The tyre is the most important and the least appreciated element of your car. While accessorizing your car with the tyres of your choice, you should consider a couple of factors to make the most out of your driving experience. So the next time you feel like your car needs some new tyres, look at things like their tyre speed rating and load index.
It was the Germans who came up with the system of speed rating. The speed rating of your car tyres tells you how fast you can safely drive your vehicle on that set of tyres. That is, it is the maximum speed the tyre can take without giving in.
Alphabets are used to represent the speed rating. Each alphabet corresponds to a particular speed represented in kilometre or miles per hour. You can consult a tyre speed rating chart like the one given below to see what each alphabet would mean.
|Speed Rating||Maximum Speed
When the speed rating Z was introduced, the people who came up with it thought that cars won’t possibly go above 240 km in an hour. Therefore they named the maximum speed rating Z, which is the literal end of the alphabet. But, technology in cars has evolved a lot, since then. They had to rethink the maximum speed rating and came up with W and Y. But now Y in parenthesis or (Y) is the maximum speed rating there is. The tyres rated (Y) can go over a whopping speed of 300 km/hr.
Usually, higher alphabets correspond to higher speed ratings. This means that speed rating progressively increases as we go down the list of alphabets from A-Z. But that said, there are exceptions to this rule. Z itself and H are the odd ones. H shows a rating 210 km/hour This speed is greater than the speed M or N would indicate. Another such anomaly is Z.
That said, it is important to remember that high-speed rating does not give you permission to break traffic rules. Always remember to drive at a responsible speed!
How do manufactures calculate a tyre’s speed rating?
A new tyre carries treads. They have tread patterns or grooves that provide good traction for the vehicle. The tread pattern affects how fast the rubber can go without being destroyed. Along with this, the vertical part of the tyre or its sidewall, as well as the material used for manufacturing the tyre, affects how it is rated. If tyres are made with good components they won’t wear quickly even at very high temperatures. And they can take higher speed with much more grace.
To rate the tyre, the manufacturing company would inflate the tyre and position it on a testing machine. After whirling it at a certain speed they would assess it for damage. If the tyre is still in good condition the tyre passes the test. And later the tyre maker rates the tyre accordingly.
Finding the speed rating on a tyre
You can find the tyre’s speed rating value by inspecting its sidewall. The alphabet(s) that follows the tyre size code and immediately after the load index shows the tyre speed rating. Here in the picture, P215/65R15 denotes the dimensions of the tyre. The speed symbol of H is given after the load index.
Similarly, if the tyre speed rating is V, it means that the fastest the tyre can go is 240 km per hour. And if the vehicle with V tyres goes faster than 240 kilometres per hour, the tyres would blow out. The sidewall of your tyres can come off.
What is the speed rating of my car?
The auto manufacturer specifies the minimum required speed rating the tyres of a particular car would need. This is because the tyres should be able to withstand the maximum possible speed of the vehicle.
The factory tyres or the tyres that came with the car would comply with the required speed rating of the vehicle. But sooner or later you would need to put in new tyres. Then you need to make sure that the new tyres match the vehicle’s specified speed rating. It could be above but never below the manufacturer’s recommended speed rating. This is because if the car goes faster than what the tyres were made to endure, the latter would eventually fail.
So how do you know recommended speed rating for your vehicle? You should look at the car owner’s manual for this. The label on the driver’s door jamb would also show what speed rating your vehicle goes by. While getting a new set of tyres always make sure that the speed rating of your tyres matches the speed rating of your car.
Your car tyres carry the bulk of your vehicle. They lug the weight of the passengers, your stuff plus the cargo in the trunk. So it is important to have good tyres for your vehicle. If your car needs a tyre replacement, one of the most important things you need to keep in mind is the load index. The load index tells you whether tyres can shoulder the load that comes with the vehicle. It is the indicator of the maximum weight the tyres can support.
Say your car is 2500 pounds. Let’s imagine you can fit 2000 pound worth of cargo and people to it. So the weight the tyres would have to bear is more than 4500 pounds. So you should choose the tyres that can carry 4500 pounds or more. Your carmaker usually specifies the load index of the tyres your machine would need.
What does it look like?
The load index of a tyre is moulded into its sidewall along with the tyre size sequence and the speed rating. It is the two-digit or three-digit number that comes before the alphabet that acts as the speed symbol. The tyre in the picture has a load index of 83 with a speed rating of H.
Likewise, if the load index of the tyre is 92, it means that when it is fully inflated the tyre can carry up to 630 kilograms. A car mounted on four such tyres can carry a load of 630 times 4 kilograms. That is 2520 kilograms.
It is crucial to look at the speed rating of a tyre before buying it. This is because the speed rating has an impact on the car’s performance and handling as well. It also affects how easy it would be to drive your car and how much control you have over it.
But it is important to remember that once the tyre is worn down its performance would drop. This would be irrespective of its speed rating. So when should you get your tyres replaced?