Tyres. There are four of them on your car and you change them when they look bald or when your mechanic says they won’t pass WOF. And when he does, you hand over your money without really knowing what you’ve bought. Sound about right? It’s probably a common experience for all but the automotively minded, but it shouldn’t be. Tyres are too important to your safety to be treated as an afterthought.
Choose Tyres Like an Expert
By spending a few minutes with the information below you’ll be able to choose tyres like an expert. You’ll also be able to nod knowingly when your tyre specialist starts dazzling you with facts about tread depth, aspect ratio, and speed performance rating.
The most obvious aspect of tyre safety is tread depth. The minimum legal requirement is that your tyres have at least 1.5mm deep tread across 75% of the width of the tyre and around the entire circumference. Tyre tread allows your car to corner and break with stability and effectiveness and provides grip in wet weather. The necessity for good tread is illustrated by the fact that at 100kph on a wet road a tyre has to move 5 litres of water per second from the area where the tyre touches the road (the “contact patch”).
When replacing car tyres, the recommended method is to change all four at the same time. If this is too much of a strain on the budget, then try to at least change them in pairs on the same axle. Tyres that share a common axle must be of the same construction and size. Never mix them – it’s dangerous and illegal.
Inflating your tyres to the correct pressure is essential for safe braking, maximum grip and long tyre life. Tyres that are too soft will increase petrol consumption and will negatively impact handling. Over-inflated tyres will reduce the car’s grip on the road. And in both cases your tyres will wear out faster. You can find the correct pressure rating for your tyres in you car’s handbook, or by asking your tyre supplier.
Having your wheels aligned and balanced every six months will extend tread life by preventing uneven wear – it’ll also give you a smoother ride. Rotating your wheels at regular intervals, too, will extend tyre life by keeping wear patterns even.
Check the sidewalls of your tyres every so often for damage. Check your tread for signs of uneven wear. As a rule of thumb:
- Wear on one edge of a tyre = an unbalanced or unaligned wheel.
- Wear on both edges = a persistently under-inflated tyre.
- Wear along the centre of the tyre surface = persistent over-inflation.
When choosing car tyres, don’t adopt a “on size fits all” approach. Different tyres have different capabilities and you need to match your tyres to your vehicle and the kind of driving you do. Do you drive at high speeds? Do you regularly carry heavy loads? Is much of your driving done in wet weather? All of these things will factor into determining the safest type of tyre for your car and should be discussed with your tyre supplier.
The various characteristics of your tyres are expressed in a number of ways.
- Tyre size – for cars this is expressed as the width of the tyre surface in millimetres.
- Aspect Ratio – is the ratio of the tyre’s width to its height (from the wheel rim). Tyres with a very low aspect ratio, low profile tyres for instance, are generally fitted to performance cars as they provide greater control and handling. They provide a harder ride, though, and are not generally suited to the family sedan.
- Speed Performance Rating – all tyres have a maximum speed rating. Tyres with a high speed rating are designed to tolerate higher speeds and will generally provide better performance at speed. Speed performance rating codes are found on the side of the tyre and are interpreted as follows:
- L – 160 km/h
- S – 175 km/h
- H – 210 km/h
- V – greater than 210 km/h
- Load Capacity – as with speed, all tyres have a maximum load bearing capacity. If you carry heavy loads, make sure your tyres are rated accordingly.
Reading Tyre Markings
Ever wondered how you read those markings on the side of your tyres? Here’s an example explained: 195/65R15 is:
- 195 – width of tyre in millimetres i.e. 195mm
- 65 – the aspect ratio of the tyre
- R – stands for “Radial”, the type of construction used in the tyre. Nearly all tyres today are of radial construction.
- 15 – the width of the wheel rim in inches i.e. 15 inches.
Choose your car tyres carefully, pay attention to their characteristics – are they right for your car? Discuss the various options with your tyre specialist and, once purchased, maintain your tyres through correct pressure levels, wheel balancing and regular damage/wear checks. On a wet night, driving a difficult stretch of road, the investment in time and money will all seem worth it.