Comparison
235/50 R18 vs 245/40 R20
Switching from 235/50 R18 to 245/40 R20 is a plus-2 upgrade that wraps a shorter sidewall around a larger 20-inch wheel. This tire combination moves rolling diameter a touch off the original spec.
The speedometer offset is small but measurable; worth keeping in mind if you watch the dash closely. Expect a more planted steering feel, at the cost of some of the cushioning a taller sidewall provides. More tread on the ground tends to improve dry grip and stance, with a small fuel-economy and clearance tradeoff. The larger wheel shows more of the brake hardware and tightens up the wheel-gap look. 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: 245/40 R20 is 11.8 mm taller than 235/50 R18, shifting the speedometer by +1.70%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+11.8 mm
1.70%
Speedometer at 100
101.7 km/h
+1.70% error
Ground clearance
+5.9 mm
ride height delta
Sidewall change
-19.5 mm
revs/km: 452.1
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/compare/235-50-r18-vs-245-40-r20Detailed comparison
| Metric | 235/50 R18 | 245/40 R20 | Difference |
|---|---|---|---|
| Overall diameter | 692.2 mm | 704.0 mm | +11.8 mm (+1.70%) |
| Sidewall height | 117.5 mm | 98.0 mm | -19.5 mm |
| Circumference | 2.175 m | 2.212 m | +37.1 mm |
| Revs / km | 459.9 | 452.1 | -7.7 |
| Ground clearance | reference | +5.9 mm | +5.9 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 101.7 km/h | +1.70 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 101.7 km/h after switching to 245/40 R20 — a +1.70% 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 +5.9 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.
Back to
235/50 R18
Back to
245/40 R20
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