- #1

petterg

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- TL;DR Summary
- Ground pressure from a wheel - knowing the max load on a small wheel, how big must a wheel be to carry a large load?

I need to drive a tractor across and area of soft ground without leaving deep tracks. I tested the ground carrying capacity with car and concluded that 700kg is max load on a 265/70-17 wheel, with 2,2bar tire pressure. (That wheel is 265mm wide, 401mm outer radius, unloaded.)

As the ground is soft, the tire threads will sink in. Hence I don't think we need to account for thread pattern.

The tractor (with load) weights 3500kg on the most loaded wheel. I need to figure out how big tyre I should buy for the tractor tire in order to get similar ground pressure as the car tire. Tire pressure should not go below 1,1bar because of risk of tire falling off the rim in terrain.

Available tire widths are 520mm, 600mm, 650mm and 700mm. For these widths, which radius is required?

(Tire cost increases exponentially with size)

The main challenge in this question is calculation of the tire contact area from the wheel dimensions and pressure. When a 265mm wide tire carries 700kg, a 600mm tire of the same radius and pressure will carry (700kg * 600mm/265mm = ) 1585kg. I need a contact area to be 2,2 times this in order to carry 3500kg. How much will the contact area increase when tire pressure is down from 2,2bar to 1,1bar? How much will the wheel radius need to increase to the rest of the needed area?

As the ground is soft, the tire threads will sink in. Hence I don't think we need to account for thread pattern.

The tractor (with load) weights 3500kg on the most loaded wheel. I need to figure out how big tyre I should buy for the tractor tire in order to get similar ground pressure as the car tire. Tire pressure should not go below 1,1bar because of risk of tire falling off the rim in terrain.

Available tire widths are 520mm, 600mm, 650mm and 700mm. For these widths, which radius is required?

(Tire cost increases exponentially with size)

The main challenge in this question is calculation of the tire contact area from the wheel dimensions and pressure. When a 265mm wide tire carries 700kg, a 600mm tire of the same radius and pressure will carry (700kg * 600mm/265mm = ) 1585kg. I need a contact area to be 2,2 times this in order to carry 3500kg. How much will the contact area increase when tire pressure is down from 2,2bar to 1,1bar? How much will the wheel radius need to increase to the rest of the needed area?