John_Mc
Elite Member
- Joined
- Aug 11, 2001
- Messages
- 4,045
- Location
- Monkton, Vermont
- Tractor
- NH TC33D Modified with belly pan, limb risers & FOPS. Honda Pioneer 520 & antique Coot UTV
A friend and were discussion soil compaction during small-scale logging operations -- using a compact tractor, vs using a mini tracked skidder. The two were approximately the same weight. Obviously, the skidder exerts less PSI on the ground than the CUT, due to the skidder's hugely greater footprint.
My friend claimed that you can figure out the pounds per square inch that a tractor is putting on the ground just by looking at the PSI in the tires. The theory her is that if you run your tires at 20 PSI, then they will just deform until they have flattened out enough to match that 20 PSI onto the ground.
I can see the thinking here, but to me that would just be in ideal situations. It does not take into account the fact that the tires are not infinitely elastic. They have some stiffness, and limits to how much they will deform. In fact, R4 tires (and perhaps other, heavier duty tires) are designed to be stiff. To take it to an extreme, consider the run-flat tires on some cars. Even with a hole in the sidewall, they will barely deform (at least not until you drive it around enough to start breaking down the sidewalls). The PSI this tire exerts on the ground does not go down when it's empty. (In fact, it may go up, since almost all of the weight is on the edges of the tire. The center of the tread is probably not supporting as much of a load).
An example at the other extreme: If I go from 20 PSI up to 60 PSI in my tires, does my tractor's footprint really decrease to 1/3 of what it was at 20? That is what would be necessary for the PSI exerted on the ground to match the PSI in the tires (given constant tractor weight).
I'm interested in people's thoughts on this, and particularly if anyone can provide a link to an authoritative source with something written on the subject.
John Mc
My friend claimed that you can figure out the pounds per square inch that a tractor is putting on the ground just by looking at the PSI in the tires. The theory her is that if you run your tires at 20 PSI, then they will just deform until they have flattened out enough to match that 20 PSI onto the ground.
I can see the thinking here, but to me that would just be in ideal situations. It does not take into account the fact that the tires are not infinitely elastic. They have some stiffness, and limits to how much they will deform. In fact, R4 tires (and perhaps other, heavier duty tires) are designed to be stiff. To take it to an extreme, consider the run-flat tires on some cars. Even with a hole in the sidewall, they will barely deform (at least not until you drive it around enough to start breaking down the sidewalls). The PSI this tire exerts on the ground does not go down when it's empty. (In fact, it may go up, since almost all of the weight is on the edges of the tire. The center of the tread is probably not supporting as much of a load).
An example at the other extreme: If I go from 20 PSI up to 60 PSI in my tires, does my tractor's footprint really decrease to 1/3 of what it was at 20? That is what would be necessary for the PSI exerted on the ground to match the PSI in the tires (given constant tractor weight).
I'm interested in people's thoughts on this, and particularly if anyone can provide a link to an authoritative source with something written on the subject.
John Mc