Tire size comparison
285/65R18 vs 33x12.50R18
33x12.50R18 is +1.3% taller than 285/65R18: 33.0 in vs 32.6 in (+0.41 in), and 1.3 in wider. With 33x12.50R18 on a vehicle set up for 285/65R18, the speedometer shows 60 mph at an actual 60.8 mph. That is within the ±3% difference many shops use as a rule of thumb (not a manufacturer or legal limit).
Set up for: checking a replacement size (33x12.50R18 instead of 285/65R18) · 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
285/65R18 vs 33x12.50R18: full comparison
| 285/65R18 | 33x12.50R18 | Difference | |
|---|---|---|---|
| Overall diameter | 32.59 in | 33.00 in | +0.41 in (+1.3%) |
| Width | 11.22 in | 12.50 in | +1.28 in (+11.4%) |
| Sidewall height | 7.29 in | 7.50 in | +0.21 in |
| Circumference | 102.4 in | 103.7 in | +1.3 in |
| Revs per mile (nominal) | 619 | 611 | −8 |
| Wheel diameter | 18 in | 18 in | ±0 in |
| Diameter in mm | 828 | 838 | +10 mm |
Speedometer difference
Your speedometer is calibrated for 285/65R18. Fitted with 33x12.50R18, the actual speed is the reading × 33.00 ÷ 32.59.
| Speedometer shows | Actual speed | Difference |
|---|---|---|
| 20 mph | 20.3 mph | +0.3 mph |
| 30 mph | 30.4 mph | +0.4 mph |
| 45 mph | 45.6 mph | +0.6 mph |
| 55 mph | 55.7 mph | +0.7 mph |
| 60 mph | 60.8 mph | +0.8 mph |
| 70 mph | 70.9 mph | +0.9 mph |
| 80 mph | 81.0 mph | +1.0 mph |
Real tires: published diameters
285/65R18: 32.5–32.83 in published by 5 makers; 33x12.50R18: 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: 285/65R18 · 33x12.50R18
Related comparisons
FAQ
Which is bigger, 285/65R18 or 33x12.50R18?
33x12.50R18 is +1.3% taller than 285/65R18: 33.0 in vs 32.6 in (+0.41 in).
How much will my speedometer be off with 33x12.50R18 instead of 285/65R18?
The speedometer is calibrated for 285/65R18. With 33x12.50R18 it shows 60 mph when you are doing 60.8 mph, and 70 mph at 70.9 mph (+1.3%). Your speedometer also has its own factory tolerance.
Can I replace 285/65R18 with 33x12.50R18?
The diameter difference is +1.3%. 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.