Comparison
245/35 R18 vs 255/40 R17
255/40 R17 drops the rim from 18 to 17 inches versus 245/35 R18, trading wheel size for taller sidewall. This setup lands within OEM rolling-diameter tolerance.
Speedometer drift stays small enough that most drivers won't notice it day to day. More sidewall typically improves comfort and curb protection, especially on city streets. More tread on the ground tends to improve dry grip and stance, with a small fuel-economy and clearance tradeoff. The smaller wheel is also lighter and easier to find affordable winter rubber for. 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 7.1 mm taller than 245/35 R18, shifting the speedometer by +1.13%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+7.1 mm
1.13%
Speedometer at 100
101.1 km/h
+1.13% error
Ground clearance
+3.5 mm
ride height delta
Sidewall change
+16.3 mm
revs/km: 500.6
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/compare/245-35-r18-vs-255-40-r17Detailed comparison
| Metric | 245/35 R18 | 255/40 R17 | Difference |
|---|---|---|---|
| Overall diameter | 628.7 mm | 635.8 mm | +7.1 mm (+1.13%) |
| Sidewall height | 85.8 mm | 102.0 mm | +16.3 mm |
| Circumference | 1.975 m | 1.997 m | +22.3 mm |
| Revs / km | 506.3 | 500.6 | -5.7 |
| Ground clearance | reference | +3.5 mm | +3.5 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 101.1 km/h | +1.13 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 101.1 km/h after switching to 255/40 R17 — a +1.13% 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 +3.5 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
245/35 R18
Back to
255/40 R17
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