Tms951

I have been prepping y car car for the track next weekend. I put on a wing and a splitter, my track wheels and tires, and lowered the car.

It was lower than stock befor, enought hat the front controle arms were slightly inverted. I lowered it around another 3/4" and now all of the tops of the tires are at the same hieght as the fenders. So now the control arms are more inverted. Next week it is being aligned and corner balanced.

I like the hieght now but I am concerned about effects on handling the control arms will have, I can;t decide if I need to raise so the controle arms are flat.

What exactly does the inverted control arms do to handling?

333pg333

I think you are putting a lot of stress on the hubs and spindles if you're using stock components. There have been enough cases of fractured hubs on race cars to convince me to upgrade these components. Really don't need anything coming apart at speed.

ehall

It's only a matter of time, with track use, until you bind the ball joints in the CA's. Look in the sponsor links for Rennbay. Travis sells a longer ball joint kit to compensate for this angle problem. I believe it's a 19 mm ball joint with an extended shaft. The joint itself will, (if I recall correctly) need to machined from 17 mm diameter to 19mm diamter.
Obviously you don't want to destroy at CA at high speed.

billindenver

I agree with the premise that the control arms are stressed more on a lowered car and having seen arms break on the track (only after a serious off track excursion however) I can say it's a bad thing. As a data point, however I can tell you that although I keep an eye on them just in case...I have never had any difficulties with my car riding at the below height and it's been tracked more times than I can count.

ehall

That's good to hear. The pics of cracked CA's and beat up joints was enough to sway me from lowering too much.

Trucho-951

From a performance handling point of view, it's not a good thing because even though lowering the front of the car does lower the center of gravity (CG) a little bit, however, on a stock MacPherson strut front suspension, the front roll center (RC) drops quicker than the CG, therefore, the car will tend to "roll" easier on turns due to the greater distance (more leverage) between the CG and RC. So it defeats the purpose of lowering the car. But on the bright side, a lowered car looks better.

Tms951

That was pretty much the answer I was looking for. I knew there was something but not what. Now does the "geometry corecting" control arms on the market fix this relationship?

Skip Wolfe

Yes, the Racers Edge arms with the longer pins will lower the roll center and prevent the jacking that Trucho outlined.

333pg333

+1

HIGHBOOST

If these control arms lower the roll center, then the difference between COG and RC will be greater, which will cause the car to roll more according to Trucho. I think that's what I'm getting out of this, somebody enlighten me! ha

Trucho-951

No, I think what Skip meant to say was that the longer pins correct the geometry and "raise" the roll center to improve the car's handling characteristics.

FYI, here is an interesting post form a few weeks ago which raises concern about installing longer pins.

https://rennlist.com/forums/showthre...ferrerid=33434

Oddjob

Keep in mind that the US cars were "jacked" up to meet US bumper height requirements. And when we are lowering the cars, most of us are not lowering significantly past the RoW ride height (the height that Porsche designed the suspension for). I would guess most of us are not going much more than a 1/2" lower than the Euro/RoW ride height. So, we really dont need to worry about correcting too much geometry with the suspension.

The concern with going really low, the balljoint is at such an angle, that its range of motion is decreased. So if you hit a hole, or curbing and compress the suspension, the balljoint may bind in the socket and cause it to shear or bend. A lot of factors need to be considered with this - to include how stiff the suspension is, location of shock/strut bump stops, etc. The stiffer the suspension, the less this is a problem.

I think the longer balljoint pins are a bad idea. Its a longer moment arm, which will increase the stress at the base of the pin and in the control arm cup. Others have commented on this also, and some of the discussion is listed in the thread linked by Trucho.

Failures do happen, but its not an absolute. I DE'd and Club Raced many years and 10s of thousands of track miles on stock/factory control arms. I did replace a few, with factory new arms (I personally would never use rebuilt balljoints on a track car) when the balljoint bushings were worn, but I never had a catastrophic failure. Was I lucky, maybe. But the odds are in your favor, that the arms and pins dont normally break.

reno928s

I heard years ago that the rears of our cars were raised 1" to meet bumper requirements but the front height was untouched, is this true?