Comparison
245/40 R18 vs 255/40 R17
Going from 245/40 R18 to 255/40 R17 is a minus-1 setup that adds sidewall on a smaller 17-inch wheel. This wheel and tire pairing shifts overall diameter slightly from OEM. The wider section adds contact patch and lateral stability, while eating into fender and suspension clearance.
Expect a slight but noticeable shift in indicated speed compared to the original tires. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeTypical choice for a dedicated winter or off-road setup where extra sidewall pays off.
Quick math: 255/40 R17 is 17.4 mm shorter than 245/40 R18, shifting the speedometer by -2.66%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-17.4 mm
-2.66%
Speedometer at 100
97.3 km/h
-2.66% error
Ground clearance
-8.7 mm
ride height delta
Sidewall change
+4.0 mm
revs/km: 500.6
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/compare/245-40-r18-vs-255-40-r17Detailed comparison
| Metric | 245/40 R18 | 255/40 R17 | Difference |
|---|---|---|---|
| Overall diameter | 653.2 mm | 635.8 mm | -17.4 mm (-2.66%) |
| Sidewall height | 98.0 mm | 102.0 mm | +4.0 mm |
| Circumference | 2.052 m | 1.997 m | -54.7 mm |
| Revs / km | 487.3 | 500.6 | +13.3 |
| Ground clearance | reference | -8.7 mm | -8.7 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 97.3 km/h | -2.66 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 97.3 km/h after switching to 255/40 R17 — a -2.66% 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 -8.7 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 R18
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255/40 R17
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