245/45R17 vs 255/40R18
255/40R18 is 9.0 mm taller than 245/45R17 in overall diameter (+1.4%), within the usual 3% limit, so it can replace it where the wheels and clearance allow. With 255/40R18 fitted, the speedometer reads 100 km/h when you are doing 101.4 km/h.
Dimensions side by side
| 245/45R17 | 255/40R18 | |
|---|---|---|
| Overall diameter | 652 mm (25.7″) | 661 mm (26.0″) |
| Section width | 245 mm | 255 mm |
| Sidewall height | 110 mm | 102 mm |
| Rim | 17″ | 18″ |
| Revolutions per km | 488 | 482 |
| In stock | 18 tires from $113.00 | 13 tires from $238.00 |
What changes
- Overall diameter: 255/40R18 is 9.0 mm taller (+1.4%).
- Speedometer: reads 100 km/h at an actual 101.4 km/h with 255/40R18.
- 255/40R18 is 10 mm wider, so check clearance and the recommended rim width.
- Wheel size changes from 17″ 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 245/45R17
Vehicles that use 255/40R18
See every alternate size for 245/45R17
Frequently asked questions
Can I use 255/40R18 instead of 245/45R17?
Usually, yes: 255/40R18 is within 3% of the overall diameter of 245/45R17 (+1.4%). 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 245/45R17 and 255/40R18?
With 255/40R18 instead of 245/45R17, the speedometer shows 100 km/h when you are actually doing 101.4 km/h.
Which vehicles came with both 245/45R17 and 255/40R18?
Both sizes were original equipment, on different trims or packages, on the 2010–2015 Lexus IS 250C, 2010–2015 Lexus IS 350C, 2006–2013 Lexus IS 250, 2006–2013 Lexus IS 350.