255/40R20 vs 285/30R21
285/30R21 is 8.0 mm shorter than 255/40R20 in overall diameter (−1.1%), within the usual 3% limit, so it can replace it where the wheels and clearance allow. With 285/30R21 fitted, the speedometer reads 100 km/h when you are doing 98.9 km/h.
Dimensions side by side
| 255/40R20 | 285/30R21 | |
|---|---|---|
| Overall diameter | 712 mm (28.0″) | 704 mm (27.7″) |
| Section width | 255 mm | 285 mm |
| Sidewall height | 102 mm | 86 mm |
| Rim | 20″ | 21″ |
| Revolutions per km | 447 | 452 |
| In stock | 47 tires from $164.00 | 2 tires from $606.00 |
What changes
- Overall diameter: 285/30R21 is 8.0 mm shorter (−1.1%).
- Speedometer: reads 100 km/h at an actual 98.9 km/h with 285/30R21.
- 285/30R21 is 30 mm wider, so check clearance and the recommended rim width.
- Wheel size changes from 20″ to 21″: 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 255/40R20
Vehicles that use 285/30R21
See every alternate size for 255/40R20
Frequently asked questions
Can I use 285/30R21 instead of 255/40R20?
Usually, yes: 285/30R21 is within 3% of the overall diameter of 255/40R20 (−1.1%). 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 255/40R20 and 285/30R21?
With 285/30R21 instead of 255/40R20, the speedometer shows 100 km/h when you are actually doing 98.9 km/h.
Which vehicles came with both 255/40R20 and 285/30R21?
Both sizes were original equipment, on different trims or packages, on the 2023–2024 Mercedes-Benz EQE350, 2022–2024 Mercedes-Benz S500, 2022–2024 Mercedes-Benz S580, 2023–2024 Mercedes-Benz EQE500, 2024 Mercedes-Benz S580e, 2019–2022 BMW Alpina.