Comparison
245/40 R20 vs 275/40 R18
Switching from 245/40 R20 to 275/40 R18 steps down to a 18-inch wheel — a familiar move for winter and dedicated all-terrain sets. This tire combination noticeably changes overall diameter compared to OEM. The speedometer error is noticeable and may warrant a recalibration if you rely on indicated speed. The wider section adds contact patch and lateral stability, while eating into fender and suspension clearance. Diameter delta falls in the cautious 3–5% range, where speedometer recalibration and a careful clearance check are worth doing.
TakeTypical choice for a dedicated winter or off-road setup where extra sidewall pays off.
Quick math: 275/40 R18 is 26.8 mm shorter than 245/40 R20, shifting the speedometer by -3.81%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
-26.8 mm
-3.81%
Speedometer at 100
96.2 km/h
-3.81% error
Ground clearance
-13.4 mm
ride height delta
Sidewall change
+12.0 mm
revs/km: 470.0
Permalink for this comparison:
/compare/245-40-r20-vs-275-40-r18Detailed comparison
| Metric | 245/40 R20 | 275/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 704.0 mm | 677.2 mm | -26.8 mm (-3.81%) |
| Sidewall height | 98.0 mm | 110.0 mm | +12.0 mm |
| Circumference | 2.212 m | 2.127 m | -84.2 mm |
| Revs / km | 452.1 | 470.0 | +17.9 |
| Ground clearance | reference | -13.4 mm | -13.4 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 96.2 km/h | -3.81 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 96.2 km/h after switching to 275/40 R18 — a -3.81% 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 -13.4 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
245/40 R20
Back to
275/40 R18
Drivers also compare
Closely-related fitments and plus-size swaps for 245/40 R20 and 275/40 R18.
245/45 R18 vs 275/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 0.07%
245/40 R20 vs 275/35 R20
Wider variation on the same rim — more grip, less clearance.
Δ 0.50%
245/40 R20 vs 285/35 R20
Wider variation on the same rim — more grip, less clearance.
Δ 0.50%
225/50 R18 vs 275/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 0.73%
265/40 R18 vs 275/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.20%
235/45 R18 vs 275/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.27%
255/45 R18 vs 275/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.38%
245/40 R20 vs 265/35 R20
Wider variation on the same rim — more grip, less clearance.
Δ 1.49%
Related topics