Comparison
235/45 R18 vs 285/30 R20
285/30 R20 is a plus-2 alternative to 235/45 R18 — the bigger wheel shows through a thinner sidewall. This swap shifts overall diameter slightly from OEM. 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.
TakeA solid pick for drivers chasing a more aggressive stance without abandoning OEM rolling diameter.
Quick math: 285/30 R20 is 10.3 mm taller than 235/45 R18, shifting the speedometer by +1.54%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+10.3 mm
1.54%
Speedometer at 100
101.5 km/h
+1.54% error
Ground clearance
+5.1 mm
ride height delta
Sidewall change
-20.3 mm
revs/km: 468.8
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/compare/235-45-r18-vs-285-30-r20Detailed comparison
| Metric | 235/45 R18 | 285/30 R20 | Difference |
|---|---|---|---|
| Overall diameter | 668.7 mm | 679.0 mm | +10.3 mm (+1.54%) |
| Sidewall height | 105.8 mm | 85.5 mm | -20.3 mm |
| Circumference | 2.101 m | 2.133 m | +32.4 mm |
| Revs / km | 476.0 | 468.8 | -7.2 |
| Ground clearance | reference | +5.1 mm | +5.1 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 101.5 km/h | +1.54 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 101.5 km/h after switching to 285/30 R20 — a +1.54% 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 +5.1 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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235/45 R18
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285/30 R20
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