Comparison
245/45 R18 vs 255/35 R20
Going from 245/45 R18 to 255/35 R20 steps up to a 20-inch rim while trimming sidewall to stay near OEM rolling diameter. This sizing approach keeps overall diameter very close to stock. The shorter sidewall gives the tire a firmer, more responsive feel and sharpens steering input.
The speedometer offset is mild and well inside what most cars can tolerate without recalibration. 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: 255/35 R20 is 8.8 mm taller than 245/45 R18, shifting the speedometer by +1.30%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+8.8 mm
1.30%
Speedometer at 100
101.3 km/h
+1.30% error
Ground clearance
+4.4 mm
ride height delta
Sidewall change
-21.0 mm
revs/km: 463.7
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/compare/245-45-r18-vs-255-35-r20Detailed comparison
| Metric | 245/45 R18 | 255/35 R20 | Difference |
|---|---|---|---|
| Overall diameter | 677.7 mm | 686.5 mm | +8.8 mm (+1.30%) |
| Sidewall height | 110.3 mm | 89.3 mm | -21.0 mm |
| Circumference | 2.129 m | 2.157 m | +27.6 mm |
| Revs / km | 469.7 | 463.7 | -6.0 |
| Ground clearance | reference | +4.4 mm | +4.4 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 101.3 km/h | +1.30 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 101.3 km/h after switching to 255/35 R20 — a +1.30% 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 +4.4 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
245/45 R18
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255/35 R20
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