Comparison
275/35 R18 vs 285/30 R20
Plus-sizing from 275/35 R18 to 285/30 R20 keeps overall diameter close to factory while opening room for a larger 20-inch wheel. This alternative fitment swings rolling diameter far enough to feel on the road. Indicated speed will drift far enough that recalibration is worth considering. The shorter sidewall gives the tire a firmer, more responsive feel and sharpens steering input. The 3–5% diameter gap puts this in caution territory: doable on many cars, but verify clearance and consider recalibration.
TakeA solid pick for drivers chasing a more aggressive stance without abandoning OEM rolling diameter.
Quick math: 285/30 R20 is 29.3 mm taller than 275/35 R18, shifting the speedometer by +4.51%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+29.3 mm
4.51%
Speedometer at 100
104.5 km/h
+4.51% error
Ground clearance
+14.6 mm
ride height delta
Sidewall change
-10.8 mm
revs/km: 468.8
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/compare/275-35-r18-vs-285-30-r20Detailed comparison
| Metric | 275/35 R18 | 285/30 R20 | Difference |
|---|---|---|---|
| Overall diameter | 649.7 mm | 679.0 mm | +29.3 mm (+4.51%) |
| Sidewall height | 96.3 mm | 85.5 mm | -10.8 mm |
| Circumference | 2.041 m | 2.133 m | +92.0 mm |
| Revs / km | 489.9 | 468.8 | -21.1 |
| Ground clearance | reference | +14.6 mm | +14.6 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 104.5 km/h | +4.51 km/h |
Verdict: warning
Between 3% and 5% — noticeable speedometer drift; recalibration may be advisable.
Speedometer impact
At a true 100 km/h, your dashboard will read 104.5 km/h after switching to 285/30 R20 — a +4.51% 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 +14.6 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.
Back to
275/35 R18
Back to
285/30 R20
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