Understanding how tread is being consumed and the maintenance actions we can take to extend tread life is critical to safety and controlling tire spend.
It wasn’t my intention to have a career in the automotive industry, but it happened that way and I could not be happier. My career started off at a family owned mechanic shop in Northern Virginia where we were a Virginia Safety Inspection Station. The Motor Vehicle Safety Inspection was a safety check performance annually by state certified technicians that would inspect several components of the vehicle, tires were a major source of failing inspections. One of the rules related to tires requires each tire to have at least 2/32” of tread depth at the time of inspection, otherwise it fails. Many Virginians felt that this was just a way for the shops to make money, and yes, it created some business, but the intention was safety. I often discussed with customers the dangers of lower tread depth, but recent studies really illustrate the risk of lower tread depth. Some of those are – increased likelihood to be involved in an accident, increased stopping distance, and hydroplaning. Let’s discuss.
Increased Likelihood of Being Involved in an Accident
In a study conducted in 2012 by the National Highway Traffic Safety Administration, vehicles that were involved in tire-related crashes were arranged into 4 different categories, 0-2/32”, 3/32”-4/32”, 5/32”-6/32”, and 7/32”+. In that study, tires with tread depth in the range of 0-2/32”, were observed to experience tire problems in the pre-crash phase 3 times more than vehicles with the tread depth range of 3-4/32”.1 Also worth noting that in the tread depth range of 3-4/32” compared to tread depth range of 5-6/32”, vehicles were observed to have 2 times more tire related problems in the pre-crash phase.
Increased Stopping Distances
If you follow any racing series that compete in the rain, you probably already know that many races are won solely based on tire strategy. Most of the time, race cars will have tires with no tread to maximize grip during dry racing, but if rain is in the forecast during the race, timing is everything when it comes to swapping from dry to wet tires. Most racing series can also make a pit stop, swap tires, and top off their fuel in less than 20 seconds. Unfortunately, not all of us have that luxury when we are out for a drive so keeping an eye on tread depth and planning for tire replacements in your fleet is important.
There are some pretty alarming statistics around accidents and stopping distance on wet surfaces. According to the Federal Highway Administration, on average, there are over 5,891,000 accidents annually, 21% of those (nearly 1,235,000) are weather related.2 Furthermore, of those 1,235,000 accidents, 70% of those accidents occurred on wet pavement, while a much smaller amount were attributed to winter weather conditions – only 18%.3 Sure, there are a variety of reasons for crashes on wet pavement, but stopping distances on lower tread depth certainly played a role.
As referenced above, the law in Virginia requires a minimum tread depth of 2/32” to pass inspection, but in tests conducted by Consumer Reports, it was found that tires can give up a significant amount of grip at 50% tread.4 Furthermore, a study conducted by the National Highway Traffic Safety Administration showed that 50% of the 11,500 cars, pickup trucks, vans, and sport-utility vehicles the agency checked had at least one tire with half worn tread and another 10% had at least one bald tire.5
Much like a boat comes out of the water and glides on the surface as it increases speed, tires with lower tread depth also have less contact with wet surfaces at higher speeds. That problem is amplified in tires with lower tread depth because the groves between the tires are not as deep and cannot channel the water through the tires as fast. In the image below, Consumer Reports demonstrated how a tire is more susceptible to hydroplaning on a wet surface the faster it goes. Interestingly, or should I say, more troubling, the images of those tires are new tires traveling at 20 MPH on the left picture (full tire/ground contact), 40 MPH in the middle picture, and 60 MPH on the right picture.
What’s The Big Deal
So why does all of this matter? We can assume that if a tire doesn’t fail prematurely, most tires will make it to a tread depth of less than 4/32 of an inch…and probably even 2/32 of an inch. As vehicle owners or fleet operators, the goal is to extend the life of the tire as much as possible BEFORE it hits 4/32 of an inch. The reality is, tire maintenance has always been a reactive maintenance item for most. Sure, you can be proactive, rotate tires and do alignments on certain maintenance intervals. The problem is, tires don’t operate on a schedule. Tire pressures fluctuate with ambient temperature. The load on tires changes quite a bit. Road surface conditions are unforgiving. Pot holes don’t care. Drivers are always in a hurry to accelerate and then stop. We know tire tread will be consumed, there is nothing we can do about that. But better understanding how that tread is being consumed and maintenance actions we can take to extend tread life is critical not only to safety, but important when it comes to controlling tire spend. Have eyes on your tires in between shop visits. Be Proactive! Check out Revvo’s Tire Management Platform!