Comparison
255/45 R18 vs 275/35 R20
Plus-sizing from 255/45 R18 to 275/35 R20 keeps overall diameter close to factory while opening room for a larger 20-inch wheel. This sizing approach trims or stretches rolling diameter by a small margin. The speedometer offset is small but measurable; worth keeping in mind if you watch the dash closely. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeA solid pick for drivers chasing a more aggressive stance without abandoning OEM rolling diameter.
Quick math: 275/35 R20 is 13.8 mm taller than 255/45 R18, shifting the speedometer by +2.01%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+13.8 mm
2.01%
Speedometer at 100
102.0 km/h
+2.01% error
Ground clearance
+6.9 mm
ride height delta
Sidewall change
-18.5 mm
revs/km: 454.4
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/compare/255-45-r18-vs-275-35-r20Detailed comparison
| Metric | 255/45 R18 | 275/35 R20 | Difference |
|---|---|---|---|
| Overall diameter | 686.7 mm | 700.5 mm | +13.8 mm (+2.01%) |
| Sidewall height | 114.8 mm | 96.3 mm | -18.5 mm |
| Circumference | 2.157 m | 2.201 m | +43.4 mm |
| Revs / km | 463.5 | 454.4 | -9.1 |
| Ground clearance | reference | +6.9 mm | +6.9 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 102.0 km/h | +2.01 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 102.0 km/h after switching to 275/35 R20 — a +2.01% 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 +6.9 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 R18
Back to
275/35 R20
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