Comparison
215/40 R18 vs 245/45 R17
245/45 R17 drops the rim from 18 to 17 inches versus 215/40 R18, trading wheel size for taller sidewall. This alternative fitment noticeably changes overall diameter compared to OEM. Indicated speed will drift far enough that recalibration is worth considering. The taller sidewall adds cushioning over potholes and rougher roads, with a softer overall ride. The 3–5% diameter gap puts this in caution territory: doable on many cars, but verify clearance and consider recalibration.
TakeTypical choice for a dedicated winter or off-road setup where extra sidewall pays off.
Quick math: 245/45 R17 is 23.1 mm taller than 215/40 R18, shifting the speedometer by +3.67%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+23.1 mm
3.67%
Speedometer at 100
103.7 km/h
+3.67% error
Ground clearance
+11.5 mm
ride height delta
Sidewall change
+24.3 mm
revs/km: 488.0
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/compare/215-40-r18-vs-245-45-r17Detailed comparison
| Metric | 215/40 R18 | 245/45 R17 | Difference |
|---|---|---|---|
| Overall diameter | 629.2 mm | 652.3 mm | +23.1 mm (+3.67%) |
| Sidewall height | 86.0 mm | 110.3 mm | +24.3 mm |
| Circumference | 1.977 m | 2.049 m | +72.6 mm |
| Revs / km | 505.9 | 488.0 | -17.9 |
| Ground clearance | reference | +11.5 mm | +11.5 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 103.7 km/h | +3.67 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 103.7 km/h after switching to 245/45 R17 — a +3.67% 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 +11.5 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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245/45 R17
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