255/65R17 vs 245/70R17

245/70R17 is 0.45 in (11.5 mm) taller than 255/65R17, a +1.51% diameter difference. With the speedometer set for 255/65R17, an indicated 60 mph is 60.9 mph on 245/70R17.

Is this a safe swap?

Diameter difference +1.51%: within the ±3% guideline

By overall diameter alone, 245/70R17 falls inside the ±3% range commonly used as a guideline when replacing 255/65R17. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

Side profile and tread width, drawn to the same scale.

255/65R17 vs 245/70R17 differences
Measurement	255/65R17	245/70R17	Difference	% diff
Overall diameter	30.05 in (763.3 mm)	30.50 in (774.8 mm)	+0.45 in (+11.5 mm)	+1.51%
Sidewall height	6.53 in (165.8 mm)	6.75 in (171.5 mm)	+0.23 in (+5.8 mm)	+3.47%
Section width	10.04 in (255.0 mm)	9.65 in (245.0 mm)	−0.39 in (−10.0 mm)	−3.92%
Circumference	94.41 in (2,398.0 mm)	95.83 in (2,434.1 mm)	+1.42 in (+36.1 mm)	+1.51%
Revolutions per mile	671	661	−10	−1.48%

True speed with the speedometer calibrated for 255/65R17
Indicated	Actual on 255/65R17	Actual on 245/70R17	Difference
30 mph	30.0 mph	30.5 mph	+0.5 mph
60 mph	60.0 mph	60.9 mph	+0.9 mph
75 mph	75.0 mph	76.1 mph	+1.1 mph

Ride-height change: 245/70R17 raises the vehicle by 0.23 in (5.8 mm) at the axle (half the +11.5 mm diameter difference).

245/70R17 is 0.45 in taller than 255/65R17 and 10 mm narrower, a 1.51% difference in overall diameter.

With the speedometer calibrated for 255/65R17, an indicated 60 mph is actually 60.9 mph on 245/70R17, and revolutions per mile change from 671 to 661.

Both sizes mount on 17-inch wheels.

Size pages

Other comparisons with 255/65R17

Other comparisons with 245/70R17

Source: Calculated from standard tire geometry formulas. Verified 2026-09-27. How these numbers are calculated.