Let’s talk about tires. I recently had a conversation with someone about tire performance and how it relates to the price of a tire.
The question was essentially, “Is it worth it to buy expensive tires for my car?”
There is a study from AAA that answers that question, but in the process of exploring the question I encountered what I think is even more important – how long you keep your tires on your car.
First, a response to the original question. In a recent study, AAA bought three different sets of expensive all-season tires and three different sets of cheap all-season tires. (Cheap by comparison – no matter what tires you buy, it doesn’t feel cheap when it comes time to pay for a set of four.)
They conducted the test on a Toyota Camry and a Ford F-150. The outcomes didn’t diverge much between the two vehicles, so I’ll just use the data from the Camry results. The study measured stopping distance on a wet road, maximum lateral acceleration (grip during cornering) on a wet road, and noise-vibration-harshness (NVH). From a safety perspective, we’re concerned with the first two.
To over-simplify the 65-page report, the price of the tire is not a great way to determine its performance.
That’s not to say that some expensive tires aren’t worth the money; it’s just that you still have to do the research, because the price doesn’t automatically determine the performance.
When the testers measured the results of stopping the Toyota Camry on wet pavement from 60 mph, the results varied from 192 feet to 229 feet, with an average of 214 feet. The best and worst tires varied from the average by about 10 percent.
I won’t go into the details on grip during cornering, but the results were similar to the stopping test, again concluding that a more expensive tire is not necessarily better.
Here’s where it gets interesting (at least, I think it’s interesting). The study also compared brand new tires to the same tires after they’ve been used a while. The testers used a machine to shave the tires down to 4/32 of an inch. When I was in math class, I would have been marked down for not reducing that fraction to 1/8, but apparently tire treads are measured in 32nds of an inch.
With worn tires, the stopping distance for the Camry ranged from 247 feet to 327 feet. The best performing tire when worn down to 4/32 doesn’t offer nearly the stopping ability of a cheap new tire.
I’ll point out that while the testers used a wear measurement of 4/32, Washington law allows drivers to use their tires until they’re worn down to 2/32 of an inch. Presumably, stopping distance would be even worse with that amount of tire wear. This is an instance where the best practice (replacing your worn tires at 4/32) and the minimum requirements don’t align.
I mentioned earlier that these tests were done on wet road surfaces.
Tire tread doesn’t give you better grip on dry pavement. In fact, tires with no tread would give you the best results. That’s essentially what a racing slick is; a bald tire (built to perform at high speeds). Race car drivers want the maximum surface area possible between the tires and the road.
That’s also what we want on our daily drivers, but we have to factor in the possibility of rain. Once the road is wet, tire treads provide channels for the water to escape, allowing the tread to stay in contact with the road. Without treads, you’d have a thin film of water under the whole tire, which is what causes hydroplaning and loss of control.
As the treads wear down, the channels for the water get shallower, reducing traction on wet surfaces.
In northwest Washington, about a third of our days involve rain, so having tires that can displace that water effectively can be the difference between stopping safely and getting in a collision.
Let’s go back to stopping distances for a moment. No matter which set of tires you choose from the AAA test, you could go from 60 mph to a complete stop in less than five seconds on brand new tires. Worn down you’d add an average nearly 90 feet and 1.3 seconds to your stopping time.
Considering that many people have been taught to keep a two-second following distance (which really isn’t enough) and some drivers leave even less space, a set of worn tires (even if they’re still legal according to Washington law) that adds an extra 1.3 seconds of stopping time will turn into a rear-end collision.
But, you may argue, that two seconds isn’t entirely used up by the worn tires, so you could still stop in time. Once you add reaction time, which is about .75 to 1.5 seconds for a driver paying close attention, you’re somewhere between a fender-bender at a few miles per hour and a serious crash.
If you’re texting or otherwise distracted, you don’t have a chance.
Now let’s get back to the price of tires. If you can afford the best, most expensive tires, and you do your homework, you’ll get a top-performing tire. However, if the price of a premium tire is causing you to delay replacement, a new less-expensive tire will outperform your worn out high-end tires and keep you safer on the road.
Road Rules is a regular column on road laws, safe driving habits and general police practices. Doug Dahl is the Target Zero Manager for the Whatcom County Traffic Safety Task Force. Target Zero is Washington’s vision to reduce traffic fatalities and serious injuries to zero by 2030. For more traffic safety information visit TheWiseDrive.com. Ask a question.