How Advancements in Tire Tech Are Injecting New Life Into Older Cars
Advancements in modeling, materials science, and manufacturing are raising the bar for tire performance. And not just for new cars.
After years of commuting, numerous runs through the canyons, and a couple of track days, the summer tires on our 2007 Dodge Magnum SRT-8 had definitely seen better days. Beyond the fact that the wear indicator was nearly flush with the tread, it was clear that the rubber itself had lost a step or two over time. Even under ideal conditions, the braking distances had grown, the turn-in response had become less urgent, and any feel that those tires had previously bestowed upon this steering rack was now long gone.
Clearly, it was time to swap these puppies out for a new set, and that got me thinking about a conversation I’d had with a Bridgestone engineer while I was out at Willow Springs Raceway for the U.S. launch of the Maserati MC20 earlier this year. The company’s Potenza Sport is the factory-installed summer tire not only on Maserati’s new sports car, but also other exotics like the Lamborghini Huracán STO and Ferrari Roma. Horsepower, I posited to this engineer, is something that automakers seem to have collectively “solved” years ago; The trick these days is more about figuring out how to effectively use all of it, and that challenge is increasingly becoming tire manufacturers’ responsibility.
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Granted, it’s his job to say this, but he insisted tire tech is up to the task and told me why. “The technology is evolving at a rate that’s almost like cell phones,” he said. “There are things we can do today that weren’t possible even just a few years ago.”
While researching tire replacement options for the wagon a few weeks later, I discovered that Bridgestone now makes the Potenza Sport in the same staggered sizes as the Goodyear Eagle F1 summer tire that was originally equipped on the Magnum SRT-8. That got me wondering about how much tire design has changed since this Dodge was new, and what that might equate to a decade and a half later for a near-stock vehicle like this.
And as Dale Harrigle, Bridgestone’s chief engineer for replacement tires in the Americas, explained to me recently, ditching older tires for new ones tends to have inherent benefits regardless of how much meat is left on the bone.
“It’s especially true for tires that have seen a number of heat cycles from track days and spirited driving,” Harrigle said. “The rubber goes from what’s called a “green” state to the “cured” state during the manufacturing process, but that curing process never completely stops – it always continues to a small degree. When you heat the tire up during a track day or something like that, you accelerate that curing process through those heat cycles, and that’s why the grip degrades over time.”
But after bolting up a set of these Potenza Sports, it’s clear the benefits go beyond just fresh materials. Improvements in steering feel and weight were immediately obvious even just plodding around town, and a quick jaunt out to the network of epic canyon roads in the Angeles Forest just a few miles northeast of downtown L.A. revealed noticeably sharper turn-in and more urgent braking response with no discernable compromise in ride quality or road noise.
The Bridgestone rubber doesn’t wholly reinvent the car – which makes sense considering it was already on summer tires to begin with – but the performance improvements are tangible in comparison to the set that it was previously getting around on. And all things being equal, I also think it's fair to say that the car would out-perform another stock Magnum SRT-8 on the OE tire in the vast majority of real-world metrics.
I was curious about how seemingly disparate parameters like noise and grip have been improved across the board over the years, so I asked Harrigle about how performance tire development has changed over the past decade or so.
“A lot of our initial development work used to be done through trial and error,” Harrigle said. “The single biggest thing that we can do today that we couldn’t do 10 years ago involves digital modeling. We can model so much more of the tire performance and how the tire works with the vehicle as a system. We have robust digital models of things like the tire profile and the contact patch, and we’re moving that technology into additional areas like tread compounds.
The balance of winter, wet, and wear performance of a tread compound can now be simulated on the computer to a substantial degree, along with things like hydroplaning characteristics and rolling resistance, he told me.
“Just about every key performance parameter of the tire can be modeled to some extent before we ever build our first development tire, and the technology continues to improve all the time,” Harrigle said.
Considering the fact that the Potenza Sport is going up against some formidable competition in the max performance summer tire segment that includes the Michelin Pilot Sport 4S, the Pirelli P Zero, and the Continental ExtremeContact Sport, Bridgestone certainly couldn’t afford to phone this one in.
Michelin, for instance, used similar simulation tools to develop and optimize tires like the Pilot Sport 4S K1 for the new Ferrari 296 GTB, while their other summer tire offerings like the Primacy 4+ combine multiple layers of rubber into their design in order to provide consistent braking performance as the tires wear and tread depth is reduced. Meanwhile, Pirelli has integrated a polyurethane sponge into the internal design of tires like the P Zero in order to absorb vibrations and reduce noise, improving comfort levels in a segment that normally requires significant compromise in that regard.
Interestingly, Harrigle says that winter capability, wet grip, and tread wear are still core design metrics that need to be considered even during the development of a summer tire like this.
“Just about every tire compound out there is a trade-off between those parameters – winter, wet, and wear,” he said. “Those are the performance attributes where we’re making engineering trade-offs. So for a tire like Potenza Sport, where winter performance is obviously not really a concern, we can focus more of our engineering efforts on the trade-off between wet grip and wear life. We can use those digital models to get us in the ballpark of where we want that balance to be, and also how we balance the compound performance with the geometry of the tread pattern.”
Dry grip is of course high on the list of priorities as well, but the physics behind dry grip is more readily understood than what’s occurring with, say, wet grip, so it’s a bit more straightforward to tune a tire to hit a specific target for dry grip. “The goal here is to achieve a certain level of dry grip while also making sure that these other aspects of the tire’s performance hit their targets as well,” he adds.
Beyond the use of digital modeling, there have also been significant advances in material technology over the past few years that have changed the internal construction of performance tires like these. “For example, this tire uses a hybrid cap ply, which is the layer just underneath the tread surface,” he said. “It’s a mixture of nylon and aramid in the same cord composite, and that provides several benefits. Nylon shrinks when it gets hot, so it does a great job of controlling the tire growth at the high speeds that this tire is rated for. Meanwhile, aramid is very stiff, so the combination of those two materials gives us high-speed control, as well as great steering feel from that stiffness.”
Other technical advances have also enabled tire manufacturers like Bridgestone to do things with their tread designs that formerly weren’t possible. 3D printing, for instance, allowed engineers to create unique shapes for the Potenza Sport’s sipes, the small slits that are cut into the tread surface which primarily benefit wet weather handling. Here those unique shapes are designed so that the sipes can intermesh under braking and during other maneuvers. “And when those sipes intermesh, it makes the tires much stiffer,” Harrigle says. “So we can improve cornering performance and braking performance, but still have enough siping in the tire to give us that wet grip when it’s required.”
Although the iterations of the Potenza Sport for the Maserati MC20 and Lamborghini Huracán STO were developed specifically for those vehicles, while the Magnum now rolls around on what is ostensibly an off-the-shelf version, it turns out that OE-spec tires are usually very similar to their garden-variety counterparts. “Many of the OE targets that we receive are geared toward making sure that the car ‘feels’ like that particular brand of vehicle. A lot of the difference in feel between, for example, a VW sedan, a Honda sedan, and a Nissan sedan within the same category is achieved by the tuning of the tires during the OE development process,” Harrigle says.
Looking down the road, he points to ongoing advancements in both digital modeling and materials as factors that will continue to elevate the performance metrics for tires like the Potenza Sport, but he sees other aspects of tire design taking on increasing importance as well.
“The modeling is also only going to get better over time, and that’s going to allow us to balance those engineering trade-offs on a much finer scale,” he said. “But I think fundamental materials science is where Bridgestone really excels, and that’s where we’re going to see the biggest gains over the next five to ten years. There’s plenty of performance still to be had here. And in the context of our other product lines, that materials science is going to drive improvements in aspects like sustainability and rolling resistance as well.”
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