that they pick up small stones but I suspect that this would happen with all off road tyres.
Bloody good tyres.
Steve