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High speed instability

G
For what it's worth I took Ross's diameter measurement at 15mm down and used a top dimension from Moog for a C5/C6 corvette tie rod end and got a taper of 1.6095" per foot. With all of the assumptions made and the short length of taper measured, I'm surprised how close to 1.5" per foot it comes That only about 0.004 inches out over the 15mm length that Ross used. Unfortunately the same procedure for a Cobalt tie rod didn't get me anything that looks standard so my procedure might be crap.
 
Desert Sasqwatch
From reading several sources on Dr. GOOGLE, it appears the 1.5 inch per foot taper is 7 degrees - which is pretty much an SAE standard. The 2 inch per foot taper, which is the other common dimension discussed in the articles, is a 10 degree taper. But looks like most 'metric' tie rod ends are 6 degree taper - which jibes with Ross' finding for the tight fit at the wide end of the tapered hole on the steering arm. Again, this all on internet and maybe some of it is actually true. :oops::cool:
 
Ross
Another option to a bump steer kit, would be to grab a file (or milling machine), and modify the DF uprights.
My steering arm needs to go about 1/2" lower. It currently is as low as it can go using the 2 diagonal holes with the red circles.
But if I were to slot those holes, I could mount my steering arms lower, and find the sweet spot to eliminate bump steer.
32812
 
G
Ross said:
Another option to a bump steer kit, would be to grab a file (or milling machine), and modify the DF uprights.
My steering arm needs to go about 1/2" lower. It currently is as low as it can go using the 2 diagonal holes with the red circles.
But if I were to slot those holes, I could mount my steering arms lower, and find the sweet spot to eliminate bump steer.
Click to expand...
That’s sort of what I did, but I just drilled a new hole for the back one instead of slotting both of them. Adjusted the steering arm to the no bumpsteer location and clamped it in place and drilled. I would be a little worried about it moving with slotted holes. One of my new holes overlapped with an existing hole so I cut a stop out of thick aluminum with a bolt through the other existing hole so it couldn’t move back up.
 
C
I took my car to an actual alignment shop. A good bunch of guys that deal with race cars and seem to actually care about this sort of stuff.

It cost way too much, but it fixed my car. It's a totally different animal after having it professionally aligned. They set everything to the recommended specs, except for camber, which is now -2.0 deg in the rear, and -1.5 deg in the front. They thought the extra in the rear would be worth it since I intend to autoX and track the car. So as much as it cost ($360), it was worth it. It isn't scary anymore.

I am baffled as to how I got it so wrong though. My rear toe, especially, was about 3/8" OUT. How is that possible? I bought toe plates. I checked them again and again. I was careful. How could they be so wrong? The shop said they adjusted them to be 1/8" in. When I measure them now, they appear more like 1/16...but whatever. Close enough.

Camber was also pretty whacky. I tried to set all of them to -1.5 at home, but they were actually anywhere between about -.7 and -2.1. I have the angle gauge. I followed the directions. But again, I got it wrong.
 
G
I don't put much faith in toe plates, I've never been able to get very consistent results. Stringline is the way to go for DIY toe adjustments. I feel like my camber measurement is ok but I'm using the Quicktrick alignment tools.

I would consider the DF "instructions" as a ball park adjustment only.
 
Rttoys
It is very tricky doing it the old school way. It’s measuring, reference points and good ol “eyeball” to get it right (enough).

I don’t use toe plates, I use the QuickTrick alignment setup. It takes time. Lots of time to get it right. I even used it on my truck, but later went to a shop for an alignment (I wish I could justify a real alignment rack and machine), just to make sure it was right, due to its my daily driver. Their numbers came out to my numbers, except toe. I was at 0* and needed a little bit of toe.
 
G
My coil overs already had a little bit of a slotted hole, although it wasn't enough to get it to the 0.5 degree that I was trying to get. The 1.5 to 2.0 was within it's adjustment range.
 
Sluggonaut
Gtstorey said:
I don't put much faith in toe plates, I've never been able to get very consistent results. Stringline is the way to go for DIY toe adjustments. I feel like my camber measurement is ok but I'm using the Quicktrick alignment tools.

I would consider the DF "instructions" as a ball park adjustment only.
Click to expand...

This is not reassuring as I wait for my toe plates to arrive today. lol
 
G
Actually, what I have is the QuickTrick set up, which isn't exactly toe plates, but similar concept, just works off of wheel instead of tire. This really should be better than typical toe plates, but anything that is measured with a tape measurement doesn't have enough precision.
 
G
For my toe adjustment I found a video that suggested taking 2 pieces of PVC, and cutting two slots in each piece wider than the car. Cut the slots in both pipes at the same time so they are the exact same distance apart. Hang weighted fishing line over the pipe at a height to match the center of the wheels and use a good steel ruler to adjust the fishing line so it is the same distance from the center of all four wheels. This can be a little time consuming to do by yourself. You can then measure off the string to adjust your toe.
 
C
Rttoys said:
@Chubbs

how did they adjust rear camber? Did they grind the strut or use the aftermarket adjuster bolts?
Click to expand...


I already had aftermarket camber bolts. The weird ones with the cam lobes on them.

XtremeAmazing 12mm Cam Bolt Kit Adjustable Camber Correction Alignment Kit for Vehicles Four Wheel Pack of 4 Army Green https://www.amazon.com/dp/B099DYDV4M/ref=cm_sw_r_apan_i_T6QCA7APPDP8H6CKA405

They seem a little sketchy, as what was once a thicker bolt has been necked down to make room for the cam lobe. I'm not sure what their yield strength is compared to a full size bolt. They seem to work though, for now.

Rather than using a full alignment rack, the guy that did it said he had better results with an optical system, whatever that is. I actually wonder if it's similar to that laser that warmPepsi posted.


Whatever he did, it worked. The car will still tram line a bit if it gets into a rut, but for the most part it feels very tight, and it certainly resists directional changes. I may actually have to loosen it up for track duty, but for now it's nice to drive a car that drives straight.
 
Rttoys
Doing autocross, keep an eye on those bolts. I used those and had them slip a few times. I ended up cranking them well beyond specs to keep them from moving. It made me nervous they would break, so I put the stock bolts back and just ran what negative camber it gives me (about -1.3 or so).

I knew when one of the struts would move, because my steering wheel would be off center when driving straight.
 
Whidbey Goblin
Waterdriver said:
4 clicks seems pretty soft.
Try turning in more dampening and test in a safe area. Try starting off at 8 clicks and go from there.
I've run typically between 8 to 14 clicks, transforming the car. Increasing stability and confidence in the car. That's for my driving style and dont mind the harsh ride. You dont get one without the other.

You could double check your alignment using the DF alignment procedure. Just to see if if there's anything that's off/different.

Aero will make a big difference at 120. Really about 60mph and up. Our cars are aero dirty and anything to help manage the air around it at those speeds will help. Wings, continous flat floor, tire air flow deflector, turning vanes to rear diffuser.
You can easily get carried away with it. Which is half the fun.
Click to expand...
I made a ton of changes over the last few weeks leading up to my track day Friday. New control arms with all new bushings (delrin in the forward and spherical in the rear). Added the sway bar. Most importantly aligned the car myself after talking to Lonnie. I had too much toe front and rear. Car handles like a dream now, I was seeing 130 miles an hour in the front straight at the Ridge with no stability issues .
 
Waterdriver
Nice job! The bushing replacements is a nice piece of mind that the rear end alignment isn't floating around, especially at those speeds.
Glad you found out the main issue. Self alignment is the way to go and DF has such a great documented process on how to do it. Seems daunting for a lot of folks but it really isn't.
 
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