SDIF

Here are my alignment specs...


Car is for Road Race only

LF RF
Toe 0 0
Camber 3.25 3.5
Caster 6.0 6.5

Tyers Toyo RA1 shaved 275/40/17

Corner Weights Wet with Driver

LF 897 RF 825 Total Front 1722 57%
LR 678 RR 621 Total Rear 1299 43%
52% 1575 48% 1446 Total 3021

Smyptoms

Car track great and is very stable in strait line.
Car Turns in Exceptional
Car is loose Mid corner and fast sweepers

My belief is that the extreme caster is unloading the inside rear tire mid corner and causing loose condition. This same unloading could the the cause of the exceptional turn in.

Ideas...

dennis teichera

I have never seen a case where excessive caster could "unload" the tire causing a loose condition. Even if that were the case it would take much more 6*, I ran almost 9* on my last dual purpose car and never had any problems. What does the rest of your combo look like and do you happen to have any video footage from outside the vehicle?

A side note, especially if this a rack only car; you might want to try a little toe out. I run about 1/8 out total as track settings. Turn in feels a little better.

SDIF

Turn in is fine. I don't think I need any toe out.

The caster will make the inside front wheel gain weight in a turn by lifting the chassis. This will also make the outside wheel gain load do to the cross.

If the outside wheel is already on the edge this could be breaking it loose.

I may soften the rear springs or add more rear spoiler, before changing the caster.

DENN_SHAH

iTrader: (1)

just a thought, but the camber seems pretty high, have you ever tried closer to 0 or maybe even a little negative?

dennis teichera

Quote:

Originally Posted by SDIF

Turn in is fine. I don't think I need any toe out.

Explain, I have a few years of suspension design and over a decade of alignment experience. I have never heard this described as such nor experienced it first hand. Positive caster inclines the upright forward in relation to the perpendicular axis run through the upper and lower mounting points. How does this inclination move weight?

Quote:

Originally Posted by DENN_SHAH

just a thought, but the camber seems pretty high, have you ever tried closer to 0 or maybe even a little negative?

I'm sure his camber is negative, the specs are just missing the "-".

Axoid

I don't think alignment directly can cause the inside rear to 'unload' as you put it, unless this alignment has caused the front to gain so much grip that too much weight is transferring to the front corner. If that is happening the front is really under sprung.

I would think the most likely problems is one of the following:
- Too big of a sway bar on the rear. When the loaded side is pushed up, it's causing the unloaded side to be pulled up as well.
- The front is having too much body roll. You need ether higher rate springs or a bigger sway bar or both.
- Some type of bind in the rear suspension preventing the axle to twist freely (least likely reason).

What spring rates and sway bars are you running?

-3.5 degree of camber? That is an awful lot. I only run -2 degrees camber with +6 degrees caster.

SDIF

Thanks for all the replys! And great questions! You are making me think


"Explain, I have a few years of suspension design and over a decade of alignment experience. I have never heard this described as such nor experienced it first hand. Positive caster inclines the upright forward in relation to the perpendicular axis run through the upper and lower mounting points. How does this inclination move weight?"

I believe...
The Caster moves the uppper mounting point closer to the windshield.
The inside tire would turn into the turn and down toward the pavement, lifting the chassis on that side and adding weight. This weight would also show up on the oposite rear the same as if the chassis were wedged. I will put car back on scales to confirm weigth transfer.


"I would think the most likely problems is one of the following:
- Too big of a sway bar on the rear. When the loaded side is pushed up, it's causing the unloaded side to be pulled up as well.
- The front is having too much body roll. You need ether higher rate springs or a bigger sway bar or both.
- Some type of bind in the rear suspension preventing the axle to twist freely (least likely reason)."

What spring rates and sway bars are you running?

The cars specs are...

Front Bar 36 MM
Front Springs 700lbs / Afcoils w / wt jack
Ride Height to fender lip 24.5 LF and 24.75 RF


Rear Bar 12MM
Rear Springs 225lbs / Afcoils w / wt jack
Rear roll center lowered via Unbalanced Engineering kit
Ride Height to fender lip 25.5 LF and 25.75 RR


All trailing arm and panhard bar joints are heims. Front are Del a Lums

The front may be a bit soft, BUT the front end is the end that is working and I dont want to mess it up.

The Camber angles are the ones recommended by TOYO and the car will turn.


After all of the help and support offered, I may just lower the rear spring rate and give that a try, or disconnect the rear bar and see if that helps.

dennis teichera

I believe you are over thinking this and the affects of alignment on the rest of the chassis. Going more positive caster than neutral would move the upper strut mount towards the rear of the vehicle but a negligible amount. I don't think the small amount of movement in the strut plate would move the weight placement enough to cause the type of jacking effect you are describing.

I agree with the above post that you have a spring rate/stabilizer bar/tuning problem.

GMan 3MT

iTrader: (4)

I'ld leave toe where it is too. For AX, a little toe out works well, but for track, that's a little too darty for my personal taste.

I'ld start by softening the rear springs. Springs are cheap and plentiful. I think 225 is a bit much paired with 700s. I've got 1000/175 right now, may order a 200 just to have for tuning. I do mostly Ax right now, getting more and more into tracking/RR.

If you add too much rear spoiler, then you gotta work something to get the front downforce up.

SDIF

Thanks to all for all the excellent advice.

Axoid

That is what I would start with trying.

Just for reference I'm running 800# springs on weight jacks and 34mm solid bar on the front and currently 150# springs on weight jacks and 19mm bar on the rear and my car is a little loose, specially when trail braking.

The only people that I know that are running 200# + rear springs are CP cars running like 1000# fronts and no rear bar.

SDIF

Axoid

Thanks, I appreciate the advice from a Champ.

I run the higher rear springs due to the lowered rear roll center. See comparison between track day car and race car.

[B]Track Day Car aka Church Car
My track day car is a stock drive train, full interior, alpine radio, 91 z28 with sub fram connectors, all heims, lowered rear roll center and 900lb fronts w 36mm bar and 300 rears with 12mm bar. Camber 2 5/8 Caster 5.5 / toe Zero Car runs on same tires RA1 275/40/17s weight 3464 wo driver. The car handles better than anything that I have ever driven. Explanation.. with the stock 305 TPI there is not enough power to upset the car. It is easier to drive than the 930 Porsche, 300 zx, 280Z V8, ZZ4 crate motor stock car, and AS Mustang that I have driven at the same track. No these cars do not belong to me.

I drive it this way on slow corners... Brake, trail Brake, turn in, and floor through apex and track out. The car rotates well and when I put the "power" down the weight transfers to the rear and is extremely stable.
On fast corners I lift or tap the brakes to transfer a little weight to the fronts, turn in, chassis sets and its throttle through APEX and then hammer down to track out.

I hoped to duplicate that feel with the lighter higher horsepower race car. On paper the race car should be head and sholders above track day car on handling.

[B]Race Car
Race car wet weight 2821 w/o driver. 355 / 10.5:1 / AFR ported 195s / solid Roller / Victor Jr. / 750 dp/ 1 3/4 headers throught Dr Gass crossover and boom tube. T10 close ratio / 9 in Detroit locker w 3.80 gears / Willwooods front and rear

Goal
I tried to pick an initial spring rate that was in proportion to the track day car's weight and spring combo. My goal was to be close off the trailer.

The race car turns in very well, and exits well. I am loosing to much time mid corner waiting to put the power down. On a carasell turn, double APEX turn, or fast sweeper I am too slow. If I drive any faster the car gets upset and I have to slow down further. I can not throttle steer the car in a long turn. The car will not 4 wheel drift. The front just sticks and the rear trys to pass it.

Do you think I should spring this race car the same as the heavier and lower powered track day car?

Dewey316

how much adjustment do you have left with the PHB, you could try lower the rear roll center even more, to see if that changes things.

When you say it is loose on "fast sweepers", how fast are you talking?

dennis teichera

I wouldn't recommend that, lowering the RRCH more may be what is inducing the the rear jacking affect to begin with. If anything maybe try raising it some to see what happens. With 225# springs things are already way too tight.

Axoid

It's something to try, but I'm not sure what else I can recommend.

You might post your question on frrax.com, there are a bunch of guys on there know way more than I do.

DAVECS1

iTrader: (2)

I would maybe work with the Toe a little. I am not sure how big the track is or how tight the corners are, but if you are using the stock upright geometry these cars have no ackerman steering to them. This can cause the front to bind a little on tight sweepers causing the rear to raise and walk out a little under throttle. If you can keep your hand steady enough a little toe out helps this.

I wouldn't change the caster that much, I and many of my fellow thirdgen racers run around the 6 degree mark with great results. That seems to be the sweet spot regardless of spring or sway bar rates

I have seen torque arms mess these cars up something fierce, and no one can seem to explain it. Some of the aftermarket arms have a pivoting mount that changes the location of force applied to the car under acceleration or braking, which can easily upset a car that has tendancies to be loose when setup right.

If it is rear spring rate or rear trailing arm geometry, a quick test maybe to reduce rear tire pressures drastically just for testing purposes. If this helps.

1. I would move the lower trailing arms down a notch on the axle
2. I would try 100lb more spring on the back.

I also agree with trying to work on the rear bar. If you have poly bushings on it, switch them back to rubber and see what happens. Or even try som different length links.

This is just my 2 cents take it for what you will

SDIF

Here is the track diagram and survey.

http://www.turn1motorsports.com/imag...diagrambig.jpg

Results and times are posted here

http://www.nasa-southeast.com/

I did not race, due to rotor failure in practice. Qualfying time was in 1:49 range see thunder and lighting race results for other car times or check qualifying results. Come out and join NASA it has nothing to do with the space program and is alot of fun.



You were all a tremendous help!!!!!!!!!!!!!!!!!!!

All the posts convinced me that my caster is fine and should be left alone. I am going to work on the rear of the car with sping rates, shock adjustments, ride height and tire pressures.

I will report back after next test day on March 2nd.

camarodarrell

I would lower the rear spring rate. I also think the rear suspension works best when the lower control arms and panhard bar are exactly flat or parrallel to the ground at ride height.

My car is a street car that will see the track when the new drivetrain is installed but the setup consists of front: 36 mm sway bar with poly end links, 700 lb moog springs, bilstein struts, spohn spherical bearing strut mounts, 2" drop spindles, subframe connectors, 3 pt. strut tower brace. The rear is: 23 mm sway bar, Jamex rear springs (not sure of spring rate, probably somewhere between 150-175), poly/spherical bearing panhard, stock lcas with relocation brackets, poly bushing on the stock torque arm. The lcas front and rear are exactly level with the ground as is the panhard.
Camber is around -.5, caster is maxed at 4.2.

The car is very neutral handling and I think the rear sticks so well because it is somewhat soft and I basically tried to enhance (not change) GM's original design.