Well, here is the vid from this past weekend, best lap at Barber. Two places to note:

At 40 seconds I enter the 'Spider turn' near off camber segmented 180. I spent the weekend chasing a guy in Danny Popp's old Blue Vette running TT2. He noted this was one corner where I was way better. I get back on the power real early and just hang on. The slide towards the end is almost dead neutral, front and rear. No plowing understeer, no snappy rear end.

Then at 1:10 I enter the high speed dogleg on the back end of the track. The car is actually loose on that exit but I only have to just breathe on the wheel. The front and the rear are in balance.

I am a rank novice. I only know I am going way faster now in TT than I was before and it is much easier to approach the limit with the car.

 

it is entirely possible I am clueless. Of the 3 cars that I've helped with suspension setup, all 3 of them won solo national championships this year in ASP, STU, and AM. Maybe I just get lucky?

 

lol!

 

...knew that was coming.

 

Saw that coming from a mile away...

 

Or maybe it's just autocross.......

Of the 3 most recent cars I had a hand in, all 3 were podiums in open wheel formula series. Don't ever for a second think a good autox setup is anywhere near optimal for a road course


But I digress. Camber and roll couple manifest themselves in completely different ways. And this argument is stupid since you're insinuating I'm allowing more than 1 variable to change at a time.

 

You have pretty limited control over roll couple in the EVO though as there really isn't any parts to even allow adjustment to roll center. There are the Whiteline parts that do VERY LITTLE for roll center on the front then ride height adjustments and that's about it.

 

There is definitely room for roll center correction in an 18" wheel. Actually, there's enough room to get the lower control arm back to factory angles with 2.5" of lowering.

 

Is there anyone willing to walk me through taking measurements of my car? I would like to figure out where my CG is, roll center, etc.
without this information I'm pretty much make my changes based on feel and the knowledge of others which seems to be working but I would rather have hard data to back everything up.
I have no problem paying for the time and information.

 

I'd be impressed if you're evaluating suspension changes while maintaining constant camber under load. Most people don't reset alignment after making small ride height/rake changes. Some people do reset static camber and toe settings after making a ride height change and that is better but still doesn't give you the full answer. changing the ride height changes where in the camber curve you operate and the curves are not always linear. Specifically, when you lower the rear the camber curve gets more aggressive, so without changing anything else you will operate with more negative camber on the outside rear tire at max lateral load, even if you start off with the same static camber setting. the car will be more pushy as a result of that camber change at full load.

I have also done the opposite experiment, where I kept the lateral load transfer distribution constant after accounting for the change in roll center height before and after a rake change, with the results still showing substantial balance changes with changes in rake even though the load transfer was the same.

so if you really are constraining your testing to 1 variable at a time and still think that the roll center change is the dominant factor in the change of balance with rake changes on an evo then I guess we'll just have to agree to disagree.

 

The big problem with evaluating the effects of roll center is that so many other variables are affected at the same time like camber curve, roll couple, roll axis, etc. which in turn relate to roll resistance and how that effects the need for springs and bars. The multivariate modeling required is exceedingly complex and I don't see a possible way of looking at that one variable in isolation.

Regardless, given my experience with roll center compensation and the difference it makes in driving different types of lowered cars on anything but a smooth track I am surprised it is not more universally embraced and there not more kits available that address this - Whiteline ideally is for a car that is only lowered 5/8".

 

Sure...well, I question if their is enough room for the tie rod to do that much correction...but that wasn't my point.

Where are the parts available to do it is my question?

I know you are working on something. I'm just saying currently the parts don't exist unless you get them custom made.

 

http://racefab.co.nz/

 

You are right about the steering be a limiting factor. Without changing the steering ratio, zero bump steer limits the correction to about 2.5" if you want to put the steering link in double shear.


In my model I iterated on the factory suspension to find the needed position of the tie rod pivot. Maybe I just couldn't find the right info elsewhere and this is common knowledge, but it just so happened to be that most linear bump steer and at the inflection point came from the steering link equal in length to the lower control arm and parallel.


If I'm correct, and assuming we cant change the steering arm length without changing ackerman, then we need to move the steering joint as much as the ball joint.

 

It looks like the OEM tie-rod sits a little lower then the control arm (from parallel) so that with the rear steer geometry, the car toes in under compression.

You really want to just be able to adjust tie-rod height since caster, camber, and tow adjustments all impact the bumpsteer curve to some degree.

Looking at the racefab arms, it doesn't look like the balljoint is on the right angle for use with the factory hub carrier?