Top Speed Calculator
The drag-limited top speed physics allows your power - solved from the road-load equation with cited body-shape presets, an honest CdA sensitivity band, and the cube law drawn instead of asserted.
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Top Speed Results
The cube-law wall
Power the road demands (curve, with the CdA ±10% band shaded) against the power you have (line). Where they meet is your ceiling. The curve steepens with the cube of speed, which is why the line's height matters so much less than the curve's width.
The price of going faster
| Speed | Power needed | Increase |
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The road-load equation
At a steady top speed the engine is doing exactly two jobs: pushing air out of the way and rolling the tires. Air takes 0.5 x rho x Cd x A x v cubed; the tires take Crr x weight x v. This calculator solves that equation directly at sea-level air density (1.225 kg/m³) - no fitted shortcut formula, which is why the widely quoted race-car figure reproduces here: at 200 mph, a car with a competition-slick CdA of 0.60 m² spends about 352 hp just on air. The cube is the whole story: doubling speed needs eight times the aero power, so each extra 10 mph costs more than the last, as the table above prices out.
CdA is the input you know least
Drag coefficient times frontal area is the product that actually matters, and it is the number owners know worst. Manufacturers publish Cd measured on their best day and rarely publish frontal area at all. The presets carry cited anchors - the average full-size car has a drag area around 0.74 m², a Tesla Model 3 posts Cd 0.219, a Jeep Wrangler 0.454, a Ram 1500 a published 1.21 m² of drag area - but they are starting points, not your car. That is why the verdict shows the speed at CdA plus and minus ten percent instead of pretending to a single mph, and the cube law is merciful here: a 10% CdA error only moves the answer about 3%.
This is the aero ceiling, not a promise
The number here answers one question: the speed where aerodynamic drag eats all your power. Many cars never get there - a speed limiter or the redline in top gear stops them first. The gear ratio calculator answers the gearing-limited question; this one answers the power-limited question, and your real ceiling is whichever is lower. If your power number is a guess, work it out from a time slip with the quarter mile calculator, and if the plan is to raise the line with boost, the boost to horsepower calculator estimates how far it moves - remembering that the cube law gives back only a third of what you feed it.