Comparison
235/45 R18 vs 235/55 R17
Going from 235/45 R18 to 235/55 R17 is a minus-1 setup that adds sidewall on a smaller 17-inch wheel. This tire combination swings rolling diameter far enough to feel on the road.
Indicated speed will drift far enough that recalibration is worth considering. More sidewall typically improves comfort and curb protection, especially on city streets. Minus-sizing keeps replacement costs down and opens up a wider range of winter and all-terrain tires. Diameter delta falls in the cautious 3–5% range, where speedometer recalibration and a careful clearance check are worth doing.
TakePractical direction for winter wheels, chains, or rougher pavement where cushioning matters.
Quick math: 235/55 R17 is 21.6 mm taller than 235/45 R18, shifting the speedometer by +3.23%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+21.6 mm
3.23%
Speedometer at 100
103.2 km/h
+3.23% error
Ground clearance
+10.8 mm
ride height delta
Sidewall change
+23.5 mm
revs/km: 461.1
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/compare/235-45-r18-vs-235-55-r17Detailed comparison
| Metric | 235/45 R18 | 235/55 R17 | Difference |
|---|---|---|---|
| Overall diameter | 668.7 mm | 690.3 mm | +21.6 mm (+3.23%) |
| Sidewall height | 105.8 mm | 129.3 mm | +23.5 mm |
| Circumference | 2.101 m | 2.169 m | +67.9 mm |
| Revs / km | 476.0 | 461.1 | -14.9 |
| Ground clearance | reference | +10.8 mm | +10.8 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 103.2 km/h | +3.23 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 103.2 km/h after switching to 235/55 R17 — a +3.23% 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 +10.8 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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235/45 R18
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235/55 R17
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