Driveline Lab

Created by Chris Pangilinan · © 2026

Follow torque and rpm from the pistons to the tire contact patch. Set the throttle and pick a gear, then watch what reaches the road and what pushes back.

0mph
800 rpm · 3rd
Drag to rotate. Right-drag or two fingers to pan. Scroll or pinch to zoom. Click a part to read about it.

Vehicle

Weight
Sets how much acceleration the left-over force buys. Also scales rolling resistance and tire grip.
Drag area
Frontal area times drag coefficient. It barely matters in town and dominates at highway speed.
Wind
Drag depends on air speed, not road speed. A headwind adds to it, a tailwind subtracts.

What the engine makes

What reaches the road, by gear

The five relationships

Throttle sets torque

The pedal controls how much air and fuel each cylinder gets, which sets how hard each piston is pushed. At any given rpm, more throttle means more torque at the crank.

More air, more torque

An engine is an air pump. Torque is set by how much air it traps in each cylinder, because that sets how much fuel it can burn. Opening the throttle, breathing better through the valves, and forcing air in with a turbo or supercharger all work the same way.

Power is torque times rpm

Torque is how hard the crank twists. Power is how fast that twist does work. The same torque at twice the rpm is twice the power. In US units, hp = lb·ft × rpm ÷ 5,252.

Gears trade rpm for torque

A gear pair cannot create power. It divides rpm by its ratio and multiplies torque by the same ratio. First gear hands the wheels about 14.5 times the engine's torque at 1/14.5 of its speed. Sixth hands them about 2.6 times.

Speed settles where push equals resistance

The tires push with wheel torque ÷ tire radius. Air drag grows with the square of speed, so the power needed to beat it grows with the cube. Whatever push is left after drag, rolling resistance and grade accelerates the car. When nothing is left, speed holds.

Things to try
  • Same speed, different gear. Cruise at a steady in 6th, then drop to 3rd and trim the throttle until speed holds again. Resistance has not changed, so power at the wheels is the same. Rpm is up and engine torque is down.
  • Same throttle, different gear. Floor it at in 4th, then in 2nd. The engine is the same. The push at the tires is about twice as large in 2nd.
  • Find top speed. Floor it in 5th and wait for the speed to settle. Then shift to 6th. Speed drops, because 6th pulls the engine down off its power peak.
  • Add a hill. Set a 10% grade in 6th. Gravity alone now needs more push than 6th can deliver at most speeds. Downshift until the ledger balances.
  • Engine braking. Lift off completely at speed in 2nd, then try the same in neutral. In gear, the wheels have to spin the engine against its own friction.
  • Too much of a good thing. From a stop, floor it in 1st. The gearbox can multiply torque past what the rear tires can grip.
  • Feel the lag. Choose Turbo, settle near 1,500 rpm in 4th on light throttle, then floor it. Boost builds slowly at first and the push at the tires follows it. Repeat with the supercharger and boost is there at once.
  • Compare the curves. Switch between the three induction choices at full throttle and watch the engine chart. The turbo adds the most through the mid-range. The supercharger adds less, and part of what it adds goes back into driving it.
  • Weight versus drag. Raise the weight and floor it. Acceleration falls but top speed hardly moves. Then raise the drag area instead. Low-speed acceleration hardly changes and top speed drops.