Comparison
235/40 R18 vs 235/45 R18
235/45 R18 is a taller-sidewall alternative to 235/40 R18 on the same 18-inch rim. This sizing approach noticeably changes overall diameter compared to OEM. Extra sidewall absorbs impacts more readily — a sensible bias for daily commuting and broken pavement.
Indicated speed will drift far enough that recalibration is worth considering. Diameter delta falls in the cautious 3–5% range, where speedometer recalibration and a careful clearance check are worth doing.
TakeA comfort-leaning direction that's easier on wheels and suspension over rough surfaces.
Quick math: 235/45 R18 is 23.5 mm taller than 235/40 R18, shifting the speedometer by +3.64%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+23.5 mm
3.64%
Speedometer at 100
103.6 km/h
+3.64% error
Ground clearance
+11.8 mm
ride height delta
Sidewall change
+11.8 mm
revs/km: 476.0
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/compare/235-40-r18-vs-235-45-r18Detailed comparison
| Metric | 235/40 R18 | 235/45 R18 | Difference |
|---|---|---|---|
| Overall diameter | 645.2 mm | 668.7 mm | +23.5 mm (+3.64%) |
| Sidewall height | 94.0 mm | 105.8 mm | +11.8 mm |
| Circumference | 2.027 m | 2.101 m | +73.8 mm |
| Revs / km | 493.4 | 476.0 | -17.3 |
| Ground clearance | reference | +11.8 mm | +11.8 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 103.6 km/h | +3.64 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 103.6 km/h after switching to 235/45 R18 — a +3.64% 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 +11.8 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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235/40 R18
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235/45 R18
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