Driveshaft speed calculator: enter your tire size, rear axle ratio and road speed to get driveshaft RPM at any speed - a starting point when planning a driveshaft or a transmission swap.
Driveshaft speed calculator
Your setup
Result
| Road speed | Wheel RPM | Driveshaft RPM |
|---|
How driveshaft speed is calculated
On a rear-drive car the driveshaft spins at the rear axle's pinion speed, which is the wheel speed multiplied by the axle ratio. Wheel speed comes from road speed and tire diameter:
Wheel RPM = MPH × 336.135 ÷ tire diameter (in)
Driveshaft RPM = Wheel RPM × axle ratio
The 336.135 is 63,360 inches in a mile divided by 60 minutes and by π - Tremec's published gear ratio formula uses the same constant, rounded to 336. Speeds entered in km/h are converted at 1.609344 km/h per mph.
Why your transmission gear doesn't change it
The transmission sits ahead of the driveshaft, so the gear you're in changes engine RPM, not driveshaft RPM. At 100 mph the driveshaft turns the same speed whether you're in 4th or 6th. In an overdrive gear (ratio below 1.00) the driveshaft turns faster than the engine, because driveshaft RPM = engine RPM ÷ gear ratio. To see engine RPM in every gear, use our gear ratio and RPM calculator.
Computed vs. real tire diameter
Metric sizes are converted with diameter = wheel diameter + 2 × width × aspect ratio ÷ 100 ÷ 25.4. That's the theoretical diameter - the actual diameter of a specific tire comes from the tire maker's data. If your tire's spec sheet lists revolutions per mile, use that mode. On the road, wheelspin and tire growth at high speed also change the real number.
This applies to front-engine, rear-drive layouts where the driveshaft feeds the rear axle's pinion. The result is driveshaft speed only - it doesn't check driveshaft critical speed, balance, or U-joint angles.
Planning a transmission swap? Our DCT and ZF 8HP swap basics guide covers parts, controllers, sourcing and costs.
DCT / 8HP Swap Billet Transmission Crossmember - BMW E31/E32/E34 Mounts a Getrag 7-speed DCT (GS7D36SG, GS7D36BG and F8x M2/M3/M4 boxes) or ZF 8HP45/50/70/75/90 on the factory crossmember mounting points.