The reason the front puls off the ground isn't that the sled is pulling it up, rather that the rear is digging in harder and the torque of the axle is raising the truck up. The sled is just giving more resistance, not downward pressure. The front end weights are needed to keep the nose dowm. We use front end weights on farm tractors all the time, for the torque reason. They get great traction, and if the front end weights aren't there, you can do a wheelstand pulling equipment. On the pulling track, the ground is packed and that gives your tires more bite, so the natural action is for the truck to raise up if it can not move forward. Those forces balance out with the nose of the truck hanging in the air unless you counter it with more weight.

 

Im not sure about that. when i see all the crazy tractors running multiple super charged motors, their tires spin like crazy, but they do wheelies. But i do agree when you have traction, and lots of torque, but cant move, a wheelie is likely.

"On the pulling track, the ground is packed and that gives your tires more bite, so the natural action is for the truck to raise up if it can not move forward"

I'm not sure about that either, whenever the trucks very near the end of the pull distence, its going around 4 mph and spinning the tires like crazy. I've never seen a truck in a sled pull, and at or near the end of its pull, all the tires are biteing.

Now i might be wrong and probobly am, so hopefully someone explains

 

if the ground wasn't packed, they would be digging a heck of a hole. If you have ever tried to pull something on soft dirt, you likely just dug in, but if you try it on packed ground like a road or such, you don't dig in, and the traction is better. As for the tires spinning, you have to remember that you can still spin tires on pavement, but isn't that better traction than dirt? The horsepower is high, and going to overcome the tires catching. Traction isn't about not spinning the tires by any means, but I could guarantee if the track were not packed, they wouldn't go nearly as far because they would leave some very deep ruts.
at the end of the track, the sled has a lot of weight on the skid part to try and stop the truck from pulling it due to the friction of the sled on the ground, which is traction of it's own. Traction =friction, whether it be the tires or the sled. Imagine the traction the truck would have in a similar situation on pavement, wouldn't it be likely the tires would be spinning there too, or the truck would stall? Same story. By spinning the tires, the traction relatively is better than expecting it to just dig and go, that would break parts and the engine wouldn't be able to do as much. Too much traction and the trucks would tend to roll over. This has actually happened a time or two with tractors stuck in the mud or such, they would tie something to the wheel, and when it got down into the mud, instead of coming out of the mud, it rotated the whole tractor around the rear axle, flipping it over backwards.

 

Oh thanks for clearing that up. I usually dont watch the tractors, just the diesel trucks (290,00 dodges, 10 fords and a few chevys ususally.)(always tons of dodges and a few fords and bow ties)