GARAGE CALCS FOR THE HOME BUILDER

Driveshaft critical speed calculator

Every driveshaft has a speed where it starts to whip and vibrate. This finds it from your tube size and length, and translates it into the top speed your gearing allows.

Free, no sign-upUpdated September 2026
Your numbers
Driveshaft tube
Vehicle

Critical speed

Rotating speed where the shaft starts to whip.
Safe operating limit
Top speed at that limit
Inside diameter

The formula

Critical speed (rpm) = 4,705,000 × √(OD² + ID²) ÷ length²

This is the standard formula for a steel tube, with diameters and length in inches. Aluminum's stiffness-to-weight ratio is close to steel's, so the result is similar for aluminum tubes of the same size. Carbon fiber shafts differ and should use the manufacturer's rating.

Driveshaft speed equals wheel speed times the axle ratio, so numerically higher gears and smaller tires spin the shaft faster at a given road speed. Staying well below critical speed, commonly at 65 to 75% of it, leaves room for balance and u-joint condition.