Comparison
225/55 R18 vs 265/40 R20
Going from 225/55 R18 to 265/40 R20 steps up to a 20-inch rim while trimming sidewall to stay near OEM rolling diameter. This sizing approach moves rolling diameter a touch off the original spec. 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: 265/40 R20 is 15.3 mm taller than 225/55 R18, shifting the speedometer by +2.17%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+15.3 mm
2.17%
Speedometer at 100
102.2 km/h
+2.17% error
Ground clearance
+7.6 mm
ride height delta
Sidewall change
-17.8 mm
revs/km: 442.1
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/compare/225-55-r18-vs-265-40-r20Detailed comparison
| Metric | 225/55 R18 | 265/40 R20 | Difference |
|---|---|---|---|
| Overall diameter | 704.7 mm | 720.0 mm | +15.3 mm (+2.17%) |
| Sidewall height | 123.8 mm | 106.0 mm | -17.8 mm |
| Circumference | 2.214 m | 2.262 m | +48.1 mm |
| Revs / km | 451.7 | 442.1 | -9.6 |
| Ground clearance | reference | +7.6 mm | +7.6 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 102.2 km/h | +2.17 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 102.2 km/h after switching to 265/40 R20 — a +2.17% 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 +7.6 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
225/55 R18
Back to
265/40 R20
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