Road and Track Dyno - Tuning Dynamometers from Dreamscience

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How does wheel torque compare to engine torque?

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Wheel force is the acceptable translation of Tractive Effort, which describes what happens between the tire patch and the road. Tractive Effort is a tangential force, a product of prime mover torque and a vehicle's transmission, and can be described as,

Tractive Effort = (TE * R1 * R2 / r) E

Where: R1 = Transmission Ratio, R2 = Final Drive Ratio, r = Tyre Radius,

E = Drivetrain Efficiency

So, an engine generating 250-lb.-ft of torque @ 3500 RPM, a 1:1 ratio in fourth gear, a drivetrain efficiency of .75, an axle ratio of 2.5, and tyres having a diameter of 24-inches will produce the following Tractive Effort at the corresponding road speed - 100-mph,

Tractive Effort = (250 * 1 * 2.5) / 1) * .75 = 468.75-lbs. of force

Regardless of what's been said about engine torque and the role it plays with respect to aggregate vehicle performance, the only vehicle performance that counts occurs between the tire and the road. The more kinetic energy the vehicle is able to take advantage of, the faster it will move from point A to point B - which is what wins races. Anyone with money and resources can get their hands on a robust engine - top-notch racecar building is an art form and tyres, aerodynamics, thermal dynamics, suspension, and steering separate the men from the boys.

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