Tire size comparison
285/75R18 vs 35x12.50R18
35x12.50R18 is +0.5% taller than 285/75R18: 35.0 in vs 34.8 in (+0.17 in), and 1.3 in wider. With 35x12.50R18 on a vehicle set up for 285/75R18, the speedometer shows 60 mph at an actual 60.3 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 (35x12.50R18 instead of 285/75R18) · 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
285/75R18 vs 35x12.50R18: full comparison
| 285/75R18 | 35x12.50R18 | Difference | |
|---|---|---|---|
| Overall diameter | 34.83 in | 35.00 in | +0.17 in (+0.5%) |
| Width | 11.22 in | 12.50 in | +1.28 in (+11.4%) |
| Sidewall height | 8.42 in | 8.50 in | +0.08 in |
| Circumference | 109.4 in | 110.0 in | +0.5 in |
| Revs per mile (nominal) | 579 | 576 | −3 |
| Wheel diameter | 18 in | 18 in | ±0 in |
| Diameter in mm | 885 | 889 | +4 mm |
Speedometer difference
Your speedometer is calibrated for 285/75R18. Fitted with 35x12.50R18, the actual speed is the reading × 35.00 ÷ 34.83.
| Speedometer shows | Actual speed | Difference |
|---|---|---|
| 20 mph | 20.1 mph | +0.1 mph |
| 30 mph | 30.1 mph | +0.1 mph |
| 45 mph | 45.2 mph | +0.2 mph |
| 55 mph | 55.3 mph | +0.3 mph |
| 60 mph | 60.3 mph | +0.3 mph |
| 70 mph | 70.3 mph | +0.3 mph |
| 80 mph | 80.4 mph | +0.4 mph |
Real tires: published diameters
285/75R18: 34.8–35.1 in published by 5 makers; 35x12.50R18: 34.5–35.1 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: 285/75R18 · 35x12.50R18
Related comparisons
FAQ
Which is bigger, 285/75R18 or 35x12.50R18?
35x12.50R18 is +0.5% taller than 285/75R18: 35.0 in vs 34.8 in (+0.17 in).
How much will my speedometer be off with 35x12.50R18 instead of 285/75R18?
The speedometer is calibrated for 285/75R18. With 35x12.50R18 it shows 60 mph when you are doing 60.3 mph, and 70 mph at 70.3 mph (+0.5%). Your speedometer also has its own factory tolerance.
Can I replace 285/75R18 with 35x12.50R18?
The diameter difference is +0.5%. 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.