275/30R20 vs 275/40R18
275/40R18 is 4.0 mm taller than 275/30R20 in overall diameter (+0.6%), within the usual 3% limit, so it can replace it where the wheels and clearance allow. With 275/40R18 fitted, the speedometer reads 100 km/h when you are doing 100.6 km/h.
Dimensions side by side
| 275/30R20 | 275/40R18 | |
|---|---|---|
| Overall diameter | 673 mm (26.5″) | 677 mm (26.7″) |
| Section width | 275 mm | 275 mm |
| Sidewall height | 83 mm | 110 mm |
| Rim | 20″ | 18″ |
| Revolutions per km | 473 | 470 |
| In stock | 14 tires from $269.00 | 8 tires from $273.00 |
What changes
- Overall diameter: 275/40R18 is 4.0 mm taller (+0.6%).
- Speedometer: reads 100 km/h at an actual 100.6 km/h with 275/40R18.
- Wheel size changes from 20″ to 18″: 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 275/30R20
Vehicles that use 275/40R18
See every alternate size for 275/30R20
Frequently asked questions
Can I use 275/40R18 instead of 275/30R20?
Usually, yes: 275/40R18 is within 3% of the overall diameter of 275/30R20 (+0.6%). 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 275/30R20 and 275/40R18?
With 275/40R18 instead of 275/30R20, the speedometer shows 100 km/h when you are actually doing 100.6 km/h.
Which vehicles came with both 275/30R20 and 275/40R18?
Both sizes were original equipment, on different trims or packages, on the 2020–2022 BMW 840i.