Comparison
235/55 R17 vs 245/45 R18
Plus-sizing from 235/55 R17 to 245/45 R18 keeps overall diameter close to factory while opening room for a larger 18-inch wheel. This setup moves rolling diameter a touch off the original spec. The speedometer offset is small but measurable; worth keeping in mind if you watch the dash closely. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement. 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: 245/45 R18 is 12.6 mm shorter than 235/55 R17, shifting the speedometer by -1.83%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-12.6 mm
-1.83%
Speedometer at 100
98.2 km/h
-1.83% error
Ground clearance
-6.3 mm
ride height delta
Sidewall change
-19.0 mm
revs/km: 469.7
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/compare/235-55-r17-vs-245-45-r18Detailed comparison
| Metric | 235/55 R17 | 245/45 R18 | Difference |
|---|---|---|---|
| Overall diameter | 690.3 mm | 677.7 mm | -12.6 mm (-1.83%) |
| Sidewall height | 129.3 mm | 110.3 mm | -19.0 mm |
| Circumference | 2.169 m | 2.129 m | -39.6 mm |
| Revs / km | 461.1 | 469.7 | +8.6 |
| Ground clearance | reference | -6.3 mm | -6.3 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 98.2 km/h | -1.83 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 98.2 km/h after switching to 245/45 R18 — a -1.83% 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 -6.3 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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235/55 R17
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245/45 R18
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