Comparison
205/50 R17 vs 235/45 R18
Going from 205/50 R17 to 235/45 R18 steps up to a 18-inch rim while trimming sidewall to stay near OEM rolling diameter. This sizing approach swings rolling diameter far enough to feel on the road. Expect a more planted steering feel, at the cost of some of the cushioning a taller sidewall provides.
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.
TakeTreat as a serious modification — verify clearance, recalibrate the speedometer and reassess load capacity.
Quick math: 235/45 R18 is 31.9 mm taller than 205/50 R17, shifting the speedometer by +5.01%.
Current Tire
New Tire
Ground line · scaled comparison
Not Recommended
Over 5% — speedometer & ABS may misread
Diameter change
+31.9 mm
5.01%
Speedometer at 100
105.0 km/h
+5.01% error
Ground clearance
+16.0 mm
ride height delta
Sidewall change
+3.3 mm
revs/km: 476.0
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/compare/205-50-r17-vs-235-45-r18Detailed comparison
| Metric | 205/50 R17 | 235/45 R18 | Difference |
|---|---|---|---|
| Overall diameter | 636.8 mm | 668.7 mm | +31.9 mm (+5.01%) |
| Sidewall height | 102.5 mm | 105.8 mm | +3.3 mm |
| Circumference | 2.001 m | 2.101 m | +100.2 mm |
| Revs / km | 499.9 | 476.0 | -23.8 |
| Ground clearance | reference | +16.0 mm | +16.0 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 105.0 km/h | +5.01 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 235/45 R18 — a +5.01% 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 +16.0 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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205/50 R17
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235/45 R18
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