Comparison
215/45 R18 vs 235/40 R18
On the same 18-inch wheel, 235/40 R18 grows the section width by 20 mm versus 215/45 R18. This swap barely shifts the rolling circumference.
Speedometer drift stays small enough that most drivers won't notice it day to day. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement. More tread on the ground tends to improve dry grip and stance, with a small fuel-economy and clearance tradeoff. 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: 235/40 R18 is 5.5 mm shorter than 215/45 R18, shifting the speedometer by -0.85%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-5.5 mm
-0.85%
Speedometer at 100
99.2 km/h
-0.85% error
Ground clearance
-2.8 mm
ride height delta
Sidewall change
-2.8 mm
revs/km: 493.4
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/compare/215-45-r18-vs-235-40-r18Detailed comparison
| Metric | 215/45 R18 | 235/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 650.7 mm | 645.2 mm | -5.5 mm (-0.85%) |
| Sidewall height | 96.8 mm | 94.0 mm | -2.8 mm |
| Circumference | 2.044 m | 2.027 m | -17.3 mm |
| Revs / km | 489.2 | 493.4 | +4.2 |
| Ground clearance | reference | -2.8 mm | -2.8 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 99.2 km/h | -0.85 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 99.2 km/h after switching to 235/40 R18 — a -0.85% 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 -2.8 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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215/45 R18
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235/40 R18
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