Comparison
225/45 R18 vs 255/35 R20
Going from 225/45 R18 to 255/35 R20 steps up to a 20-inch rim while trimming sidewall to stay near OEM rolling diameter. This alternative fitment noticeably changes overall diameter compared to OEM. Indicated speed will drift far enough that recalibration is worth considering. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement. The 3–5% diameter gap puts this in caution territory: doable on many cars, but verify clearance and consider recalibration.
TakeA solid pick for drivers chasing a more aggressive stance without abandoning OEM rolling diameter.
Quick math: 255/35 R20 is 26.8 mm taller than 225/45 R18, shifting the speedometer by +4.06%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+26.8 mm
4.06%
Speedometer at 100
104.1 km/h
+4.06% error
Ground clearance
+13.4 mm
ride height delta
Sidewall change
-12.0 mm
revs/km: 463.7
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/compare/225-45-r18-vs-255-35-r20Detailed comparison
| Metric | 225/45 R18 | 255/35 R20 | Difference |
|---|---|---|---|
| Overall diameter | 659.7 mm | 686.5 mm | +26.8 mm (+4.06%) |
| Sidewall height | 101.3 mm | 89.3 mm | -12.0 mm |
| Circumference | 2.073 m | 2.157 m | +84.2 mm |
| Revs / km | 482.5 | 463.7 | -18.8 |
| Ground clearance | reference | +13.4 mm | +13.4 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 104.1 km/h | +4.06 km/h |
Verdict: warning
Between 3% and 5% — noticeable speedometer drift; recalibration may be advisable.
Speedometer impact
At a true 100 km/h, your dashboard will read 104.1 km/h after switching to 255/35 R20 — a +4.06% 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 +13.4 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
225/45 R18
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255/35 R20
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