33x12.50R20 vs 285/55R20: full comparison
| Measurement | 33x12.50R20 | 285/55R20 | Difference |
|---|---|---|---|
| Diameter | 33.00 in | 32.34 in | −0.66 in−2.0% |
| Section width | 12.50 in | 11.22 in | −1.28 in−10.2% |
| Sidewall height | 6.50 in | 6.17 in | −0.33 in−5.1% |
| Circumference | 103.67 in | 101.61 in | −2.07 in−2.0% |
| Revs per mile | 611 | 624 | +12+2.0% |
Speedometer: indicated vs actual speed
With 285/55R20 fitted where 33x12.50R20 was the stock/calibrated size:
| Speedometer shows | Actual speed | Difference |
|---|---|---|
| 20 mph | 19.6 mph | −0.4 mph |
| 30 mph | 29.4 mph | −0.6 mph |
| 40 mph | 39.2 mph | −0.8 mph |
| 50 mph | 49.0 mph | −1.0 mph |
| 55 mph | 53.9 mph | −1.1 mph |
| 60 mph | 58.8 mph | −1.2 mph |
| 65 mph | 63.7 mph | −1.3 mph |
| 70 mph | 68.6 mph | −1.4 mph |
| 75 mph | 73.5 mph | −1.5 mph |
| 80 mph | 78.4 mph | −1.6 mph |
Recalculate for a gear ratio change too →
Will 285/55R20 fit where 33x12.50R20 was?
At −2.0%, 285/55R20 is within the ±3% most tire shops and manufacturers accept without recalibrating the speedometer or expecting rubbing -- it should generally bolt on, though wheel width, offset, and suspension travel still matter.
Related tire size comparisons
- 275/60R20 vs 285/55R20
- 275/55R20 vs 285/55R20
- 275/55R20 vs 33x12.50R20
- 275/60R20 vs 33x12.50R20
- 295/65R20 vs 33x12.50R20
More tire tools
- Tire size comparison tool: compare any two sizes yourself, including flotation sizes.
- Tire size calculator: full dimensions of one size, plus every equivalent size within 3%.
- Speedometer calculator: true speed after a tire or gear ratio change.
Frequently asked questions
How much bigger is 285/55R20 than 33x12.50R20?
285/55R20 is 0.66 in shorter in overall diameter (−2.0%) and 1.28 in narrower in section width (−10.2%) than 33x12.50R20.
Will 285/55R20 fit in place of 33x12.50R20?
At −2.0%, 285/55R20 is within the ±3% most tire shops and manufacturers accept without recalibrating the speedometer or expecting rubbing -- it should generally bolt on, though wheel width, offset, and suspension travel still matter.
Does swapping to 285/55R20 affect my speedometer?
With 285/55R20 fitted where 33x12.50R20 was calibrated, an indicated 60 mph is really about 58.8 mph. That small a difference is within the ±3% most shops treat as close enough not to recalibrate.
Does 285/55R20 change the ride height?
Yes -- half the diameter difference shows up at the axle, so 285/55R20 changes ride height by about 0.33 in lower compared with 33x12.50R20.
Can I compare a metric size (like 285/55R20) with a flotation size (like 33x12.50R20)?
Yes -- both are converted to inches and millimeters before comparing, so the diameter, width and speedometer numbers above are directly comparable regardless of which sizing system each tire uses.