Tractive Effort To Horsepower Calculator takes the drive force at the tire contact patch, road speed, vehicle weight, and tire diameter, then returns the wheel and crank power.
Convert Tractive Effort and Road Speed Into Wheel and Crank Horsepower
This tractive effort to horsepower calculator turns the forward force at the tire contact patch into wheel power, crank power, acceleration, wheel torque, and power-to-weight. Chassis tuners, drag racers, and anyone checking a simulation or a pull test against real numbers use it.
What to Enter From Your Force Reading and Vehicle Spec
Pick Imperial (lbs, mph, lbs, inches) or Metric (Newtons, km/h, kg, mm). Switching resets every field to that system’s defaults. Enter tractive effort, road speed, vehicle weight, drivetrain loss percent, and overall tire diameter. Power reads in HP or kW to match the system you picked.
How Force and Speed Become Wheel and Crank Power
Power is force times speed. The divisor just fixes the units. One horsepower is 33,000 ft-lb per minute, and one mph is 88 ft per minute. Divide 33,000 by 88 and you get 375. Metric needs no such trick: Newtons times metres per second gives watts directly, so km/h is divided by 3.6 and watts by 1,000.
$$WHP = \frac{F \times v}{375} \qquad kW = \frac{F_N \times v_{km/h}}{3600}$$
Crank power then divides by drivetrain efficiency. That direction matters. With 15 percent loss, 320 WHP becomes 376.5 HP, not 368. Adding 15 percent to wheel power is the most common mistake here and it always reads low.
$$HP_{crank} = \frac{WHP}{1 – Loss/100}$$
The 15 percent figure is a shop convention, not a standard. SAE J1349 covers engine power correction at the crank. It says nothing about what the driveline eats. Real losses vary with transmission type, driveline layout, and oil temperature.
The math rejects zero and negative values for force, speed, weight, and tire diameter. Loss must fall between 0 and 50 percent. The field minimums shown in the tool are not enforced by the calculation, so a 100 lb vehicle weight still returns numbers. At 0 percent loss the crank and wheel figures match. At 50 percent the crank figure is exactly double.
How Tire Radius Links Ground Force to Wheel Torque
How the Torque, Acceleration, and Power-to-Weight Rows Are Derived
Wheel torque is force times the tire radius. Radius comes from half the overall diameter, converted to feet or metres. Tire RPM comes from road speed divided by rolling circumference. Acceleration in g is force divided by weight. Time and distance then use constant-acceleration physics.
$$T_{wheel} = F \times r \qquad g = \frac{F}{W} \qquad t = \frac{v}{a} \qquad d = \frac{v^2}{2a}$$
Enter the weight the car actually runs at. Curb weight with no driver and half a tank makes the g-force and the 0-to-speed time look better than the car will ever be. Real acceleration also depends on tire condition and road surface, so treat the time and distance rows as a ceiling rather than a target.
Two behaviours surprise people. Tire diameter never touches wheel power or acceleration. It only moves wheel torque and tire RPM. A taller tire raises the torque number while the car accelerates exactly the same. The time and distance rows also assume the tractive effort you entered holds all the way from a standstill, with no drag. No car does that. Above about 1.0 g you are past what street tires hold, and the tool still prints the number.
Input Mistakes That Skew the Power Figure
Entering wheel torque in lb-ft into the tractive effort field, which is a linear force in pounds, not a rotational one.
Typing kilograms-force into the metric effort field, which expects Newtons — multiply kgf by 9.81 first.
Entering rim diameter or section width instead of the tire’s overall diameter, which throws off torque and RPM.
Tractive Effort and Wheel Power Questions Tuners Ask
Is the main result wheel or crank power?
Wheel power. Force at the contact patch is already past the driveline. The crank figure is shown separately and is the larger of the two.
What drivetrain loss should I enter?
Fifteen percent is the common starting point for a manual rear-drive car. Automatics and all-wheel drive usually lose more. If you have both a chassis and an engine dyno number for your car, use those instead.
Why does the same force give more horsepower at higher speed?
Power is force times speed. Hold the force constant and double the speed, and the power doubles. This is why top-gear pulls need far more power than first-gear pulls at the same force.
Does a taller tire change the horsepower result?
No. Tire diameter only affects the wheel torque and tire RPM rows. Power comes from force and speed alone, and neither one moves when you change tire size here.
Why is my real 0-60 time slower than the calculated one?
The calculation assumes constant force, perfect traction, and no aerodynamic drag. Real cars shift gears, spin tires, and fight drag that climbs with speed.