Comparison
235/40 R18 vs 245/40 R18
On the same 18-inch wheel, 245/40 R18 grows the section width by 10 mm versus 235/40 R18. This setup preserves rolling diameter within a hair of the original. Extra width broadens the footprint for more grip, but check inner liner and strut clearance before fitting.
Speedometer drift stays small enough that most drivers won't notice it day to day. 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: 245/40 R18 is 8.0 mm taller than 235/40 R18, shifting the speedometer by +1.24%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+8.0 mm
1.24%
Speedometer at 100
101.2 km/h
+1.24% error
Ground clearance
+4.0 mm
ride height delta
Sidewall change
+4.0 mm
revs/km: 487.3
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/compare/235-40-r18-vs-245-40-r18Detailed comparison
| Metric | 235/40 R18 | 245/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 645.2 mm | 653.2 mm | +8.0 mm (+1.24%) |
| Sidewall height | 94.0 mm | 98.0 mm | +4.0 mm |
| Circumference | 2.027 m | 2.052 m | +25.1 mm |
| Revs / km | 493.4 | 487.3 | -6.0 |
| Ground clearance | reference | +4.0 mm | +4.0 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 101.2 km/h | +1.24 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 101.2 km/h after switching to 245/40 R18 — a +1.24% 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 +4.0 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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235/40 R18
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245/40 R18
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