After more than a year of on-again-off-again preparation, I recently got to drive my new M52-powered, fully-caged, and aero-sporting E30 race car for the first time. For it being the first shake down of the car, I have to say that it went surprisingly well. The car performed admirably, and with only a few minor issues that were already overcome, my focus has been on dialing in the setup of the car.
Being as though this was my first experience driving an aero car, setting up this car is going to be a fun learning process for me. Tweaking the setup of a car through alignment, corner balancing, suspension changes, and ergonomics is one of my favorite aspects of track car ownership.
There's no denying that the car was pushy, which is to say that it was understeer prone. Thankfully, the car was quite predictable and planted, and it made me confident in pushing the limit of the new car pretty quickly.
This didn't come as a surprise to me, since the rear wing is rather large (Bimmerworld V3, 65" wide, 12" chord), and NASA ST/TT5 cars are typically limited by the front downforce they can generate. With a splitter that has to be flat (no end fences or diffuser tunnels), and a max protrusion of only 4", there's only going to be so much you can gain up front.
I built my splitter to NASA ST/TT5 spec and set it at about 1° angle of attack. The wing was initially set to about 2° angle of attack.
Since the car was pushing, I started making some basic tweaks at the track to try and improve the setup, and help the car rotate better.
What I've Tried Already
I tried to make at least one tweak each session. Here is what I tried, and what the perceived result was.
1) Adjusted the AST 4100 dampers, which are only high speed rebound adjustable. I went softer in the front and stiffer in the rear. In the front I ended up about in the middle of the adjustment range, and in the rear close to full stiff. It didn't make much difference with the understeer. I think I'd have preferred to adjust compression in this instance, if I could. With the adjustment being rebound-only, I don't think this is a setting that I will change all that often, once it is dialed in for the spring rates on the car.
2) Messed with tire pressures. I lowered them quite a bit overall, but as far as balance, I lowered the fronts more than the rears, trying to get some more bite into the front end. This was again a minor change – not enough.
I will say that overall, the Yokohama A052 tires that I was running felt much better at relatively low pressures. I was running them around 30-32psi hot (24-25psi cold), and it was a significant improvement in grip versus the 37-39psi hot I was previously running them at.
3) Adjusted the wing. While I was not running much angle of attack, I took another 1.5° out of it, leaving it with just 0.5° angle of attack. I believe that you can run these wings neutral or even at positive angle without ill effects (it will still make downforce, but have more drag). That seemed like a strange thing to do, so I left it with a slight negative angle of attack. I didn't notice much difference when making this change.
While these small but cumulative effects helped the car, it wasn't enough. It was still very understeer prone, and it will take further adjustment to dial in.
My fastest time of the weekend was actually on the test day before the competition, but that is mainly because the track got considerably worse on the competition days, due to the drifting and racing that was also taking place on those days. There were so many rubber marbles and so much dust on the track the rest of the weekend that everyone's times slowed down.
That said, despite the track conditions, and the tires nearing 20 heat cycles, I was just about able to match my time from the test day during the last competitive session of the weekend. Overall I would say that was a win when the conditions are taken into consideration.
Ideas To Try Next
The car still needs more front end bite, or rotation, especially in mid-speed sweepers.
I've heard second-hand that you want to set up the car to be a bit over-steer prone in low- to mid-speed sections, and allow the wing to provide the needed stability in higher speed sections. That seems to make sense. I was taking The Kink @ CMP on-throttle and about 12mph faster than I usually do in my other E30 (in which I usually fully lift).
Here are the things that I would like to try next:
1) Installing a rear sway bar. Many E30s benefit from no rear sway bar, for the sake of keeping the rear end planted and being able to get on the throttle earlier leaving a corner. On the other hand, most E30s don't have a 780 sq/in wing on the trunk, either.
The car rolls and pitches quite a bit, so I think adding a small sway bar to the rear, as well as stiffening the front bar, will help the car overall. Especially when I run stickier tires on it.
2) More front downforce. This might be an obvious one, but I will see if I can make a tangible difference in front downforce by increasing the angle of attack on the splitter, and adding a hood vent in the center. Hood vents reduce lift on the front end, with improved cooling being a welcome side effect.
3) Alignment changes. I would like to add a bit more camber in the front, but it is maxed out already. The change that I will make is to try some front toe-out (coming from 0 front toe). I think the rear camber and toe are okay, and will likely not make further adjustments to the rear alignment.
4) Stiffer rear springs. Based on my experience, the front/rear spring split on an E30 is best when in the realm of a 100-250lb difference (the front being stiffer). My TT6 car has a 200lb split. This new aero car only has a 100lb split. While I think stiffer rear springs are probably the better change here, I don't have 900lb springs on hand, but I do have the sway bar already. So I am trying the sway bar first.
So far, that is my short-list of things to try before the next time on track with this car. Hopefully this can spark some discussion between those of you with more experienced than I, because there could certainly be some good ideas that I'm missing!