Tire Size Box

305/35R17 vs 305/45R17

305/45R17 compared with 305/35R17

+9.5% diameter, 0.0" width

305/45R17 is 27.81" tall vs 25.41". More than the 3% rule of thumb, so check carefully before switching.

25.4"17" rim4.2"12.0" wide
305/35R17 (solid) compared with 305/45R17 (dashed outline), drawn to scale

With 305/45R17 tires, when your speedometer says 60 mph you are really going

65.7 mph

305/45R17 is +2.40 inches (+9.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/35R17305/45R17Difference%
Overall diameter25.41"27.81"+2.40"+9.5%
Section width12.01"12.01"0.00"0.0%
Sidewall height4.20"5.40"+1.20"+28.6%
Circumference79.81"87.36"+7.54"+9.5%
Revolutions per mile793.8725.3−68.6−8.6%

Speedometer difference

If your vehicle came with 305/35R17 and you fit 305/45R17, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.9 mph+1.9 mph
30 mph32.8 mph+2.8 mph
40 mph43.8 mph+3.8 mph
50 mph54.7 mph+4.7 mph
60 mph65.7 mph+5.7 mph
65 mph71.1 mph+6.1 mph
70 mph76.6 mph+6.6 mph
75 mph82.1 mph+7.1 mph
80 mph87.6 mph+7.6 mph

Each size on its own

Questions

Which is bigger, 305/35R17 or 305/45R17?
305/45R17 is taller by 2.40 inches (27.81" vs 25.41"). 305/35R17 is the same width.
Can I replace 305/35R17 with 305/45R17?
It is not recommended without checking carefully. The diameter difference is +9.5%, more than the 3% most shops and makers allow. It will throw off the speedometer and may affect ABS, stability control and clearance.
How much will 305/45R17 change my speedometer?
When your speedometer reads 60 mph with 305/45R17 fitted (calibrated for 305/35R17), your real speed is 65.7 mph. Your odometer will under-count miles by about 9.5%.
Will 305/45R17 lift my vehicle?
Ride height changes by half the diameter difference: +1.20 inches of ground clearance at the axle.

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