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11/23/2019 7:05 AM  #1


Adding caster to upper control arms

I understand that the upper ball joint is shifted towards the rear.

How do you calculate degrees to distance?
Are there “known offsets” to “degrees added”?

This will be on a 65 with Shelby/Arning 1” drop.


65 coupe, 5.0L, T5, 3.25 Currie traction lock, strong arming for now
 

11/23/2019 9:40 AM  #2


Re: Adding caster to upper control arms

Normally you can get away with one revolution offset of the UCA shaft.  That will will work out to about 1/8".  With that and the Arning drop you may be able to achieve up to 5 degrees of caster.  But...to get five degrees I had what turned out to be excessive shim stack thickness and I had a problem keeping the UCA bolts tight...not good.   Also, if you align for Zero camber it just gets worse, or at least on the Heap it did. 
I made some 3 degree wedges from 1/2" steel strap to replace most of the shims.  This seems to work well but with zero camber I still found it comfortable to limit caster to four degrees.  Any more started making the shim stack a bit thick and I was about to run out of thread on the UCA bolts. 

 


To "Do It Right Once" you must first be prepared to "Do it Over"...and over...and sometimes over again.
 

11/23/2019 10:52 AM  #3


Re: Adding caster to upper control arms

My advice is get a set of adjustable strut rods.  This is a much better way to adjust caster, because it does it directly with minimal change is camber. 

 

11/23/2019 1:14 PM  #4


Re: Adding caster to upper control arms

I should clarify my question.

To build caster into the control arm.
This would minimize shims and dial in more caster if desired.


65 coupe, 5.0L, T5, 3.25 Currie traction lock, strong arming for now
     Thread Starter
 

11/23/2019 2:45 PM  #5


Re: Adding caster to upper control arms

TKOPerformance wrote:

My advice is get a set of adjustable strut rods.  This is a much better way to adjust caster, because it does it directly with minimal change is camber. 

Agreed.  Actually, my plan is to add adjustable strut rods and add a camber kit and make a set of 4.5 to 5 degree UCA wedges.  But that's after the Bash.  The Heap is working too good to mess with until then.


 


To "Do It Right Once" you must first be prepared to "Do it Over"...and over...and sometimes over again.
 

11/23/2019 4:14 PM  #6


Re: Adding caster to upper control arms

The instructions for my adjustable strut rods on the 65, clearly states to only use the rods to equalise settings side to side. Not as a major adjustment.


"Those telephone poles were like a picket fence"
 

11/23/2019 8:30 PM  #7


Re: Adding caster to upper control arms

50vert wrote:

The instructions for my adjustable strut rods on the 65, clearly states to only use the rods to equalise settings side to side. Not as a major adjustment.

That's why I will continue to use the Arning drop, offset UCA shaft, and solid wedge/shim, and a camber kit.  The camber kit should allow me to use a few shims only for caster adjustment....I hope.  No more FWB disasters!

Looking forward to seeing Leonie and you Barry. 

BB
 

Last edited by Bullet Bob (11/23/2019 8:31 PM)


To "Do It Right Once" you must first be prepared to "Do it Over"...and over...and sometimes over again.
 

11/24/2019 6:28 AM  #8


Re: Adding caster to upper control arms

By installing adjustable strut rods you are effectively converting the fixed setup from the '65-'66 to the later '67-up setup.  On a '67-up shims are not used.  Caster is set by adjusting the rods and camber is set via eccentric adjusters on the bolts for the LCAs.  If you want any meaningful caster adjustment you are gong to need to do it with the strut rods, otherwise there's no point in having them. 

Adjustable rods are great, but in and of themselves aren't going to get you to the amount of positive caster most of us want, or need to get return to center if you're running something like a Borgeson system.  My '67 pre Shelby/Arning drop would max at less than 3 degrees positive caster.  With the drop I was able to get 3.5+ on the left and 3.75+ on the right with ease (the additional 0.25+ on the right side accounts for road crown and makes the car track dead straight).  The drop moves the UCA rearward about 1/8", and I would guesstimate that this is worth about 1-1.5 degrees of positive caster. Using the spindle height and some trig you can easily determine the exact amount.  Tangent, opposite over adjacent, or 1/8" over spindle height will give you the tangent of the angle, then you just look up the degree value to which this corresponds in a tangent table to get the exact amount of spindle inclination per 1/8" move to the rear. 

If you custom built a set of UCAs you could move the balljoint location, or even offset the bolt holes in the shafts to gain positive caster without having much of an effect on camber setting.  The issue with moving the shaft rearward is that at some point it contacts the inside of the shock tower. 

The Shelby/Arning drop will also add negative camber to the static setup.  This will then need to be shimmed back to 0-0.5 degrees negative to avoid rapid tire wear.  The drop has such a better camber curve that you won't need the typical ton of negative camber a stock setup requires to get acceptable handling at speed. 

 

11/24/2019 10:35 AM  #9


Re: Adding caster to upper control arms

There is no wizardry involved in figuring out caster change. 

If you take the distance between the upper pivot point on the spindle and the lower pivot point of the spindle it is somewhere in the neighborhood of 10". (center of ball joint on UCA to center of ball joint on the LCA).  This number might be closer to 10.5" which would change the answer to about .183" / degree of caster…

That 10" measurement is going to translate into a 10" radius of a circle.

10" x  2 = 20" (diameter of circle)
20" x PI (3.1415) = 62.83" (circumference of the circle)
62.83" / 360 (degrees) = .175" per degree

So for every .175" you move the UCA back you will gain one degree of caster.
Same is true for the LCA - for every .175" you move it forward you gain one degree of caster.


 

 

11/24/2019 4:03 PM  #10


Re: Adding caster to upper control arms

Its a small amount for sure, but there are a couple issues with using a circle for the reference.  First, the one degree you are translating into distance isn't flat; its an arc.

Second, its not an arc above a flat line; its an arc heading downward.  When you move the arm or location of the balljoint you are doing so parallel to the ground in a flat, straight line. 

How far off is it?  Tough to say without an actual measurement on that spindle height, but if it were off by 0.050" that would bear out my observation that a 1/8" move rearward seemed to produce an additional 1 degree of positive caster. 
 

 

11/24/2019 4:43 PM  #11


Re: Adding caster to upper control arms

TKOPerformance wrote:

Its a small amount for sure, but there are a couple issues with using a circle for the reference.  First, the one degree you are translating into distance isn't flat; its an arc.

Second, its not an arc above a flat line; its an arc heading downward.  When you move the arm or location of the balljoint you are doing so parallel to the ground in a flat, straight line. 

How far off is it?  Tough to say without an actual measurement on that spindle height, but if it were off by 0.050" that would bear out my observation that a 1/8" move rearward seemed to produce an additional 1 degree of positive caster. 
 

We’ll have to agree to disagree.  I stand by the circle math- it is close - very close (less than 10% error).  When you do move the upper or lower control arm it actually is in an arc. And at 3-5 degrees the difference between the adjacent side of the right triangle vs the hypotenuse is peanuts.

 

11/24/2019 6:18 PM  #12


Re: Adding caster to upper control arms

I love it when "math eggheads" go at it!!!
I can't understand either one of 'em!!
Cool!
6sally6
Ron..........where you at?!!


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

11/24/2019 8:08 PM  #13


Re: Adding caster to upper control arms

Observations from my direct experience on my 66...

Using adjustable strut rods makes it easier to pull the lower ball joint forward, BUT it also puts the lower control arm pivot bushing in a pretty good bind and can cause it to work loose from the control arm. I wound up tack-welding the pivot bushings in the LCA so they could not slide. I was still not happy with the resulting bind with five degrees caster. I wound up going with 3.5 degrees caster to lessen the problem.   A LCA with a spherical rod end will eliminate that problem, but I would not wish those on anybody who wants a car that is comfortable to drive on the street.

You are asking for trouble if you go with more than one revolution off center on the upper control arm bushings.  One bushing starts getting short of threads. 

Moving the bottom ball joint forward without moving the lower ball joint rearward an equal amount repositions the wheel front-back in the wheelwell and can cause tire rub issues at the lower front corner of the fender.

I have not noticed any discernible driving differences in my car With 3.5 degrees caster or with five degrees caster.

3.5 degrees is easy to get without taking extreme measures, so my conservative side says that is the best number to shoot for.

A small digital level attached to the bottom of your spindle will give you a baseline measurement.  Make your changes and take another reading. The difference is the amount of change your modification achieved.


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

11/24/2019 10:03 PM  #14


Re: Adding caster to upper control arms

6sally6 wrote:

I love it when "math eggheads" go at it!!!
I can't understand either one of 'em!!
Cool!
6sally6
Ron..........where you at?!!

Rat Cheer!  No math from me. I don’t have a dog in this fight.

 

11/25/2019 5:40 AM  #15


Re: Adding caster to upper control arms

Bentworker wrote:

TKOPerformance wrote:

Its a small amount for sure, but there are a couple issues with using a circle for the reference.  First, the one degree you are translating into distance isn't flat; its an arc.

Second, its not an arc above a flat line; its an arc heading downward.  When you move the arm or location of the balljoint you are doing so parallel to the ground in a flat, straight line. 

How far off is it?  Tough to say without an actual measurement on that spindle height, but if it were off by 0.050" that would bear out my observation that a 1/8" move rearward seemed to produce an additional 1 degree of positive caster. 
 

We’ll have to agree to disagree. I stand by the circle math- it is close - very close (less than 10% error). When you do move the upper or lower control arm it actually is in an arc. And at 3-5 degrees the difference between the adjacent side of the right triangle vs the hypotenuse is peanuts.

To be clear there's a couple different concepts hiding in here.  When the arms move, as in when the suspension cycles, the farthest point of the arms from the shock towers do move in arcs, as though the arms were the radius of a circle, with the center point at the mounting locations on the chassis.  The arcs not being the same between the UCA and LCA is what creates the camber curve, because the two arms are not the same length.  The upper arm being shorter is what pulls the top of the tire inward as the suspension cycles, creating camber gain. 

However, this isn't what I was referencing.  I was talking about moving the actual mounting point of the UCA as in the Shelby/Arning drop, which is done in a flat plane. 

We could go WAY down a rabbit hole here with geometry, but in practice the actual difference in measurement between the two methods is quite small, and for our purposes barely significant.  BUT, you never know how someone is going to use the information you put on the web, and in some instances of chassis engineering it may be more significant. 
 

 

11/25/2019 5:45 AM  #16


Re: Adding caster to upper control arms

MS wrote:

Observations from my direct experience on my 66...

Using adjustable strut rods makes it easier to pull the lower ball joint forward, BUT it also puts the lower control arm pivot bushing in a pretty good bind and can cause it to work loose from the control arm. I wound up tack-welding the pivot bushings in the LCA so they could not slide. I was still not happy with the resulting bind with five degrees caster. I wound up going with 3.5 degrees caster to lessen the problem. A LCA with a spherical rod end will eliminate that problem, but I would not wish those on anybody who wants a car that is comfortable to drive on the street.

You are asking for trouble if you go with more than one revolution off center on the upper control arm bushings. One bushing starts getting short of threads.

Moving the bottom ball joint forward without moving the lower ball joint rearward an equal amount repositions the wheel front-back in the wheelwell and can cause tire rub issues at the lower front corner of the fender.

I have not noticed any discernible driving differences in my car With 3.5 degrees caster or with five degrees caster.

3.5 degrees is easy to get without taking extreme measures, so my conservative side says that is the best number to shoot for.

A small digital level attached to the bottom of your spindle will give you a baseline measurement. Make your changes and take another reading. The difference is the amount of change your modification achieved.

MS, you ever try one of these in a control arm application:

https://metalcloak.com/metalcloak-duroflex-joints-suspension-builder-parts.html

The idea is that they provide the highway ride of a rubber bushing with the greater articulation of a rod end.  A lot of off road guys swear by them.
 

 

11/25/2019 8:52 AM  #17


Re: Adding caster to upper control arms

TKOPerformance wrote:

Bentworker wrote:

TKOPerformance wrote:

Its a small amount for sure, but there are a couple issues with using a circle for the reference.  First, the one degree you are translating into distance isn't flat; its an arc.

Second, its not an arc above a flat line; its an arc heading downward.  When you move the arm or location of the balljoint you are doing so parallel to the ground in a flat, straight line. 

How far off is it?  Tough to say without an actual measurement on that spindle height, but if it were off by 0.050" that would bear out my observation that a 1/8" move rearward seemed to produce an additional 1 degree of positive caster. 
 

We’ll have to agree to disagree. I stand by the circle math- it is close - very close (less than 10% error). When you do move the upper or lower control arm it actually is in an arc. And at 3-5 degrees the difference between the adjacent side of the right triangle vs the hypotenuse is peanuts.

To be clear there's a couple different concepts hiding in here.  When the arms move, as in when the suspension cycles, the farthest point of the arms from the shock towers do move in arcs, as though the arms were the radius of a circle, with the center point at the mounting locations on the chassis.  The arcs not being the same between the UCA and LCA is what creates the camber curve, because the two arms are not the same length.  The upper arm being shorter is what pulls the top of the tire inward as the suspension cycles, creating camber gain. 

However, this isn't what I was referencing.  I was talking about moving the actual mounting point of the UCA as in the Shelby/Arning drop, which is done in a flat plane. 

We could go WAY down a rabbit hole here with geometry, but in practice the actual difference in measurement between the two methods is quite small, and for our purposes barely significant.  BUT, you never know how someone is going to use the information you put on the web, and in some instances of chassis engineering it may be more significant. 
 

  
I went round and round with all this stuff and finally ended up making custom upper control arms with tubing. That was a few years ago and I have since done the Mustang II conversion (with custom upper control arms). Both ways, 8 degrees of positive caster is easy to get. With 5 degrees of negative camber track days on those Hoosier DOT race tires are awesome.

 

11/25/2019 9:07 AM  #18


Re: Adding caster to upper control arms

Thanks for all of the information guys!
I understand the camber gain/changes.
I was having difficulty understanding how to determine caster changes relating to ball joint placement.
I have a better understanding of how to approach the caster changes now.
Thank goodness I understand trigonometry and geometry and hands on approach.
Calculus....eh?🤔


65 coupe, 5.0L, T5, 3.25 Currie traction lock, strong arming for now
     Thread Starter
 

11/25/2019 12:03 PM  #19


Re: Adding caster to upper control arms

DC wrote:

  I went round and round with all this stuff and finally ended up making custom upper control arms with tubing. That was a few years ago and I have since done the Mustang II conversion (with custom upper control arms). Both ways, 8 degrees of positive caster is easy to get. With 5 degrees of negative camber track days on those Hoosier DOT race tires are awesome.

FIVE? 5? Degrees of negative caster? Not .5°? Wow! I ran 1.5° for a while and thought that was a lot.

I also have tubular arms, with 1" UCA ball joint rear offset and 1/2" LCA bj front offset. 8° caster and -.5° camber. I too couldn't feel the change in caster, even with manual steering. I suppose there might come a time when I don't like great handling and return my 69 to stock suspension.

I don't think it would be terribly difficult to offset the ball joints on stock control arms. That way you could keep those granny ride rubber bushings The smiley face means I'm kidding. The way we set up our cars is after all personal preference. My thinking is if your car rides too soft or too firm, change it to your liking.


Bob. 69 Mach 1, 393W, FMX, Armstrong  steering.
 

11/25/2019 2:27 PM  #20


Re: Adding caster to upper control arms

My understanding is if you get too much caster, the steering becomes lazy (slow) at returning to center.
Kinda like bikes with “Easy Rider” front forks man...so you have to assist the return to zero. 

https://i.ibb.co/Jc7NdpG/DE035994-A948-40-DB-ACE5-79-D26-A9-BC46-C.png


65 coupe, 5.0L, T5, 3.25 Currie traction lock, strong arming for now
     Thread Starter
 

11/25/2019 4:11 PM  #21


Re: Adding caster to upper control arms

Its actually the exact opposite.  The more positive caster you have the better the return to center.  Now, go the other way with negative caster and yes, return to center basically goes out the window.  Borgeson specifies at least 3.5 degrees of positive caster to get proper return to center with their power steering systems, and I can tell you, they are correct.  Prior to the Shelby/Arning drop with maybe 1.5 degrees of positive caster the return was lazy at best.  With the new setting its much better. 

 

11/25/2019 4:58 PM  #22


Re: Adding caster to upper control arms

TKOPerformance wrote:

MS wrote:

Observations from my direct experience on my 66...

Using adjustable strut rods makes it easier to pull the lower ball joint forward, BUT it also puts the lower control arm pivot bushing in a pretty good bind and can cause it to work loose from the control arm. I wound up tack-welding the pivot bushings in the LCA so they could not slide. I was still not happy with the resulting bind with five degrees caster. I wound up going with 3.5 degrees caster to lessen the problem. A LCA with a spherical rod end will eliminate that problem, but I would not wish those on anybody who wants a car that is comfortable to drive on the street.

You are asking for trouble if you go with more than one revolution off center on the upper control arm bushings. One bushing starts getting short of threads.

Moving the bottom ball joint forward without moving the lower ball joint rearward an equal amount repositions the wheel front-back in the wheelwell and can cause tire rub issues at the lower front corner of the fender.

I have not noticed any discernible driving differences in my car With 3.5 degrees caster or with five degrees caster.

3.5 degrees is easy to get without taking extreme measures, so my conservative side says that is the best number to shoot for.

A small digital level attached to the bottom of your spindle will give you a baseline measurement. Make your changes and take another reading. The difference is the amount of change your modification achieved.

MS, you ever try one of these in a control arm application:

https://metalcloak.com/metalcloak-duroflex-joints-suspension-builder-parts.html

The idea is that they provide the highway ride of a rubber bushing with the greater articulation of a rod end.  A lot of off road guys swear by them.
 

Looks like something that might work for LCA bushing and strut rod bushing..  I wonder how they do on rotational?  Where does it rotate?
 


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

11/25/2019 8:59 PM  #23


Re: Adding caster to upper control arms

Question.

Why do you need so much caster?

I've been running about 3 deg for the last number of decades.  Mullholland Dr, Angeles Crest, and numerous roads up here in NorCal.  Never had a problem with return to center.  Even now on city streets I don't even think about it.

Would someone enlighten me.

Thanks.


Original owner - 351w,T-5, 4whl disks, power R&P
 

11/25/2019 10:32 PM  #24


Re: Adding caster to upper control arms

lowercasesteve wrote:

Question.

Why do you need so much caster?

I've been running about 3 deg for the last number of decades.  .

Would someone enlighten me.

Thanks.

From what I've read from suspension/handling guru Ron Sutton, is for the best handling you want the caster degree number to be as close to the steering axis inclination (king pin inclination) degree number as possible. Getting those two angles close keeps the tire contact patch as flat as possible throughout the entire steering movement.

How much difference does that make on the street? I not know. I do know my car hasn't under or over steered while taking some pretty fast 90 & 180° turns.


Bob. 69 Mach 1, 393W, FMX, Armstrong  steering.
 

11/26/2019 8:36 AM  #25


Re: Adding caster to upper control arms

Bearing Bob wrote:

lowercasesteve wrote:

Question.

Why do you need so much caster?

I've been running about 3 deg for the last number of decades.  .

Would someone enlighten me.

Thanks.

From what I've read from suspension/handling guru Ron Sutton, is for the best handling you want the caster degree number to be as close to the steering axis inclination (king pin inclination) degree number as possible. Getting those two angles close keeps the tire contact patch as flat as possible throughout the entire steering movement.

How much difference does that make on the street? I not know. I do know my car hasn't under or over steered while taking some pretty fast 90 & 180° turns.

 
How is it possible for caster to be different than steering access inclination. Are they not the same thing?

As for return to center on a classic Mustang, the cars came with ZERO DEGREES caster. Any return to center was achieved by the rubber bushing in the idler arm.


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

Board footera


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