Comparison
245/45 R20 vs 255/50 R20
On the same 20-inch wheel, 255/50 R20 grows the section width by 10 mm versus 245/45 R20. This swap 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. More sidewall typically improves comfort and curb protection, especially on city streets. Diameter delta falls in the cautious 3–5% range, where speedometer recalibration and a careful clearance check are worth doing.
TakeUseful when extra dry grip and stance matter more than a small fuel-economy hit.
Quick math: 255/50 R20 is 34.5 mm taller than 245/45 R20, shifting the speedometer by +4.74%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+34.5 mm
4.74%
Speedometer at 100
104.7 km/h
+4.74% error
Ground clearance
+17.3 mm
ride height delta
Sidewall change
+17.3 mm
revs/km: 417.2
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/compare/245-45-r20-vs-255-50-r20Detailed comparison
| Metric | 245/45 R20 | 255/50 R20 | Difference |
|---|---|---|---|
| Overall diameter | 728.5 mm | 763.0 mm | +34.5 mm (+4.74%) |
| Sidewall height | 110.3 mm | 127.5 mm | +17.3 mm |
| Circumference | 2.289 m | 2.397 m | +108.4 mm |
| Revs / km | 436.9 | 417.2 | -19.8 |
| Ground clearance | reference | +17.3 mm | +17.3 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 104.7 km/h | +4.74 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 104.7 km/h after switching to 255/50 R20 — a +4.74% 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 +17.3 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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245/45 R20
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255/50 R20
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