Comparison
255/35 R20 vs 305/30 R20
305/30 R20 is a wider variation of 255/35 R20 on the same 20-inch rim, adding 50 mm of tread footprint. This tire combination lands within OEM rolling-diameter tolerance. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement.
Dashboard speed shifts only marginally — within the noise of normal OEM tolerance. Overall the swap sits inside the safe ±3% diameter window, so ABS, traction control and gearing behave normally.
TakeReasonable performance-leaning swap as long as fender and suspension clearance check out.
Quick math: 305/30 R20 is 4.5 mm taller than 255/35 R20, shifting the speedometer by +0.66%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+4.5 mm
0.66%
Speedometer at 100
100.7 km/h
+0.66% error
Ground clearance
+2.3 mm
ride height delta
Sidewall change
+2.3 mm
revs/km: 460.7
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/compare/255-35-r20-vs-305-30-r20Detailed comparison
| Metric | 255/35 R20 | 305/30 R20 | Difference |
|---|---|---|---|
| Overall diameter | 686.5 mm | 691.0 mm | +4.5 mm (+0.66%) |
| Sidewall height | 89.3 mm | 91.5 mm | +2.3 mm |
| Circumference | 2.157 m | 2.171 m | +14.1 mm |
| Revs / km | 463.7 | 460.7 | -3.0 |
| Ground clearance | reference | +2.3 mm | +2.3 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 100.7 km/h | +0.66 km/h |
Verdict: excellent
Within ±3% — speedometer, ABS and traction control should behave normally.
Speedometer impact
At a true 100 km/h, your dashboard will read 100.7 km/h after switching to 305/30 R20 — a +0.66% offset. Use the speedometer error calculator to recheck for other indicated speeds, and the speedometer error guide for the full background.
Ground clearance change
The new tire's half-diameter changes ride height by +2.3 mm. Small differences are absorbed by suspension travel, but anything beyond ±10 mm can affect headlight aim, fender clearance and bump-stop margin. See the plus-sizing guide before committing.
Back to
255/35 R20
Back to
305/30 R20
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