Tire Size Box

305/65R17 vs 305/70R17

305/70R17 compared with 305/65R17

+3.7% diameter, 0.0" width

305/70R17 is 33.81" tall vs 32.61". More than the 3% rule of thumb, so check carefully before switching.

32.6"17" rim7.8"12.0" wide
305/65R17 (solid) compared with 305/70R17 (dashed outline), drawn to scale

With 305/70R17 tires, when your speedometer says 60 mph you are really going

62.2 mph

305/70R17 is +1.20 inches (+3.7%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/65R17305/70R17Difference%
Overall diameter32.61"33.81"+1.20"+3.7%
Section width12.01"12.01"0.00"0.0%
Sidewall height7.81"8.41"+0.60"+7.7%
Circumference102.45"106.22"+3.77"+3.7%
Revolutions per mile618.5596.5−22.0−3.6%

Speedometer difference

If your vehicle came with 305/65R17 and you fit 305/70R17, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.1 mph+1.1 mph
40 mph41.5 mph+1.5 mph
50 mph51.8 mph+1.8 mph
60 mph62.2 mph+2.2 mph
65 mph67.4 mph+2.4 mph
70 mph72.6 mph+2.6 mph
75 mph77.8 mph+2.8 mph
80 mph82.9 mph+2.9 mph

Each size on its own

Questions

Which is bigger, 305/65R17 or 305/70R17?
305/70R17 is taller by 1.20 inches (33.81" vs 32.61"). 305/65R17 is the same width.
Can I replace 305/65R17 with 305/70R17?
It is not recommended without checking carefully. The diameter difference is +3.7%, 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 305/70R17 change my speedometer?
When your speedometer reads 60 mph with 305/70R17 fitted (calibrated for 305/65R17), your real speed is 62.2 mph. Your odometer will under-count miles by about 3.7%.
Will 305/70R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.60 inches of ground clearance at the axle.

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