Comparison
215/40 R18 vs 215/50 R17
Going from 215/40 R18 to 215/50 R17 is a minus-1 setup that adds sidewall on a smaller 17-inch wheel. This sizing approach trims or stretches rolling diameter by a small margin. The speedometer offset is small but measurable; worth keeping in mind if you watch the dash closely. The taller sidewall adds cushioning over potholes and rougher roads, with a softer overall ride. Overall the swap sits inside the safe ±3% diameter window, so ABS, traction control and gearing behave normally.
TakePractical direction for winter wheels, chains, or rougher pavement where cushioning matters.
Quick math: 215/50 R17 is 17.6 mm taller than 215/40 R18, shifting the speedometer by +2.80%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+17.6 mm
2.80%
Speedometer at 100
102.8 km/h
+2.80% error
Ground clearance
+8.8 mm
ride height delta
Sidewall change
+21.5 mm
revs/km: 492.1
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/compare/215-40-r18-vs-215-50-r17Detailed comparison
| Metric | 215/40 R18 | 215/50 R17 | Difference |
|---|---|---|---|
| Overall diameter | 629.2 mm | 646.8 mm | +17.6 mm (+2.80%) |
| Sidewall height | 86.0 mm | 107.5 mm | +21.5 mm |
| Circumference | 1.977 m | 2.032 m | +55.3 mm |
| Revs / km | 505.9 | 492.1 | -13.8 |
| Ground clearance | reference | +8.8 mm | +8.8 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 102.8 km/h | +2.80 km/h |
Verdict: excellent
Within ±3% — speedometer, ABS and traction control should behave normally.
Speedometer impact
At a true 100 km/h, your dashboard will read 102.8 km/h after switching to 215/50 R17 — a +2.80% 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 +8.8 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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215/40 R18
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215/50 R17
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