If you’re anything like me—and heaven help you if you’re too much like me—buying tires for your car is a tedious chore you’d rather get over with as quickly as possible. It must have shown on my face then, recently, when the guy behind the counter at the tire store said, “And you’ll want those new tires siped, right?” Huh?
In a breathless rush of words, I was told that siping was the process of putting thousands of small cuts in the tire’s tread to improve traction, increase cooling, decrease braking distances, and extend tire life. All of that would cost just $15 per tire, and could be done on the premises before my new tires were installed, and if I’ll just sign here on the work order we’ll get going. This tire shop, a Les Schwab here in Oregon, has a website that repeated those claims, further explaining that the reason the manufacturers don’t do this already is because “the siping process we use would be too expensive and time-consuming.” Uh-huh.
By this point, my bullshit detector was blaring pretty loudly. And, indeed, Steve Carpino, a former head of research and development at Pirelli, later confirmed my suspicions. Aftermarket siping, Carpino said, is generally a terrible idea. It likely voids your tires’ warranties, for one thing, and while it might provide some additional traction in snowier climes, you’re better off just spending the extra $10 or $15 on better tires. Like proper snow tires. Or pretty much anything else. Like a movie.
“On dry pavement, siping works against you,” Carpino said, because it increases tread squirm, which increases heat, which increases wear. “If you’re in Southern California or someplace like that, it’s a total waste of money, a gimmick that the tire shop uses to get another 10 or 15 bucks per tire out of you.”
Legend has it that siping was invented by John Sipe, a slaughterhouse worker who cut slits in his shoes in the 1920s to improve traction. Which it probably did back then.
That’s what tire siping is: the process of cutting additional thin slits across the surface of the tire, allegedly to improve braking, traction and acceleration. It’s billed as something especially good for snow and ice, which seem to be never-ending if you live on the East Coast this year.
Some of what I found on the Les Schwab website made some sense, in that it was sort of fact-adjacent; some was total nonsense. What seems clear is that Les Schwab is one of the few chains that offer aftermarket siping; the service doesn’t appear on the websites for NTB, Mavis Discount Tire, Pep Boys, or Tire Kingdom; the sole mention of it on Discount Tire’s website (up until a few days ago, at least) is a recommendation not to do it. (A spokesman for Les Schwab did not comment by press time for this story, but I will update if they do.)
Google, meanwhile, found me lots of car and truck forums where posters debated the merits of cutting into new tires, but what was missing were objective third-party tests.
One such test I did find was a single page in Consumer Reports with a short piece about siping that compared siped to non-siped tires under controlled conditions. Its conclusion is a concise argument against siping:
The siped version of both models showed modest but measurable improvements in snow-traction and ice-braking performance. But braking distances on wet and dry pavement were a few feet longer. Besides costing $60 or so for a set of four, having your tires siped potentially voids any tread-wear warranty. We don’t think the modest gains are worth the extra costs.
Carpino, now a senior consultant for Pirelli on product and design, agreed. When I asked about siping I could almost hear a weary Not this shit again sigh on the other end of the line.
“It’s a concept that’s been around for a long time,” he said. “You typically find it in parts of the country where they get a lot of snow and people are looking for a little extra traction on new tires, and sometimes you’ll see people hyping it for tires that are half worn to recover some traction in snow.”
I mentioned the Consumer Reports article.
“It can slightly improve snow traction,” Carpino agreed, “but not enough that the typical consumer will notice it. We know more sipes in a tire helps, because that’s what we do on winter tires, fit as many sipes in there as we can.”
Among the negatives? Tire noise, for one thing. Carpino said the tire will also wear irregularly, further increasing noise and possibly decreasing tire life, not increasing it as the tire shop claimed.
“The original siping is one of the tools we have to reduce the noise level on a tire; the placement of the sipes and the stiffness of the tread blocks affect the noise levels and the frequency of the noise that comes out of the rolling tire,” Carpino said. “Any time you add enough siping to affect traction it’s almost always going to affect noise, and potentially wear, because when you change the stiffness of those blocks you get more squirm in the blocks and over time you get what’s called irregular wear, which leads to a significant increase in noise.”
All of these negative effects are only made worse on dry pavement, where an aftermarket siped tire will have greater braking distance, less traction, and will wear out more quickly. (We should also note that what we’re talking about is siping on regular car tires, not, say, siping for racing, where it’s an accepted practice; aftermarket siping for tractor-trailer tires, though, is also not recommended.)
There’s also that bit about the warranty.
“If you’re talking about siping a new tire, you’re really crazy, because you lose any warranty protection, and if you do it to a half-worn tire you lose any warranty protection you have for early wear-out,” Carpino said.
All of which made siping seem to me like a scam, or at the very least a highly dubious buying decision. But then I thought back to Les Schwab’s website, and the studies cited there. At around the two-minute mark in a video is this claim:
An independent study by the U.S. National Safety Council found that siping dramatically improves stopping distances, breakaway traction, and rolling traction on vehicles of all kinds.
The National Safety Council is an industry group, and when I contacted them to ask about the study referred to in the video, I got an almost instant response.
The response was a letter NSC sent 18 years ago to a firm that makes siping machines and had been advertising its services as having a firm basis in NSC studies. The letter was a swift takedown that the NSC said still applies today:
Your brochure on SAF-TEE siping refers to studies the National Safety Council conducted in 1968 and 1978 [emphasis added] regarding siped tires. No studies on tires have been conducted by the Council since that time and we are not currently recommending or endorsing the siping procedure.
Especially since tire design has evolved in the last 22 years, we feel it may be misleading to consumers to quote our old study. In addition, the brochure wording wronging [sic] implies that the National Safety Council proved that SAF-TEE siped tires, in particular, were proven to have better traction on ice. Therefore, we ask that you please remove the following reference to the National Safety Council from your brochure, “22% better on ice (National Safety Council test),” and discontinue use of the remaining brochures with that claim.
While aftermarket siping might improve traction on your car tires, everything else about it is bad. Or counterproductive. Or just pointless. If you drive a lot on snowy or icy roads, just get some dang winter tires.
Update, March 29, 5:20 p.m.: Dale Thompson, Les Schwab’s Chief Marketing Officer, emailed a statement, which reads in full:
With more than 65 years in the tire business, we’ve seen tire siping perform well in real-world situations across the West. We’ve heard from customers who appreciate how improved traction on snow and ice makes it an affordable alternative to winter tires, and we’ve seen how it wears in different climates and driving conditions.
We understand that our customer’s purchase is an investment in more than just tires – they’re critical to your safety and your vehicle’s performance, affecting everything from steering and balance to how smooth a ride you enjoy. That’s why we stand behind every product and service with our Best Tire Value Promise, which often goes above and beyond a manufacturer’s warranty. Our experienced crew members make recommendations for each customer based on his or her driving habits and conditions, so we can help protect their investment.
Jerry Smith has been a freelance writer for… well, a very long time. When he’s not writing about motorcycles, cars, RVs, or dogs, he makes up stories about people who don’t exist. His latest novel, Dents, is about some of those people, and the awful and funny things he makes happen to them.