30x9.50R15 vs 235/75R15

30x9.50R15 is 1.1" taller than 235/75R15 (3.7%)

Diameter difference−3.74%diameter 30.00" → 28.88"
30x9.50R15235/75R15
30x9.50R15235/75R15Difference
Overall diameter30.00"28.88"−1.12"
Section width9.50"9.25"−0.25"
Sidewall height7.50"6.94"−0.56"
Circumference94.2"90.7"−3.5"
Revolutions per mile672698+26
Wheel diameter15"15"±0"

Speedometer

ShowsActualDiff
30 mph28.9 mph−1.1
45 mph43.3 mph−1.7
60 mph57.8 mph−2.2
70 mph67.4 mph−2.6
80 mph77.0 mph−3.0

Gear ratio to match

CurrentEquivalent
3.423.29
3.553.42
3.733.59
4.103.95

235/75R15 is 1.12" shorter than 30x9.50R15, a −3.74% change in diameter. That is more than the 3% many tire shops use as a limit, so plan on recalibrating the speedometer and checking ABS and stability control.

Ground clearance changes by 0.56" (half the diameter change), and the tire needs 0.56" less room above it.

30x9.50R15 is 0.25" wider. On the same wheel offset about half of that, 0.12", moves toward the suspension and half toward the fender.

Both fit a 15" wheel; the sidewall is 0.56" shorter on 235/75R15.

Details: 30x9.50R15 in inches · 235/75R15 in inches · change sizes in the calculator

FAQ

What is the difference between 30x9.50R15 and 235/75R15?

235/75R15 is 1.12" shorter (−3.74%) and 0.25" narrower than 30x9.50R15.

Will 235/75R15 change my speedometer?

Yes, by −3.74%. When the speedometer shows 60 mph you would be going 57.8 mph.

Can I replace 30x9.50R15 with 235/75R15?

It is a −3.7% diameter change, larger than the common 3% guideline, so check clearance and plan to recalibrate.