Comparison
245/60 R18 vs 275/40 R20
Switching from 245/60 R18 to 275/40 R20 is a plus-2 upgrade that wraps a shorter sidewall around a larger 20-inch wheel. This alternative fitment moves rolling diameter well outside the usual OEM tolerance. Indicated speed will drift far enough that recalibration is worth considering. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement. 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: 275/40 R20 is 23.2 mm shorter than 245/60 R18, shifting the speedometer by -3.09%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
-23.2 mm
-3.09%
Speedometer at 100
96.9 km/h
-3.09% error
Ground clearance
-11.6 mm
ride height delta
Sidewall change
-37.0 mm
revs/km: 437.2
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/compare/245-60-r18-vs-275-40-r20Detailed comparison
| Metric | 245/60 R18 | 275/40 R20 | Difference |
|---|---|---|---|
| Overall diameter | 751.2 mm | 728.0 mm | -23.2 mm (-3.09%) |
| Sidewall height | 147.0 mm | 110.0 mm | -37.0 mm |
| Circumference | 2.360 m | 2.287 m | -72.9 mm |
| Revs / km | 423.7 | 437.2 | +13.5 |
| Ground clearance | reference | -11.6 mm | -11.6 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 96.9 km/h | -3.09 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 96.9 km/h after switching to 275/40 R20 — a -3.09% 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 -11.6 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
245/60 R18
Back to
275/40 R20
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