The February 2019 issue of Car & Driver had an enlightening article about the physics of dragster tires and how they are an active part of the drivetrain. Specifically, it explained how the rear tires of a top fuel dragster channel its 11,000 hp. and convert it into a 3.7 sec., 335 mph. run. The process was described as "black magic." The technical explanation said that "different parts of the tread move at different speeds. As the tire's leading edge bunches up (i.e., "the squat"), the tread momentarily slows down. This changing momentum creates a force acting in the direction of the ground contact angle. The vertical component of this force more than doubles the downward load on the tires, allowing torque to be channeled into extraordinary acceleration rather than a fruitless burnout." The more simplified explanation, breaks the physics down into three parts: 1. The Squat- "The massive torque channeled through the rear axle shifts the load of the car rearward and tries to twist the tire on its 16-inch beadlock rim. The sidewalls wrinkle as the tire- generally running between 6-10 psi- shrinks in radius by more than six inches and the tread effectively balls up at the front of the contact patch. That compression of the tire expands the contact patch to almost 250 square inches...and effectively shortens the final drive ratio for a harder launch. By the time the tire has released the torque stored in its wrinkled sidewalls and the tread has grown back to its original size, the top fueler is pulling more than 4.00g's of acceleration." (see Photo #1). 2. The Growth- "After the car launches, the inertia grows the tire to as much as 38 inches in diameter, simultaneously lengthening and narrowing the contact patch. This effectively lets the final-drive ratio grow taller for higher speeds and reduces rolling resistance as the vehicle reaches terminal velocity." (see Photo #2). 3. The End- As the dragster finishes its run, the engine is shut down and the compression helps brake the machine. The rear tires distort again as the car slows, sometimes developing flat spots at the trailing edges. (See Photo #3). Note- Used top fuel tires are either re-used in slower classes or are turned into "draggers" (i.e., pulled up and down the track between runs to coat the surface with a layer of rubber for improved grip).
Very well done. What you don't get from those pictures (unless you have experienced it) is the smell of the burning rubber, & Nitro and the inability to even breath as one of those monsters makes a pass
Tire technology has certainly come a long way since the mid-50s. The original M & H Racemaster drag racing tire was nothing more than a 10-inch wide recapped truck tire with a special rubber compound (notice the sidewall).
