Comparison
255/35 R21 vs 275/40 R20
275/40 R20 drops the rim from 21 to 20 inches versus 255/35 R21, trading wheel size for taller sidewall. This sizing approach 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 taller sidewall adds cushioning over potholes and rougher roads, with a softer overall ride. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakePractical direction for winter wheels, chains, or rougher pavement where cushioning matters.
Quick math: 275/40 R20 is 16.1 mm taller than 255/35 R21, shifting the speedometer by +2.26%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+16.1 mm
2.26%
Speedometer at 100
102.3 km/h
+2.26% error
Ground clearance
+8.1 mm
ride height delta
Sidewall change
+20.8 mm
revs/km: 437.2
Permalink for this comparison:
/compare/255-35-r21-vs-275-40-r20Detailed comparison
| Metric | 255/35 R21 | 275/40 R20 | Difference |
|---|---|---|---|
| Overall diameter | 711.9 mm | 728.0 mm | +16.1 mm (+2.26%) |
| Sidewall height | 89.3 mm | 110.0 mm | +20.8 mm |
| Circumference | 2.236 m | 2.287 m | +50.6 mm |
| Revs / km | 447.1 | 437.2 | -9.9 |
| Ground clearance | reference | +8.1 mm | +8.1 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 102.3 km/h | +2.26 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 102.3 km/h after switching to 275/40 R20 — a +2.26% 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 +8.1 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
255/35 R21
Back to
275/40 R20
Drivers also compare
Closely-related fitments and plus-size swaps for 255/35 R21 and 275/40 R20.
245/45 R20 vs 275/40 R20
Wider variation on the same rim — more grip, less clearance.
Δ 0.07%
265/40 R20 vs 275/40 R20
Wider variation on the same rim — more grip, less clearance.
Δ 1.11%
255/45 R20 vs 275/40 R20
Wider variation on the same rim — more grip, less clearance.
Δ 1.29%
275/40 R20 vs 295/35 R20
Wider variation on the same rim — more grip, less clearance.
Δ 1.85%
255/35 R21 vs 275/35 R21
Wider variation on the same rim — more grip, less clearance.
Δ 1.97%
275/40 R20 vs 295/40 R20
Wider variation on the same rim — more grip, less clearance.
Δ 2.20%
275/40 R20 vs 285/35 R20
Wider variation on the same rim — more grip, less clearance.
Δ 2.82%
255/35 R21 vs 285/35 R21
Wider variation on the same rim — more grip, less clearance.
Δ 2.95%
Related topics