Tire Size Calculator & Comparison
Compare any two tire sizes — including ST trailer and LT sizes. See exactly how diameter, sidewall and revolutions per mile change, and what your speedometer will really read.
Current tire — 215/60R15
/R
New tire — 235/80R16
/R
235/80R16 is 22.4% larger in diameter than 215/60R15. ⚠ More than 3% — expect noticeable speedometer error and possible clearance issues. Check fitment carefully.
Size comparison — drawn to scale
1 · 215/60R15 2 · 235/80R16
| Measurement | 215/60R15 | 235/80R16 | Difference |
|---|---|---|---|
| Overall diameter (in) | 25.16 | 30.80 | +5.65 (+22.4%) |
| Section width (in) | 8.46 | 9.25 | +0.79 (+9.3%) |
| Sidewall height (in) | 5.08 | 7.40 | +2.32 (+45.7%) |
| Circumference (in) | 79.0 | 96.8 | +17.7 (+22.4%) |
| Revolutions per mile | 802 | 655 | -147 (-18.3%) |
Speedometer error
If your speedometer was calibrated for 215/60R15 and you install 235/80R16:
| Speedometer reads | 30 mph | 45 mph | 55 mph | 65 mph | 75 mph |
|---|---|---|---|---|---|
| Actual speed | 36.7 | 55.1 | 67.3 | 79.6 | 91.8 |
How to read the results
The industry rule of thumb is to stay within ±3% of your original overall diameter. Beyond that, your speedometer and odometer error becomes noticeable, gearing changes, and on trailers the tire can contact fenders or frame under load.
What each number affects
- Overall diameter — ground clearance, gearing, and whether the tire fits without rubbing.
- Speedometer error — a larger tire makes your speedometer read low (you're going faster than shown); a smaller tire reads high.
- Revolutions per mile — a smaller-diameter tire turns more times per mile and runs hotter at highway speed. This matters most on trailers, where heat is the number-one tire killer, but it also affects odometer accuracy and fuel-economy readings on any vehicle.
- Section width — wider tires may need a wider rim or extra fender clearance.
Need the tires once you've picked a size? Get a wholesale quote or find installation near you.