# Tire Size RPM Calculator

Estimate Tacoma cruising RPM from tire diameter, axle ratio, and transmission gear. See highway RPM to judge lugging versus buzzing and to plan a regear.

## Canonical URL
https://tacotires.com/rpm-calculator

## What It Does
- Highway RPM: Calculates engine RPM at a range of speeds from tire diameter, axle ratio, and transmission gear.
- Regear planning: Compare RPM before and after a tire change to see how much a numerically higher axle ratio would help.
- Tacoma presets: Factory axle ratios and transmission top-gear ratios by generation are built in.

## Summary
- Estimates engine RPM at a road speed from tire diameter, axle ratio, and transmission top-gear ratio.
- Uses the standard RPM equation with the 336.135 constant derived from 63,360 inches per mile.
- Helps decide whether a tire or gearing change leaves the engine lugging or buzzing at highway speed.

## FAQ
### What is a good highway cruising RPM?
Most gas trucks feel best cruising around 2,000 to 2,600 RPM at 70 mph. Much lower can lug and hunt gears; much higher is buzzy and thirsty.

### How does tire size change RPM?
A taller tire lowers cruising RPM for a given speed, which can feel undergeared and cause the transmission to downshift on hills. A regear restores the original RPM.

### What formula does this use?
RPM equals axle ratio times MPH times transmission ratio times 336.135, divided by tire diameter in inches. The 336.135 constant comes from 63,360 inches per mile divided by 60 minutes and pi.

## Related Tools
- [Gear ratio calculator](https://tacotires.com/gear-ratio-calculator)
- [Tire size calculator](https://tacotires.com/tire-calculator)

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