Comparison
285/30 R20 vs 305/30 R20
305/30 R20 is a wider variation of 285/30 R20 on the same 20-inch rim, adding 20 mm of tread footprint. This sizing approach trims or stretches rolling diameter by a small margin.
The speedometer offset is small but measurable; worth keeping in mind if you watch the dash closely. The wider section adds contact patch and lateral stability, while eating into fender and suspension clearance. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeUseful when extra dry grip and stance matter more than a small fuel-economy hit.
Quick math: 305/30 R20 is 12.0 mm taller than 285/30 R20, shifting the speedometer by +1.77%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+12.0 mm
1.77%
Speedometer at 100
101.8 km/h
+1.77% error
Ground clearance
+6.0 mm
ride height delta
Sidewall change
+6.0 mm
revs/km: 460.7
Permalink for this comparison:
/compare/285-30-r20-vs-305-30-r20Detailed comparison
| Metric | 285/30 R20 | 305/30 R20 | Difference |
|---|---|---|---|
| Overall diameter | 679.0 mm | 691.0 mm | +12.0 mm (+1.77%) |
| Sidewall height | 85.5 mm | 91.5 mm | +6.0 mm |
| Circumference | 2.133 m | 2.171 m | +37.7 mm |
| Revs / km | 468.8 | 460.7 | -8.1 |
| Ground clearance | reference | +6.0 mm | +6.0 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 101.8 km/h | +1.77 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 305/30 R20 — a +1.77% 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 +6.0 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
285/30 R20
Back to
305/30 R20
Drivers also compare
Closely-related fitments and plus-size swaps for 285/30 R20 and 305/30 R20.
245/35 R20 vs 285/30 R20
Wider variation on the same rim — more grip, less clearance.
Δ 0.07%
265/35 R20 vs 305/30 R20
Wider variation on the same rim — more grip, less clearance.
Δ 0.36%
255/35 R20 vs 305/30 R20
Wider variation on the same rim — more grip, less clearance.
Δ 0.66%
255/35 R20 vs 285/30 R20
Wider variation on the same rim — more grip, less clearance.
Δ 1.09%
275/35 R20 vs 305/30 R20
Wider variation on the same rim — more grip, less clearance.
Δ 1.36%
245/35 R20 vs 305/30 R20
Wider variation on the same rim — more grip, less clearance.
Δ 1.69%
245/40 R20 vs 305/30 R20
Wider variation on the same rim — more grip, less clearance.
Δ 1.85%
265/35 R20 vs 285/30 R20
Wider variation on the same rim — more grip, less clearance.
Δ 2.09%
Related topics