Comparison
255/45 R20 vs 275/40 R20
Stepping from 255/45 R20 to 275/40 R20 keeps the 20-inch wheel but widens the section by 20 mm. This swap keeps overall diameter very close to stock. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement.
The speedometer offset is mild and well inside what most cars can tolerate without recalibration. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeUseful when extra dry grip and stance matter more than a small fuel-economy hit.
Quick math: 275/40 R20 is 9.5 mm shorter than 255/45 R20, shifting the speedometer by -1.29%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-9.5 mm
-1.29%
Speedometer at 100
98.7 km/h
-1.29% error
Ground clearance
-4.8 mm
ride height delta
Sidewall change
-4.8 mm
revs/km: 437.2
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/compare/255-45-r20-vs-275-40-r20Detailed comparison
| Metric | 255/45 R20 | 275/40 R20 | Difference |
|---|---|---|---|
| Overall diameter | 737.5 mm | 728.0 mm | -9.5 mm (-1.29%) |
| Sidewall height | 114.8 mm | 110.0 mm | -4.8 mm |
| Circumference | 2.317 m | 2.287 m | -29.8 mm |
| Revs / km | 431.6 | 437.2 | +5.6 |
| Ground clearance | reference | -4.8 mm | -4.8 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 98.7 km/h | -1.29 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 98.7 km/h after switching to 275/40 R20 — a -1.29% 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 -4.8 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.
Back to
255/45 R20
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275/40 R20
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