Comparison
225/40 R18 vs 235/45 R18
235/45 R18 is a wider variation of 225/40 R18 on the same 18-inch rim, adding 10 mm of tread footprint. This swap moves rolling diameter well outside the usual OEM tolerance.
The speedometer error is noticeable and may warrant a recalibration if you rely on indicated speed. 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. Diameter delta falls in the cautious 3–5% range, where speedometer recalibration and a careful clearance check are worth doing.
TakeUseful when extra dry grip and stance matter more than a small fuel-economy hit.
Quick math: 235/45 R18 is 31.5 mm taller than 225/40 R18, shifting the speedometer by +4.94%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+31.5 mm
4.94%
Speedometer at 100
104.9 km/h
+4.94% error
Ground clearance
+15.8 mm
ride height delta
Sidewall change
+15.8 mm
revs/km: 476.0
Permalink for this comparison:
/compare/225-40-r18-vs-235-45-r18Detailed comparison
| Metric | 225/40 R18 | 235/45 R18 | Difference |
|---|---|---|---|
| Overall diameter | 637.2 mm | 668.7 mm | +31.5 mm (+4.94%) |
| Sidewall height | 90.0 mm | 105.8 mm | +15.8 mm |
| Circumference | 2.002 m | 2.101 m | +99.0 mm |
| Revs / km | 499.5 | 476.0 | -23.5 |
| Ground clearance | reference | +15.8 mm | +15.8 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 104.9 km/h | +4.94 km/h |
Verdict: warning
Between 3% and 5% — noticeable speedometer drift; recalibration may be advisable.
Speedometer impact
At a true 100 km/h, your dashboard will read 104.9 km/h after switching to 235/45 R18 — a +4.94% 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 +15.8 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.
Back to
225/40 R18
Back to
235/45 R18
Drivers also compare
Closely-related fitments and plus-size swaps for 225/40 R18 and 235/45 R18.
235/45 R18 vs 265/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 0.07%
225/40 R18 vs 255/35 R18
Wider variation on the same rim — more grip, less clearance.
Δ 0.24%
235/45 R18 vs 255/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.12%
225/40 R18 vs 235/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.26%
235/45 R18 vs 275/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.27%
215/40 R18 vs 225/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.27%
225/40 R18 vs 245/35 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.33%
235/45 R18 vs 245/45 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.35%
Related topics