![\"Tyre](\"http:\/\/blog.privatefleet.com.au\/wp-content\/uploads\/2013\/11\/Tyre-profile.gif\")
<\/a>this: “225\/60\/17”. Tyres are, naturally, wrapped around wheels. The wheels will have a diameter and in a metric age are still listed by inches. Smaller cars will generally have wheel diameters of 14 to 16 inches, medium cars generally up to 17 whilst large cars can be up to 19 as standard and certain cars can be fitted with up to 22 inch diameter wheels. The tyres then will have that info and will be showing the diameter as the last number. The other two work hand in hand, with the biggest number being the width across the tread of the tyre in millimetres (225) and the sidewall height or profile, from the rim of the wheel to the tread, expressed as a percentage of the tread width. This means that our 225\/60 tyres will have a sidewall being equalling 60 percent of the width of the tread.<\/p>\nTossed into that set of numbers could be something like this: 225\/60VR\/17. Compounds: rubber can be soft, it can be hard and anywhere in between. Followers of motorsport will be aware of hard\/soft\/medium compounds being bandied around as easy as we talk about the weather and really, that’s pretty much all this means. Soft tyre compounds will give more grip overall however may wear quicker due to the extra grip, whereas hard compound may not grip quite so well, will last longer and may not give a softer ride. However, there’s a little bit more to it such as where the tyres will be used as weather conditions on a ongoing basis.<\/p>\n Tyre pressures: these can be read as PSI (pounds per square inch) or kilopascals. Run flat\/spacesaver tyres: run flats are intended to give some measure of sidewall support should the tyre have deflated past its normal recommended pressure for any reason and will allow the vehicle to be driven, to a point, where the tyre can be replaced. Comfort levels are not included as part of the design. Space savers are becoming more and more common, partly to save weight but primarily Brands: there are heaps to choose from, such as Bridgestone, Dunlop, Kumho, Firestone, just to name a few; the actual construction quality will be of a higher standard in the better known brands and independent testing tends to show better overall grip and performance levels.<\/p>\n Tread patterns: there’s a couple of terms, such as asymmetric and directional, that catch people. Most “normal” tyres are symmetrical, in that the tread looks the same on the left and right of the tyre and are generally for everyday use. Asymmetrical tyres, generally for performance applications, will have an unbalanced look, for example with an unbroken groove or two one one side and a broken up tread pattern on the other. Directional tyres are akin to an arrowhead patter, with grooves leading from the outside to the centre at an angle and intended to give <\/a> For over 40 years, tyres have been constructed in a radial design (http:\/\/en.wikipedia.org\/wiki\/Radial_tire<\/a>) and have speed rating applied to them for certain intended purposes. A V rating permits that tyre to be run up to 240km\/h with the R denoting a Radial construction. Although Australia, for example has a maximum permitted road speed of 110 km\/h, there are places where a car can be travelling above that limit, such as a race track plus, in a world market, other countries have higher permissable speeds.<\/p>\n<\/a>Rolling diameter: this is nothing more complicated than how to mix and match tyre and wheel sizes to give, effectively, the same size circle. Let’s use 205\/65\/15 tyres for a mid 1990s Commodore. The OVERALL diameter is about 647mm. The driver decides to fit some 19 inch diameter wheels; if they were to fit the same PROFILE (65) tyres the overall diameter would be well over 700mm. This is both currently illegal and in real and serious danger of the rubber fouling the inside of the wheel arches plus can give a false reading to the speedometer. Therefore a LOWER profile tyre needs to be used. By using 35 profile tyres (height is 35% of the width of the tyre) the overall diameter is brought back to 647mm. Of note is how a profile can affect the perceived ride of a car; a higher profile tyre will have more sidewall “give” than a lower; think of a well padded cushion versus a slim one of the same material. The tyre and wheel increase can also be known as “plus one\/two etc”.<\/p>\n<\/a> Most companies use PSI and it’s and indication of how much pressure is required to stop excessive wear of the tyre balanced against the expected load the tyres will carry (car, passengers and cargo). This information for each car can be found on a placard attached to the car and also on the tyre sidewall. It’s important to have correctly pressure tyres to stop wear either on the centre of the tyre (over inflated) or on the edges (underinflated) plus ride quality and handling can be severely affected<\/p>\n<\/a>to, as the name implies, save space, generally in the boot of the car. They are NOT intended to be used for anything other than to temporarily replace a normal tyre and are an emergency item.<\/p>\n<\/a>maximum water dispersion.<\/a><\/p>\n