FFR Tests Toyo's For Drivers

At the end of last season NASA, the sanctioning body for the Factory Five Challenge Series, dictated that a new brand of tire would be used for the 2007 season and beyond.  Due in part to the fact that these were as of yet mostly untested on the cars and that the new tires replace both the dry and wet choices, three different sizes were made eligible. In order to get some initial impressions and help ease the transition, Factory Five sent it’s engineering team out to Phoenix to do a pre-season test of the new tires in the various sizes as well as comparing them to a baseline form the previous seasons tire.  Tire pressure testing was also done to help get a good starting point from where to begin the new season. 

The test:

The Bondurant School of High Performance Driving provided the test setting with all tests being completed on the main or “Bondurant” course.  Challenge car number 51, that has been driven competitively in the hands of four different drivers at four separate national championship events, was used for the test. All driving was performed by veteran Challenge Series driver Spencer Sharp, who is well at home on this track having long been employed as an instructor at the Bondurant school.  Data collection was handled by a Racepak G2X GPS-based data acquisition system with Engineer Mike Pisani at the controls.  And, last but not least, the monster task of tire changing duty was handled by Factory Five race mechanic Andy Cole.

Testing began by running some familiarization laps to get Spencer comfortable in the car and install and check the Racepak system.  Once the car was up to temperature and the data system was checked out the first test run was a baseline of last season’s very sticky Kumho V710 tires.  The tires used for this test had 5 heat cycles and were set at a hot temperature of 26 psi, determined from what had worked best for this particular car over the past season.

Following a successful baseline test, the tires were then switched to the 275 Toyo’s and the pressures were set to the same hot psi as the baseline.  Successive tests included the 255s and 235s on all four corners and the old fast combination of 275 front and 255 rear that had proven quick in years past on the Kuhmo V700 Victoracers.  

All Toyo RA-1s were shaved as per manufacturer’s recommendation for running on a dry track.  Kumho V710s were left unshaved as per their manufacturer’s recommendation.

The results:

Once the results were recorded we took the single best lap from each session as well as the average of the top 3 laps.   The times were as follows: 

Test II tire pressure:

All pressure testing was done using the 255 Toyo’s on all four corners.  Hot pressures were started at 37 psi and lowered in 2 psi intervals (slightly more at the ends of the spectrum) until the car was noticeably falling off in performance and Spencer remarked that the car no longer felt stable. 

Test II results:

Summary:

In addition to the hard data, Spencer’s comments were written down at the end of each run.  Most sessions he was able to predict, by car feel, which set-ups were working and which were not and the lap times would agree. Note, however, that even though the 235’s posted pretty good numbers he was not as comfortable in the car with them on.  His comments are as follows:

V710’s: no comments

275 Toyo’s: felt like less overall grip and less grip coming out of turns

255 Toyo’s: good feel, car felt faster and noticeably changed shift points

235 Toyo’s: Wheels skating, not stable under braking

275/255 Toyo’s: Best overall feel, stable braking and throttle on quicker

While the results of this test showed a slight advantage to the 255’s, it is still entirely possible that different drivers will have different preferences so it is important to stress that this test does not give a hard and fast set of rules as much as a guidelines and a starting point from which to begin the season. 

Thanks again to Ken and Mike and the Bondurant School for the generous use of their facilities, Spencer Sharp for driving some nights until after the sun had gone down, and John George for his help in decoding all of the information and putting it in usable form.

For any questions about the test email jim@factoryfive.com.

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