Comparison
225/40 R18 vs 245/45 R17
Minus-sizing from 225/40 R18 to 245/45 R17 pairs a smaller 17-inch wheel with more rubber between the rim and road. This sizing approach moves rolling diameter a touch off the original spec. Expect a slight but noticeable shift in indicated speed compared to the original tires. The taller sidewall adds cushioning over potholes and rougher roads, with a softer overall ride. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeTypical choice for a dedicated winter or off-road setup where extra sidewall pays off.
Quick math: 245/45 R17 is 15.1 mm taller than 225/40 R18, shifting the speedometer by +2.37%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+15.1 mm
2.37%
Speedometer at 100
102.4 km/h
+2.37% error
Ground clearance
+7.5 mm
ride height delta
Sidewall change
+20.3 mm
revs/km: 488.0
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/compare/225-40-r18-vs-245-45-r17Detailed comparison
| Metric | 225/40 R18 | 245/45 R17 | Difference |
|---|---|---|---|
| Overall diameter | 637.2 mm | 652.3 mm | +15.1 mm (+2.37%) |
| Sidewall height | 90.0 mm | 110.3 mm | +20.3 mm |
| Circumference | 2.002 m | 2.049 m | +47.4 mm |
| Revs / km | 499.5 | 488.0 | -11.6 |
| Ground clearance | reference | +7.5 mm | +7.5 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 102.4 km/h | +2.37 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 102.4 km/h after switching to 245/45 R17 — a +2.37% 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 +7.5 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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225/40 R18
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245/45 R17
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