Comparison
255/45 R19 vs 305/30 R20
305/30 R20 is a plus-1 alternative to 255/45 R19 — the bigger wheel shows through a thinner sidewall. This wheel and tire pairing trims or stretches rolling diameter by a small margin. Expect a slight but noticeable shift in indicated speed compared to the original tires. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement. Overall the swap sits inside the safe ±3% diameter window, so ABS, traction control and gearing behave normally.
TakeCommon upgrade for sportier handling and a tighter wheel-gap look on the same vehicle.
Quick math: 305/30 R20 is 21.1 mm shorter than 255/45 R19, shifting the speedometer by -2.96%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-21.1 mm
-2.96%
Speedometer at 100
97.0 km/h
-2.96% error
Ground clearance
-10.5 mm
ride height delta
Sidewall change
-23.3 mm
revs/km: 460.7
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/compare/255-45-r19-vs-305-30-r20Detailed comparison
| Metric | 255/45 R19 | 305/30 R20 | Difference |
|---|---|---|---|
| Overall diameter | 712.1 mm | 691.0 mm | -21.1 mm (-2.96%) |
| Sidewall height | 114.8 mm | 91.5 mm | -23.3 mm |
| Circumference | 2.237 m | 2.171 m | -66.3 mm |
| Revs / km | 447.0 | 460.7 | +13.6 |
| Ground clearance | reference | -10.5 mm | -10.5 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 97.0 km/h | -2.96 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 97.0 km/h after switching to 305/30 R20 — a -2.96% 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 -10.5 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
255/45 R19
Back to
305/30 R20
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