Advanced Suspension Mods

[Movin]

I LOVE ADVANCEDYNAMIX'S CAR! My wife gave me GREEN lights to go ahead to built our '93 Festiva like advancedynamix's car, 95% my wife WON'T let me spent money to built any cars I wanted in the past.. Now she's saving up money for our future Mini Rod Festiva, because it's not that expsensive plus she want to drive our future car... i have owned 48 vehicles in my life time, I think this is going to be my favorite car ever! I dream and cant keep it off my mind everyday since i drove his car about 6 months ago.... THANKS ADVANCEDYNAMIX FOR ALLOW US DRIVE AND YOUR CAR! YOU SURE MADE OUR WEEKEND TRIP WORTH!!! [/QUOTE]

:shock: Mini Rod ??

[Arnie]

I don't see how bending the control arm changes the ball joint location. In order to change the ball joint location the distance between the axle centerline and ball joint centerline would have to change. The shape of the control arm is irrelevant to roll center and camber curve, however the length of the control arm is relevant. Now, your caster adjustment is sensible, but would be difficult to duplicate on a festiva control arm due the the shape and material used. This is why I would make my own adjustable arms. Also, the festiva arm doesn't extend 90 degrees perpendicular from the body, it angles slightly forward, making the bend less effective.

Your drawing needs to display wheel centerline and shock length to show how bending the control arm does nothing except adjust the working angle of the ball joint. The Festiva has plenty of ball joint articulation for all but the most exotic setups ( yes Movin, your setup is very exotic and a special case where the factory ball joint falls short, lol).
One other factor that needs to be considered is the placement of the struts upper pivot. Since the strut top pivot is much further inward than the ball joint, negative camber will continue to increase as the shock travels through its stroke, even with the control arm far past it's tangenal parallel point. The increase in negative camber is actually quite aggressive for a street car that was not sold with the intentions of high performance.

Here's a nice diagram I found. One component of determining the instant center and roll center is by drawing a line through the center of the control arm pickup point and the rotational center of the ball joint, NOT through the center of the control arm. If you bend the arm to move the ball joint up or down from its original position, you will change the rotational center of the ball joint (and all the corresponding geometry) in relation to the center of the control arm pickup point. And this can raise or lower your roll center.

[Advancedynamix]

The two pivot points of the control arm are not located by the shape of the control arm, other than it's length. They are located by the wheel on the ground attached to the hub, captured by the knuckle which holds the ball joint on the outer end and the chassis mounting bolt on the inner end. the control arm could be shaped like a pretzel and it would have no effect on this until the ball joints were in a binding state, then it will lift the wheel off the ground (not good). To visualize this you have to put the wheel, hub and knuckle in the picture as well as the body mounting point (these are constants, not variables in this example.) To visualize camber gain you'll also need the upper strut mount in the picture(again, a constant.) The upper strut mounts relation to the length of the control arm and it's mounting point dictates the camber arc. without showing what the ends of that control arm are attached to, you cannot see that what effect (or lack thereof) bending the control arm will have. I'll draw a picture of this when I get back to Arizona. There will be a straight line from ball joint centerline to pivot centerline even if the control arm is bent, it will only lower the ball joint when the wheel is lowered, which would lift the car. In other words, the ball joint centerline will remain consistent with the axle centerline unless a spacer is used between the two. Bending the control arm will not have the same result as a spacer. Bending the control arm will only correct (or aggravate) an over articulated ball joint. The festive has plenty of ball joint articulation for 99% of us (check out movin's pictures for an example of the other 1%.)
Does this make sense or am i going crazy? I still can't see how bending the control arm changes the camber arc.

[Christ]

He's saying that it doesn't actually change the arc, it just puts you in a more desirable part of the arc so that the up and down movement of the tire doesn't translate into as much in and out movement of the hub relative to the car body, but it doesn't work that way... The moment arc of a control arm is defined as the centerline between the mounting points and the center of the ball in the joint. Bending the control arm, while putting the control arm itself back into reasonable alignment, doesn't change the position of the centerline laterally from the ball joint back to the mounting point. That is determined by the strut length in a MacPherson strut setup.

However, if your bend moves the centerline of the ball joint closer to the mounting point, it will change the arc length negative, and obviously if it moves the centerline further from the mounting point, the arc length is changed positive. Positive increase in arc length means more travel to achieve the same degree change in the lateral centerline.

[Advancedynamix]

Well, I found a company that sells complete poly bushings for the festiva! Here are some control arm bushings ( only because I have blown out the stock rubber ones a couple of times and I have some otherwise perfect control arms to try these on.)

I'd like to visit Australia, if only to come back with luggage full of trick Festiva parts. I paid around 60usd for these, but they are cheap (35USD) in the kangaroo country.

[Ford Fester]

Score!

[rbrown]

Awesome.

[Advancedynamix]

He's saying that it doesn't actually change the arc, it just puts you in a more desirable part of the arc so that the up and down movement of the tire doesn't translate into as much in and out movement of the hub relative to the car body, but it doesn't work that way... The moment arc of a control arm is defined as the centerline between the mounting points and the center of the ball in the joint. Bending the control arm, while putting the control arm itself back into reasonable alignment, doesn't change the position of the centerline laterally from the ball joint back to the mounting point. That is determined by the strut length in a MacPherson strut setup.

However, if your bend moves the centerline of the ball joint closer to the mounting point, it will change the arc length negative, and obviously if it moves the centerline further from the mounting point, the arc length is changed positive. Positive increase in arc length means more travel to achieve the same degree change in the lateral centerline.

Yeah, that's exactly what I was thinking. One other note, if you think of the arc being relative to a perpendicular plain to the control arm, it would make sense that the car would begin to lose negative camber after the control arm has passed the centerline, however this isn't the case with the Festiva chassis. Because the strut upper mounting point is inward of the ball joint (strut travel is not perpendicular to control arm), the car will continue to gain negative camber as the ball joint moves toward upper strut mount (strut being compressed through it's travel, or a shorter strut being used). This arc is actually ideal "as is" for a stock Festiva Body. The car does well at maintaining a contact patch with weight on the outside wheel and uses all available wheel well. It's the inside wheel on a corner that begins to loose traction. I think this can be remedied by deleting the sway bar (replacing it with isolated links like a kia rio has) and increasing the caster angle. This would keep the inside wheel planted to the ground rather than trying to lift it. it would require stiffer front springs or different bump stops to control body roll though.
Thanks guys for contributing to the brainstorming. With a few simple adjustments I think it's possible to improve my lap time considerably.

[Advancedynamix]

Here is a picture to illustrate what Christ mentioned about the shape of the control arm not affecting the centerline between the ball joint and the control arm mounting point.


However, if bending the control arm shortens the control arm it will change the amount of camber gained through suspension travel. It would reduce the amount of negative camber gained by bringing the ball joint closer to the vertical centerline of the upper strut mount. (not good)
Another note, Aspire control arms are longer than Festiva arms and actually offer more camber gain. Just switching to aspire arms will help more than any control arm bending will accomplish (if your axle length lets you get away with this).

[Safety Guy]

A long time ago I believe someone used Aspire control arms, stabilizer bar and axles on his Festiva, with the obvious increase in front track.

Karl

[Advancedynamix]

I used them with the stock festiva sway bar and Capri knuckles/ brakes. I couldn't use them with my aspire swap because my drivers side axle was too short, but my engine/ tranny should be mounted a quarter inch toward the passenger side to center the axles. I bet aspire arms will work with a car that is setup differently. I never used r compound tires with the aspire arms so I don't have a comparison of the two. In theory they should work better.

[alpaccino]

A lot of people are interested in the way I've modified my rear shocks, well, here is an example of the versatility of the setup.

There is an entire BP engine in the back, with other spare parts, tools and a pallet and a couple of tires. I just turned my rear spring adjusters three turns to accommodate all the weight. No rubbing.

Advancedynamix, i am in dialog which raceland via email they are saying that the kit comes with all four coilovers and they don't sell just the front two (which for me is great for the price) i was wondering what was the reason why you didn't used the rear coilovers, and since i would still have to do some machine work, couldn't i just modify the rear coilovers to fit if thats the prob?

[Advancedynamix]

Good Question. The reason I didn't use the VW coilovers for the rear is because they are too long. With the car at the ride height That I wanted to run, they are bottomed out. Also, the KYB setup that I have uses the 1 7/8" springs which are not only a much lighter setup (very important on a FWD car) but also are lower profile and allow for a wider tire and more adjustment in the rear than the 2.5" coilovers do.

This setup allows for a 7" Wide rim in the rear without any cutting to the bodywork. This is a 15x7" rim with a 38MM offset tucked into the fender of a Festiva. Try that with a 2.5" coilover.

[Christ]

You must spread some Reputation around before giving it to Advancedynamix again.

Dern it.

[Christ]

This brings up a point... which is actually better, centered for weight, or centered for axle spacing?