235/55R18 vs 245/40R21
245/40R21 is 13.0 mm taller than 235/55R18 in overall diameter (+1.8%), within the usual 3% limit, so it can replace it where the wheels and clearance allow. With 245/40R21 fitted, the speedometer reads 100 km/h when you are doing 101.8 km/h.
Dimensions side by side
| 235/55R18 | 245/40R21 | |
|---|---|---|
| Overall diameter | 716 mm (28.2″) | 729 mm (28.7″) |
| Section width | 235 mm | 245 mm |
| Sidewall height | 129 mm | 98 mm |
| Rim | 18″ | 21″ |
| Revolutions per km | 445 | 437 |
| In stock | 60 tires from $128.00 | 10 tires from $398.00 |
What changes
- Overall diameter: 245/40R21 is 13.0 mm taller (+1.8%).
- Speedometer: reads 100 km/h at an actual 101.8 km/h with 245/40R21.
- 245/40R21 is 10 mm wider, so check clearance and the recommended rim width.
- Wheel size changes from 18″ 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 235/55R18
Vehicles that use 245/40R21
See every alternate size for 235/55R18
Frequently asked questions
Can I use 245/40R21 instead of 235/55R18?
Usually, yes: 245/40R21 is within 3% of the overall diameter of 235/55R18 (+1.8%). 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 235/55R18 and 245/40R21?
With 245/40R21 instead of 235/55R18, the speedometer shows 100 km/h when you are actually doing 101.8 km/h.
Which vehicles came with both 235/55R18 and 245/40R21?
Both sizes were original equipment, on different trims or packages, on the 2019–2022 Volvo XC40, 2018–2019 Volvo V90 Cross Country.