Comparison
235/40 R18 vs 245/45 R18
Stepping from 235/40 R18 to 245/45 R18 keeps the 18-inch wheel but widens the section by 10 mm. This tire combination swings rolling diameter far enough to feel on the road. More sidewall typically improves comfort and curb protection, especially on city streets.
The dashboard speed will be significantly off — plan on recalibration before daily use. A diameter change beyond 5% is aggressive enough to influence ABS, traction control and gearing; treat it as a serious modification.
TakeRecommended only after a professional fitment check and speedometer recalibration.
Quick math: 245/45 R18 is 32.5 mm taller than 235/40 R18, shifting the speedometer by +5.04%.
Current Tire
New Tire
Ground line · scaled comparison
Not Recommended
Over 5% — speedometer & ABS may misread
Diameter change
+32.5 mm
5.04%
Speedometer at 100
105.0 km/h
+5.04% error
Ground clearance
+16.3 mm
ride height delta
Sidewall change
+16.3 mm
revs/km: 469.7
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/compare/235-40-r18-vs-245-45-r18Detailed comparison
| Metric | 235/40 R18 | 245/45 R18 | Difference |
|---|---|---|---|
| Overall diameter | 645.2 mm | 677.7 mm | +32.5 mm (+5.04%) |
| Sidewall height | 94.0 mm | 110.3 mm | +16.3 mm |
| Circumference | 2.027 m | 2.129 m | +102.1 mm |
| Revs / km | 493.4 | 469.7 | -23.7 |
| Ground clearance | reference | +16.3 mm | +16.3 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 105.0 km/h | +5.04 km/h |
Verdict: danger
Over 5% diameter difference — likely to affect speedometer accuracy, ABS calibration and gearing. Not recommended without professional review.
Speedometer impact
At a true 100 km/h, your dashboard will read 105.0 km/h after switching to 245/45 R18 — a +5.04% 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 +16.3 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.
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235/40 R18
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245/45 R18
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