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Frequently Asked Questions About Tyres
What does 255/45 R18 mean?The numbers 255/45 R18 are 3 very important pieces of information in regards to a tyre's size. They tell you the width, profile and diameter of a tyre. For a tyre that is 255/45 R18 this information can be broken down into the following: 255 - the width in millimetres of the tyre. In this case 255mm wide. 45 - the height of the sidewall as a percentage of the width. For this tyre that is 45% R18 - the diameter, in inches, of the tyre's inner rim. Letting you know what size of wheel this tyre should be fitted to. For this size, that is a 18 inch wheel
If you are looking for the recommended tyre pressure for 255/45 R18 tyres, you will find that this will depend on the manufacturer and model. Each vehicle manufacturer has their own tyre pressure recommendation for their model, that will deliver an optimal performance for your vehicle. Check the following if you are unsure what the correct tyre pressure is for your 255/45 R18 tyres Tyre label - this is often the best place to find your tyre pressure information. It is located on the door jamb on the driver’s side of the vehicle. It is a small rectangular label that provides the driver with the recommended tyre pressure and tyre sizes. Vehicle handbook - Quite often the vehicle handbook with contain a section that relates to the technical details for the tyre. This should include the required tyre size, load rating, speed rating and recommended tyre pressure.
The sidewall height of a 255/45 R18 tyre is calculated by using the profile information of the tyre size. In this instance 45. This tells us that it is 45% of the tyre's cross-section width. When looking at a tyre, the sidewall height is the distance between the tread line of the tyre and the rim line. Given that this tyre size has a cross-section width which equals 255mm, we can work out that the sidewall height is 45% of 255 – this comes to 114.75mm.
Yes, it is very important that the tyre size of a tyre is exact. As the only part of a vehicle in contact with the road, there is a lot of reliance on tyres to be accurate, correctly constructed and exact. Different parts of the vehicle require accurate tyres so they can function correctly. The speedometer, for example, is only able to accurately calculate the speed and distance you are travelling if the tyres are exact and what it has been calibrated to. This is also true for the different section of your vehicle which deal with the handling, braking and suspension of your vehicle. These all need accurate and exact tyres as they have been calibrate to function based on tyres of a specific size. If the tyres were not exact your vehicle’s performance and the your safety would suffer.
There is no standardised recommendation on whether tyres should be the same on the front and back, as this depends on the vehicle you drive and the requirements as set out by the vehicle manufacturer. As a general rule of thumb, you will find that front-wheel drive vehicles tend to have the same size on all axles, whilst rear-wheel drive vehicles tend to require wider wheels and tyres on the rear of the vehicle. Please make sure that you check the requirements of your specific vehicle. Each model of vehicle is different and requires different criteria of it’s tyres to ensure the best performance. Check your vehicle handbook for the right tyre size(s) for your vehicle.