Comparison
275/35 R21 vs 285/35 R20
Minus-sizing from 275/35 R21 to 285/35 R20 pairs a smaller 20-inch wheel with more rubber between the rim and road. This sizing approach shifts overall diameter slightly from OEM.
Expect a slight but noticeable shift in indicated speed compared to the original tires. Extra width broadens the footprint for more grip, but check inner liner and strut clearance before fitting. The smaller wheel is also lighter and easier to find affordable winter rubber for. Overall the swap sits inside the safe ±3% diameter window, so ABS, traction control and gearing behave normally.
TakeTypical choice for a dedicated winter or off-road setup where extra sidewall pays off.
Quick math: 285/35 R20 is 18.4 mm shorter than 275/35 R21, shifting the speedometer by -2.53%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-18.4 mm
-2.53%
Speedometer at 100
97.5 km/h
-2.53% error
Ground clearance
-9.2 mm
ride height delta
Sidewall change
+3.5 mm
revs/km: 449.9
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/compare/275-35-r21-vs-285-35-r20Detailed comparison
| Metric | 275/35 R21 | 285/35 R20 | Difference |
|---|---|---|---|
| Overall diameter | 725.9 mm | 707.5 mm | -18.4 mm (-2.53%) |
| Sidewall height | 96.3 mm | 99.8 mm | +3.5 mm |
| Circumference | 2.280 m | 2.223 m | -57.8 mm |
| Revs / km | 438.5 | 449.9 | +11.4 |
| Ground clearance | reference | -9.2 mm | -9.2 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 97.5 km/h | -2.53 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 97.5 km/h after switching to 285/35 R20 — a -2.53% 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 -9.2 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.
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275/35 R21
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285/35 R20
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