Comparison
265/40 R18 vs 285/30 R20
Plus-sizing from 265/40 R18 to 285/30 R20 keeps overall diameter close to factory while opening room for a larger 20-inch wheel. This wheel and tire pairing barely shifts the rolling circumference. The shorter sidewall gives the tire a firmer, more responsive feel and sharpens steering input.
Speedometer drift stays small enough that most drivers won't notice it day to day. 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 9.8 mm taller than 265/40 R18, shifting the speedometer by +1.46%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+9.8 mm
1.46%
Speedometer at 100
101.5 km/h
+1.46% error
Ground clearance
+4.9 mm
ride height delta
Sidewall change
-20.5 mm
revs/km: 468.8
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/compare/265-40-r18-vs-285-30-r20Detailed comparison
| Metric | 265/40 R18 | 285/30 R20 | Difference |
|---|---|---|---|
| Overall diameter | 669.2 mm | 679.0 mm | +9.8 mm (+1.46%) |
| Sidewall height | 106.0 mm | 85.5 mm | -20.5 mm |
| Circumference | 2.102 m | 2.133 m | +30.8 mm |
| Revs / km | 475.7 | 468.8 | -6.9 |
| Ground clearance | reference | +4.9 mm | +4.9 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 101.5 km/h | +1.46 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 +1.46% 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 +4.9 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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265/40 R18
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285/30 R20
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