So what is going on? Like much of life, it’s all about balance. Ever since I put the new motor in the car late last year, it has been extremely loose. Obviously the motor didn’t have anything to do with the sudden change in balance but I have a feeling that the nearly 4 months that the car sat on jack stands might have finally killed the large rear trailing arm bushings. I’m sure it didn’t help that they had ~260k miles on them. Even though I didn’t touch the suspension the entire time it was out of commission, I could barely drive the car at the first event with the new motor. I like a loose car as much as the next guy but something was clearly wrong.
After examining the rear closely, I noticed that one of the trailing arm bushings was nearly completely torn through on the bottom side and the remaining rubber was cracked in several places. Considering I had new bushings sitting on my shelf for the past 2 years, the obvious thing would be to replace them, right? Hah, you obviously don’t know me very well!!! Considering it was late in November and I didn’t have a garage, I decided to swap some softer rear springs in the car I had lying around. Changing the rear trailing arm bushing is non-trivial unless you have “the special tool” and, at the time, I didn’t have it. So I swapped my 500lb rear springs for some 300lb springs and signed up for an Evo school! Weeeeeeee!
While the 300lb springs helped, it was clear that the car was still way too loose. My instructor and I laughed about it during the day as we both wrestled with the car nearly spinning every time we turned the wheel. So did I run home and fix it after that? Nope. Hey, loose is fast, right?
After the Dixie Tour of this year, it was clear I needed to fix the bushings instead of continuing to put a bandaid over the symptoms. Right before the Laurinburg event I managed to score a used “special tool” on EBay and I replaced my bushings. I figured since the rear end wasn’t flopping around anymore, I should probably put the 500lb rear springs back in the car.
It turns out that combination worked pretty well at Laurinburg. The car was still loose but it was definitely manageable and rotated very well everywhere. I honestly thought it could stand to be a bit looser but I was having trouble seeing the course that day so I didn’t try to make any adjustments. Considering I was at the “tight” end of the adjustments in the car and Laurinburg is allegedly uber-grippy, I probably should have known Greensboro might be a tad tricky the following week.
Boy was I in for a big surprise! The car was looser in Greensboro than it has *ever* been!
What’s up with that? In general, when you move a car from a grippy surface to a not so grippy surface, it tends to accentuate whatever issue the car already has. If the car is loose on a grippy surface, you better watch out when the grip goes away! Combine that with very cold tires and the car was flat-out evil.
OK, we have no grip and the car is evil. It really sounds like there is no way we should have ever seen any peak g’s even close to the previous week but the data doesn’t lie, right? It’s kind of like looking at the results of an event and trying to draw meaningful conclusions. Unless you know the conditions and what was happening with each car and competitor, you’re just shooting in the dark. Like much of life, it’s all about context. Um, and balance.
If you look at the data from my previous runs that day, you’ll see that I didn’t really didn’t generate peak g’s close to what was seen in Laurinburg very often at all. There were a couple of spots but that was mostly a result of getting super loose and thus can be considered just spikes in the data. I broke a motor mount on my 3rd run and had to abort it but I decided to run my 4th anyway. Would you expect anything different at this point?
By the time I got to my 4th run, I was aggravated by the balance issue as well as the motor mount and I decided I was going to go for it and spin in every turn. I can honestly say that outside of a RallyX event, I have never been more sideways longer than I was on that run. There is no way in hell I could ever reproduce it consistently so, in a sense, the data is worthless. Considering the drivability issues, it makes the setup worthless as well.
The accelerometers can’t tell when the car is sliding and if you look at the data closely, you’ll see that the car really couldn’t brake very well in Greensboro at all. In the places where I was actually able to brake in a straight line, I was never able to pull more than ~0.5 g’s. Yep, the grip wasn’t all that great. Where did the other peak braking numbers come from? It turns out that was generated as I was completely sideways trying to slow down for the last turn. It’s clear that the car can’t do that in a straight line and it took a combination of sliding sideways and a *ton* of steering lock to generate those numbers. In contrast, the peak braking numbers from Laurinburg were generated in a straight line.
The lateral acceleration peak numbers are actually genuine and were achieved at many points on the course. They were on the average about 0.1 g lower than Laurinburg which is significant and does point to a lower overall grip level. The peaks are only seen at initial turn in and given how loose the car was, I was able to somewhat take advantage of that through the transitions. The steady state numbers were a good 0.2 g’s lower than in Laurinburg.
I think there is an important lesson in there. The street tires were capable of generating excellent g numbers for a *very* short time even when they were ice-cold and the chassis was completely out of balance. If you can take advantage of that high transitional grip and not let the tires reach steady state, you can get around a course surprisingly quick. Doing it consistently is nearly impossible, however.
So what happened in Greenville? Was I completely sideways all over the place skewing the data? Nope. I did make 2 big changes to the car so we’ll try to see if we can spot the effects.
Jim
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