Less BS about changing tire alignment specs from stock (a.k.a. let's rant about Mopar suspension some more)

[Bird 426]

Don't care, I knew that you would jump me, was waiting for it. You always do. My cars drive great on the street without all of the drama.

 

[RemCharger]

The caster shimmy is generally induced with negative caster.

 

[Kern Dog]

Boy, I sure am glad I ditched my stock suspension for tubular rack and pinion coil over. Jeeze Louise.

What makes you think that? The coil over stuff is inferior in every way except for header clearance and oil pan access.

Don't care, I knew that you would jump me, was waiting for it. You always do. My cars drive great on the street without all of the drama.

Uhhh, "Jump you" ??
Not even close. I merely pointed out facts. If you are happy with your setup, that is fine.
I strongly disagree with any assertion that any coil over setup is a step up from a factory based system. This not to assume that I think that everything that Ma Mopar did was superior to other manufacturers. The Aspen/Volare transverse torsion bar design was a huge step backward but was necessary to make room for catalytic converters. Ma Mopar had sold the public on the virtues of the torsion bar system for so long, they were obligated to keep using it even in the bastardized form used from 1976-1989 in the FMJ models.
To the people that drive their cars easy on smooth roads, you may never experience the shortcomings of the coil over replacement stuff.
I don't drive mine easy. My stuff will last despite that.

 

[Rebelrouser]

View attachment 1772492

"More than 4 degrees of caster could cause caster shimmy" ???? I've ran 4 1/2 degrees for about 20 years and have since switched to QA 1 UCAs that allowed 8 degrees. There is no shimmy of any kind. I've never felt anything that could be describes as a shimmy from the caster in anything. Maybe the alignments you did in the 70s were on Bias Ply tires or cheap radials?



I've done it twice in B bodies but the A bodies that I have done it to seem to result in less caster than I could get with the B bodies. Lowered ride height does help though, as shown in published alignment curves.



Good points made here.



What makes you think that? The coil over stuff is inferior in every way except for header clearance and oil pan access.

70's Monte Carlo's were what GM called a high caster suspension they had 4 to 5 degrees caster, GM had to put a shock absorber steering stabilizer to stop the caster shimmy, all GM 4x4 trucks that vintage also had a stabilizer for the same reason. I have seen a lot of Jeeps develop caster shimmy as well. Ever go to drag strip and see a dragster go into caster shimmy when backing up? I am not saying it happens always just that it can be an issue especially as the suspension wears with age. And if you have ever had a vehicle, go into caster shimmy trust me you will always remember it.

 

[Rebelrouser]

The caster shimmy is generally induced with negative caster.

Nope push a grocery cart fast enough and the wheel will caster shimmy, grocery carts have lots of positive caster.

good info on trying to fix caster shimmy https://www.thedieselstop.com/threads/horrific-death-wobble-on-2011-resolved.385754/

 

[Kern Dog]

Please forgive my limited knowledge of the Chevy or other brands....I certainly don't know as much as others do about other cars.
I figured that we were discussing Mopar stuff exclusively.
I do know that some think that the higher the caster number, the greater the amount of bump steer. That is logical since bump steer is directly related to a difference in the length and angle of the steering linkage versus the lower control arm. If the angles are different, the tie rods will travel in a different arc and either toe IN or OUT more during suspension travel.
The A/E knuckle has been determined to have LESS toe change than the later B/FMJR knuckle does.
When you get deeper into the aspects of steering axis inclination, roll centers and thrust angle, I start to get confused since I tend to be better at understanding what I can actually see.

 

[cudak888]

It does help but you make an excellent point. The self centering is influenced by the steering box by some degree. I'll add though that a tire that is really wide will induce more of the self centering since you can see that large amounts of caster will cause the wheel to take on a bit more negative camber at full left and right. This tilts the tire on it's edge which takes effort to do. That effort means resistance that you as a driver has to overcome with additional steering effort. In other words, wider tires may result in better self centering response.

My neighbor has a 4-liter YJ with larger tires but shot factory leafs. I've driven it a few times and I can absolutely feel that the alignment is both off and not centered, but the camber gain on turns help it self-center really, really well.

Ironically, a family member's Kia Sorento (the old body-on-frame BL) tends to achieve this with negative camber on the inside wheel, and I continually scratch my head why the vehicle was engineered that way.

Interesting tidbit: My other hobby are vintage English bicycles, including those with very slack frame geometry. Rake and trail of a bicycle's front fork (and the headtube angle) are, in a way, a manifestation of caster and trail. With access to the right bikes at a slow enough speed (anything that's not a crawl tends to self-right itself thanks to the gyroscopic effects) one can experience certain elements - granted, not all - of auto steering.

The self-centering isn't present due to the narrow tire width or the single track of rubber, but one can experience some of the elements of excess caster with some bikes. You can feel the flop at low speeds when controlling this '79 Raleigh-built Rudge (based on a pre-1940's design) with its extremely slack angles:

'

This 1950 Raleigh Sports Superbe Tourist with a more conventional 73/73 degree frame doesn't have this flop.

I'm not a beer drinker or any alcohol, really. I do love a good cheeseburger though!

Same, but beer jokes always go over well

Cheeseburger it is.

You know, I never followed the factory method for ride height settings. Yeah, I know....it is the "correct way" but I always adjusted the torsion bar bolts to get the tire reveals as close as possible. By the time an old Mopar gets to me, it has probably had 3-10 owners, maybe even had the front end rebuilt at least once. My red '70 was pretty original when I got it....

You can see the tops of the tire, a 215-70-14 which is listed as being 25.9". The next picture is with a 275-40-18 which measures 26.7"

The tire is about 3/4" taller but you can't see the top of the tire here. Just a guess but the front looks to be at least an inch lower here compared to the picture when the car was green.

I think I'm pretty close to factory specs in terms of ride height, but I knew this was one of the few cars where the rocker panel is reasonably parallel with the unibody (unlike my '71 Mustang, where the rocker and unibody are at completely different angles).

Holy crap, that tire is listed as 28.9" ! That is tall.

I'll have to get a few photos.

I don't want to cut the man down. I have learned a lot from him. I agree with him on most matters. The cancellation of the Mopar Action magazine is a terrible loss to many, myself included.

 

[cudak888]

Nope push a grocery cart fast enough and the wheel will caster shimmy, grocery carts have lots of positive caster.

good info on trying to fix caster shimmy https://www.thedieselstop.com/threads/horrific-death-wobble-on-2011-resolved.385754/

Caster shimmy is a thing. I'm not enough of an engineer to know the specifics of why it happens, but this can happen on bicycles too; we call it death wobble.

If the frame or fork material is soft enough to allow the harmonics of a given critical speed to keep vibrating, the front end will try to shake itself loose. Think of a crankshaft without a harmonic balancer, but the forces are not rotational.

This pile of crap 1984 Raleigh Alyeska I used to own could be induced into shimmy; the fork had been jigged incorrectly from the factory. Though the fork was cold-set straight with proper alignment tools to get the wheel to sit straight, the blades between the dropouts and the crown were never identical to each other. The front rack (shown here only as a mockup) was enough to reliably replicate the shimmy once one hit about 17-18mph.

-Kurt

 

[Cranky]

I love threads like this!! And I might start wearing ear rings very soon!

 

[khryslerkid]

Adjustments are not that complicated and I think it's a good setup with torsion bars. Better than some manufacturers.

I rebuilt my front end last year. You must start with all new components. I set everything using just a tape measure and a two foot square.

When setting up the upper control arms have the rear adjuster turned all the way in and leave it there. The front adjuster will be used to adjust your camber plus or minus.

Ride height needs to be determined before anything. I adjust from the lowest point on the lower control arm. Make both the same. If the adjusters are clean and greased you don't need to jack up the car.

Setting the camber with a two foot square.

Keep a check on toe in when changing camber.

Roll the car back about 3/4 the length of it and foward after making adjustments. This is what I ended up with at the alignment shop and what corrections that were made to even out camber and caster. He closed up the toe a little also. Thrust angle is almost a 1/4".

I think the biggest problem is not finding a front end shop that has a tech that knows what he's doing.

This guy had no problem with me bringing my numbers and checking what he was doing. We discussed what our goal was and where to leave the settings after trying different settings. Sometimes you have to split the difference when one setting throws off the other too much. Getting things equal on both sides was more important to me.

This was done with stock components. More than likely the offset upper control arm bushings would have gotten me some negative camber. The car handles great, steering returns better than before, tracks good. It's standard steering now, see how it acts when I convert it to power steering in the future.

 

[j-c-c-62]

So, quickly wading thru the OP's heartfelt diatribe, and other replies, it seems the biggest takeaway concerns are:
1. Bias tires are outdated
2. Caster is God
3. "Handling" here is defined by amount of caster self-centering
4. There is no such thing as too much caster
5. Heaven forbid a seasoned driver actually might have to steer the car
6. Nobody understands or has yet shared here any concern about what pitfalls having more caster then needed might cause real handling wise
7. Shimmy, as possible as it may be, is not a problem until it is, no matter what the cause.

I have my own likely diverging views on the merits of the above

 

[Kern Dog]

Setting the camber with a two foot square.
View attachment 1772662
View attachment 1772663View attachment 1772664

While I applaud your initiative and your efforts, I don't see how you can get accurate camber readings by having a framing square resting on the sidewalls of the tires since they will bulge at the bottom. Even resting on the wheel edge does not take into account any wheel runout that might exist. The hub mounted Longacre gauge seems to be a better way to go.

 

[cudak888]

2. Caster is God

Not exactly. From reading other posts, I was led to believe it was the major determinant towards improving self-centering (short of tire width, of course).

Knowing what I’ve experienced since, caster has since become a much lesser, secondary deity.

-Kurt

 

[j-c-c-62]

Not exactly. From reading other posts, I was led to believe it was the major determinant towards improving self-centering (short of tire width, of course).

Knowing what I’ve experienced since, caster has since become a much lesser, secondary deity.

-Kurt

Understand this is my slightly sarcastic opinion that I have of my perception of the many who chase it seems unlimited amounts of caster with little or no concern of the downsides from a handling standpoint. Meaning we agree more than we disagree on this point.
Also, I make a subtle distinction between handling and driving, which it also seems many in these discussions do not, mainly one being more dynamic and the other more static.

 

[cudak888]

Also, I make a subtle distinction between handling and driving, which it also seems many in these discussions do not, mainly one being more dynamic and the other more static.

Agreed. Just the word "handling" itself is only a catchall for perceived stability vs. a vehicle's ability to actually follow through on a driver's commanded input, and that alone differs between the street and the track.

Case in point: There are cars out there that grip extremely well through a corner, but they do it with a boat's worth of body roll to transfer weight to the front wheel on the outside of the turn. But they technically handle. On the other end of the spectrum are cars set up to be dead flat in cornering which some owner might perceive as "good handling," but they never transfer weight during cornering and chronically understeer.

-Kurt

 

[j-c-c-62]

While I applaud your initiative and your efforts, I don't see how you can get accurate camber readings by having a framing square resting on the sidewalls of the tires since they will bulge at the bottom. Even resting on the wheel edge does not take into account any wheel runout that might exist. The hub mounted Longacre gauge seems to be a better way to go.

His picture is shown measuring from the rim, tire bulge is irrelevant in that case, I can't see rim runout being a significant factor here if we are using tape measures. A simple spin test visually will indicate if it is enough to be concerned with IMO.

 

[j-c-c-62]

Agreed. Just the word "handling" itself is only a catchall for perceived stability vs. a vehicle's ability to actually follow through on a driver's commanded input, and that alone differs between the street and the track.

Case in point: There are cars out there that grip extremely well through a corner, but they do it with a boat's worth of body roll to transfer weight to the front wheel on the outside of the turn. But they technically handle. On the other end of the spectrum are cars set up to be dead flat in cornering which some owner might perceive as "good handling," but they never transfer weight during cornering and chronically understeer.

-Kurt

I see I opened a can of worms here. First "driving" is like driving down the road, and the car is self-centering, and the driver is as happy as can be with little or no steering inputs. Handling is when the driver is making steering inputs intentionally, often quickly, to change directions as needed/desired and the car reliably and predictably responds to those inputs.

Your "case in point" above is flawed, which is very common. You're understanding above is 100% backwards. The visual clue above regarding weight transfer is actually the opposite.
I can handle (pun intended) this two ways, seemingly lecture you online in public, or let you dig out some handling books and let you at your own pace discover the precise causes and dynamics of and reduction of body roll and how in many ways that effects handling. I have high confidence you being a bright guy will see the light on this topic.

I'll give you and others a tiny hint here on IFS, both wheels are pushing equally down against the ground, resisting gravity's force of the weight of the car. In a turn, the inside tire has less weight, put the spring is still pushing down, the result as it pushes down with less weight on it, it lifts that side of the car, helping to cause body roll. The use of a sway bar prevents the inside pushing down, so it no longer wants to lift that side car of the car, making the car appear flatter, but in reality, most of the weight now has transferred to the outside tire, leading to understeer. Being "dead flat" is beneficial for tire grip, just as is having both tires equally loaded weight wise. Hard to have both.

 

[AR67GTX]

When setting up the upper control arms have the rear adjuster turned all the way in and leave it there. The front adjuster will be used to adjust your camber plus or minus.

This is the same approach I use also - turn the rear adjuster all the way in on both sides and adjust camber with the front adjuster. Check caster. If one side is more caster than the other then I adjust both front and rear adjusters on the high side, out slightly to maintain camber but lessen caster to where it matches. Pass side caster a bit higher than driver side is preferable to combat road crown effects as Rebelrouser noted.

 

[khryslerkid]

I don't see how you can get accurate camber readings by having a framing square resting on the sidewalls of the tires since they will bulge at the bottom. Even resting on the wheel edge does not take into account any wheel runout that might exist.

As jc62 stated you stay away from the tire bulge and measure to the rim itself. I do check runout of the rim because I've had the problem in the past with inferior rims. Once set up on the alignment machine the sensors take in account for any runout.

What I posted is to get you close to specs before finding a good shop with a alignment machine. You can see from the readouts how close I was. I wouldn't accept my settings as final.

 

[j-c-c-62]

Once set up on the alignment machine the sensors take in account for any runout.

How is that? Don't many machines also reference directly off the rim flange?