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Weekend Testing with Chin Track Days, and Splitter Update

Testing

Spent Memorial Day weekend at Road Atlanta with Chin Track Days. For those not familiar with Chin, they run a great event with tons of seat time, usually far in excess of what I need per day (up to 2 hours of open track per day, if you take full advantage of all hot sessions). The goal of the weekend was to get a better feel for the car prior to the June NASA event (get a feel for the recently increased front spring rate to 700 lb/in, specifically), evaluate tire temps and pressures with current alignment specs, and try to improve my line through the first two sectors.


Conditions were hot. Like, really hot; above 100 degrees in the paddock, and surface temps warm enough in the sun that you didn't want to sit on them for any prolonged period of time. Went through 10 bottles of water per day, plus a couple Gatorades. So, conditions were expected to be somewhat slippery in the afternoons, and dehydration on track was something to watch for.


In my typical ying/yang fashion, Saturday sucked, but Sunday was a fair bit more helpful. On Saturday I managed to burn out the trailer's emergency brake controller battery, lose my phone (left on back of car on way to grid, was returned after about four hours of cars driving over it on the way to pit-out), nearly understeered into a wall on cold tires at T12, and developed a severe mis-fire after the second session.


Sunday started early, pulling all plugs and wires in hopes of an easy fix for the misfire. As luck would have it, found a wire that had severe heat damage from the header. Swapped to new GM Performance wires, and all good. Even made it out for the first morning session at 9:40.


With respect to the goals for the weekend:

1. Tire Temps: Joseph with Corsa Crew was on hand to help take hot temps and pressures in the pit lane. Basically, temps and pressures were fairly consistent around the car after three hot laps on A7s; temps were generally 175 degrees on the inside of each tire, and 150 on the outside, with each tire roughly at 32 psi. So, pretty close to on the nose.


2. Feel: The front felt fairly unstable in the T12 entry bump, generating an unsettling feeling and a sense of oscillation. Once the car took a set, however, steady-state handling was great. So, guessing a change to dampening in the front is needed. Also, worth noting the stability over bumps improved dramatically with a passenger.


3. Line: Starting earlier in the week, I purchased a virtual track walk with Ross Bentley. The two hour video was just under $50, and went turn-by-turn in an exhaustive fashion. It has hugely helpful, and probably the best $50 I've spent in terms of lap time benefit; I will be buying these for each track I run on in the future. I was able to slash more than .5 second from my personal best in the first sector, and had I not screwed up braking into 10a getting around a slower car in the braking zone, I would've been into the high 1:35s, and that's with slower Continental race tires on a > 100 degree track, and with an extra 160 lbs for the passenger and seat.


So, overall it was a successful weekend. Hopefully this improvement can continue through the June NASA event at Road Atlanta.


Select laps from the Sunday session can be found here (please note: data connection busted in the paddock, and the sound on the GoPro somehow leads the video by roughly 2.5 seconds):



Splitter Update

Work has begun on a new splitter. This splitter is a flat design, as tested in a previous post, so no fancy venturi tunnels yet. It is a 3" length, three layers of 6k carbon fiber on the top and bottom around a 3/8" high density foam core, with an additional layer of Kevlar on the bottom for abrasion resistance. Vacuum bagging is used to keep the resin content reasonably low. The intention is to mount the front in the to bumper (the actual metal bit, not the urethane fascia), with the rear anchored to the radiator support cross bar.



Most of the mounts are made from carbon fiber. The reasoning being this is, due to the brittle nature of the material, hopefully the mounts will act as a fuse on an impact, sparing the chassis and, with some luck, the splitter as well. Also, for small-scale mock-ups, making bits from carbon fiber is easier, quicker, and cheaper for me relative to having a prototype milled from aluminum. So, though carbon fiber seems a bit unnecessary for the application, it's actually the most feasible for me in these circumstances.


From the previous post on splitter testing, we estimated a 3" splitter at 3" ride height should produce roughly 420 lbs of front downforce at 100 MPH. Assuming that is mostly at the front of the splitter (lets say 75%), that means the front three mounts of this splitter need each to support 105 lbs of force at 100 MPH. If we assume that scales with the square of the relative velocity, that means roughly 235 lbs each at 150 MPH. The mounting system will be tested (via load simulation in Fusion 360) in the future to ensure proper strength for the aero load, but there are challenges properly evaluating composite strength due to variances in fiber strength, resins, and fiber/resin content.


A full write-up on the splitter construction and mountings will be posted in the near future, prior to the June NASA event.

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