Comparison
245/40 R18 vs 255/35 R18
255/35 R18 is a wider variation of 245/40 R18 on the same 18-inch rim, adding 10 mm of tread footprint. This alternative fitment moves rolling diameter a touch off the original spec. The speedometer offset is small but measurable; worth keeping in mind if you watch the dash closely. The shorter sidewall gives the tire a firmer, more responsive feel and sharpens steering input. 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: 255/35 R18 is 17.5 mm shorter than 245/40 R18, shifting the speedometer by -2.68%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-17.5 mm
-2.68%
Speedometer at 100
97.3 km/h
-2.68% error
Ground clearance
-8.8 mm
ride height delta
Sidewall change
-8.8 mm
revs/km: 500.7
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/compare/245-40-r18-vs-255-35-r18Detailed comparison
| Metric | 245/40 R18 | 255/35 R18 | Difference |
|---|---|---|---|
| Overall diameter | 653.2 mm | 635.7 mm | -17.5 mm (-2.68%) |
| Sidewall height | 98.0 mm | 89.3 mm | -8.8 mm |
| Circumference | 2.052 m | 1.997 m | -55.0 mm |
| Revs / km | 487.3 | 500.7 | +13.4 |
| Ground clearance | reference | -8.8 mm | -8.8 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 97.3 km/h | -2.68 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 255/35 R18 — a -2.68% 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 -8.8 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.
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245/40 R18
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255/35 R18
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