PLY RATING

How is the load capacity of a tire determined?

Let’s begin by reminding ourselves that it is not the tire that carries the load, but the air inside it. The tire is just the container for the air. So, if you need to carry more load, you need more air. You might accomplish that with a larger air chamber or by forcing more air molecules into the same size air chamber you’d normally use for a tire with a lower load capacity. In other words, you might use a bigger tire or a tire running at a higher inflation pressure. Either way, the tire needs to be strong enough to handle the higher capacity. The traditional ways of defining this are “Ply Rating,” “Load Range,” and “Load Index.”

What is meant by “Ply Rating?”

In the early days of bias tires, casing strength was built up by adding layer upon layer of cotton fabric. The layers were placed with the thread in each layer at an angle to each other. That added strength, because the tensions would be distributed throughout the layers of fabric. The Ply Rating used to refer to the number of layers of cotton.

Ply Rating	Load Range
2	A
4	B
6	C
8	D
10	E
12	F
14	G
16	H
18	J
20	L

Why aren’t there any odd numbers?

Since you have to have at least two plies to have a “bias” arrangement, bias ply tires always had an even number of plies.

Is cotton still used?

Cotton went away a long time ago. One of the major improvements was making plies out of nylon. Nylon is so much stronger that if you’re old enough, you may remember seeing your tires stamped with the words, “2 Ply/4 Ply Rating.” That meant there were only two nylon plies, but they were so strong the tire was equivalent to one made of four cotton plies.

And that’s about when things started to get complicated.

How so?

Ply materials continued to improve, especially with the introduction of steel ply materials and radial construction, making the old Ply Number less and less meaningful. And that resulted in the newer designation we use today, called “Load Range.” 

On the chart, you can see how today’s Load Ranges correspond to the older Ply Rating system.

And why isn’t there an “I” or a “K” Load Range?

Just to avoid confusion. An “I” might, depending on the typeface, look like the numeral “1″ and “K” is a very common abbreviation for “kilo” meaning “thousand.”

What does Load Range really mean?

Load Range indicates the maximum load recommended for the tire. This varies by tire size and inflation pressure: A bigger tire can hold more air and can be rated for a higher load. Also, a given tire size at a higher air pressure results in a higher-rated load.

Load Capacities for Some “G” Load Range Single Tires

Size	Maximum Single Load (lbs.)	Inflation Pressure (psi)
295/75R22.5	6175	110
285/75R24.5	6175	110
11R22.5	6175	105
11R24.5	6610	105
12R22.5	6610	105
12R24.5	7160	105

And here are the same tire sizes, but in a higher load rating:

Load Capacities for Some “H” Load Range Single Tires

Size	Maximum Single Load (lbs.)	Inflation Pressure (psi)
295/75R22.5	6610	120
285/75R24.5	6780	120
11R22.5	6610	120
11R24.5	7160	120
12R22.5	7390	120
12R24.5	7830	120

So what’s the difference between tires of the same size but different load ranges?

It’s no longer the number of plies. Most radial truck tires, for example, have a total of five plies. There’s one steel body ply and four belts under the tread. What is different today is the strength of the steel cables in those plies or the number of cables per inch. We’re now at the point where we no longer add more and more plies, but instead, adjust the strength of the entire casing to achieve the desired load capacity.

Will a tire with a higher Load Range last longer?

It might, but it also might not. What usually determines tire life is the rate at which the tread wears and whether or not the tread wears evenly. Or how many retreads you can get from its casing. As long as the tire has enough load capacity for the maximum load you will be putting on it, buying extra load capacity may not increase your tire life.

Traction-tread wearing-temperature

It isn’t just size that matters when choosing tyres for your vehicle.  There are some other numbers and letters on the side of the tyre that you should pay attention to.   You will find the tread wear listed in three digit numeric format such as “320” and the traction and temperature in letters such as AA, A, B, or C.

Tread wear

The tread wear rating is a relative measurement of the tyre’s durability and treads life. It is important to remember that road surfaces, driving habits, and other factors determine actual tread life. Each tyre manufacturer independently determines tread wear through their own tests. Tread wear is not based on any one industry or government standard.  The higher the number the longer the tyre should last compared to similar tyres from the same manufacture with lower numbers.  A tyre with a tread wear rating of 800 should theoretically last about twice as long as a tyre with a tread wear rating of 400.  A longer life tyre will be designed with a harder rubber compound to withstand wear better.

Traction

Unfortunately, while a harder compound tyre will last longer it will do so at the expense of some traction – particularly on wet surfaces.  The softer tyre compounds will grip the road surface better for improved handling and braking performance.  The traction specification is listed beside the tread wear in the form of letters such as AA, or A, or B with AA being the highest grade possible.  The traction rating is a measurement of a tyre’s ability to stop on a straight, wet surface under controlled conditions. It does not indicate the tyre’s cornering ability on a wet surface or its traction on ice or snow.

Temperature

The temperature rating is a measurement of a tyre’s resistance to heat generation under normal operating conditions at recommended inflation pressures. Temperature grades range from A to C, with A being highest rated and therefore most resistant to heat generation.  Tyres graded A effectively dissipate heat up to a maximum speed that is greater than 115 mph. B rates at a maximum between 100 mph and 115 mph. C rates at a maximum of between 85 mph to 100 mph. Tyres that cannot grade up to C or higher cannot be sold in the US.

Source: http://finixx.com/traction/

Dangers Of Using Worn Tyre

Worn tyres need a longer stopping distance on wet roads!

Worn tyres are a sign of danger. Tread grooves are vital for safe driving! Tread wear causes poor tyre performance and can lead to serious problems!

Replace the tyre immediately when the tread wear indicator shows!

The Tread wear indicator appears when the tread has worn out to 1.6mm.Never use a tyre where even just one tread wear indicator is exposed.

Advantages of Tyre Rotation

1. Prevention of Uneven Tread Wear
   2. Extension of Tyre Service Life
   3. Averaging of Tyre Fatigue

Note: The front-wheel tyres of an FF vehicle wear two or three times faster than the rear-wheel tyres because the front-wheel tyres function for both driving and steering.

Friction and Stopping Distance

Friction is defined as a force that opposes motion.

When two objects are brought into contact the molecules from the surface of one object get very close to the molecules on the surface of the other object. This results in forces of attraction between the molecules and this must be overcome so that one surface can move over the other.

Objects moving through fluids such as air or water also encounter frictional forces which reduce their motion. This is known as drag.

Friction prevents objects from moving or slows them down. It also causes wear on surfaces as they rub against each other and generates heat. Thus energy is wasted in overcoming friction.

Reducing friction

1.Lubrication

Oil is used as a lubricant and provides a thin layer of liquid which separates the moving surfaces.

2.Bearings

Ball bearings reduce frictions by making the moving surface roll rather than slide.

 3.Streamlining

By designing the object to allow the easy flow of fluid around it (streamlining) as is done for rockets and racing cars the drag can be reduced considerably.

 Uses of friction

Although in a lot of cases friction is a hindrance but it is also very essential. In order to walk we depend on the friction between the soles of our feet or shoes and the ground. The tyres and brakes on vehicles depend on friction to stop, slow down and start moving. It is the air resistance or drag that slows down a parachute.

Stopping Distance

Cars rely on friction at the brakes and tyres in order to stop.

The total distance a car requires to stop is called the total stopping distance. This is the sum of the distance covered in the time it takes for the driver to react known as the thinking distance and the distance the car travels before coming to rest after the brakes are pressed called the braking distance.

Total stopping distance = thinking distance + braking distance

The diagram below gives the shortest stopping distances for a car on a dry road with good brakes and tyres.

From the diagram a clear pattern can be seen between the velocity of the car and the total stopping distance. The average reaction time of a driver is about 0.7s as the velocity of the car increases so will the thinking distance from the relationship;

Distance travelled = velocity x reaction time

The braking distances increases because at a faster velocity the car possesses more kinetic energy. This energy has to be transferred to the brakes; this is transferred as heat and is the reason why brakes become hot. The relationship between velocity and kinetic energy is,

Kinetic Energy (Joules) = ½ x mass x velocity2

Therefore if the car travels three times the velocity it has 9 times the kinetic energy which means the braking distance will be nine times longer.

 Factors affecting the total stopping distance

The driver’s reaction time

The thinking distance depends on the driver’s reaction time. Reactions are strongly influenced by the state of the mind. Thus, a driver under the influence of a drug such as alcohol will have a much reduced reaction time which will increase the thinking distance. Tiredness and fatigue also influence reaction time. A tired driver will react a lot slower than an alert driver.

Velocity

As illustrated in the chart above the braking distance increases with velocity. This is explained by the relationship between kinetic energy and velocity. The greater the velocity the greater the kinetic energy the brakes have to transfer.

 Mass

The mass of the vehicle is also related to kinetic energy in the relationship;

Kinetic Energy (Joules) = ½ x mass x velocity2

The greater the mass the greater the kinetic energy, thus a heavier car will require a longer braking distance.

Road Surface

Friction between the car tyres and the road surface stop it from skidding and sliding. On a wet or icy road surface the contact between the tyres and the road is considerably reduced. If the driver brakes hard the car will skid therefore the driver needs to apply a reduced force on the brakes increasing the braking distance.

Tyre Condition

Tyres are designed with grooves which channel the water away on wet roads in order to ensure contact of the tyre is made with the road. If the tyres are worn the friction between the road and tyres is reduced increasing braking distance.

Brake Condition

Worn brakes will take longer to transfer the kinetic energy of the car increasing the braking distance.

Source: http://finixx.com/friction/

How Tyres Fight Water to Keep You Safe

Rain Tyres Need Greater Grip

Level of grip on wet surfaces is a crucial performance factor for wet weather tyres. Unlike tyres which can move easily on dry surfaces, the requirement for a stronger grip on slippery or wet surface, increases triple fold for wet weather tyres.

While driving over water-logged roads, ordinary tyres tend to get submerged in water, often causing the vehicle to topple or skid. In case of wet weather tyres, the tread is made of softer rubber that allows the rubber to heat up and generate more traction. This helps the vehicle stay put on wet surfaces.

That is why wet-weather tyres are equipped with a higher quantity of silica or rubber content that augments their wet grip properties. The high silica content also helps the tyres counter icy conditions during hail storms.

Deeper Grooves

Another very important feature of rain tyres is their special tread pattern that can make a significant difference to how they perform on wet roads. The specially designed grooves help quick dispersal of water from the tyre tread.

This ability to disperse water from the contact patch increases the tyre’s aquaplaning resistance, which simply means the ability to stay steady and not slip on a wet surface. A greater aquaplaning resistance also translates to better grip on wet roads, and easier handling capabilities.

Apart from the specially designed grooves, for water dispersal, rain tyres also have other features such as special tread blocks and cuts to channelize water away and improve road adhesion.

The Challenge in Developing Wet Weather Tyres

Interestingly, rain tyres are not the standard fitments on factory finished vehicles! This is because; for a superior grip wet weather tyres need greater friction, for enhancing grip. This results in increased rolling resistance for the tyres, which in turn increases fuel consumption and brings down the fuel economy. And of course increased fuel consumption also means more harmful emissions into the environment.

Hence the challenge in developing wet weather tyres is achieving a balance between these two parameters. Luckily for us, tyres manufacturers are investing in R&D efforts and the emergence of innovative tyre technologies have made this a reality for several tyres.

For instance, in the Michelin Energy Saver tyres, known for their fuel efficiency, Michelin has incorporated the Durable Security Compound, a patented ingredient complex into the tread compound so that wet grip is not compromised.

 The New EU Regulation on Wet Weather Tyre Safety Norms

In a country like the UK, wet weather exists for most part of the year. Wet weather or rain, tyres are always in demand. That apart, the new EU regulation also states that tyres need to now showcase the EU tyre label which includes a rating for wet grip and braking performance.

Tyre labels are marked from categories A to G, with ‘A’ suggesting shorter braking distance in wet weather and ‘G’ allowing the longest wet weather braking distance. For instance, this tyre below has a rating of ‘B’.

So a tyre with ‘A’ rating has the best wet braking ability and that with a ‘G’ rating stops 18 meters farther (than the A rated tyre) when brakes are applied.

Source: http://finixx.com/how-tyres/

WINTER _ SNOW TIRES VS ALL SEASON TIRES

Many drivers ask themselves, “Do I need winter tires if I have all season tires on my car?” The short answer is, possibly. To understand what tires you’ll need, you must first understand the differences in winter tires vs. all season tires. Every driver’s needs are different depending on the weather and road conditions they encounter throughout the year.

All Season Tires

Many vehicles are fitted with all season tires when they leave the factory. Since they are built to provide a relatively quiet ride, good tread life and fuel economy, its no wonder why they are so popular. All season tires offer versatile performance and are designed to perform in a variety of conditions including wet roads and light winter driving. All season tires are designed to offer a combination of benefits from summer and winter tires.

Does being both summer and winter-ready mean all season tires combine the best capabilities of summer and winter tires? Unfortunately, it doesn’t. In an effort to provide good performance in many conditions, all season tires tend to compromise some max summer and winter performance capabilities. What does that mean? That means all season tires won’t provide the same amount of extreme grip and sharp handling of a summer tire. Likewise, an all season tire is not designed to handle extreme winter conditions like trekking through snow or driving on ice. Think of all season tires like tennis shoes. You can wear tennis shoes all year, but they aren’t ideal for all situations. It’d be much better to have flip flops on the beach in the summer and boots for the snow.

All season tires are a great option for drivers who live in moderate climates and do not encounter extreme cold, ice and snow in the winter months.

Winter & Snow Tires

When it comes to driving in winter weather, having the right tire matters. From heavy snowfall to black ice, winter roads are extremely unpredictable. These conditions challenge tires to provide traction like no other season of the year. The combination of cold temperatures, ice, and snow can be best met by winter tires, which are specially designed to perform in winter conditions.

There are specific features of winter tires that make them unique – tread rubber, tread rubber, and biting edges.

The Tread Rubber. 

In extreme cold temperatures, the tread rubber of an all season or summer tire stiffens and becomes less able to provide sufficient traction. To combat this, tread rubber compounds of winter tires are designed to remain flexible, allowing the tire to grip the road better.

The Tread Depth and Patterns.

A unique feature of winter tires is deeper tread depths and unique tread patterns. Deeper tread depths reduce snow buildup and provide better traction on the snow. Winter tire tread patterns are designed to channel snow and slush and expel water.

 Biting Edges.

Winter tires also feature an increased number of biting edges and high sipe densities, or in other words, thousands of tiny slits in the tread that provide traction on ice.

 Snow Tires vs. All Season Tires: Which Are Best?

The solution to the winter or snow tires vs all season tires question will depend on where you live and the conditions in which you drive.

If you only see a few snow flurries each year and slick, icy roads are more of a fluke than an annual ordeal, all season tires are probably the way to go. But if you know there’s a period when icy roads are always an issue, mounting winter tires isn’t an over-the-top precaution – it’s an essential safety measure that could save your life.

When mounting winter tires for the season, always install a full set. Just changing out the front tires increases the likelihood that the rear tires will skid. Likewise, just putting snow tires on the rear wheels could cause the front tires to lose traction and make it impossible to steer your vehicle.

And remember to re-mount those all season tires when spring rolls around. While winter tires are undeniably superior in extreme winter conditions, they’ll wear down faster on warm, dry pavement.

WHAT’S THE DIFFERENCE BETWEEN ALL SEASON TYRES VS SUMMER TYRES

When debating between all season tires vs summer tires, the differences between the two types can be easily misunderstood. Depending on your vehicle, driving conditions, and personal preferences, one may be a better option than the other. When choosing between summer and all season tires, it helps to understand the benefits and limitations of each.

All Season Tires

An all season tire offers a balance of capabilities, providing acceptable performance in wet and dry conditions, as well as traction in snow.

Built for the average driver, all-season tires have moderate tread depths and rubber compounds that are engineered to provide longer tread life than summer tires, which have shallower tread depths. All-season tires are offered in many types/models, sizes, load capacities, and speed ratings for use on a wide variety of vehicles from economy cars to sedans to mini-vans to pickup trucks.  They tend to provide ride comfort, handling, and other performance attributes suitable for most drivers.

All-season tires perform well in warm weather, but they may offer less grip than summer tires, sacrificing some steering, braking, and cornering capabilities. This trade off is necessary for all-season tires to be able to provide acceptable performance in light winter conditions and provide longer tread life.

All-season tires are capable of providing traction in winter, but are not the best tire to use in extreme winter driving conditions. Drivers who encounter extreme winter weather may want to consider switching to snow tires in the winter.

Because all-season tires offer a blend of summer and winter performance, they are often a good option for drivers in moderate climates and driving conditions.

Summer Tires

Summer tires are ideal for high performance vehicles, and are built for speed and agility. They offer increased responsiveness, cornering, and braking capabilities. This is typically attributed to specialized tread patterns and rubber compounds that allow for improved precision on the road. The tread patterns of summer tires have less grooving and put more rubber in contact with the road. They are designed to provide maximum road-holding grip. The tread compounds of summer tires are designed to remain more flexible, allowing for better traction and grip. Summer tires may have shallower tread depths that allow for more stability when pushed closer to their limits.

Dimensional characteristics (such as the tire’s width, aspect ratio, and rim diameter), speed capability, and other design features make summer tires more suitable and capable for increased performance in wet and dry conditions on high-performance, sports-oriented vehicles. Surprising to some, summer tires provide better performance in wet driving conditions, thanks to unique tread patterns that help evacuate water and resist hydroplaning.

When it comes to winter driving, all-season tires may be more suitable than summer tires, given their blend of summer and winter performance capabilities, but we recommend considering making the switch to winter tires to get optimal traction and performance in extreme winter conditions.

Choosing the Right Tire

Choosing the right tire isn’t as simple as mounting a set and never looking back. When contemplating between a summer and all-season tire, consider your driving conditions, the climate you live in, and performance needs.

It is best that all tires on your vehicle are the same type of tire – such as winter, all season, summer, etc. Your vehicle’s tires should meet the manufacturer’s recommended size, speed rating, load capacity, as well as any other recommended specifications.

Source: http://www.bridgestonetire.com/