Tire Size Box

195/40R17 vs 195/45R17

195/45R17 compared with 195/40R17

+3.3% diameter, 0.0" width

195/45R17 is 23.91" tall vs 23.14". More than the 3% rule of thumb, so check carefully before switching.

23.1"17" rim3.1"7.7" wide
195/40R17 (solid) compared with 195/45R17 (dashed outline), drawn to scale

With 195/45R17 tires, when your speedometer says 60 mph you are really going

62.0 mph

195/45R17 is +0.77 inches (+3.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

195/40R17195/45R17Difference%
Overall diameter23.14"23.91"+0.77"+3.3%
Section width7.68"7.68"0.00"0.0%
Sidewall height3.07"3.45"+0.38"+12.5%
Circumference72.70"75.11"+2.41"+3.3%
Revolutions per mile871.5843.5−28.0−3.2%

Speedometer difference

If your vehicle came with 195/40R17 and you fit 195/45R17, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.0 mph+1.0 mph
40 mph41.3 mph+1.3 mph
50 mph51.7 mph+1.7 mph
60 mph62.0 mph+2.0 mph
65 mph67.2 mph+2.2 mph
70 mph72.3 mph+2.3 mph
75 mph77.5 mph+2.5 mph
80 mph82.7 mph+2.7 mph

Each size on its own

Questions

Which is bigger, 195/40R17 or 195/45R17?
195/45R17 is taller by 0.77 inches (23.91" vs 23.14"). 195/40R17 is the same width.
Can I replace 195/40R17 with 195/45R17?
It is not recommended without checking carefully. The diameter difference is +3.3%, 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 195/45R17 change my speedometer?
When your speedometer reads 60 mph with 195/45R17 fitted (calibrated for 195/40R17), your real speed is 62.0 mph. Your odometer will under-count miles by about 3.3%.
Will 195/45R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.38 inches of ground clearance at the axle.

Other comparisons