Comparison
205/50 R17 vs 245/40 R18
245/40 R18 is a plus-1 alternative to 205/50 R17 — the bigger wheel shows through a thinner sidewall. This tire combination trims or stretches rolling diameter by a small margin. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement.
Expect a slight but noticeable shift in indicated speed compared to the original tires. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeCommon upgrade for sportier handling and a tighter wheel-gap look on the same vehicle.
Quick math: 245/40 R18 is 16.4 mm taller than 205/50 R17, shifting the speedometer by +2.58%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+16.4 mm
2.58%
Speedometer at 100
102.6 km/h
+2.58% error
Ground clearance
+8.2 mm
ride height delta
Sidewall change
-4.5 mm
revs/km: 487.3
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/compare/205-50-r17-vs-245-40-r18Detailed comparison
| Metric | 205/50 R17 | 245/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 636.8 mm | 653.2 mm | +16.4 mm (+2.58%) |
| Sidewall height | 102.5 mm | 98.0 mm | -4.5 mm |
| Circumference | 2.001 m | 2.052 m | +51.5 mm |
| Revs / km | 499.9 | 487.3 | -12.6 |
| Ground clearance | reference | +8.2 mm | +8.2 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 102.6 km/h | +2.58 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 102.6 km/h after switching to 245/40 R18 — a +2.58% 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 +8.2 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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245/40 R18
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