InfernalVortex

iTrader: (4)

I've spent a little while messing with the toe on my car, trying to get it to track straight with the wheel straight. I've finally realized both tires need to be significantly pointed towards one side to make the car track straight.

I marinated on this for a little while and decided to go measure where my rear wheels sit inside the wheel wells (fore and aft). I've got 2.75 inches of gap on one side, and 3 inches of gap on the other. I don't remember exactly, but it's about 1/4-1/2 inch off from side to side. I though this sounded a little alarming. I was already wondering if the axle was even centered in the car since the car is lowered and I have an adjustable panhard bar. Not really sure of a good way to verify that but visually it looks right on. Anyone know of a good reference point to measure from for this?

This corresponds pretty well to my port-side skewed toe settings. Digging a little farther, I I have about 3/4 of an inch extra wheel gap ABOVE the wheel on the side that is pulled in towards the front of the car.So Im thinking the LCA on that side is angled more, so it's horizontal distance is less. Simple trigonometry.

I did cut some factory springs, but my car has never really sat level on any springs I've had in it. I see no evidence of a crash, and I know all cars have some range of flex/warpage at some level, NO car is perfectly straight. So it's just a matter of figuring out how to compensate.

The frustrating thing is that the axle side that sits high is a spring I've already trimmed more off than the other to try to level it. I was more concerned with keeping the rates even than keeping the ride height even, but now Im not sure that wasn't a mistake. I don't want to have one spring at drastically higher rate on one side than the other because I'm having to cut them uneven to get the geometry correct. This is really the main reason I wanted to go to weight jacks, but that's a ways off. I've removed the upper spring isolators and replaced them with hose, so it's not the isolators throwing it off either. I suppose it's possible I could put one of them back in, but I'd need to cut both rear springs a lot more to make that worth it. I don't want both sides sitting that high and I want to keep the front/rear rates balanced so I'd rather not do that.

Has anyone else dealt with anything like this? Should I just get some adjustable LCA's and call it a day? Are weight jacks the real answer? If the car IS hypothetically twisted that much, wouldnt it be pretty much impossible to corner weight it properly with it sitting level? Should I throw the car into a lake?

My panhard bar has a rod end and a jam nut in it, and it has a little less than a half inch of adjustment in it. That seems like plenty to me, would you guys agree that's plenty? I did some math and if the phb is 44 inches, and there's a 5 inch drop on the driver's side for a pretty steep angle, the difference in length is .4 inches. So Im thinking my phb has enough adjustment in it that I don't need to bother with a double adjustable one, but thats a pretty drastic shift so now Im not really seeing the advantage of a proper adjustable PHB?

Just not really sure where to go from here. but I think i've got a constant axle steer situation going on causing my toe settings to need some weird measurements. Is that plausible? Am I barking up the right tree? I don't know if I should cut that other spring more to level it out or not.

tvc 15

A four wheel alignment would tell you if the rear end is tracking properly. As for weight bias four wheel scales is the only way to be sure.

InfernalVortex

iTrader: (4)

I've already verified this through other means, althoguh crude, they are definitive. The axle is not straight in the car. How should I go about properly aligning the rear end?

As far as weight bias, it's about being able to corner weight the car with spring preload properly AND keeping the car level. Im not so sure both are simultaneously possible. I am assuming I will have to choose to make the car level or make the car properly corner weighted, not both.

JamesC

iTrader: (5)

I installed adjustable LCA's and panhard and had a four-wheel alignment. The result was darned near perfect.

JamesC

InfernalVortex

iTrader: (4)

Thats pretty much what I was leaning towards. I figure I will get that done after christmas.

Formula 305

Have you driven the car since you put the springs in it? After a car is up in the air and the weight is off the suspension the car needs to be driven a little for everything to 'settle'

If you haven't driven it, it may have something to do with the one side sitting higher.

InfernalVortex

iTrader: (4)

Yeah I've been changing springs and cutting them for years in this car. The springs havent been trimmed in a couple of years.

Actually, now that I think about it, I wonder if its my polyurethane LCA bushings binding up. I've been wanting to ditch those anyway. It always settles back to about the same position, so thats not completely it, but it may be part of it.

mw66nova

iTrader: (13)

you have those old lca's from greg's car right? you know they were built by some local 'joe-shmoe' that was going to go into building suspension goodies, had a couple of prototype sets go out, and then he basically disappeared. i wonder if they're even the same length side to side? lol

InfernalVortex

iTrader: (4)

They may not be, but I would imagine someone would have noticed when they were right next to each other... at some point. I never noticed them being different lengths. Doesn't mean they're not...

TEDSgrad

iTrader: (4)

Here's some Dean text before he and Pablo went off the reservation and got the thread locked ("The Grip"):

Roll induced understeer is simply put= rear wheel steer. So lets just go over basics.

The rear wheels on a solid axle can change direction based on the arch of the LCA attachment arms. When the arms are out at starightest point (parallel to the ground) they are at their longest geometry.

When both lcas are at the same angle thier is no thrust angle of the axle (this is ideal with a proper alignment, given the proper aftermarker adjustments with adjustable LCA's)

However, when the car body rolls, the rear swaybar will try and keep the LCA's the same but they still differ. If you can keep the LCA geomerty on the inside wheel to articlulate to where the INSIDE LCA stays parallel to the ground while the OUTER LCA archs upward towards in geometry from the chassis mount to the axle, this parallel distance between the mount and the axle vertical centerline will decrease as the axle on that side will be pulled forward more than the other side of the axle. This causes rear steer.

Now with rear steer, the rear wheel pointing towards the corner of turning will cause the car not to rotate as the car leans to set. It wants to hold the back of the car towards the inside of the corner. Roll induced oversteer would throw the rear of the car outward and would make it harder to recover- and ths harder to retrieve the car back to straight tracking becuase of increased momentum of the chassis. So whith that said, I hope you can understand how roll UNDERsteer will resist polar motion and allow the car to hold the rearend tight, as well as help bring the rear end back staight after steadystate and going into corner exit.

The added benefit of this is the roll understeer makes a little more slip angle beause of the rear wheel steering- just like how front wheel steering does this, we are matching the rear a little closer to the front rather than the rear being neutral with only load slip angle. The rear now has load and steering angle just as the front does so the footprints are much closer if veiwed from under the road.

Please read this- It will talk about slip angles and slide angles. Remember also that the inside of the car is better weighted when the overall car gets to set mid corner chassis roll. To best example this, lets say if most cars did 100% outside and 60% inside, mine was doing 100% outside and 75% inside

http://www.mgf.ultimatemg.com/group2...slip_angle.htm