Comparison
235/50 R18 vs 285/30 R20
Switching from 235/50 R18 to 285/30 R20 is a plus-2 upgrade that wraps a shorter sidewall around a larger 20-inch wheel. This tire combination trims or stretches rolling diameter by a small margin. Expect a slight but noticeable shift in indicated speed compared to the original tires. 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.
TakeA solid pick for drivers chasing a more aggressive stance without abandoning OEM rolling diameter.
Quick math: 285/30 R20 is 13.2 mm shorter than 235/50 R18, shifting the speedometer by -1.91%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-13.2 mm
-1.91%
Speedometer at 100
98.1 km/h
-1.91% error
Ground clearance
-6.6 mm
ride height delta
Sidewall change
-32.0 mm
revs/km: 468.8
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/compare/235-50-r18-vs-285-30-r20Detailed comparison
| Metric | 235/50 R18 | 285/30 R20 | Difference |
|---|---|---|---|
| Overall diameter | 692.2 mm | 679.0 mm | -13.2 mm (-1.91%) |
| Sidewall height | 117.5 mm | 85.5 mm | -32.0 mm |
| Circumference | 2.175 m | 2.133 m | -41.5 mm |
| Revs / km | 459.9 | 468.8 | +8.9 |
| Ground clearance | reference | -6.6 mm | -6.6 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 98.1 km/h | -1.91 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 98.1 km/h after switching to 285/30 R20 — a -1.91% 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 -6.6 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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235/50 R18
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285/30 R20
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