| Gear | Ratio | RPM @ 110 kmh | Top speed @ 6,000 RPM |
|---|---|---|---|
| 1 | 4.03:1 | 11,141 RPM | 59 km/h · 37 mph |
| 2 | 2.36:1 | 6,524 RPM | 101 km/h · 63 mph |
| 3 | 1.53:1 | 4,230 RPM | 156 km/h · 97 mph |
| 4 | 1.15:1 | 3,179 RPM | 208 km/h · 129 mph |
| 5 | 0.86:1 | 2,377 RPM | 278 km/h · 173 mph |
| 6 | 0.69:1 | 1,907 RPM | 346 km/h · 215 mph |
RPM shown for each gear at the entered road speed; the “top speed” column is the speed each gear reaches at redline. A taller tire or numerically lower axle ratio lowers cruising RPM.
How this math works
Every result is governed by an exact equation — no guessed numbers, no hidden constants:
- Engine RPM:
RPM = (MPH × gear ratio × final drive × 336.135) ÷ tire diameter (in)— The constant 336.135 = (5280 ft/mi × 12 in/ft) ÷ (60 min/hr × π). It is derived from the units, not a fudge factor. - Road speed:
MPH = (RPM × tire diameter) ÷ (gear ratio × final drive × 336.135)
Worked example
A truck cruising at 70 mph in a 1.00:1 top gear, with a 3.73 axle and a 31-inch tire, turns about (70 × 1 × 3.73 × 336.135) ÷ 31 ≈ 2,830 RPM. Swapping to a taller 33-inch tire drops that to about 2,660 RPM — quieter, more relaxed highway cruising.
FAQ
What is the difference between gear ratio and final drive ratio?
The gear ratio is the ratio inside the transmission for the selected gear (top gear is often around 0.7–1.0:1). The final drive is the differential/axle ratio (commonly 3.0–4.5:1). Engine RPM depends on both multiplied together, plus tire diameter.
Why does a bigger tire lower my RPM at the same speed?
A larger tire travels farther per revolution, so the wheels — and therefore the engine — turn fewer times to cover the same distance. That lowers cruising RPM, which can help fuel economy but reduces low-speed torque at the wheels.
Does this account for torque converter slip or tire growth at speed?
No. This is the exact geometric (mechanical) RPM. Automatic torque-converter slip and high-speed tire “growth” cause small real-world deviations, but the geometric figure is the correct baseline for gearing decisions.
How do I find my transmission and axle (final drive) ratios?
The axle ratio is often on a door-jamb or glovebox code, an axle tag, or in the owner’s manual (common values are 3.23–4.10:1). Transmission gear ratios are listed in the factory service data for your specific gearbox. Use the presets in this tool for common axle ratios if you are unsure.
Why is my engine revving higher than this figure on the highway?
If real cruising RPM is much higher than the calculated value, the transmission may not be shifting into top gear or the torque-converter clutch may not be locking. That can indicate a transmission fault — check for codes such as P0730 (incorrect gear ratio), P0741 (torque-converter clutch performance) or P0700 (transmission control system).
Related trouble codes
More calculators
- Tire Size & Speedometer Error Calculator — Compare two tire sizes and see the exact speedometer & odometer error.
- Engine Compression Ratio Calculator — Calculate static compression ratio and displacement from engine dimensions.