305/70R18 vs 35x12.50R18

35x12.50R18 is 0.2" taller than 305/70R18 (0.5%)

Diameter difference+0.54%diameter 34.81" → 35.00"
305/70R1835x12.50R18
305/70R1835x12.50R18Difference
Overall diameter34.81"35.00"+0.19"
Section width12.01"12.50"+0.49"
Sidewall height8.41"8.50"+0.09"
Circumference109.4"110.0"+0.6"
Revolutions per mile579576−3
Wheel diameter18"18"±0"

Speedometer

ShowsActualDiff
30 mph30.2 mph+0.2
45 mph45.2 mph+0.2
60 mph60.3 mph+0.3
70 mph70.4 mph+0.4
80 mph80.4 mph+0.4

Gear ratio to match

CurrentEquivalent
3.423.44
3.553.57
3.733.75
4.104.12

35x12.50R18 is 0.19" taller than 305/70R18, a +0.54% change in diameter, inside the 3% range most shops treat as a safe swap.

Ground clearance changes by 0.09" (half the diameter change), and the tire needs 0.09" more room above it.

35x12.50R18 is 0.49" wider. On the same wheel offset about half of that, 0.25", moves toward the suspension and half toward the fender.

Both fit a 18" wheel; the sidewall is 0.09" taller on 35x12.50R18.

Details: 305/70R18 in inches · 35x12.50R18 in inches · change sizes in the calculator

FAQ

What is the difference between 305/70R18 and 35x12.50R18?

35x12.50R18 is 0.19" taller (+0.54%) and 0.49" wider than 305/70R18.

Will 35x12.50R18 change my speedometer?

Yes, by +0.54%. When the speedometer shows 60 mph you would be going 60.3 mph.

Can I replace 305/70R18 with 35x12.50R18?

Often yes: the diameter change of +0.5% is within the common 3% guideline. Check the load index, speed rating and clearance.