235/40R17 vs 235/45R17

235/45R17 is 0.93 in (23.5 mm) taller than 235/40R17, a +3.79% diameter difference. With the speedometer set for 235/40R17, an indicated 60 mph is 62.3 mph on 235/45R17.

Is this a safe swap?

Diameter difference +3.79%: outside the ±3% guideline

By overall diameter alone, 235/45R17 falls outside the ±3% range commonly used as a guideline when replacing 235/40R17; speedometer and ride-height changes are larger. 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.

235/40R17 vs 235/45R17 differences
Measurement	235/40R17	235/45R17	Difference	% diff
Overall diameter	24.40 in (619.8 mm)	25.33 in (643.3 mm)	+0.93 in (+23.5 mm)	+3.79%
Sidewall height	3.70 in (94.0 mm)	4.16 in (105.8 mm)	+0.46 in (+11.8 mm)	+12.50%
Section width	9.25 in (235.0 mm)	9.25 in (235.0 mm)	0.00 in (0.0 mm)	0.00%
Circumference	76.66 in (1,947.2 mm)	79.57 in (2,021.0 mm)	+2.91 in (+73.8 mm)	+3.79%
Revolutions per mile	827	796	−30	−3.65%

True speed with the speedometer calibrated for 235/40R17
Indicated	Actual on 235/40R17	Actual on 235/45R17	Difference
30 mph	30.0 mph	31.1 mph	+1.1 mph
60 mph	60.0 mph	62.3 mph	+2.3 mph
75 mph	75.0 mph	77.8 mph	+2.8 mph

Ride-height change: 235/45R17 raises the vehicle by 0.46 in (11.8 mm) at the axle (half the +23.5 mm diameter difference).

235/45R17 is 0.93 in taller than 235/40R17 and the same width, a 3.79% difference in overall diameter.

With the speedometer calibrated for 235/40R17, an indicated 60 mph is actually 62.3 mph on 235/45R17, and revolutions per mile change from 827 to 796.

Both sizes mount on 17-inch wheels.

Size pages

Other comparisons with 235/40R17

Other comparisons with 235/45R17

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