Tire size comparison
275/55R20 vs 33x12.50R20
33x12.50R20 is +3.4% taller than 275/55R20: 33.0 in vs 31.9 in (+1.09 in), and 1.7 in wider. With 33x12.50R20 on a vehicle set up for 275/55R20, the speedometer shows 60 mph at an actual 62.1 mph. That is more than the ±3% difference many shops use as a rule of thumb, so check carefully before switching.
Set up for: going bigger (33x12.50R20 instead of 275/55R20) · Different situation?
Your current size
e.g. 265/70R17, 2657017 or 33x12.50R20
Where do I find my size?
It's on the tire sidewall, e.g. P265/70R17 115T, and on the tire placard sticker on the driver's door jamb (also in the owner's manual). The placard shows the size the vehicle came with; the sidewall shows what is fitted now. If they differ, use the placard as your starting point. Digits are enough here: 2657017 or 33125020.
Size you're considering
275/55R20 vs 33x12.50R20: full comparison
| 275/55R20 | 33x12.50R20 | Difference | |
|---|---|---|---|
| Overall diameter | 31.91 in | 33.00 in | +1.09 in (+3.4%) |
| Width | 10.83 in | 12.50 in | +1.67 in (+15.5%) |
| Sidewall height | 5.95 in | 6.50 in | +0.55 in |
| Circumference | 100.2 in | 103.7 in | +3.4 in |
| Revs per mile (nominal) | 632 | 611 | −21 |
| Wheel diameter | 20 in | 20 in | ±0 in |
| Diameter in mm | 810 | 838 | +28 mm |
Speedometer difference
Your speedometer is calibrated for 275/55R20. Fitted with 33x12.50R20, the actual speed is the reading × 33.00 ÷ 31.91.
| Speedometer shows | Actual speed | Difference |
|---|---|---|
| 20 mph | 20.7 mph | +0.7 mph |
| 30 mph | 31.0 mph | +1.0 mph |
| 45 mph | 46.5 mph | +1.5 mph |
| 55 mph | 56.9 mph | +1.9 mph |
| 60 mph | 62.1 mph | +2.1 mph |
| 70 mph | 72.4 mph | +2.4 mph |
| 80 mph | 82.7 mph | +2.7 mph |
Real tires: published diameters
275/55R20: 31.8–32.13 in published by 7 makers; 33x12.50R20: 32.5–33 in published by 5 makers. Calculated figures assume a nominal tire; the exact difference between two specific tires depends on their models.
More about each size: 275/55R20 · 33x12.50R20
Related comparisons
FAQ
Which is bigger, 275/55R20 or 33x12.50R20?
33x12.50R20 is +3.4% taller than 275/55R20: 33.0 in vs 31.9 in (+1.09 in).
How much will my speedometer be off with 33x12.50R20 instead of 275/55R20?
The speedometer is calibrated for 275/55R20. With 33x12.50R20 it shows 60 mph when you are doing 62.1 mph, and 70 mph at 72.4 mph (+3.4%). Your speedometer also has its own factory tolerance.
Can I replace 275/55R20 with 33x12.50R20?
The diameter difference is +3.4%. Whether it fits depends on things this calculation can't see: wheel width and offset, clearance at full lock and over bumps, load index and speed rating, and your vehicle maker's approval. Check your door-jamb placard and owner's manual and ask a tire professional.