275/35R20 vs 305/30R20

275/35R20 is 0.4" taller than 305/30R20 (1.4%)

Diameter difference−1.36%diameter 27.58" → 27.20"
275/35R20305/30R20
275/35R20305/30R20Difference
Overall diameter27.58"27.20"−0.37"
Section width10.83"12.01"+1.18"
Sidewall height3.79"3.60"−0.19"
Circumference86.6"85.5"−1.2"
Revolutions per mile731741+10
Wheel diameter20"20"±0"

Speedometer

ShowsActualDiff
30 mph29.6 mph−0.4
45 mph44.4 mph−0.6
60 mph59.2 mph−0.8
70 mph69.1 mph−0.9
80 mph78.9 mph−1.1

Gear ratio to match

CurrentEquivalent
3.423.37
3.553.50
3.733.68
4.104.04

305/30R20 is 0.37" shorter than 275/35R20, a −1.36% change in diameter, inside the 3% range most shops treat as a safe swap.

Ground clearance changes by 0.19" (half the diameter change), and the tire needs 0.19" less room above it.

305/30R20 is 1.18" wider. On the same wheel offset about half of that, 0.59", moves toward the suspension and half toward the fender.

Both fit a 20" wheel; the sidewall is 0.19" shorter on 305/30R20.

Details: 275/35R20 in inches · 305/30R20 in inches · change sizes in the calculator

FAQ

What is the difference between 275/35R20 and 305/30R20?

305/30R20 is 0.37" shorter (−1.36%) and 1.18" wider than 275/35R20.

Will 305/30R20 change my speedometer?

Yes, by −1.36%. When the speedometer shows 60 mph you would be going 59.2 mph.

Can I replace 275/35R20 with 305/30R20?

Often yes: the diameter change of −1.4% is within the common 3% guideline. Check the load index, speed rating and clearance.