Attended a Test and Tune at the Ridge Motorsports Park on July 5th 2016. Attendance was very minimal (day after the 4th of July) which provided plenty of traffic-free open lapping. Primarily, this day was used as a shake down of the car after 8 months of minimal activity. I experimented with a few aero changes and ran all but one session on new R888’s. The open lapping format is perfect for running some laps, reviewing data, making changes, rinse and repeat. The weather was overcast and low 60’s all day which also helped maintain track consistency. Overall, a great day for testing.
I was initially planning to test some major aero changes but while doing some routine maintenance about a week before this event, I found some major issues that needed to be addressed before spending time on aero. I dropped my oil pan and discovered some stringy plastic debris which looked like timing chain guide material. A quick inspection revealed that the oil pump chain was damaged. The three inner plates on one link were fractured and cutting into the chain guides. I’m amazed that the chain didn’t fail completely as only the side plates on that link were intact. I have no idea how this could have happened but very lucky I caught it before the chain failed and I lost all oil pressure. I threw some new plugs in, inspected my original valve spring retainers, and adjusted the valves along with an oil and filter change.
I mounted a new set of Toyo R888’s (245’s) to a set of Forgestar 17 X 10’s. I figured I’d try a “track day” type tire rather than burn up more Hoosiers if I’m not currently competing anyway. This represented a major change to the cars dynamics. The overall grip is lower than the Hoosiers as expected but the tires have significantly more slip angle and massive squirm. Not sure if it’s tread squirm due to full tread depth or tire construction but the car was a handful. The tires would take a set with a lot more yaw vs the Hoosiers and then they would rebound at transition. The tires were very consistent and took repeated slides with no complaints. Right out of the gate, I was running consistent 1:51’s on the R888’s. After lunch, I put a set of Hoosiers (245 A7’s mounted on the same wheels) on the car and dropped 2 seconds with way less drama. These Hoosiers are far from peak condition as they had over 10 long abusive heat cycles and are 2 years old. I’m guessing they are a few seconds off the pace of a sticker set (estimated laptime difference between new R888’s and new A7’s is 4 seconds). My fastest lap using 245 Hoosier A7’s at the Ridge is a 1:46 but that was before the change to T12 which I believe added about a second to my time. The car is incredibly precise and crisp with the Hoosiers which confirmed my suspicion that the the R888’s were the cause of all the yaw action and not a chassis/suspension set-up issue. I tried running higher pressures in the R888’s and it didn’t seem to improve the response. I hear that this squirm gets better after a few track days – we shall see.
Observing the data shows a few things regarding track layout and tires. The R888’s achieve nearly the same peak grip (as seen in max and min lateral G) but don’t achieve as much combined loads (as seen in G-G plot). I’ve found the same results with sticker vs old Hoosiers as well. You lose time in the areas of combined loading where you turn and brake or accelerate at the same time. Below are screen shots of data comparing my previous 1:46 on Hoosiers (prior to T13 change) with the 1:49 on old Hoosiers and also comparing my fastest laps of the day on old Hoosiers vs R888’s. A big difference with the R888’s is the instability under braking with minor steering transitions. This instability required earlier and lighter braking especially into T11 (Thumb). Red lines below are the 1:49 on Hoosiers in all data plots.
I went out for my last session a little after 4:00 PM and ran some cat and mouse laps with a very nice guy in a 996 GT3 with a 450 whp 4.0 liter. The car was on Hoosiers and was fully prepped for track work (stripped interior, lexan windows, big wing, 2650 lbs, etc). It was a very fun session as we were running the same times despite the GT3 pulling many car lengths on the straights. Of course my GoPro battery died on the first lap of the final session so I didn’t get any video.