Zestino Gredge 07RS Race Track Tire Test


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.

Willow Springs International Raceway was our choice for testing, also known as “the fastest track in the West.”

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 test session was pleasantly surprising and rather satisfying, as the Gredge 07RS displayed its super high grip levels when needed and then peer-pressured me into some fun past the limits. Once over the limit, they will audibly communicate with you and will never get upset with some sideways action. In fact, their very progressive nature makes them very easy to control and drive on, and they may possibly tempt you to induce oversteer. You have been warned. 

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.


Now for the data: Clint Boisdeau checks the tire pressures after the first test session.

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.


Coming into the hot pits to gather data after the second session.

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.


Clint was a trooper and measured tire temperatures depite the extreme heat. The results, listed in order from outer temperatures to inner in degrees, were as follows: left front- 185, 190, 200; right front- 197, 180, 145; left rear- 155, 172, 170; right rear- 182, 160, 125.


  1. Between these and an AR-1, whichin your opinion is the softer compound more appropriate for short hillclimbs?

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