Comparison
235/55 R18 vs 245/45 R20
Going from 235/55 R18 to 245/45 R20 steps up to a 20-inch rim while trimming sidewall to stay near OEM rolling diameter. This swap 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. The shorter sidewall gives the tire a firmer, more responsive feel and sharpens steering input. The wider section adds contact patch and lateral stability, while eating into fender and suspension clearance. The larger wheel shows more of the brake hardware and tightens up the wheel-gap look. Overall the swap sits inside the safe ±3% diameter window, so ABS, traction control and gearing behave normally.
TakeA solid pick for drivers chasing a more aggressive stance without abandoning OEM rolling diameter.
Quick math: 245/45 R20 is 12.8 mm taller than 235/55 R18, shifting the speedometer by +1.79%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+12.8 mm
1.79%
Speedometer at 100
101.8 km/h
+1.79% error
Ground clearance
+6.4 mm
ride height delta
Sidewall change
-19.0 mm
revs/km: 436.9
Permalink for this comparison:
/compare/235-55-r18-vs-245-45-r20Detailed comparison
| Metric | 235/55 R18 | 245/45 R20 | Difference |
|---|---|---|---|
| Overall diameter | 715.7 mm | 728.5 mm | +12.8 mm (+1.79%) |
| Sidewall height | 129.3 mm | 110.3 mm | -19.0 mm |
| Circumference | 2.248 m | 2.289 m | +40.2 mm |
| Revs / km | 444.8 | 436.9 | -7.8 |
| Ground clearance | reference | +6.4 mm | +6.4 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 101.8 km/h | +1.79 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 101.8 km/h after switching to 245/45 R20 — a +1.79% 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 +6.4 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
235/55 R18
Back to
245/45 R20
Drivers also compare
Closely-related fitments and plus-size swaps for 235/55 R18 and 245/45 R20.
245/45 R20 vs 275/40 R20
Wider variation on the same rim — more grip, less clearance.
Δ 0.07%
245/45 R20 vs 265/40 R20
Wider variation on the same rim — more grip, less clearance.
Δ 1.17%
245/45 R20 vs 255/45 R20
Wider variation on the same rim — more grip, less clearance.
Δ 1.24%
225/55 R18 vs 235/55 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.56%
245/45 R20 vs 295/35 R20
Wider variation on the same rim — more grip, less clearance.
Δ 1.92%
245/45 R20 vs 295/40 R20
Wider variation on the same rim — more grip, less clearance.
Δ 2.13%
245/45 R20 vs 285/35 R20
Wider variation on the same rim — more grip, less clearance.
Δ 2.88%
235/55 R18 vs 255/55 R18
Wider variation on the same rim — more grip, less clearance.
Δ 3.07%
Related topics