Tractor Pulling Tyre Dynamics 1

[willturner1]

Please can someone provide formulae that explain the very high drawbar pulls that can be generated by competition Pulling Tractors. I am aware of cut down tread lugs and tyre peripheral speeds of maybe 200 mph. Is it some form of energy transfer from speeding up hunks of clay?

WillTurner

 

[Fabrico]

It's the combination of the tire and weight transfer. Even a bald tire can get quite a bit of traction if loaded down enough.

 

[CSLufkin]

As I understand it, the idea is to get the entire powertrain up to high speed at the short end of the track while the transfer sled pulls relatively easy, thus the cut tread to allow wheel spin, and traed cleaning. As the weight starts to come down onto the hitch at mid-track it increases traction. The momentum of the drivetrain can then be hooked up to the track and that momentum can carry you out the far end. This seems to work pretty well, and gives an impressive show, although I always wondered what would happen if you put some tall lug tires on and pulled in a low gear without the wheel spin. My son pulls a garden tractor with the no-spin, slow speed approach and wins almost every time. Not nearly as impressive as the National Quarter Scale tractors antics though.

 

[willturner1]

Thanks for these, guys.
However, my first guesses are that "something" is adding maybe 100% to the drawbar pull obtainable from friction on moist clay..
That is allowing for weight transfer effects and pulling chain angles
Some mathematics would be most welcome...

Willturner

 

[Compositepro]

With little tire slip the traction force is limited by the strength of the soil. Standard tractor tires are designed to push loose soil to the side as the tire slips so that the tire can try to grip some stronger soil below. Significant additional thrust is obtained at very high tire slip if a large mass of dirt is thrown back at high velocity. Its know as jet power .