Comparison
225/50 R18 vs 245/40 R20
245/40 R20 is a plus-2 alternative to 225/50 R18 — the bigger wheel shows through a thinner sidewall. This sizing approach swings rolling diameter far enough to feel on the road. The speedometer error is noticeable and may warrant a recalibration if you rely on indicated speed. 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.
TakeCommon upgrade for sportier handling and a tighter wheel-gap look on the same vehicle.
Quick math: 245/40 R20 is 21.8 mm taller than 225/50 R18, shifting the speedometer by +3.20%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+21.8 mm
3.20%
Speedometer at 100
103.2 km/h
+3.20% error
Ground clearance
+10.9 mm
ride height delta
Sidewall change
-14.5 mm
revs/km: 452.1
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/compare/225-50-r18-vs-245-40-r20Detailed comparison
| Metric | 225/50 R18 | 245/40 R20 | Difference |
|---|---|---|---|
| Overall diameter | 682.2 mm | 704.0 mm | +21.8 mm (+3.20%) |
| Sidewall height | 112.5 mm | 98.0 mm | -14.5 mm |
| Circumference | 2.143 m | 2.212 m | +68.5 mm |
| Revs / km | 466.6 | 452.1 | -14.4 |
| Ground clearance | reference | +10.9 mm | +10.9 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 103.2 km/h | +3.20 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 103.2 km/h after switching to 245/40 R20 — a +3.20% 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 +10.9 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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225/50 R18
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245/40 R20
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