Comparison
225/45 R18 vs 245/40 R18
On the same 18-inch wheel, 245/40 R18 grows the section width by 20 mm versus 225/45 R18. This setup lands within OEM rolling-diameter tolerance.
Dashboard speed shifts only marginally — within the noise of normal OEM tolerance. Expect a more planted steering feel, at the cost of some of the cushioning a taller sidewall provides. The wider section adds contact patch and lateral stability, while eating into fender and suspension clearance. Overall the swap sits inside the safe ±3% diameter window, so ABS, traction control and gearing behave normally.
TakeReasonable performance-leaning swap as long as fender and suspension clearance check out.
Quick math: 245/40 R18 is 6.5 mm shorter than 225/45 R18, shifting the speedometer by -0.99%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-6.5 mm
-0.99%
Speedometer at 100
99.0 km/h
-0.99% error
Ground clearance
-3.3 mm
ride height delta
Sidewall change
-3.3 mm
revs/km: 487.3
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/compare/225-45-r18-vs-245-40-r18Detailed comparison
| Metric | 225/45 R18 | 245/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 659.7 mm | 653.2 mm | -6.5 mm (-0.99%) |
| Sidewall height | 101.3 mm | 98.0 mm | -3.3 mm |
| Circumference | 2.073 m | 2.052 m | -20.4 mm |
| Revs / km | 482.5 | 487.3 | +4.8 |
| Ground clearance | reference | -3.3 mm | -3.3 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 99.0 km/h | -0.99 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 99.0 km/h after switching to 245/40 R18 — a -0.99% 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 -3.3 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.
Back to
225/45 R18
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245/40 R18
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