August 17, 2012

Suspension Work @ Flatout Motorsports

Pop Quiz: Which is higher, front or rear?
After fixing some of the problems I encountered after the last event at NHMS and taking some personal time to myself, I decided to reevaluate our alignment setup once again. I heard great things about Flatout Motorsports, so I wanted to give them a try and see what they think would help the car handle better.

When I arrived, I got to speak with their suspension wizard, Evan Consolazio. Evan and I discussed a lot about the current setup of the car, the changes over the season that I have done and their impact, and then what behavior we'd like to see from the car. Ultimately, the car still understeers a LOT more than we'd like, and oversteers at the wrong time. We felt as though the front tires are being over-worked and are essentially doing nothing. To remedy all of this, Evan came up with some good ideas.

"First, I took into account the cars tendency to understeer on throttle. This tells me the rear needs less toe in, hence bringing the toe from 1/16" in per side to 1/32" in per side. 

Next, I looked at the the unpredictable oversteer tendencies off throttle as well as corner exit. These characteristics point to improper diff lockup, but adding camber can help to increase traction and stability, so I increased rear camber from -2.7 ° to -3.2 °.

Finally, your co-driver said he felt that the front tires lost grip when more steering angle was added and weren't "working". This tells me there is either too much caster or KPI in the front. As the wheels are turned, the arc that they follow forces the wheels into the ground, effectively putting more weight on the front tires. When the car is already fully loaded and this happens, you abruptly exceed the tire's limit, causing understeer. Since KPI is not adjustable, I removed roughly a degree of caster from the front, bringing it around 3.5°, reducing the range of the horizontal arc."
One of the culprits with height issues
Before we were going to do the alignment and corner weights however, I mentioned my concern about how much free space the rear springs have from the top-hat when at full-droop. He agreed with me that it could cause issues and is something I should take care of. Given what I have to work with, it's not an easy feat. The Ohlins RX-8 rear shock is rather long unfortunately. The picture above is of the bottom cup that threads into the coilover sleeve.

"The fact that the spring is loose means that the shock is too long. If you're able to shorten the body more after modding those threads inside the sleeve, the shock won't have to sag that extra 1" before reaching static ride height. That means you have 1" more room on the nitrogen/separating piston side (essentially, the working piston will be closer to it's center of travel)."
Cut a lot shorter!
I was hoping that cutting the cups like the above picture would help with the height issues because we could just thread this all the way into the sleeve like before, but thread the sleeve higher on the shock body, right? Wrong. The sleeve is not fully threaded inside, so there is a limit as to how high up on the shock it can go. Because of that, we could not complete the task. I'll just need to take the sleeve off, bring it to a machine shop, and have the inside of the sleeve fully threaded all the way through. Once done, I can then move the sleeve higher up on the shock, and then I will be able to have the springs nice and snug up against the rear top-hats.

Once everything went back together, Evan performed the alignment and corner balance. Guess we'll have to see how she does at Devens tomorrow, won't we? Thanks a million to Evan and Flatout Motorsports for the time and effort they put in to helping me out. Be sure to check out clean Evan's EP3 Civic build over at Honda-Tech. I'm anxious for tomorrow's race now, so stay tuned to see what happens!
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