The functions of tyres are to support the weight of a vehicle, provide traction, and bring the car to a safe stop. They also need to run at low pressures without risk of bursting or shredding, have enough grip in both wet and dry conditions while being lightweight so that they don't affect fuel consumption too much. Additionally, they must be durable because drivers can't pull over if their Continental Tyres Airdrie starts coming apart immediately.
Tyre sizes are measured by an alphanumeric combination representing its three key dimensions: section width, rim diameter, and tyre profile. The first number you'll come across is the section width - this measures the tire’s widest point when considering sidewall design (i.e. not including external thread). So if you see 185 section widths, then the enormous bulge that can fit into this tyre is 185 millimetres. Next, you'll come across the rim diameter, so 26 inches in the case of OE fitments. Lastly, there's something called a tyre profile - think about it as how 'pointed' or 'flat' the sidewalls are at their widest point. So, for example, if you've ever bought tyres online and noticed that its measurements are described as 80/90-10 or 90/80-10, then this tells us that its sidewall measures an 80% (i.e. very flat) at its widest point where it meets to treads.
The final alphanumeric jigsaw puzzle is the load index and speed index, which don't seem immediately apparent from a glance at a tire’s size. The load index measures a tyre's maximum load-carrying capacity and the speed it can support before being damaged, so for example, if your OE tyres have a 94 as their load index, then multiplied by four, this equates to 380kg. Suppose you replace those with 95 load-indexed tyres, assuming they're all fitted to the same axle. In that case, this figure now becomes 390kg - not an enormous difference but certainly noticeable over time, especially if you're regularly carrying that weight or more. Another essential thing to remember is that these indexes are relative - there's no industry standard stating which tyres should have what numbers, so every brand's sizing is different.
Because of this, it's always a good idea to check your tyre size when replacing tyres in case you need to buy a different brand or model. You should also get your tyres checked if you've had any issues with them because they could be dangerously underinflated or overloaded - both of which are illegal and could land you with a hefty fine.
Pushing the boundaries
Another aspect engineers have to consider is what happens when the weather fails to play along. This can mean designing tyres that can grip in wet conditions but excel at it too. Tyres for sports cars do this by using unique asymmetric tread designs that can improve grip tenfold compared to non-sports models through clever construction and design. However, unique tread designs aren't just limited to whizzy models - a look at the tyres of cars from any decade will show you that there's been an ongoing quest for better grip, even with base-spec units.
To get a better grip on wet surfaces, tyre engineers have had to rethink how their treads work entirely. This has led to new and improved compounds that can provide more bite when it counts and revised siping designed to help water escape faster so that it doesn't become trapped in the tread blocks. There are also new tread patterns designed to churn through standing water effortlessly while still reaching peak performance on dry tarmac roads. Combined with all these changes are advancements in the construction process, leading to an increase in sidewall rigidity. This has meant that tyres can now be designed with enough compliance to allow them to grip in wet conditions without skidding even when travelling at speed.
All these changes have given rise to new tyre technologies, which means you'll find all manner of acronyms on the side of your chosen rubber, but what do they all mean? Here are some of the most commonly used ones
· S - The letter S stands for 'sport' and denotes a tyre Car Tyres Airdrie built from a durable compound and reinforced with belts beneath its tread blocks. This makes it more structurally rigid to deliver improved levels of handling, whatever the weather condition.
· T - The letter T or 'turbo' denotes that a tyre has been approved for the use of run-flat technology, which means it's designed with an internal structure that constantly monitors its calorimetry and can sustain its performance even when pierced - this allows safe emergency driving to a service station if your tyre is punctured on the motorway for example. ZR, VR, or W-rated tyres –
· This stands for 'performance' and denotes a tyre with a high top speed rating, usually around 150mph, depending on manufacturer and model specification.