285/75R18 vs 305/70R18

285/75R18 is 0.0" taller than 305/70R18 (0.1%)

Diameter difference−0.06%diameter 34.83" → 34.81"
285/75R18305/70R18
285/75R18305/70R18Difference
Overall diameter34.83"34.81"−0.02"
Section width11.22"12.01"+0.79"
Sidewall height8.42"8.41"−0.01"
Circumference109.4"109.4"−0.1"
Revolutions per mile579579+0
Wheel diameter18"18"±0"

Speedometer

ShowsActualDiff
30 mph30.0 mph−0.0
45 mph45.0 mph−0.0
60 mph60.0 mph−0.0
70 mph70.0 mph−0.0
80 mph80.0 mph−0.0

Gear ratio to match

CurrentEquivalent
3.423.42
3.553.55
3.733.73
4.104.10

305/70R18 is 0.02" shorter than 285/75R18, a −0.06% change in diameter, inside the 3% range most shops treat as a safe swap.

Ground clearance changes by 0.01" (half the diameter change), and the tire needs 0.01" less room above it.

305/70R18 is 0.79" wider. On the same wheel offset about half of that, 0.39", moves toward the suspension and half toward the fender.

Both fit a 18" wheel; the sidewall is 0.01" shorter on 305/70R18.

Details: 285/75R18 in inches · 305/70R18 in inches · change sizes in the calculator

FAQ

What is the difference between 285/75R18 and 305/70R18?

305/70R18 is 0.02" shorter (−0.06%) and 0.79" wider than 285/75R18.

Will 305/70R18 change my speedometer?

Yes, by −0.06%. When the speedometer shows 60 mph you would be going 60.0 mph.

Can I replace 285/75R18 with 305/70R18?

Often yes: the diameter change of −0.1% is within the common 3% guideline. Check the load index, speed rating and clearance.