On-board video of the Karla Pestotnik Racing AP1 S2000 lapping Willow Springs "Big Willow" course on the Zestino Gredge 07RS street tires.
Continue reading for the test results-
Zestino Gredge 07RS Race Track Tire Test
by Karla Pestotnik
It would be pretty comical if we saw Usain Bolt running the 100 meter dash in the Olympics without shoes. He would most likely not be breaking any world records or winning any gold medals without shoes on. Undoubtedly, a good pair of track spikes has helped Usain gain the traction he needs to push himself forward and eclipse the run in record breaking pace. The same can be said for someone looking to whip up some quick lap times with just wheels and no tires on. A good set of high-performance tires can make or break the handling capabilities of any vehicle. This concept applies even more so on a purpose-built vehicle designed to push the limits of lateral g's around a race track.
Every year, tire manufacturers develop new compounds and tread patterns designs to aid in the road holding capabilities of the tire. It's no surprise that we see more records being broken year after year. One of the newcomers (to the United States) looking to make their mark in the high-performance driving arena is Zestino Tyres, with their newly developed, ultra-high performance tire- the Gredge 07RS. These tires are DOT approved, with a 140 tread wear rating. With an aggressive tread design, shown below, we were curious to see what they were capable of.
We chose to test the Gredge 07RS on the Karla Pestotnik Racing Honda S2000. What good is a tire test without knowing more about the vehicle being used? Relatively moderate upgrades have been made to the Time Attack oriented AP1 generation S2000 and include a stock, full AP2 driveline swap: F22 engine, transmission, and differential. Power modifications include a Berk exhaust and Mugen headers. Suspension modifications include KW Clubsports coilovers, J’s racing camber kit, J’s racing roll center adjuster, J’s racing bump steer kit, and Spoon Sports rigid collars. Finally, aerodynamic modifications include a Kognition wing and custom front splitter.
With ample tire size options available, we chose to test the Gredge in 255/40ZR17, which fit comfortably and provided a nice stretch on the 10" wide Volk Racing wheels. New sizes are also being released, so be sure to check their website for the most current sizes available.
On their website, Zestino advertises the Gredge 07RS’s as high performance tires that “provides drivers with the confidence to drive at the maximum limit.” My first question was, what exactly is it about these tires that will provide me, as a driver, confidence?
Every aspect to the tread design of these tires has significance, with the most exciting being the lightning-shaped grooves and the shorter, horizontal grooves. The lightning-shaped grooves aid in lateral traction. The shorter, horizontal grooves aid in directional stability. All it takes is one push to exceed the limit in order for me to agree with Zestino’s advertised confidence boost- these tires are very progressive beyond the limit and are incredibly easy to drive on. I must say, however, that I am glad that this type of forgiving tire technology didn’t exist in all street tires when I first started to learn performance driving, or else I would probably not have the skill set that I have today. For all advanced drivers out there, these tires will be a breath of fresh air for you.
We decided to test the Zestinos at Willow Springs International Raceway, also known as "Big Willow." Coming into a tire test, choosing alignment settings and initial tire pressures can be a guessing game, as each tire can have its own unique characteristics and “sweet spots.” We made educated guesses with the settings based on test data from other high-grip, street performance tires. We kept the KPR S2000 alignment settings at -3.1 degrees camber in the front, -2.9 degrees camber in the rear, max caster, 0.22 degrees total toe in the rear, and zero toe in the front. We set the tire pressures to 29 PSI left front, 30 PSI right front, 30 PSI left rear, and 31 PSI right rear in preparation for the first test session.
While piloting the S2000 for the first test session, my first thought was an instant surprise of how much grip the Zestinos had. I was able to clock in an instant 1:33.1 lap time while feeling the car out, followed by two more mid 1:32 laps. On the third hot lap, I had the tires hot enough to fade grip and decided to do two more punishing laps in order to monitor their behavior past the limit.
These super soft tires have a very high limit. Once over the limit, they are very progressive and will communicate audibly with you- if you listen for it. They won’t get upset with you for taking them over the limit, and they are very easy to control. They are enticing to exceed the limit on!
The only thing that I don’t like about them, however, is the strange smell they make. It’s an interesting qualm to have with them I suppose. Perhaps I am overly sensitive to smells, but it is definitely noticeable and goes away after the first heat cycle.
The first session was a warm morning, with a 75 degree ambient temperature and already a 95 degree surface temperature. Tire pressures increased with a 7-9 PSI delta all around after three hot laps and 2 additional test laps. This large delta is to be expected for five abusive laps on a performance street tire. The left front increased from 29 PSI cold to 37 PSI hot, right front increased from 30 PSI cold to 37 PSI hot, left rear increased from 30 PSI cold to 39 PSI hot, and the right rear increased from 31 PSI cold to 39 PSI hot.
The second test session brought on pretty brutal conditions for the tires, with the ambient temperature at 90 degrees and the surface temperature at a whopping 115 degrees! I was able to maintain consistent 1:32-1:33 lap times for three hot laps, however it was definitely not as pretty to do so- compared to the morning session. Like any soft, high delta grip tire, the maximum grip levels during the second session fell off and exposed the car’s behavior biases. The extreme weather conditions definitely contributed to this as well.
The tire pressures saw a 6-7 PSI increase after three hot laps during the second session, which is generally what I see for most performance street tires. The left front increased from 29 PSI cold to 35 PSI hot, right front increased from 30 PSI cold to 36 PSI hot, left rear increased from 30 PSI cold to 36 PSI hot, and the right rear saw an increase from 31 PSI cold to 38 PSI hot.
Unfortunately, the KPR S2000’s timing chain tensioner decided that it had had enough, so we ended the day early to avoid a complete failure. The positive side is that we just so happened to do testing during a Redline Time Attack event, and the Zestinos were good enough for a first place win in Street Rear Wheel Drive class!
Since we weren’t able to test as much as I wanted to due to the S2000’s TCT, we went back for another test after replacing it. This time we chose to test at Buttonwillow Raceway in the 13CW configuration. Willow Springs was great to test high-speed cornering grip and behavior, which the Zestinos really excelled in. However, I wanted to test the behavior of the tires on a samplimg of the lower speed corners that Buttonwillow Raceway has to offer. I knew this was going to be another tough test for the tires, since the weather was scheduled to be even more extreme than it was at Willow Springs, with the peak ambient temperature at 108 degrees.
Clint Boisdeau drove the KPR S2000 for the first two morning sessions while I had to drive my Civic racecar for other (non-related) testing, and his thoughts on the tires’ behavior were consistent with mine. I drove the S2000 after lunch, which was in the extreme heat. I don’t think any tire would have been happy at 108 degrees outside temperature, and the Zestinos were considerably less happy on the second day of beating. As a soft compound tire, they are intended to excel greatly during their first few heat cycles. However, despite abusing them in the heat and regardless of being beyond their prime grip, the Gredge 07RS’s never felt sloppy or overly greasy. They are still usable for track day seat time or testing, however they just obviously aren’t as fast after their prime, as is to be expected.
My opinion of the Gredge 07RS is that they are a very competitive street tire for road course track driving in a rapidly growing market demanding the fastest and highest overall grip tires. Time attack drivers that are in a class that require street tires can use them for ultimate peak performance, but be sure to have an emphasis on getting the hot lap done in the first session for the “sweet spot” on these tires. True time attack built cars generally only last 1 to 3 laps maximum, so this is not a tall task to ask from time attack drivers. I think these tires would be great for competitive autocross drivers as well, where tires see quick and intensified heat cycles. These tires would make excellent drifting tires, of course, but that is why they are already established in that market. With several options available for high limit street performance tires, I would rate the Gredge 07RS towards the top in overall fastest peak performance.