Date published: February 3, 2012
Journal code: NDRG
With few exceptions, Pro Stock Motorcycles must weigh no less than 565 pounds (620 for two-valve Harley-Davidson V-Rods, 640 for four-valve Harley-Davidson V-Rods and 615 for Buells up to 160 cubic inches, 595 for 107-cid Suzukis, 575 for 101- cid Kawasakis, 590 for 92-cid Suzukis, and 565 for 92-cid Kawasakis) with the rider aboard and have a maximum wheelbase of 70 inches. Motorcycles must be '98 or later models and retain their stock appearance, including a front fender, simulated headlight and taillight, and manufacturer identification on both sides. The engine and body make must be the same.
1Chassis: A Pro Stock Motorcycle chassis is made from 4130 chromoly steel tubing. Though the wheelbase is limited to 70 inches, the wheelie bar, which is a critical chassis-tuning component, extends up to 130 inches from centerline of front axle to centerline of wheelie-bar axle. The rear is solid-mounted, and the chassis includes a front fork, a swing arm, a 1-quart fuel tank, handlebars, foot pegs, and an engine mount.
2Body: A modern Pro Stock Motorcycle is cloaked in an aerodynamically enhanced replica of the original body following many production dimensions, and it is made from either fiberglass or a carbon-fiber composite. The body has an air box that surrounds the carburetors or fuel-injection system and acts as a forced-induction system. A standard Pro Stock Motorcycle body also incorporates a two-step seat. After leaving the starting line, riders slide back from the lower portion to help improve weight transfer and reduce wind resistance.
3Engine: Though virtually any stock motorcycle engine can be submitted for acceptance, the majority of racers use the V-Twin style or inline four-cylinder Suzuki or Kawasaki. Engines are limited to 160 cubic inches for V-Twins, 107 cubic inches for two-valve Suzukis, or 101 cubic inches for four-valve Suzukis or Kawasakis. NHRA-accepted fuel injection is permitted on all engines. Cylinder heads can be from an aftermarket supplier, and NHRA-accepted aftermarket engine cases are permitted.
4Drivetrain: Pro Stock Motorcycle transmissions are limited to six forward gears. With the exception of V-Twin-style engines, the transmission must be contained within the engine housing. The rider changes gears with an air shifter, which he or she activates with a handlebar-mounted button. The 7-inch, multistage, centrifugal lockup clutch uses 18 plates: nine fiber discs and nine steel floaters. Chain guards, covering the width and top run of the chain, are mandatory.
5Tires: The rear slick on a Pro Stock Motorcycle is 10 inches wide and 26 inches in diameter and is designed specifically for motorcycle drag racing. Mickey Thompson Performance Tires manufactures the hightraction rear slicks preferred by today's riders. The front tire is a lightweight, treadless design that aids braking. Air pressure is 4 to 5 pounds on the rear tire and 30 to 32 pounds on the front.
6Fuel: Pro Stock Motorcycles may use only high-octane spec racing gasoline. The use of propylene oxide and/or nitrous oxide is prohibited. NHRA officials test and certify all fuel by chemical analysis. A Pro Stock Motorcycle engine uses 1 quart of fuel per quarter-mile run.
7Brakes: The most common braking system uses three aftermarket carbon-fiber-composite or steel brake discs, one or two on the front and one on the rear. The two front-brake rotors must be at least 8 inches in diameter and the rear 10 inches. The front brakes are activated via a hand lever and the rear via a foot pedal. Parachutes are not required.