Comparison
245/40 R17 vs 255/40 R17
255/40 R17 is a wider variation of 245/40 R17 on the same 17-inch rim, adding 10 mm of tread footprint. This swap barely shifts the rolling circumference. The speedometer offset is mild and well inside what most cars can tolerate without recalibration. Extra width broadens the footprint for more grip, but check inner liner and strut clearance before fitting. 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: 255/40 R17 is 8.0 mm taller than 245/40 R17, shifting the speedometer by +1.27%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+8.0 mm
1.27%
Speedometer at 100
101.3 km/h
+1.27% error
Ground clearance
+4.0 mm
ride height delta
Sidewall change
+4.0 mm
revs/km: 500.6
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/compare/245-40-r17-vs-255-40-r17Detailed comparison
| Metric | 245/40 R17 | 255/40 R17 | Difference |
|---|---|---|---|
| Overall diameter | 627.8 mm | 635.8 mm | +8.0 mm (+1.27%) |
| Sidewall height | 98.0 mm | 102.0 mm | +4.0 mm |
| Circumference | 1.972 m | 1.997 m | +25.1 mm |
| Revs / km | 507.0 | 500.6 | -6.4 |
| Ground clearance | reference | +4.0 mm | +4.0 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 101.3 km/h | +1.27 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 101.3 km/h after switching to 255/40 R17 — a +1.27% 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 +4.0 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 R17
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255/40 R17
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