235/50R18 vs 245/40R20
245/40R20 is 12.0 mm taller than 235/50R18 in overall diameter (+1.7%), within the usual 3% limit, so it can replace it where the wheels and clearance allow. With 245/40R20 fitted, the speedometer reads 100 km/h when you are doing 101.7 km/h.
Dimensions side by side
| 235/50R18 | 245/40R20 | |
|---|---|---|
| Overall diameter | 692 mm (27.2″) | 704 mm (27.7″) |
| Section width | 235 mm | 245 mm |
| Sidewall height | 118 mm | 98 mm |
| Rim | 18″ | 20″ |
| Revolutions per km | 460 | 452 |
| In stock | 53 tires from $117.00 | 34 tires from $238.00 |
What changes
- Overall diameter: 245/40R20 is 12.0 mm taller (+1.7%).
- Speedometer: reads 100 km/h at an actual 101.7 km/h with 245/40R20.
- 245/40R20 is 10 mm wider, so check clearance and the recommended rim width.
- Wheel size changes from 18″ 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 235/50R18
Vehicles that use 245/40R20
See every alternate size for 235/50R18
Frequently asked questions
Can I use 245/40R20 instead of 235/50R18?
Usually, yes: 245/40R20 is within 3% of the overall diameter of 235/50R18 (+1.7%). 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 235/50R18 and 245/40R20?
With 245/40R20 instead of 235/50R18, the speedometer shows 100 km/h when you are actually doing 101.7 km/h.
Which vehicles came with both 235/50R18 and 245/40R20?
Both sizes were original equipment, on different trims or packages, on the 2016–2020 Buick Lacrosse, 2018–2019 Cadillac CT6, 2014, 2016–2018 Maserati Ghibli, 2015–2016 Chevrolet Impala.