305/50R20 vs 33x12.50R20
33x12.50R20 is outside the ±3% rule as a replacement for 305/50R20: the diameter differs by +3.10%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Side by side
| 305/50R20 | 33x12.50R20 | Difference | |
|---|---|---|---|
| Overall diameter | 32.01" | 33.00" | +0.99" (+3.10%) |
| Section width | 305 mm | 318 mm | +13 mm |
| Sidewall | 6.00" | 6.50" | +0.50" |
| Rim | 20" | 20" | same |
| Circumference | 100.6" | 103.7" | +3.1" |
| Revs per mile | 630 | 611 | -19 |
| Ride height | — | — | +0.50" |
| Speedometer reads 60 mph | 60.0 | 61.9 | +1.9 mph |
Speedometer and odometer
With 33x12.50R20 on a car calibrated for 305/50R20, the speedometer reads 58.2 mph when you're really doing 60, and the odometer under-counts by 3.1%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.9 mph |
| 45 mph | 46.4 mph |
| 60 mph | 61.9 mph |
| 70 mph | 72.2 mph |
| 80 mph | 82.5 mph |
Other sizes close to 305/50R20
- 305/50R20 vs 275/55R20-0.31%
- 305/50R20 vs 275/60R20+3.08%
- 305/50R20 vs 265/50R20-4.92%
- 305/50R20 vs 255/55R20-3.01%
- 305/50R20 vs 265/60R20+1.60%
- 305/50R20 vs 305/55R20+3.75%
- 305/50R20 vs 285/55R20+1.05%
- 305/50R20 vs 285/60R20+4.55%
- 305/50R20 vs 275/50R20-3.69%
- 305/50R20 vs 295/55R20+2.40%
- 305/50R20 vs 285/50R20-2.46%
- 305/50R20 vs 245/60R20-1.35%
Questions
Can I replace 305/50R20 with 33x12.50R20?
33x12.50R20 is outside the ±3% rule as a replacement for 305/50R20: the diameter differs by +3.10%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 305/50R20 and 33x12.50R20?
33x12.50R20 is 0.99" taller and 13 mm wider; the sidewall is +0.50". At an indicated 60 mph you'd actually be doing 61.9 mph.
Will 33x12.50R20 fit on 305/50R20 wheels?
Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 318 mm tire and the fender clearance.