The Science of Grip

In 1920, John F. Sipe worked on a slaughterhouse floor in New York City’s meatpacking district. He spent his days shoveling guts into machinery wearing work boots with thick rubber soles. These boots slipped a lot on the slick factory floor, and after falling one too many times, John started to experiment with modifying them. 

He found that carving perpendicular notches into the tread of his work boots improved his traction drastically — plummeting his rate of workplace falls. 

And thus, the “sipe” was born. 

At least, as legend would have it.

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U.S. Patent Office image.

Getting a Grip

Despite the potential application in anti-slip work boots, Sipe chose to stake his inventor’s claim in the automotive industry. Focusing his designs on solid rubber tires, John was awarded U.S. Patent #1452099 in 1923. 

They didn’t make him a rich man, (the industry moved away from solid rubber tires, nullifying John’s claims), but John Sipe’s patents are very real. And so is the science behind them. His workplace-inspired idea is used in tire design to this day.

As a tire rolls, the sipes open, funneling water and/or snow away from the center of the tire, often referred to as the “contact patch” of the tire. This is where the tire is in the most direct contact with the road. The drier the contact patch area, the more traction the tire can achieve. As well as water evacuation, sipes allow certain tire features to flex around obstacles, further enhancing grip.

Sipes are an important feature in many tire designs, but they’re just one of the traction-maximizing tools that modern engineers have at their disposal to produce and sustain grip. To learn about the full gambit, we sat down with Brandon Sturgis, a product design lead at BFGoodrich Tires.

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What is Grip?

When we think about tires, the concept of “grip” is our brain’s linguistic way of summarizing and simplifying the complicated group of forces that occur when a tire interacts with terrain. You can start to break down some of that summarization by thinking about grip at three distinct scales:

  1. Molecular Grip exists within the chemical makeup of the rubber. Even on a perfectly smooth driving surface, a tire’s vulcanized rubber can still produce grip by being chemically “sticky.”
     
  2. Micro-Mechanical Grip occurs where the surface texture of the tire makes contact with the surface texture of the terrain. Most driving surfaces are not perfectly smooth, especially on a micro-level. A “tooth-like” texture on the surface of a tire can create grip by meshing into the bumpy “teeth” of the terrain, like microscopic rubber/asphalt velcro.

    3. Macro-Mechanical Grip is achieved when the greater body and shape of the tire interact with the terrain. Tread patterns can “flex” around obstacles to produce grip and sipes can evacuate mud or snow to sustain it. With the right viewing angle, you can see these features in action with your own eyes.
     

The Science of Grip

“For a great example of macro-mechanical grip, look at the BFGoodrich Mud-Terrain T/A® KM3 Tire as it crawls over a rock. We designed that tire’s tread pattern to fold onto itself and envelope objects when aired down. The tire, like a hand grabbing onto a ledge, cups the obstacle, offering the tire superior grip as it travels over it.” – Brandon Sturgis

At BFGoodrich, different roles on each engineering team will focus on different scales of the tire’s grip. Chemists focus on molecular grip, material scientists focus on micro-mechanical grip, and tread designers focus on macro-mechanical grip, for just a few examples. From inspiration, through the design process, and then through all the testing and sizing work, hundreds of experts will have a hand in a tire’s design before it hits the mass market.

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Tools of the Traction Trade

Producing grip is one thing. Sustaining it — over thousands of miles of exploration down rainy highways, rocky detours, gravel side roads, snowy mountain passes, and anywhere else the driver wants to go — that’s another task entirely. Everything about a moment on the road, from the humidity in the air to the micro-textures on the surface of each rock, is a variable for an off-road tire to plan for. When you discover a design solution that checks many of those environmental boxes while maintaining durability, you hold on tight.

“If you look at the tread patterns, you’ll notice that BFGoodrich tires all look a little familiar. That’s not just for looks. That interlocking tread pattern is simply so successful, we’ve added it to all our products. Its magic is that it doesn’t just provide forward traction. It offers lateral traction at all sorts of steering angles, in many types of terrain. Performing well in all of those areas is not easy. So, this pattern is ‘the one.’ At least, until we experiment our way into something even better.” – Brandon Sturgis


Like chemical compounds in a recipe for rubber, these features bind and work together to create maximum grip at every scale, in every driving situation:

  1. Tread Blocks and Tread Pattern provide baseline traction for a tire across the contact patch. Tread provides the core macro-mechanical leverage that enables a stopped vehicle to produce forward motion. All BFGoodrich terrain tires feature a related tread pattern that maximizes that leverage in many driving conditions.
     
  2. Sipes help a tire maintain traction in wet or snowy environments. Like most qualities in a tire, sipes have positive and negative outcomes. Sipes are useful, but heavily-siped tires wear down faster than non-siped tires. Sipe density is an important factor in tire design. Innovations like the 3D-locking sipes featured on the BFGoodrich® Trail-Terrain T/A® Tire help to curb some of those negative effects on wear over time.  

    3. Mud-Phobic Bars help a tire maintain traction in a muddy environment by releasing compacted mud and soft soil as the tire rotates. ‎Mud is essentially fluid, and these bars act to siphon it off to be ejected during rotation. This is a key feature of the BFGoodrich® Mud-Terrain T/A® KM3 Tire. 

    4. Flex Zones help tires achieve grip when aired down in rockier environments but maintain stability when aired up in smoother driving environments, flexing to fit the situation. The iconic notched tread pattern featured on the BFGoodrich® Mud-Terrain T/A® KM3 Tire allows this balance between flexibility and durability, creating “Linear Flex Zones.”

    5. Serrated Shoulders feature “teeth” that increase the total contact surface area where the tire meets the terrain, and add a lot of physical engagement to that contact. The famously toothy shoulders of the BFGoodrich® All-Terrain T/A® KO2 Tire improve traction in many driving situations, especially when aired down.

    6. Proprietary Mold Technology enables BFGoodrich Tires engineering teams to add tread features around the far edges of their tires, creating functional real estate on the tire that competitors can’t.  

 

“If you look at our tires versus our competitors, you may notice that we have the ability to wrap the tread pattern further around the side of the tire, thanks to our proprietary tire mold technology. This technique takes advantage of that extra real estate on the tire to give you more traction.” – Brandon Sturgis

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“How the Sausage is Made.”

Grip is a relentless pursuit. It involves expertise in wide-ranging disciplines like computer simulation, chemistry, meteorology, geology, material science, structural engineering, and much more. Importantly, it also requires expertise in driving and in life. This work demands a little dirt beneath the fingernails, a little sand in the hair, and a genuine passion for the great, mud-splattered world that we tune for.

It may be perfected in the lab, but grip is always born out in the real world. On the slimy floors of slaughterhouses, on the snowy highways of the American Midwest, and on the unforgiving racecourses of events like the Baja 1000 or the Mint 400. Infinitely demanding and far from predictable, the real world continues to be the ultimate muse for the engineers at BFGoodrich Tires. 

“You can't just sit behind a desk and think up the next big thing for tires. You need to get out there and get your hands dirty. At BFGoodrich, the same people who design the tires are out at motorsports events supporting racers, trying out different tread patterns in the field, and seeing what works under the toughest conditions. Everyone is encouraged to get out there, because that's how you learn. ” – Brandon Sturgis

Life, inspiring science, enabling life. 

Rinse, tune, repeat.

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Photo credit: MadMedia

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