Cross Caster ?

[pitts64]

I had my car re-aligned because for considerable weight removal from the front end. I changed transmissions, added a mini starter and moved the battery to the trunk.

Before these mods my car was in perfect alignment and handled excellently..

After the modifications it was favoring the right side. I took it to the alignment shop and he added more positive caster to the right side. Now it goes straight but it feels like it has more bump steer and it feels like its over steers or under steers during slight corrections to keep it straight. The ride seems more harsh also..

When he first put it on the rack he said it was a little toed out.. I suggested the extra positive caster..

The caster is set at 3.0+/4.25+
Toe in 1/32"
Camber .5-/.5-

The car has rear steering linkage, 12 to 1 Lee box, Addco 1.25 bar, stock solid upper control arm bushings, and everything is in excellent condition..

Any thoughts?

Thank you,
Jeff

[silver69camaro]

IMO, that's a pretty large caster split (I don't put in any at all). If you put in too much caster, you're raising the tie rod pivot up and possibly in a position that would cause bumpsteer - although I don't think it would be enough to sense in the driver's seat.

[exwestracer]

Something doesn't sound quite right...any idea how many pounds you lost off the front end?

If you removed weight and it needed re-alignment, I'm guessing you didn't reset the front ride height? That would make Matt's concern about bumpsteer even more likely...

(If the ride height was the same after the mods, there shouldn't have been any alignment change from the way it was before.)

Also, on a rear-steer car with stock bushings, suspension deflection will cause toe-in under hard cornering. The "extra" toe-out you had before may have been the right approach...

In any case, more toe-out (within reason) will make the car feel more stable, and a little more sluggish to respond. The toe-in may be giving you that darty feeling you mentioned.

[bochnak]

The alignment tech added only +0.5° caster to one side when he did my car. I believe it was the right side.

[pitts64]

One thing to note the original alignment spec for my 64 Bonneville was 1 degree negative caster.

I removed about 300-350 lbs from the front end.. I never thought about changing the front springs to compensate for the ride height change...

I just switched front tires from side to side and found out I had a belt shift in the right front tire.

I think the best approach at this point is to start with some new tires and go from there...

Thank you for taking the time to help me with this problem..

[rrunner68]

I have 5* caster dialed into both sides. My only reccomendation is you may want to re-check the specs with you in the car.

[pitts64]

If I go to even caster or a .5 difference cross caster, how do I correct the drift to the right side? Camber?

My alignment guy always has me sit in the car during alignments. Thanks

[John Wright]

Is the rearend square in the car?...just a thought.

Although, I would have expected your alignment guy to catch that if it wasn't.

[fordsbyjay]

Is it common to have a difference in Castor or Camber from side to side? I would have thought they should be the same but I have no experience in this field.

[John Wright]

Is it common to have a difference in Castor or Camber from side to side? I would have thought they should be the same but I have no experience in this field.
Compensates for the crown in the road.

[pitts64]

I would imagion the terrain would matter also.
I notice when I go over to Ohio the roads are very flat. We have the steepest streets in the country here and our road crowns are very deep...

John he said the thrust angle is excellent. I just replaced the poly bushings on the Johnny Joint/poly rear control arms I made..

[mrn2obelvedere]

In any case, more toe-out (within reason) will make the car feel more stable, and a little more sluggish to respond. The toe-in may be giving you that darty feeling you mentioned.

Not trying to be anal or anything, but IIRC more toe out will make the car feel more responsive on turn-in, and less stable in a straight line. The reason for this is with toe-out, when you initiate a turn, both wheels are in agreement in terms of describing a turn (the inside wheel is turned slightly while the outside wheel is pointing straight; this describes a turn because of differences in wheel speed). With toe-in, when you turn-in the inside wheel is pointing straight, while the outside wheel is trying to turn; this does not describe a turn...the wheels are counteracting each other in this scenario.

As far as how toe in/out or caster changes affect ride quality and over-steer characteristics, I haven't thought it through.

[pitts64]

That sounds like my problem, the wheels counteracting each other.. While driving straight, the ride is rough because the front suspension feels "loaded"...

I think I'm going to try a different alignment shop, maybe one that knows performance alignments...

[exwestracer]

Not trying to be anal or anything, but IIRC more toe out will make the car feel more responsive on turn-in, and less stable in a straight line. The reason for this is with toe-out, when you initiate a turn, both wheels are in agreement in terms of describing a turn (the inside wheel is turned slightly while the outside wheel is pointing straight; this describes a turn because of differences in wheel speed). With toe-in, when you turn-in the inside wheel is pointing straight, while the outside wheel is trying to turn; this does not describe a turn...the wheels are counteracting each other in this scenario.

As far as how toe in/out or caster changes affect ride quality and over-steer characteristics, I haven't thought it through.

You're right about the geometry, but in most cases it does work the other way around. Toe-out (with positive caster) compensates for negative camber and puts more tread on the road in a straight line. On turn-in however, the outside (weighted) tire does not generate slip angle with the road quite as fast with toe-out, so the car typically won't change direction quite as suddenly ("sluggish" is a relative term in this case...).

The property you describe above is "Ackerman effect" and is most often built into the steering arm and spindle, although alignment does have an effect on it.

[pitts64]

My Lee 12 to 1 steering box started making a groaning noise when I turn to the left. It only does it when hot and right off the center crown.. I tightened the belt today, I hope it helps. I noticed the wheel is slightly harder to turn to the left then the right. The right has 5.5+ caster the left has around 3.75+ caster...

I'm getting new tires and having it realigned. I'm going to add only .5 more caster to the right side...

Also, the left tire is squealing during hard left turns now... Camber?

[JRouche]

You're right about the geometry, but in most cases it does work the other way around. Toe-out (with positive caster) compensates for negative camber and puts more tread on the road in a straight line. On turn-in however, the outside (weighted) tire does not generate slip angle with the road quite as fast with toe-out, so the car typically won't change direction quite as suddenly ("sluggish" is a relative term in this case...).

The property you describe above is "Ackerman effect" and is most often built into the steering arm and spindle, although alignment does have an effect on it.

I agree with you. What I dont get is why guys are using toe out. It almost sounds like they are using it as a crutch. To get a faster turn in response due to a high caster setting. Using ackerman and toe out to compensate for some heavy caster. Or worse yet too much camber.

With front end alignments its not about going for extremes. Heavy caster numbers, too far of a camber, off of forward toe.

Toe setting should be positive. Just enough to take up the slop in the steering system for a straight line moving car. The less slop in the steering the less toe you need. Toe shouldnt be used to give a faster turn in (toe out). You just increase ackerman for the inside (weak) wheel and decrease ackerman for the (strong) tire on the outside. Ackerman wants to turn the outside tire, the load bearing tire, more. If you have it toed out you are fighting the ackerman effect.

Thats why you align the suspension to have ZERO toe at driving speed.

Now you have the heaviness of some major caster? Well yeah, you will. Thats why the OEM folks dont stuff alot of caster in there. You dont like the heavy steering, remove some of the caster. Dont adjust the toe.

Now as far as camber goes. Again, I dont know why anyone thats driving a street car would have much camber in place. Heavy camber numbers on just about any car is not a good thing. Yup, even a racing car.

On a street car the travel of the suspension will be around 4-5" At ride height you want zero camber. As it sits on the garage floor. At ride height at 60mph you still want the camber at zero. In reference to the tire contact patch. You want ALL the tire on the road.

But... The control arms are moving up and down and the camber changes a lil. So we are more concerned about compression then rebound. The loaded tire in a turn or in bump. In compression the tire gets a lil more camber gain due to the control arm. Even the worst of the worst suspensions (talking about early GM cars here, (not VWs or trucks) exhibit camber gain in compression. So if you dont know how much camber gain you are getting to over camber it to begin with you may be riding on the edges of yer tires. Never getting to the sweet spot of the tire. Its ALL about the tires and contact patch.

My point???? Keep to the numbers that were designed for the car you are driving. They actually had engineers working on the designs.

Sure, the tire sizes were diff, the speeds anticipated were diff. But the simple geometry of the control arms and steering are still the same. I wouldnt stray too far from them unless you designed some of yer own control arms and steering linkages.

Right around 1/8" toe IN for a front steer with new tight parts. Maybe less for a solid bushing system that will see less deflection.

For camber .5 degrees neg will keep the tires planted.

And caster? Such a step child. But to be honest that number can be run from +1 degrees up to +5 degrees. Depends on the driver and what he wants for the feel of the car.

Just remember. The more caster you stuff in there the more it will affect the steering.

With a heavy caster you can get some additional camber gain on bump (the loaded tire) but you will loose some of the quick steering. With the ball joint more close to up and down (vertical, less caster) the steering will be faster. More caster (ball joints more tilted) it will be slower. But the camber gain will allow the tire to be planted more horizontally, more grip.

As with many things. Give and take. For my car?? Its pretty solid up front. So I use an 1/8" toe in, might even take it back to a 1/16". Camber is at .5 degrees with a 9" tire patch on the road. Caster is at 3.5 degrees. It was a compromise. Bump steer and caster. More caster gave me more bump steer that I couldnt correct for, even with the baer tracker tie rods. So at 3.5 degrees I was able to keep the bump steer down to zero for compression at ride height and all the way to full compression, rebound from ride height was not so pretty. Toe changed a 1/2" for the full stroke. But that was rebound so I chose to control the compression side.

Just a thought. JR

[pitts64]

Here are my 64 Pontiac's original specs. The only difference in my cars suspension are the 62 Pontiac upper control arms. They are the exact same size at the stock 64 uppers but have solid bushings..

64 Manual specs;

Caster 1-1/2 negative (+/-1/2 degree).

Camber 1/4 Positive (+/- 1/2 degree).

Toe in 0 to 1/8".

Compensate for drift to right due to road camber by setting left camber angle 1/4 greater than right.


Toe out on turns; 1 degree.


Front shock travel 5-1/4".

Rear shock travel 8-1/4".


What specs should I try? I just want my car to drive nice on the street..

Thank you

[John Wright]

JR, not disagreeing with what you're saying but don't forget that those factory designs were also based on bias tires of the 60's era and not the grippy modern radials we have now.

[exwestracer]

JR,
We use negative camber to compensate for side thrust in cornering and keep the majority of the tread on the ground. You are spot on about the "ideal" alignment, unfortunately we are dealing with a floppy piece of rubber (the tire) at the end of the chain of parts we so carefully design and adjust...

Have you ever seen pictures of a big GM car front tire under heavy cornering load? They definitely do NOT show negative camber gain on compression. In fact, GM had to invent the high inner bead seat on wheels to keep the tires from peeling right off the rim, they are laid over so far on the sidewall.

Now, we usually correct that by running wider, lower profile tires, but the poor geometry is still there. I'm currently finishing up the front suspension mods on the "Vintage Viper", and we lowered the upper inner pivots on the Camaro stub almost 1 1/2" to get some camber gain into it.

I totally agree that the OP is getting "out of the box" with his current alignment settings. The further you get from "zero" on any alignment angle, the more tire scrub (as he is now saying he has), noise, and abnormal wear you are going to get.

FYI, we run 3 and 6(rf) deg caster on the supermodified to help compensate for rear tire stagger. I've never heard of running that much split on a street car. I'm beginning to think something else may be wrong...

[pitts64]

My point???? Keep to the numbers that were designed for the car you are driving. They actually had engineers working on the designs.

Sure, the tire sizes were diff, the speeds anticipated were diff. But the simple geometry of the control arms and steering are still the same. I wouldnt stray too far from them unless you designed some of yer own control arms and steering linkages.

Right around 1/8" toe IN for a front steer with new tight parts. Maybe less for a solid bushing system that will see less deflection.

For camber .5 degrees neg will keep the tires planted.

And caster? Such a step child. But to be honest that number can be run from +1 degrees up to +5 degrees. Depends on the driver and what he wants for the feel of the car.

Just remember. The more caster you stuff in there the more it will affect the steering.

With a heavy caster you can get some additional camber gain on bump (the loaded tire) but you will loose some of the quick steering. With the ball joint more close to up and down (vertical, less caster) the steering will be faster. More caster (ball joints more tilted) it will be slower. But the camber gain will allow the tire to be planted more horizontally, more grip.

As with many things. Give and take. For my car?? Its pretty solid up front. So I use an 1/8" toe in, might even take it back to a 1/16". Camber is at .5 degrees with a 9" tire patch on the road. Caster is at 3.5 degrees. It was a compromise. Bump steer and caster. More caster gave me more bump steer that I couldnt correct for, even with the baer tracker tie rods. So at 3.5 degrees I was able to keep the bump steer down to zero for compression at ride height and all the way to full compression, rebound from ride height was not so pretty. Toe changed a 1/2" for the full stroke. But that was rebound so I chose to control the compression side.

Just a thought. JR