Comparison
275/40 R20 vs 275/45 R20
Going from 275/40 R20 to 275/45 R20 raises the aspect ratio by 5 points on the same 20-inch wheel. This swap swings rolling diameter far enough to feel on the road. Extra sidewall absorbs impacts more readily — a sensible bias for daily commuting and broken 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 comfort-leaning direction that's easier on wheels and suspension over rough surfaces.
Quick math: 275/45 R20 is 27.5 mm taller than 275/40 R20, shifting the speedometer by +3.78%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+27.5 mm
3.78%
Speedometer at 100
103.8 km/h
+3.78% error
Ground clearance
+13.8 mm
ride height delta
Sidewall change
+13.8 mm
revs/km: 421.3
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/compare/275-40-r20-vs-275-45-r20Detailed comparison
| Metric | 275/40 R20 | 275/45 R20 | Difference |
|---|---|---|---|
| Overall diameter | 728.0 mm | 755.5 mm | +27.5 mm (+3.78%) |
| Sidewall height | 110.0 mm | 123.8 mm | +13.8 mm |
| Circumference | 2.287 m | 2.373 m | +86.4 mm |
| Revs / km | 437.2 | 421.3 | -15.9 |
| Ground clearance | reference | +13.8 mm | +13.8 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 103.8 km/h | +3.78 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 103.8 km/h after switching to 275/45 R20 — a +3.78% 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 +13.8 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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275/40 R20
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275/45 R20
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