255/40R21 vs 255/45R20
255/45R20 is 1.0 mm taller 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 255/45R20 fitted, the speedometer reads 100 km/h when you are doing 100.1 km/h.
Dimensions side by side
| 255/40R21 | 255/45R20 | |
|---|---|---|
| Overall diameter | 737 mm (29.0″) | 738 mm (29.1″) |
| Section width | 255 mm | 255 mm |
| Sidewall height | 102 mm | 115 mm |
| Rim | 21″ | 20″ |
| Revolutions per km | 432 | 431 |
| In stock | 23 tires from $298.00 | 81 tires from $173.00 |
What changes
- Overall diameter: 255/45R20 is 1.0 mm taller (+0.1%).
- Speedometer: reads 100 km/h at an actual 100.1 km/h with 255/45R20.
- 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 255/45R20
See every alternate size for 255/40R21
Frequently asked questions
Can I use 255/45R20 instead of 255/40R21?
Usually, yes: 255/45R20 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 255/45R20?
With 255/45R20 instead of 255/40R21, the speedometer shows 100 km/h when you are actually doing 100.1 km/h.
Which vehicles came with both 255/40R21 and 255/45R20?
Both sizes were original equipment, on different trims or packages, on the 2014–2024 Audi SQ5, 2017–2024 Mercedes-Benz GLC 43, 2021–2024 Alfa Romeo Stelvio, 2017, 2021–2024 Audi Q5, 2023–2024 BMW i7, 2020–2024 BMW X3.