Comparison
255/45 R20 vs 255/50 R20
Going from 255/45 R20 to 255/50 R20 raises the aspect ratio by 5 points on the same 20-inch wheel. This tire combination moves rolling diameter well outside the usual OEM tolerance.
Indicated speed will drift far enough that recalibration is worth considering. 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.
TakeA comfort-leaning direction that's easier on wheels and suspension over rough surfaces.
Quick math: 255/50 R20 is 25.5 mm taller than 255/45 R20, shifting the speedometer by +3.46%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+25.5 mm
3.46%
Speedometer at 100
103.5 km/h
+3.46% error
Ground clearance
+12.8 mm
ride height delta
Sidewall change
+12.8 mm
revs/km: 417.2
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/compare/255-45-r20-vs-255-50-r20Detailed comparison
| Metric | 255/45 R20 | 255/50 R20 | Difference |
|---|---|---|---|
| Overall diameter | 737.5 mm | 763.0 mm | +25.5 mm (+3.46%) |
| Sidewall height | 114.8 mm | 127.5 mm | +12.8 mm |
| Circumference | 2.317 m | 2.397 m | +80.1 mm |
| Revs / km | 431.6 | 417.2 | -14.4 |
| Ground clearance | reference | +12.8 mm | +12.8 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 103.5 km/h | +3.46 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 103.5 km/h after switching to 255/50 R20 — a +3.46% 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 +12.8 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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255/45 R20
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255/50 R20
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