SRT® Hallmarks: Grand Cherokee SRT tire selection.

Selecting tires for a vehicle, and the associated work behind it, is easily and often overlooked. Choosing the correct tire can be a painstaking process, but the payoff is a worthy achievement. Such was the case with the Grand Cherokee SRT.
Posted on Jan 13, 2013

Selecting tires for a vehicle, and the associated work behind it, is easily and often overlooked. Choosing the correct tire can be a painstaking process, but the payoff is a worthy achievement. Such was the case with the Grand Cherokee SRT®.

Transforming the Grand Cherokee into a credible track monster was a major undertaking. Pairing the perfect tires was an equally painstaking task, but the end result is an amazing SUV that can tackle the commute, snowy mountain passes and track sessions all on the same tire.

As with any new vehicle program, tire suppliers received the call for submissions. OEMs are often forced to settle for an off-the-shelf tire in low-volume programs like the Grand Cherokee SRT. "Pirelli® was willing to work with us," said Jeff Roselli, Vehicle Integration Responsible, Grand Cherokee SRT. "Pirelli offered multiple compounds and constructions."

Tire construction affects ride and compound plays a major role in handling. Finding the perfect balance was a challenge SRT and Pirelli were willing to tackle together.

Extensive warm-weather testing was conducted in July at various tracks within the United States. This timing presented a challenge for proper winter assessment.

Cars and tires were shipped to New Zealand – where the temperature was frigid and snow and ice were plentiful - in search of a capable winter testing facility. All tire submissions were put through their paces in the snow and icy conditions. Roselli recalls one particular option. "The tread patterns were all nearly identical, but one of the submissions couldn't even roll out of the shop."

Quickly crossed off the list, a hard compound was the cause of this result. "Experiencing that was unreal," said Roselli. "The tires looked identical." This is a prime example of why an off-the-shelf tire would be unacceptable. Ultimately, a tire with the perfect balance of grip in all conditions was selected.

The four-season Scorpion Verde was an existing tire and is often seen on European SUVs, but was altered for use on the SRT. Pirelli altered some of the siping for a more aggressive look. Layering was also changed to improve overall stiffness. "We tried to get away from run-flat, but the sidewall stiffness just wasn't there," commented Roselli. "We knew sidewall stiffness was critical for handling."

With the relentless goal of improvement, an optional three-season tire would be necessary to eclipse the previous generation's performance. Pirelli's P-Zero was perfect for the task. Its stiffer sidewall helps minimize tire deflection resulting in more predictable handling.

When equipped with the P-Zero, the Grand Cherokee is capable of .9 lateral Gs - equal to or better than most performance SUVs. Owners seeking any competitive advantage on the track will want to equip their Grand Cherokee SRT with the P-Zero tires.

Grand Cherokee SRT tires are now the same size front and rear, measuring 295/45ZR20 at each corner. Overall they are wider than the previous generation by 40 mm and 10 mm wider in the front and rear, respectively, resulting in significantly improved grip. Restrained only by space constraints, 295 section width tires are the largest tire that will comfortably fit within the Grand Cherokee wheel openings. A 45 aspect ratio was chosen to completely fill out the wheel opening.

For those living in colder climates, snow chains were tested and do fit on the stock tires. Pirelli also offers snow tires in the same size as four- and three-season tires fitted to the car from the factory.

When it comes time for a fresh set of tires, take note from the engineers. "It's easy to dismiss the kind of work we do when we choose a tire. It's not a good idea to change from the manufacturer's tire choice, unless you're talking about race-specific rubber," Roselli cautions. "A major construction change like switching from a run-flat to a non-run-flat isn't advised. Sure, you'll get ride improvements, but handling will be sacrificed. The point of this car is not a smooth ride. It's not intended for everyone."

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