Tire size comparison
245/40R20 vs 275/35R20
275/35R20 is −0.5% shorter than 245/40R20: 27.6 in vs 27.7 in (−0.14 in), and 1.2 in wider. With 275/35R20 on a vehicle set up for 245/40R20, the speedometer shows 60 mph at an actual 59.7 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 (275/35R20 instead of 245/40R20) · 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
245/40R20 vs 275/35R20: full comparison
| 245/40R20 | 275/35R20 | Difference | |
|---|---|---|---|
| Overall diameter | 27.72 in | 27.58 in | −0.14 in (−0.5%) |
| Width | 9.65 in | 10.83 in | +1.18 in (+12.2%) |
| Sidewall height | 3.86 in | 3.79 in | −0.07 in |
| Circumference | 87.1 in | 86.6 in | −0.4 in |
| Revs per mile (nominal) | 728 | 731 | +4 |
| Wheel diameter | 20 in | 20 in | ±0 in |
| Diameter in mm | 704 | 700 | −4 mm |
Speedometer difference
Your speedometer is calibrated for 245/40R20. Fitted with 275/35R20, the actual speed is the reading × 27.58 ÷ 27.72.
| Speedometer shows | Actual speed | Difference |
|---|---|---|
| 20 mph | 19.9 mph | −0.1 mph |
| 30 mph | 29.9 mph | −0.1 mph |
| 45 mph | 44.8 mph | −0.2 mph |
| 55 mph | 54.7 mph | −0.3 mph |
| 60 mph | 59.7 mph | −0.3 mph |
| 70 mph | 69.7 mph | −0.3 mph |
| 80 mph | 79.6 mph | −0.4 mph |
Real tires: published diameters
245/40R20: 27.4–28.03 in published by 7 makers; 275/35R20: 27.3–27.87 in published by 7 makers. Calculated figures assume a nominal tire; the exact difference between two specific tires depends on their models.
More about each size: 245/40R20 · 275/35R20
FAQ
Which is bigger, 245/40R20 or 275/35R20?
275/35R20 is −0.5% shorter than 245/40R20: 27.6 in vs 27.7 in (−0.14 in).
How much will my speedometer be off with 275/35R20 instead of 245/40R20?
The speedometer is calibrated for 245/40R20. With 275/35R20 it shows 60 mph when you are doing 59.7 mph, and 70 mph at 69.7 mph (−0.5%). Your speedometer also has its own factory tolerance.
Can I replace 245/40R20 with 275/35R20?
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.