195/65R15 vs 255/40R17

255/40R17 is 0.05 in (1.3 mm) taller than 195/65R15, a +0.20% diameter difference. With the speedometer set for 195/65R15, an indicated 60 mph is 60.1 mph on 255/40R17.

Is this a safe swap?

Diameter difference +0.20%: under 1%

By overall diameter alone, 255/40R17 is a near match for 195/65R15; the speedometer changes by less than 1%. 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.

195/65R15 vs 255/40R17 differences
Measurement	195/65R15	255/40R17	Difference	% diff
Overall diameter	24.98 in (634.5 mm)	25.03 in (635.8 mm)	+0.05 in (+1.3 mm)	+0.20%
Sidewall height	4.99 in (126.8 mm)	4.02 in (102.0 mm)	−0.97 in (−24.7 mm)	−19.53%
Section width	7.68 in (195.0 mm)	10.04 in (255.0 mm)	+2.36 in (+60.0 mm)	+30.77%
Circumference	78.48 in (1,993.3 mm)	78.64 in (1,997.4 mm)	+0.16 in (+4.1 mm)	+0.20%
Revolutions per mile	807	806	−2	−0.20%

True speed with the speedometer calibrated for 195/65R15
Indicated	Actual on 195/65R15	Actual on 255/40R17	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.1 mph	+0.1 mph
75 mph	75.0 mph	75.2 mph	+0.2 mph

Ride-height change: 255/40R17 raises the vehicle by 0.03 in (0.6 mm) at the axle (half the +1.3 mm diameter difference).

255/40R17 is 0.05 in taller than 195/65R15 and 60 mm wider, a 0.20% difference in overall diameter.

With the speedometer calibrated for 195/65R15, an indicated 60 mph is actually 60.1 mph on 255/40R17, and revolutions per mile change from 807 to 806.

255/40R17 mounts on a 17-inch wheel, a plus-2 fitment from the 15-inch wheel of 195/65R15.

Size pages

Other comparisons with 195/65R15

Other comparisons with 255/40R17

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