Comparison
245/40 R18 vs 285/30 R20
Plus-sizing from 245/40 R18 to 285/30 R20 keeps overall diameter close to factory while opening room for a larger 20-inch wheel. This swap swings rolling diameter far enough to feel on the road. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement.
Indicated speed will drift far enough that recalibration is worth considering. Diameter delta falls in the cautious 3–5% range, where speedometer recalibration and a careful clearance check are worth doing.
TakeCommon upgrade for sportier handling and a tighter wheel-gap look on the same vehicle.
Quick math: 285/30 R20 is 25.8 mm taller than 245/40 R18, shifting the speedometer by +3.95%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+25.8 mm
3.95%
Speedometer at 100
103.9 km/h
+3.95% error
Ground clearance
+12.9 mm
ride height delta
Sidewall change
-12.5 mm
revs/km: 468.8
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/compare/245-40-r18-vs-285-30-r20Detailed comparison
| Metric | 245/40 R18 | 285/30 R20 | Difference |
|---|---|---|---|
| Overall diameter | 653.2 mm | 679.0 mm | +25.8 mm (+3.95%) |
| Sidewall height | 98.0 mm | 85.5 mm | -12.5 mm |
| Circumference | 2.052 m | 2.133 m | +81.1 mm |
| Revs / km | 487.3 | 468.8 | -18.5 |
| Ground clearance | reference | +12.9 mm | +12.9 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 103.9 km/h | +3.95 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 103.9 km/h after switching to 285/30 R20 — a +3.95% 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 +12.9 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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245/40 R18
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285/30 R20
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