Tire Size Box

305/55R17 vs 305/65R17

305/65R17 compared with 305/55R17

+7.9% diameter, 0.0" width

305/65R17 is 32.61" tall vs 30.21". More than the 3% rule of thumb, so check carefully before switching.

30.2"17" rim6.6"12.0" wide
305/55R17 (solid) compared with 305/65R17 (dashed outline), drawn to scale

With 305/65R17 tires, when your speedometer says 60 mph you are really going

64.8 mph

305/65R17 is +2.40 inches (+7.9%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/55R17305/65R17Difference%
Overall diameter30.21"32.61"+2.40"+7.9%
Section width12.01"12.01"0.00"0.0%
Sidewall height6.60"7.81"+1.20"+18.2%
Circumference94.90"102.45"+7.54"+7.9%
Revolutions per mile667.6618.5−49.2−7.4%

Speedometer difference

If your vehicle came with 305/55R17 and you fit 305/65R17, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.6 mph+1.6 mph
30 mph32.4 mph+2.4 mph
40 mph43.2 mph+3.2 mph
50 mph54.0 mph+4.0 mph
60 mph64.8 mph+4.8 mph
65 mph70.2 mph+5.2 mph
70 mph75.6 mph+5.6 mph
75 mph81.0 mph+6.0 mph
80 mph86.4 mph+6.4 mph

Each size on its own

Questions

Which is bigger, 305/55R17 or 305/65R17?
305/65R17 is taller by 2.40 inches (32.61" vs 30.21"). 305/55R17 is the same width.
Can I replace 305/55R17 with 305/65R17?
It is not recommended without checking carefully. The diameter difference is +7.9%, 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 305/65R17 change my speedometer?
When your speedometer reads 60 mph with 305/65R17 fitted (calibrated for 305/55R17), your real speed is 64.8 mph. Your odometer will under-count miles by about 7.9%.
Will 305/65R17 lift my vehicle?
Ride height changes by half the diameter difference: +1.20 inches of ground clearance at the axle.

Other comparisons