Comparison
245/45 R17 vs 255/40 R17
255/40 R17 is a wider variation of 245/45 R17 on the same 17-inch rim, adding 10 mm of tread footprint. This setup trims or stretches rolling diameter by a small margin. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement.
The speedometer offset is small but measurable; worth keeping in mind if you watch the dash closely. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeReasonable performance-leaning swap as long as fender and suspension clearance check out.
Quick math: 255/40 R17 is 16.5 mm shorter than 245/45 R17, shifting the speedometer by -2.53%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-16.5 mm
-2.53%
Speedometer at 100
97.5 km/h
-2.53% error
Ground clearance
-8.3 mm
ride height delta
Sidewall change
-8.3 mm
revs/km: 500.6
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/compare/245-45-r17-vs-255-40-r17Detailed comparison
| Metric | 245/45 R17 | 255/40 R17 | Difference |
|---|---|---|---|
| Overall diameter | 652.3 mm | 635.8 mm | -16.5 mm (-2.53%) |
| Sidewall height | 110.3 mm | 102.0 mm | -8.3 mm |
| Circumference | 2.049 m | 1.997 m | -51.8 mm |
| Revs / km | 488.0 | 500.6 | +12.7 |
| Ground clearance | reference | -8.3 mm | -8.3 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 97.5 km/h | -2.53 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 97.5 km/h after switching to 255/40 R17 — a -2.53% 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 -8.3 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 R17
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255/40 R17
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