Posted by Jerry Boone

Q How does the sled work?
A To help understand how a sled works a little history of the device is sometimes necessary. In the early days of pulling people used to stand beside a skid plate in which they hitched to a tractor, horse, or whatever competitive vehicle they were competing with. People stood along the side of the track at regular marked distances from the beginning of the track to nearly the end. As the skid plate drew closer they prepared to jump on it making the skid plate harder for the vehicle to pull as it progressed down the track. Today, a sled is a weight transfer machine that works similar to the original design. It still uses a skid plate (which I will now refer to as a pan) and the machine has been built over the top the pan. A large ramp is placed over the top of the pan with most of it's length existing behind the pan. The sled has regular semi truck wheels in the back that turn as the sled is drug down the track. As the wheels turn a series of transmissions, gears and large chain pull a box full of weight up the ramp as the sled progresses down the track, thus transferring more weight off of the wheels and onto the pan, thus making the entire sled much more difficult to pull as it progresses down the track.

Q How do they know how much weight to put in the sled box?
A It depends on the sled operator's experience. If a sled operator has been at the track in the past, he will have a book he logged into or may remember what weight and what gear he used on the transmission that determines the rate in which the box moves up the ramp. Some sled operators can study the ground to determine the amount of traction a vehicle will likely have, and then make the adjustments. The sled operator knows that a clay surface will need more weight than a sandy surface since clay provides more bite (traction) than a sand surface.

Q In other sports drivers/teams make adjustments on the vehicle for altitude, weather, tracks and other factors. What changes do pullers make based on those factors?
A In any fuel burning engine the altitude makes a difference on the fuel mixture. In higher altitudes there is less oxygen and you have to lean (decrease the amount of fuel) the engine to make more power. Combustion works best when just the right amount of oxygen and fuel are mixed, compressed, then ignited. Too much fuel and not enough oxygen will make a engine sound like it is blubbering at high rpm resulting in a large power loss. Most engines in the sport of truck and tractor pulling are fuel injected and use a changeable nozzle to make drastic changes in fuel delivery amounts, then use a smaller device known as a pill (or jet) to fine tune the mixture. In most fuel systems the pill actually determines the amount of fuel that returns to the tank rather than what goes into the engine meaning that the larger the pill, the leaner the fuel mixture. Many drivers lower the tire pressure if the track is loose or sandy to get more traction. This happens frequently if the track is indoors since the dirt is brought into the building and compacted by packers. Drivers are normally most concerned about what gear ratio to use based on track conditions. If the gear is to tall (high), it puts to much load on the engine and the vehicle will never develop enough rpm to make any distance in the pull. Engine in this sport make the most power when they are running at their highest rpm. Very large expense and detail are invested in these engines to make sure that they don't come apart at that rpm.

Q What fuel are you allowed to use?
A Two types of fuel are used in the sport - methanol alcohol or diesel. Vehicles that use blowers or fuel injection use alcohol while tractors that run modified stock diesel engines use alcohol with exception to some that have modified the diesel engines to use alcohol.

Q What safety regulations are there in the sport?
A See the RULES section under THE SPORT for some rulebook information.

Q Does everybody use a blower?
A Only the 2wd and open/modified tractor classes are allowed to run blowers. More information can be found in the RULES under THE SPORT. Vehicles such as the 4wd's cannot use a blower and have to run naturally aspirated. However the 4wd class has unlimited cubic inch limits. It is not uncommon to see a 4wd with 600+ cubic inches and in some cases 1000 cubic inches has been reached. On super stock tractors (smokers) running diesel fuel, you can have up to 4 staged turbo chargers. If you haven't seen one of these tractors run before you are missing technically one of the most fascinating vehicles of the sport. Manifold pressures can surpass 200psi and the amount of smoke they generate is amazing. The view is like a miniature 75ft tornado coming out of the exhaust. Click here for pictures of this awesome class.

Q How do the 2wd's and tractors steer down the track with the front end in the air?
A The steering is done with independent rear wheel brakes. If a vehicle starts to drift to the left a driver will apply the right wheel brake, which makes the left wheel spin a little faster, and the right one a little slower. The left pedal is applied if the vehicle is drifting to the right. Either way, it does cost distance to apply brakes. Whenever brakes are used it slows tirespeed and increases the load on the engine thus giving less power to make a better distance with.