Got lucky at the track

[mr. anderson]

your axle definately has forward to back travel. if you loop 1:16 to 1:17 you can see the car squats, but the rim moves forward and down, forward, back, then forward all in like a 1 second period. and your car hasn't moved other than to shift the weight.

 

[justinS197]

That pretty awesome slomo launch, just to see the tire stick to the ground off launch is pretty cool

 

[psfracer]

your axle definately has forward to back travel. if you loop 1:16 to 1:17 you can see the car squats, but the rim moves forward and down, forward, back, then forward all in like a 1 second period. and your car hasn't moved other than to shift the weight.

Actually that all took place in way less then 1 second, as my 60 foot on that pass was a 1.35. Isn't filming at 240fps great? It picks up detail a normal recording could not.

Anyway--I think the wheel is moving like that because of two reasons. First, the tire is deforming (wrinkling, wadding, whatever you want to call it), and second, the tire did make contact with the body hard enough to bend some metal in the fenderwell, so that could explain a lot of the movement we see.

I will be looking at the LCA closely though. They are double adjustables, solid ends. I plan on moving each rear tire back 1/4 inch, then measuring the pinon angle to see what I have.

 

[Sharad]

Yikes.

That did look like the wheel moved forward, which is nuts on solid arms.

 

[mr. anderson]

I would see if I could mount the camera under the rearend next time and aim it to get the LCA and the axle. might see some interesting stuff.

 

[psfracer]

Ok, I took the LCA off, no signs of failure anywhere, also looked at the mounts (which are bolted and welded), nothing out of the ordinary there either. I measured center to center and it was 18.5", lengthened it to 18.75". Cut all of the bent metal out, so now the fenderwell metal is thin just like it is on the top stock, all the way to the front and down to the side skirt.

I will look at the other side tomorrow and lengthen that side to 18.75" center to center also. Then I will look at the anti-roll bar again, as neutral isn't working for my application--the driver front is lifting alot higher vs the passenger side. I will probably have to shorten the driver side and lengthen the passenger side so it leaves flatter.

 

[Deez-67]

Damn! Glad you dodged that bullet

 

[psfracer]

your axle definately has forward to back travel. if you loop 1:16 to 1:17 you can see the car squats, but the rim moves forward and down, forward, back, then forward all in like a 1 second period. and your car hasn't moved other than to shift the weight.

I wasn't very clear on this. So what I am saying is the movement seen is obviously happening, but at 240 fps, the movement spans a total of 18 frames. (I went frame by frame).

So, at 240 fps, the camera takes a picture every .004 seconds. So all of that movement you see happens over a period of .075 seconds (almost 1/10th of a second).

When I went frame by frame, it looked like the wheel movement could be explained by the deformation of the tire, and with it contacting the fenderwell.

I took off both LCAs yesterday, did not see anything wrong. Looked at both the front/rear brackets, no signs of bending. The rear brackets are both welded and bolted. I even removed the axle just to see, nothing wrong there either.

At this point I am going to adjust the roll bar with a bunch of preload, as you can see there is quite a bit of body roll, and this is with the roll bar set at neutral. I also moved both tires back by 1/4 inch by lengthening both LCAs from 18.5 center to center to 18.75.

 

[Sharad]

At this point I am going to adjust the roll bar with a bunch of preload, as you can see there is quite a bit of body roll, and this is with the roll bar set at neutral. I also moved both tires back by 1/4 inch by lengthening both LCAs from 18.5 center to center to 18.75.

What kind of anti-roll bar are you running? Metal bushings or poly?

 

[psfracer]

What kind of anti-roll bar are you running? Metal bushings or poly?

poly bushings on the anti-roll bar. They look good, but I figured out the problem. Stay with me on this and see if I am smoking crack....


I was adjusting the anti-roll bar backwards---or at least the car is acting that way.

When I would jack up the car, I would use the Kmember bolt on the drivers side to simulate the left front coming up higher then the right front (like in my sig pic). Thats exactly how it looks in the vids when it launches, with the anti-roll bar at neutral.

Last weekend before the race, I shortened the link on the drivers side, and lengthened the passenger side just a little. Well, as you saw in the video, the roll was worse.

So just now I decided to use the right side k-member bolt for the jack to simulate the passenger front rising higher then the driver front (the opposite of what actually happens).

I then adjusted the anti-roll bar to neutral, and guess what? The link on the passenger rear is shorter then the driver rear---I thought it was supposed to be the other way around?

So now I went back to jacking up the car by using the left front k-member bolt, and guess what? The driver front still rises higher then the passenger front, but not by much at all. When I started, the driver front would be 4 inches off the ground before the passenger side would come off the ground. Now, the driver front is off the ground 1 inch when the passenger side comes up, pretty close to even.

I notice now that the tire clearance is more, as the body is rolling alot less.