Tire size comparison
245/45R17 vs 275/40R17
275/40R17 is −0.1% shorter than 245/45R17: 25.7 in vs 25.7 in (−0.02 in), and 1.2 in wider. With 275/40R17 on a vehicle set up for 245/45R17, the speedometer shows 60 mph at an actual 60.0 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 (275/40R17 instead of 245/45R17) · 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
245/45R17 vs 275/40R17: full comparison
| 245/45R17 | 275/40R17 | Difference | |
|---|---|---|---|
| Overall diameter | 25.68 in | 25.66 in | −0.02 in (−0.1%) |
| Width | 9.65 in | 10.83 in | +1.18 in (+12.2%) |
| Sidewall height | 4.34 in | 4.33 in | −0.01 in |
| Circumference | 80.7 in | 80.6 in | −0.1 in |
| Revs per mile (nominal) | 785 | 786 | +1 |
| Wheel diameter | 17 in | 17 in | ±0 in |
| Diameter in mm | 652 | 652 | ±0 mm |
Speedometer difference
Your speedometer is calibrated for 245/45R17. Fitted with 275/40R17, the actual speed is the reading × 25.66 ÷ 25.68.
| Speedometer shows | Actual speed | Difference |
|---|---|---|
| 20 mph | 20.0 mph | ±0.0 mph |
| 30 mph | 30.0 mph | ±0.0 mph |
| 45 mph | 45.0 mph | ±0.0 mph |
| 55 mph | 55.0 mph | ±0.0 mph |
| 60 mph | 60.0 mph | ±0.0 mph |
| 70 mph | 69.9 mph | −0.1 mph |
| 80 mph | 79.9 mph | −0.1 mph |
Real tires: published diameters
245/45R17: 25.5–26 in published by 7 makers; 275/40R17: 25.55–25.8 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: 245/45R17 · 275/40R17
Related comparisons
FAQ
Which is bigger, 245/45R17 or 275/40R17?
275/40R17 is −0.1% shorter than 245/45R17: 25.7 in vs 25.7 in (−0.02 in).
How much will my speedometer be off with 275/40R17 instead of 245/45R17?
The speedometer is calibrated for 245/45R17. With 275/40R17 it shows 60 mph when you are doing 60.0 mph, and 70 mph at 69.9 mph (−0.1%). Your speedometer also has its own factory tolerance.
Can I replace 245/45R17 with 275/40R17?
The diameter difference is −0.1%. 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.