225/40 R18 Tyres Explained

225/40 R18 is a popular tyre size often fitted to sportier small and mid size cars. And to vehicles that benefit from responsive steering. The numbers are simple. 225 is the tyre width in millimetres. 40 is the aspect ratio, so the sidewall height is 40% of 225mm (about 90mm). R18 means the tyre fits an 18 inch rim and is of radial construction. You'll find premium options from Michelin, Continental, Pirelli, Bridgestone and Goodyear. mid range manufacturers on the page include Hankook, Kumho, Yokohama and Falken, while Wanli, Tomket, Westlake and Mazzini cover the value end. Popular 225/40 R18 models shown include the Michelin Pilot Sport 5 and the Continental SportContact 7. To confirm this is correct for your car, check the tyre sidewall, the driver's door sticker or your vehicle handbook, or enter your registration for exact matches. Also match the load and speed ratings to the manufacturer's recommendation.

The first 3 sets of numbers that you will see when reading a tyre size tell you the width, profile and diameter of your tyre. In this case, for the tyre size 225/40 R18 this is broken down as follows: 225 - the width of the tyre in millimetres. In this case 225mm wide. 40 - the height of the sidewall as a percentage of the width. In this case 40% R18 - the diameter of the tyre's inner rim in inches. Essentially what size of wheel this is intended to be fitted onto. For this size, that is a 18 inch wheel

There is no standard recommended tyre pressure for 225/40 R18 tyres, as each vehicle manufacturer will recommend their own optimal tyre pressure so you can enjoy the best performance from your vehicle. If you are unsure as to the correct tyre pressure for your 225/40 R18 tyres, there are a few different places you can look to find this information. Vehicle handbook - There is a section in most manufacturer handbooks which covers all the technical details for a tyre. This includes the tyre size, load rating, speed rating and tyre pressure. Tyre label - The tyre label is often found on the door jamb of the driver’s side. It is a small rectangular sticker which contains the information you need to know in regards to tyre pressure and tyre sizes. It should also tell you the tyre pressure recommendation

The height of your tyre's sidewall for the tyre size 225/40 R18 can be worked out by using the tyre's profile size. For the tyre size, the profile is 40. What this tells us is that the sidewall height is 40% of the cross-section width of the tyre. The sidewall height is determined by the distance between the rim line and the tread line. So, as this tyre has a cross-section width of 225mm, the height of the sidewall is 40% of 225 – which is 90mm.