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

[j-c-c-62]

IF it is found that in a tight right turn, the right front tire is carrying minimal load while the left carries 80% or more, (As I suspect) it seems that you could go a few different ways.
I would think that body roll would aggravate the matter so I'd aim to reduce that so the inside tire carries more load.

I have to step in here, reducing body roll mechanically is NOT about equalizing wheel load, the benefit is mostly about improving wheel cambers and driver perceptions resulting mostly in better and greater total axle grip.
Best way to equalize tire load if desired on an axle when turning is by slowing cornering speed, change static weight bias L/R, widen track and/or lower COG. Better equalizing tire loading will agreed always increase total axle grip. Body roll however can change wheel cambers reducing total axle grip.
Imagine if one had an infinitely stiff suspension, and a COG above ground, on cornering at high enough speed the inside tire would simply lift off the ground, with zero load with only very slight body roll. As any "suspension" is gently added by design, the inside tire would gently start to share partial loading staying in contact with the ground as suspension became softer, however body roll would be slowly increasing.

 

[V_TastyTacos_V]

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 lowered '69 Dart with manual steering, and as much caster with stock parts as possible, you can really feel the jacking effect on self centering. You can see the front of the car lift, and feel it in the steering wheel. The steering wheel would snap back to center so fast it was a blur. Steering axis inclination plays a part, too. They both influence the scrub radius. All I know is my cars always return to center better, and track straighter, when I give them more caster. Now where do people come up with how much caster a car should have? With power steering, steering effort is never a problem, so why not more is always better unless you get to a point where the tires start leaning too much into the turns, which I have never seen.

 

[V_TastyTacos_V]

I have to step in here, reducing body roll mechanically is NOT about equalizing wheel load, the benefit is mostly about improving wheel cambers and driver perceptions resulting mostly in better and greater total axle grip.
Best way to equalize tire load if desired on an axle when turning is by slowing cornering speed down, change static weight bias L/R, widen track and/or lower COG. Better equalizing tire loading will agreed always increase total axle grip. Body roll however can change wheel cambers reducing total axle grip.
Imagine if one had an infinitely stiff suspension, and a COG above ground, on cornering at high enough speed the inside tire would simply lift off the ground, with zero load with only very slight body roll. As any "suspension" is gently added by design, the inside tire would gently start to share partial loading staying in contact with the ground as suspension became softer, however body roll would be slowly increasing.

I understand that a racecar wants to have the softest suspension they can get away with exactly for the reasons you mention, and stiffening one end or the other usually reduces grip on that end, but other constraints often force one to have to increase roll stiffness. From the looks of how these cars cornered stock, I find it hard to imagine that they were not severely under sprung.

 

[j-c-c-62]

My lowered '69 Dart with manual steering, and as much caster with stock parts as possible, you can really feel the jacking effect on self centering. You can see the front of the car lift, and feel it in the steering wheel. The steering wheel would snap back to center so fast it was a blur. Steering axis inclination plays a part, too. They both influence the scrub radius. All I know is my cars always return to center better, and track straighter, when I give them more caster. Now where do people come up with how much caster a car should have? With power steering, steering effort is never a problem, so why not more is always better unless you get to a point where the tires start leaning too much into the turns, which I have never seen.

So you are cognizant of weight jacking with caster, and I assume also than any weight jacking at the front is also found on the rear on the opposite side and more so with a stiff chassis? Not always a preferred result. Why the focus on the car self centering?
Doesn't that in performance driving mean the car and the driver are at odds of where car needs to be headed?
Sounds like the people who in decades past bragged about how their car rode like a "Cadillac" and all cushy.
Now it's "I don't even have to steer, the car drives straighter than it's driver"?

 

[V_TastyTacos_V]

So you are cognizant of weight jacking with caster, and I assume also than any weight jacking at the front is also found on the rear on the opposite side and more so with a stiff chassis? Not always a preferred result. Why the focus on the car self centering?
Doesn't that in performance driving mean the car and the driver are at odds of where car needs to be headed?
Sounds like the people who in decades past bragged about how their car rode like a "Cadillac" and all cushy.
Now it's "I don't even have to steer, the car drives straighter than it's driver"?

The car has more grip with the tires leaning into the turn, countering the vehicle leaning out of the turn, but it makes it harder for me to steer, and very hard to park. I drove a stock height, tire, and aligned Roadrunner once. It was so easy to steer at a complete stop. I knew it wasn't power steering, but had to look under the hood just to make sure. You could turn the wheel with one hand.

 

[j-c-c-62]

The car has more grip with the tires leaning into the turn, countering the vehicle leaning out of the turn, but it makes it harder for me to steer, and very hard to park. I drove a stock height, tire, and aligned Roadrunner once. It was so easy to steer at a complete stop. I knew it wasn't power steering, but had to look under the hood just to make sure. You could turn the wheel with one hand.

True, but that is not a result largely of caster.
I personally have little interest in ease of parking or a car's focused mindset to steer itself.

I will share this analogy I heard elsewhere that is rather spot on and telling IMO:
Take a pencil and place the eraser on a flat surface perpendicular, push down and try to slide it. Note the force needed.
Now lean the pencil in the direction it is sliding and again note the force.
Lastly, lean the pencil away from the direction you are sliding/pushing the pencil, and note the force needed greatly increases.
That is camber in action.

 

[V_TastyTacos_V]

True, but that is not a result largely of caster.
I personally have little interest in ease of parking or a car's focused mindset to steer itself.

I will share this analogy I heard elsewhere that is rather spot on and telling IMO:
Take a pencil and place the eraser on a flat surface perpendicular, push down and try to slide it. Note the force needed.
Now lean the pencil in the direction it is sliding and again note the force.
Lastly, lean the pencil away from the direction you are sliding/pushing the pencil, and note the force needed greatly increases.
That is camber in action.

So more positive caster, leaning the tires away from the turn, pushing the tread of both tires into it, is good, right?

 

[V_TastyTacos_V]

Do you know how to convert your measurement into camber angle?

Setting the camber with a two foot square.

View attachment 1772663View attachment 1772664

 

[V_TastyTacos_V]

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

A lot of people can't get more than +1° caster, so when people say get as much caster as you can, it's because it's impossible to get too much with the way our cars were designed. A new Charger, for instance, specs at 9° ±1° caster. So tell us what should the caster be, and what determines when it should have more or less.

 

[Kern Dog]

I don't know how people struggle to get caster unless they have damaged parts.

 

[j-c-c-62]

A lot of people can't get more than +1° caster, so when people say get as much caster as you can, it's because it's impossible to get too much with the way our cars were designed. A new Charger, for instance, specs at 9° ±1° caster. So tell us what should the caster be, and what determines when it should have more or less.

I can't answer that, since everyone's goals are different.
But so far, if hands off driving is your goal, get as much caster as you can get.
If you don't want great turn in by dialing in static camber and don't mind the downside results of caster induced weight jacking, seek more caster.
If your car already tracks straight, you want to be the one as the driver who decides where the car drives, and are OK with dialing in static camber for great turn in, and your rear end stays planted on sharp high-speed turns, you likely already have enough positive caster.
Cross weight jacking induced by big caster starts to overload outside rear tire as steering angles increase, leading to over steer.

Seeking maximum caster blindly without a defined purpose is my concern here.

 

[gtxrt]

my 67 Rt with manual steering is set to stock specs. we have yellow warning signs for curves up ahead one of the warning signs shows 35 MPH and I drive through at 50 MPH. so why would I knock myself out going crazy over caster ? I like my older cars for their characteristics if I want a modern feel I drive my 2023 challenger.

 

[Cranky]

A lot of people can't get more than +1° caster, so when people say get as much caster as you can, it's because it's impossible to get too much with the way our cars were designed. A new Charger, for instance, specs at 9° ±1° caster. So tell us what should the caster be, and what determines when it should have more or less.

I don't know how people struggle to get caster unless they have damaged parts.

Some cars came that way.....after all, production tolerance wasn't all that good back then and factory settings were not for radial tires. I wasn't worried all that much about a lot of caster but liked the way the car acted with lots of camber.

 

[khryslerkid]

Do you know how to convert your measurement into camber angle?

Like I've stated, it's just to get it close enough to get you to the alignment shop. Is it leaning in or out?

Amazing find I did recently was after changing from a manual steering box to a factory power steering box, the toe changed from 1/8" in to 1" out! I didn't expect that but there it was.

 

[oldbee]

Like I've stated, it's just to get it close enough to get you to the alignment shop. Is it leaning in or out?

Amazing find I did recently was after changing from a manual steering box to a factory power steering box, the toe changed from 1/8" in to 1" out! I didn't expect that but there it was.

How the heck did that come about??(I’m nowhere near an alignment expert!)

 

[j-c-c-62]

I agree, there has to be a reason.

 

[khryslerkid]

How the heck did that come about??(I’m nowhere near an alignment expert!)

I agree, there has to be a reason.

I used the same pitman arm from the manual steering box so it must be the location of the shaft on the power steering box. Adjustment didn't take that much and there's still threads showing out of the sleeves. If I knew ahead of time I would have taken measurements between the two.

In this picture the shaft location between the two are a bit different. Comparing the adjustment screw to the flange on each one. The adjustment screw is centered with the shaft.

 

[j-c-c-62]

Ideally all the links (3) in plan view should form a straight line at rest wheels steered directly straight.
Is or was the that the case?
If SB sector relocated with the new box, the idler would need to also relocate.

 

[V_TastyTacos_V]

Like I've stated, it's just to get it close enough to get you to the alignment shop. Is it leaning in or out?

1/4" difference along a 15" rim equals 1° of camber. Caster is measured by the change in camber when you turn the steering wheel. There is a formula, but if you just want caster equal side to side, just turn the wheel to the left, measure the left wheel the way you have been, turn it right the same amount, do it again, and the numbers will be the same if caster is the same unless your camber is different side to side. If it is, just subtract that from each side. No need for alignment shop.