255/40R21 vs 285/40R20
285/40R20 is 1.0 mm shorter than 255/40R21 in overall diameter (−0.1%), within the usual 3% limit, so it can replace it where the wheels and clearance allow. With 285/40R20 fitted, the speedometer reads 100 km/h when you are doing 99.9 km/h.
Dimensions side by side
| 255/40R21 | 285/40R20 | |
|---|---|---|
| Overall diameter | 737 mm (29.0″) | 736 mm (29.0″) |
| Section width | 255 mm | 285 mm |
| Sidewall height | 102 mm | 114 mm |
| Rim | 21″ | 20″ |
| Revolutions per km | 432 | 432 |
| In stock | 23 tires from $298.00 | 7 tires from $392.00 |
What changes
- Overall diameter: 285/40R20 is 1.0 mm shorter (−0.1%).
- Speedometer: reads 100 km/h at an actual 99.9 km/h with 285/40R20.
- 285/40R20 is 30 mm wider, so check clearance and the recommended rim width.
- Wheel size changes from 21″ to 20″: you need wheels in the new size.
- Choose a load index at least as high as the one on your door placard.
Vehicles that came with both sizes
Vehicles that use 255/40R21
Vehicles that use 285/40R20
See every alternate size for 255/40R21
Frequently asked questions
Can I use 285/40R20 instead of 255/40R21?
Usually, yes: 285/40R20 is within 3% of the overall diameter of 255/40R21 (−0.1%). Use wheels of the right size and width, match or exceed the original load index, and check clearance at full steering lock.
How much does the speedometer change between 255/40R21 and 285/40R20?
With 285/40R20 instead of 255/40R21, the speedometer shows 100 km/h when you are actually doing 99.9 km/h.
Which vehicles came with both 255/40R21 and 285/40R20?
Both sizes were original equipment, on different trims or packages, on the 2017–2024 Mercedes-Benz GLC 43, 2023–2024 BMW i7, 2021–2024 Alfa Romeo Stelvio, 2023–2024 BMW 740i, 2023–2024 BMW 760i, 2024 BMW 750e.