Tire size comparison
285/70R18 vs 35x12.50R18
35x12.50R18 is +3.8% taller than 285/70R18: 35.0 in vs 33.7 in (+1.29 in), and 1.3 in wider. With 35x12.50R18 on a vehicle set up for 285/70R18, the speedometer shows 60 mph at an actual 62.3 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 (35x12.50R18 instead of 285/70R18) · 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
285/70R18 vs 35x12.50R18: full comparison
| 285/70R18 | 35x12.50R18 | Difference | |
|---|---|---|---|
| Overall diameter | 33.71 in | 35.00 in | +1.29 in (+3.8%) |
| Width | 11.22 in | 12.50 in | +1.28 in (+11.4%) |
| Sidewall height | 7.85 in | 8.50 in | +0.65 in |
| Circumference | 105.9 in | 110.0 in | +4.1 in |
| Revs per mile (nominal) | 598 | 576 | −22 |
| Wheel diameter | 18 in | 18 in | ±0 in |
| Diameter in mm | 856 | 889 | +33 mm |
Speedometer difference
Your speedometer is calibrated for 285/70R18. Fitted with 35x12.50R18, the actual speed is the reading × 35.00 ÷ 33.71.
| Speedometer shows | Actual speed | Difference |
|---|---|---|
| 20 mph | 20.8 mph | +0.8 mph |
| 30 mph | 31.1 mph | +1.1 mph |
| 45 mph | 46.7 mph | +1.7 mph |
| 55 mph | 57.1 mph | +2.1 mph |
| 60 mph | 62.3 mph | +2.3 mph |
| 70 mph | 72.7 mph | +2.7 mph |
| 80 mph | 83.1 mph | +3.1 mph |
Real tires: published diameters
285/70R18: 33.74–34 in published by 2 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: 285/70R18 · 35x12.50R18
Related comparisons
FAQ
Which is bigger, 285/70R18 or 35x12.50R18?
35x12.50R18 is +3.8% taller than 285/70R18: 35.0 in vs 33.7 in (+1.29 in).
How much will my speedometer be off with 35x12.50R18 instead of 285/70R18?
The speedometer is calibrated for 285/70R18. With 35x12.50R18 it shows 60 mph when you are doing 62.3 mph, and 70 mph at 72.7 mph (+3.8%). Your speedometer also has its own factory tolerance.
Can I replace 285/70R18 with 35x12.50R18?
The diameter difference is +3.8%. 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.