235/50R17 vs 265/40R18
265/40R18 is 2.0 mm taller than 235/50R17 in overall diameter (+0.3%), within the usual 3% limit, so it can replace it where the wheels and clearance allow. With 265/40R18 fitted, the speedometer reads 100 km/h when you are doing 100.3 km/h.
Dimensions side by side
| 235/50R17 | 265/40R18 | |
|---|---|---|
| Overall diameter | 667 mm (26.3″) | 669 mm (26.3″) |
| Section width | 235 mm | 265 mm |
| Sidewall height | 118 mm | 106 mm |
| Rim | 17″ | 18″ |
| Revolutions per km | 477 | 476 |
| In stock | 15 tires from $118.00 | 2 tires from $341.00 |
What changes
- Overall diameter: 265/40R18 is 2.0 mm taller (+0.3%).
- Speedometer: reads 100 km/h at an actual 100.3 km/h with 265/40R18.
- 265/40R18 is 30 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 235/50R17
Vehicles that use 265/40R18
See every alternate size for 235/50R17
Frequently asked questions
Can I use 265/40R18 instead of 235/50R17?
Usually, yes: 265/40R18 is within 3% of the overall diameter of 235/50R17 (+0.3%). 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 235/50R17 and 265/40R18?
With 265/40R18 instead of 235/50R17, the speedometer shows 100 km/h when you are actually doing 100.3 km/h.
Which vehicles came with both 235/50R17 and 265/40R18?
Both sizes were original equipment, on different trims or packages, on the 2007–2013 Porsche Cayman, 2005–2012 Porsche Boxster.