Could you tell me the difference between those two tires? P:245-70-17 and LT:245-70-17. - Marc
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There is little doubt which company has mastered the art of making tires sexy, but what do you really need to know before your rubber hits the road?
There are loads of tires on the market, and it's important to know the differences. Your tire choice affects safety, fuel economy, performance and handling.
Let's start by getting to the bottom of your question. The "P" refers to passenger vehicle tires - including cars, minivans, crossover vehicles, SUVs and even small trucks. The "LT" designation is used for vehicles with higher carrying capacity - such as large pickup trucks and vans.
You shouldn't interchange these tire types.
"The actual construction of the tire is different. All tires with the prefix 'P' are four-ply. Any tire with six-ply is automatically an LT, which are basically commercial tires. The difference is maximum operating temperature; LT tires can withstand more load at a higher pressure," says Orazio Mastracchio, product manager at Pirelli Canada.
While we're at it, what do all the numbers on the tire sidewall mean? As you might expect, they refer to various dimensions of the tire. In your example (245-70-17), the first number, 245, is the tire width, in millimetres. The second number, 70, is the aspect ratio - between the height and width of the tire - expressed as a percentage. The last number in the sequence, 17, is the wheel diameter, in inches.
So why is it important to understand these measurements, and why is it important to have the right tires? Let's review some of the basics. The vehicle manufacturers' recommendations for your tires are based on weight, design, expected use and performance. You can find these specifications on a placard inside the driver's side door and in your owner's manual.
Any change in size will affect the correct working of your speedometer, and therefore odometer. With a larger tire, the number of revolutions is lower of course - so your speedometer could be showing 70 km/h when you're actually doing 80 km/h.
Proper tire designation and size are important to the safe operation of a vehicle, and so is tire pressure.
Your vehicle has a maximum load - based on tire construction, size and inflation pressure. Though not shown in your example, the load index and speed code follow the diameter reading on a tire sidewall.
"Never downgrade the speed code - that's the letter after the load range. It's a safety issue. When a car is designed, all tests are done with that specific speed code, and all tires are tested with a certain speed on the drum. Each speed code relates to a maximum speed, which is also tied to the load index," says Mastracchio.
"Correct sizing is important, and so is correct maintenance. If a tire is under-inflated, or worn down, it's not safe. In terms of fuel economy, the wrong pressure will cost you more fuel, and so will a tire that's worn out. Tires have basic needs - air and pressure," says Normand Latremouille of Michelin Canada. "Check your tire pressure monthly, and take the opportunity to make a visual inspection of your tires." Tire gauges are inexpensive, and some new vehicles have dashboard tire-pressure monitoring systems that warn you if a tire is under-inflated.
Tire manufacturers' websites will show you tire options based on your vehicle make, model and year. The smartest thing you can do is follow the manufacturers recommendations on your car, and the advice of a tire specialist.
Now that you've got your tires figured out, you can turn your attention to getting your hands on the coveted 2011 Pirelli calendar.
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