Why Does NASCAR Only Allow Four-Speed Transmissions?

NASCAR is a stickler for tradition. Safety regulations have changed greatly since the sport’s birth in the 1940s. Yet some technical aspects of the NASCAR race car, such as its transmission, remained constant until recently. When NASCAR first began, the cars were mostly unmodified aside from the interior, and straight from the factory, with the popular model among drivers being Ford’s design. In the 1950s, Ford had a four-speed transmission, a derivative of which was used in races until 2022. Another popular model from early racing days includes the Muncie four-speed transmission. The Chevrolet muscle cars powered by Muncie transmissions were affectionately called “Rock Crushers.” Debuting in 1968, but with roots in the 1950s, the transmission was high-endurance and heavy duty. The original H-design for the four-speed transmission can be traced back to the 1930s with the Borg-Warner transmission. While modern-day street cars are mostly automatic now, as of 2022, NASCAR requires that cars use a five-speed manual transmission.

Implications of a Manual Transmission

The manual transmissions mean the driver must be very in tune with the car they are driving. One may notice while watching NASCAR that the drivers use a clutch to change gears. Rather than using a clutch to change gears all the time, which can be taxing, drivers use a technique called “floating” to shift. Floating is done by carefully accelerating the vehicle until one reaches the desired RPM (revolutions per minute) and then shifting gears without depressing the clutch pedal.

Unlike manual transmissions for a street car, NASCAR stock cars use straight-cut gears and no synchros. Straight cut and helical gears are the most commonly used in cars. The advantage of a straight-cut gear while racing is that, unlike a helical gear, they produce no axial load, which means there is no restriction on the amount of torque used. Due to there being no axial load, the transmission produces comparatively less heat, which is very important for racing cars, as precautions must be taken against overheating. No axial loads also mean a smaller and lighter engine, as axial loads require bearings and output shafts. Straight-cut gears are also cheaper, which is cost-productive as gears must be changed in the transmission after every race. While helical gears provide far less noise and an easier ride, straight-cut gears have the advantage of speed.

The four-speed transmission wasn't changed for various reasons, one being that the more gears added, the heavier the transmission becomes. Keeping the car light and without unnecessary equipment weighing it down is important in NASCAR. For example, their stock cars do not have air conditioning, as those systems can weigh as much as 50 pounds. The old four-speed transmission was relatively light, weighing only 80 pounds. The current five-speed transaxle is more than twice as heavy as the outgoing model, weighing 172 pounds when equipped with standard options.

NASCAR’S Guidelines

NASCAR has strict guidelines for the cars and components with which teams are permitted to compete. Part of those guidelines limits teams to a single model of transmission in their race cars: the Xtrac P1334 five-speed sequential transaxle. Xtrac, a North Carolina-based racing parts manufacturer, was tapped to be the exclusive supplier of transmissions as they are a long-time supplier of components to NASCAR. Xtrac offers the P1334 in three different gearbox configurations, each with different gear ratios optimized for different types of tracks.

Generation 7 Five-Speed Transaxle

While the four-speed transmission was a fixture of NASCAR prior to 2021, the future of NASCAR transmissions is the five-speed transaxle transmission. The new five-speed transaxle transmission was introduced for the 2022 season. This is a radical change for NASCAR to take. Testing for this new model began in 2020 in Richmond on a short track with low speeds, then to Phoenix, where the track it was tested on is designed for cars with high speeds and heavier loads. The third track in Miami used an amalgamation of these designs, and the transmission has received positive feedback from test drivers.

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