What is it about your tire that lets your vehicle brake in time when a child darts onto the street, or swerve to miss a deer bolting from a bush? It’s the stability of your tire’s tread, the construction of the carcass, the compound of the rubber. It’s your tire speed rating, or, to be more accurate, your tire’s performance rating.
People refer to that last letter of the tire size on the sidewall of your tires as ‘tire speed rating’—the maximum speed a tire can sustain for a certain period of time without risk of tire failure. But it’s not just about speed. It’s about performance— how your tires get rid of heat and how they brake, corner, grip and swerve just in time.
In fact, your safety depends on the performance rating of your tires, and yet many drivers aren’t aware of the role they play in keeping their rubber on the road. As you get ready to switch to summer tires, and if you’re doing your research or shopping online, you need to know the tire size as well as the tire speed rating recommended by your vehicle manufacturer. One tire size could come in multiple speed ratings.
And with road trips and hot summer asphalt around the corner, it’s even more important to understand how performance rating influences the handling and safety of your vehicle.
What is speed rating or performance rating?
After years of blowouts and accidents caused by drivers flying down Germany’s Autobahn at top speeds, a global tire speed rating system was created to remind drivers of their tires’ limits. In the 1960s, there were only three ratings; now there are 14.
Today, those ratings indicate so much more about how a tire performs. Tires with higher speed ratings are better equipped to get rid of heat; they also offer better cornering, gripping and braking, which is why we think of it as a ‘performance rating.’ Tires that have been downgraded in speed rating flex and squirm under pressure, causing heat-build up and compromising traction and tire life—situations that can lead to blowouts, especially in the heat of summer.
That rating is based on rubber compound as well as tread stability, design and casing construction. Tires with bigger inter-locking tread blocks squirm less than a lot of little tread blocks. Less squirming means more staying on the road.
How does speed rating impact your vehicle’s handling and safety?
Heat is your tire’s number one enemy. Tires with low speed ratings flex and squirm under pressure, causing heat build-up.
And heat build-up, along with high temperatures—whether you’re on your morning commute or your way to the cottage—can have a big impact on your tire’s performance and durability. You could be risking tire degradation, reduced traction and even blowouts.
Tires with higher performance ratings are better equipped to get rid of heat, in part because they generally have higher quality construction and ply.
During one of our recent performance rating tests on hard braking in an emergency situation, a lower ‘S’ rated tire driving 100 kilometres per hour was still going almost 25 km/hr when the higher ‘V’ rated tire stopped. The ‘S’ rated tire took 39 metres to stop. The ‘V’ rated tire stopped in 35 metres.
Why? Performance rating has a huge impact on braking. Lower-rated tires will squirm and change shape under hard braking, taking longer to stop in emergency situations.
It isn’t the size but the quality construction of your tire that’s going to help you take sharp turns safely. If you’re heading up a highway ramp at high speeds and you’re not ready for the tight curve ahead, your vehicle will stay on the road, or not, because of your tire’s grip. Under force, the shape and contact patch of a lower-rated tire will change, reducing your traction.
As well, your vehicle operates safely because of several systems—anti-lock brakes, stability control—that can only work with the traction limits of your vehicle’s tires.
One of the biggest differences you’ll see and feel between tires with high and low performance ratings is the quickness of your steering response. You won’t have to turn your wheels as much when you have tire with better traction because they can respond more accurately.
Less tire flex also improves stability, allowing your vehicle to swerve and remain stay on the road. Whether you need to dodge a dog or a fallen suitcase on the freeway, you need lightning fast steering response.
What you need to know about speed rating
It’s critical that your performance rating and load index matches the original equipment specifications recommended by your vehicle manufacturer. You can always go up in performance rating, but you can never downgrade or you’ll compromise the handling and safety of your vehicle.
The only time it’s OK to downgrade your tire speed rating is with your winter tires, where a ‘Q’ rating is acceptable because you’re going to be driving slower and in cooler temperatures.
When you need new summer tires, have the tire experts at a Kal Tire location near you make sure you’ve got the right size and performance rating.