Comparison
245/40 R20 vs 255/45 R20
On the same 20-inch wheel, 255/45 R20 grows the section width by 10 mm versus 245/40 R20. This alternative fitment moves rolling diameter well outside the usual OEM tolerance.
The speedometer error is noticeable and may warrant a recalibration if you rely on indicated speed. The taller sidewall adds cushioning over potholes and rougher roads, with a softer overall ride. Extra width broadens the footprint for more grip, but check inner liner and strut clearance before fitting. The 3–5% diameter gap puts this in caution territory: doable on many cars, but verify clearance and consider recalibration.
TakeUseful when extra dry grip and stance matter more than a small fuel-economy hit.
Quick math: 255/45 R20 is 33.5 mm taller than 245/40 R20, shifting the speedometer by +4.76%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+33.5 mm
4.76%
Speedometer at 100
104.8 km/h
+4.76% error
Ground clearance
+16.8 mm
ride height delta
Sidewall change
+16.8 mm
revs/km: 431.6
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/compare/245-40-r20-vs-255-45-r20Detailed comparison
| Metric | 245/40 R20 | 255/45 R20 | Difference |
|---|---|---|---|
| Overall diameter | 704.0 mm | 737.5 mm | +33.5 mm (+4.76%) |
| Sidewall height | 98.0 mm | 114.8 mm | +16.8 mm |
| Circumference | 2.212 m | 2.317 m | +105.2 mm |
| Revs / km | 452.1 | 431.6 | -20.5 |
| Ground clearance | reference | +16.8 mm | +16.8 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 104.8 km/h | +4.76 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 104.8 km/h after switching to 255/45 R20 — a +4.76% 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 +16.8 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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245/40 R20
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255/45 R20
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