Comparison
235/45 R18 vs 255/35 R20
Plus-sizing from 235/45 R18 to 255/35 R20 keeps overall diameter close to factory while opening room for a larger 20-inch wheel. This swap shifts overall diameter slightly from OEM. 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: 255/35 R20 is 17.8 mm taller than 235/45 R18, shifting the speedometer by +2.66%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+17.8 mm
2.66%
Speedometer at 100
102.7 km/h
+2.66% error
Ground clearance
+8.9 mm
ride height delta
Sidewall change
-16.5 mm
revs/km: 463.7
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/compare/235-45-r18-vs-255-35-r20Detailed comparison
| Metric | 235/45 R18 | 255/35 R20 | Difference |
|---|---|---|---|
| Overall diameter | 668.7 mm | 686.5 mm | +17.8 mm (+2.66%) |
| Sidewall height | 105.8 mm | 89.3 mm | -16.5 mm |
| Circumference | 2.101 m | 2.157 m | +55.9 mm |
| Revs / km | 476.0 | 463.7 | -12.3 |
| Ground clearance | reference | +8.9 mm | +8.9 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 102.7 km/h | +2.66 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 102.7 km/h after switching to 255/35 R20 — a +2.66% 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 +8.9 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.
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235/45 R18
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255/35 R20
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