Comparison
225/55 R18 vs 245/45 R20
Going from 225/55 R18 to 245/45 R20 steps up to a 20-inch rim while trimming sidewall to stay near OEM rolling diameter. This swap swings rolling diameter far enough to feel on the road. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement.
The speedometer error is noticeable and may warrant a recalibration if you rely on indicated speed. 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: 245/45 R20 is 23.8 mm taller than 225/55 R18, shifting the speedometer by +3.38%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+23.8 mm
3.38%
Speedometer at 100
103.4 km/h
+3.38% error
Ground clearance
+11.9 mm
ride height delta
Sidewall change
-13.5 mm
revs/km: 436.9
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/compare/225-55-r18-vs-245-45-r20Detailed comparison
| Metric | 225/55 R18 | 245/45 R20 | Difference |
|---|---|---|---|
| Overall diameter | 704.7 mm | 728.5 mm | +23.8 mm (+3.38%) |
| Sidewall height | 123.8 mm | 110.3 mm | -13.5 mm |
| Circumference | 2.214 m | 2.289 m | +74.8 mm |
| Revs / km | 451.7 | 436.9 | -14.8 |
| Ground clearance | reference | +11.9 mm | +11.9 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 103.4 km/h | +3.38 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 103.4 km/h after switching to 245/45 R20 — a +3.38% 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 +11.9 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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225/55 R18
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245/45 R20
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