Tyre Speed Ratings
Ever wondered how fast you can drive with the tyres you have?
Well, you're not alone.
Usually, drivers - myself included back in the day - gauge how fast we can drive on a combination of the prescribed legal speed limit and how far we can floor it until we chicken out.
What most people don't realise is that every tyre has a prescribed speed rating which serves as a guide on how fast we can drive in them. To be more specific, it shows the maximum speed a particular tyre can handle.
Let's discuss your tyre's speed rating and find out how it can help us not only choose a set of brand new replacement tyres but also to keep your ride safe from harm.
What is tyre speed?
As we mentioned earlier, every passenger tyre has a designated speed rating which informs drivers what the tyre's maximum speed capability is.
It is the maximum speed your tyre is designed to handle, the absolute limit to how fast your tyre can go before it starts to fail.
The tyre speed rating does not mean you can floor it and expect to drive around safely at the maximum prescribed speed - especially in unfavourable weather and road conditions.
In general, the speed ratings of most tyres exceed the maximum highway speed limits. However, all tyre and vehicle manufacturers DO NOT encourage their customers to drive as fast as they can and to disregarding legal speed limits.
Tyre speed ratings are a set value - that also functions as relevant information for drivers regarding safety. It is different from the recommended travel speed of a tyre - which is how fast you should be travelling legally, taking into consideration the type of vehicle you are driving.
The tyre speed rating informs us that the tyre's design and construction allow it to handle the speed indicated by the rating. By being aware of it, drivers will be able to continue driving safely.
How is Tyre Speed Rating determined?
The Tyre speed rating of any individual tyre is set by the tyre manufacturers since they both design and produce the tyre. Similar to load ratings, they take into consideration the classification and weight of whatever vehicle it will be used for.
They then proceed to the laboratory testing stage that uses simulated speeds, loads and driving conditions. The tyre will only receive its speed rating if it can sustain a particular speed reliably.
It should also have complied with the various industry standards that guide the process of how it can reach and maintain its speed during testing.
Simulated Testing vs. Real World Driving
Drivers should take note though that the tyre's speed rating is based on ideal, almost perfect driving conditions. The ratings are not valid for damaged, repaired, modified, as well as over and under-inflated tyres.
Since tyre speed ratings are determined via lab tests, we must remember that labs still do not equal real-life experience.
This means that the tyre speed rating will show the maximum speed your tyre can handle if it is running properly and fully inflated, that the vehicle is in good working condition and that the weather is not too hot or too cold.
The safety implication here is immense. It is possible that your tyre's actual speed capacity - or how fast it can go in real life, not so perfect driving conditions, maybe a lot less slow than its speed rating. This is because the tyre - in real-life usage will be exposed or affected by other factors that might not be optimum for the tyre's performance. These factors include over-inflated tyres, misaligned wheels, poor road conditions as well as uncooperative weather.
Where do I find the Tyre Speed Rating?
You can easily find the tyre speed rating on the tyre itself. It is part of the tyre code that you see on the tyre sidewall.
The tyre code is the series of alphanumeric symbols on the tyre. It identifies the car's classification, size (tyre width, sidewall height, diameter size), tyre load rating, and the tyre speed rating.
It is easy to find the speed rating because it is the last item in the string of figures on the tyre code.
Aside from the tyre sidewall, you can also find speed rating information on the driver-side door jamb. It's located on the tyre placard placed there by the vehicle manufacturers. This placard identifies the number and location of seating positions and the total load capacity for occupants and luggage as well as the speed ration. Original Equipment tyre sizes and the vehicle manufacturer's recommended cold tyre pressure are also included on the tyre placard.
Your vehicle's manual will also have the tyre speed rating information. You can also get in touch with the car company themselves or check online - but make sure the information is valid.
How to read it
Tyre Speed ratings use letters that correspond to a particular speed. A represents the lowest speed, while Y is the highest.
On the alphanumeric tyre code that you can find on the tyre sidewall, the speed rating letter is the last symbol.
Seasonal tyres and speed rating
The different seasons affect your tyre's speed ratings.
In the summer, you should NEVER use a tyre with a lower speed rating than what was recommended by the vehicle manufacturer. This is considered illegal in some parts of the world as well.
For Winter weather, it is allowed to use a winter tyre with a lower than recommended speed rating but not lower than the Q rating - which equals to about 160km/h as stated by EU legislation (Directive 92/23/EEC).
What happens if I use wrong speed rating
Using a tyre that does not have the recommended speed rating of your vehicle's manufacturer is very dangerous.
It can cause the tyre not to be as responsive to the driver's steering - the tyre might suddenly feel too heavy or too light, making it hard to control the vehicle.
A blowout can occur as well, which can have potentially fatal consequences, not just for you but also for others on the road.
In case of an accident, your insurance company may refuse to cover your vehicle if it was using tyres not recommended by the car manufacturer.
Finally, Fitting tyres with a lower than recommended rating AND driving around with them is illegal and punishable by law.
Are speed ratings just about speed?
No. Your tyre's speed rating can give you clues about more than just how fast your tyre can legally go.
It clues you into the level of comfort your ride will have, as well as how durable your tyre is via the effects on traction, tread wear and cornering capabilities by how fast you can go. This is because tyres with higher speed ratings have exceptional grip and braking power but will not last very long and will not be able to be effective in winter weather conditions. And of course, vice versa for tyres with lower speed ratings.