Speedometer difference
With a speedometer calibrated for the 245/75R17, this is your real speed on 265/70R17 tires.
| Speedometer shows | Actual speed with 265/70R17 | Difference |
|---|---|---|
| 20 mph | 20.1 mph | +0.1 mph |
| 30 mph | 30.1 mph | +0.1 mph |
| 40 mph | 40.2 mph | +0.2 mph |
| 50 mph | 50.2 mph | +0.2 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 |
Fitment considerations
- Width: the 265/70R17 is 0.79 in wider in section width, so each sidewall sits roughly 0.39 in further out on the same wheel. Check clearance at full steering lock against the upper control arm, frame and fender liner, and confirm your wheel width is inside the tire maker’s approved rim-width range for the 265/70R17.
- Speedometer: a 0.4% change is small, but it adds up on the odometer: 1,000 miles shown would be about 1,004 real miles.
- Load rating: match or exceed the load index (and LT load range, if applicable) on your door placard. P-metric and LT tires of the same size are rated differently.
These checks are general; whether a size fits a particular vehicle depends on its suspension, wheels and body. Your door placard lists the approved original sizes, and a tire professional can confirm fitment.
How these numbers are calculated
Diameter = 2 × section width × aspect ratio ÷ 100 ÷ 25.4 + rim diameter (for inch sizes, the first number is the diameter). Revolutions per mile = 63,360 ÷ (π × diameter). Actual speed = indicated speed × 31.61 ÷ 31.47. Real tires vary by brand and model, so treat these as close estimates and use manufacturer specs for exact measurements.
Frequently asked questions
How much bigger is 265/70R17 than 245/75R17?
265/70R17 is 0.14 inches (0.4%) taller in overall diameter (31.47 in vs 31.61 in) and +0.79 inches in section width.
Will my speedometer be off with 265/70R17 instead of 245/75R17?
Yes, by about 0.4%. If the speedometer is set up for 245/75R17, it will show 60 mph when you are really going about 60.3 mph.
Is 265/70R17 within 3% of 245/75R17?
Yes. The diameter difference is +0.4%.