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Re: Alignment specs. conversion
Posted by: RobertC ()
Date: December 04, 2021 10:21AM

Jonathan Knapp Wrote:
-------------------------------------------------------
> On a performance set-up, ...

People with street cars should be aware that the main use of positive caster is directional stability - aiding the vehicle in going straight down the road.

Personally, I wouldn't use less than +2 degrees caster on a street car. You will probably find that it will "hunt" / "wander" as it goes down the street / highway - requiring correction.

Of course, this feature is not important in a racing / autocross environment where the car is constantly being "driven" - through many different / changing "features" .

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Re: Alignment specs. conversion
Posted by: RobertC ()
Date: December 04, 2021 10:25AM

gbullman Wrote:
-------------------------------------------------------
> MattNall Wrote:
> -------------------------------------------------------
> > Correct! Print out the green portion of the pic and take it with you.
>
> Am I misunderstanding? I was interpreting values at top, which are mostly red to be settings for front and those at bottom which are green to be for the rear.
>
> My interpretation is in all cases the numbers are what the car was aligned to but the red values are because they were not programmed into the machine as the target values.
>
> This info is great since radials require different alignment than bias plies and the factory had no reason to publish values for radials.

I assume the red are values that are "out of spec" for the alignment rack.

Yes, the alignment guy based the setup on radials.

The front toe is 1/16". He stated to me one time that the lesser toe value was based on radial tires having less "drag" than bias ply tires.

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Re: Alignment specs. conversion
Posted by: 66vairman ()
Date: December 04, 2021 11:18AM

Well this had gone the same route as the "oil discussion" - LOL.

As I originally stated --- the type of driving, rim/tire size, wheel offset all impact how to align the Corvair suspension.

In my case excessive caster (+3.5 degrees) caused the car to wander at highway speeds as any input to the steering wheel made the car "dart". This resulted in constant correction to keep the car in the lane.

With the wider tire and rim I found +1.5 degrees caster worked well. BTW the Corvair spec. is +2 +/-0.5 degrees caster.

For "normal" street and highway driving with original wheels and tire size I'd use +1 +/- 0.5 camber, +2.0 +/- 0.5 degrees caster, and 2/8 to 3/8" toe-in ---- as specified in the 1965 to 1969 Corvair shop Manuals (except the 1966 supplement). Note that back then the automotive magazine testers praised the LM Corvair for it's good driving and handling characteristics. I'd say the engineers got it right.

With different wheels and tires some trial and error may be required.

To each his own.

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Re: Alignment specs. conversion
Posted by: joelsplace ()
Date: December 04, 2021 03:45PM

[www.packetfilter.com]

Joel
Northlake, TX
5 Ultravans, 138 Corvairs and counting...

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Re: Alignment specs. conversion
Posted by: wittsend ()
Date: December 04, 2021 08:01PM

I always find the "inch" specification for toe to be ambiguous. A 1/16" measured from where..., to where? The edge of the rim? Edge of the tire? And assuming that one is making this adjustment themselves without a device to step under the car and then back up to the tangent of the wheel or tire that would be perpendicular to the ground accuracy is not likely. On the other hand an angle is always the (same) angle regardless to the point of measurement.

I'll see these You Tubers claim they are setting toe by using a tap measure and using the tread as the measure point. Even assuming the tread is consistent around the tire they can only get so far to the centerline of the wheel/tire and if set at the limiting obstacles they are roughly doubling (or more) the actual toe.

A number of years ago I made a toe gage for my daily driver. It is adjustable for various cars. I did the math..., (a calculator did the math) to determine at the proper angle what the measurable distance was at the tire centerline. Even though I was using the wheel (a shorter distance) as the measuring reference it's measurement was compensated for and at the tire it was proper. I believe it was something like .030 at the wheel (I used a feeler gage) to set the proper angle. The fractional measurement was something like 3/64" (at the tire).

When one considers the minimal amount of toe, the wear of the suspension, the flexing of even new bushings, settings like toe seem more a theory that an absolute while the car is in motion.

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Re: Alignment specs. conversion
Posted by: RobertC ()
Date: December 05, 2021 12:13AM

wittsend Wrote:
-------------------------------------------------------
> I always find the "inch" specification for toe to be ambiguous. A 1/16" measured from where..., to where?

Well, not that it is definitive, a quick look online "shows" that it is from centerline of rim / tire to center line.

But, there are dozens (or more) of posts for doing a toe alignment.

My Corvair mechanic of the 70's / 80's had what I will call a "toe board".

Flat metal device with moveable wire grid with a gauge on the side. You rolled the car over the board and it would give a toe measurement.

For some reason, every time that he brought the device out; I found it amusing (to myself).



Edited 1 time(s). Last edit at 12/05/2021 12:14AM by RobertC.

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Re: Alignment specs. conversion
Posted by: Frank DuVal ()
Date: December 05, 2021 07:35PM

Quote
66
If you start with 0 degrees caster and 0 degrees camber, the spindle will always be parallel to the ground

No. sad smiley You have made a not true statement. The only time 0 caster and 0 camber give a parallel to ground spindle at all times will be with a Steering Inclination Angle of Zero, as Joel says. Never will a Corvair have a Zero SIA. Just look at the ball joint spatial relationship. SIA is typically around 6.5°

I've set Corvairs to 0 degrees camber and the caster works just fine. Yes, it (camber) should be set to 1° ± .5° typically.

Quote
66
Well this had gone the same route as the "oil discussion"

People who know how they want their car to perform can adjust figures to their liking. Those who want a car just to drive with stock wheel/tires can stick with stock specifications.

Frank DuVal

Fredericksburg, VA

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Re: Alignment specs. conversion
Posted by: CoCoCo ()
Date: December 06, 2021 12:12PM

Well, this could just be adding fuel to a fire, but I thought it might come in handy for someone looking at just the numbers for reference while making changes.

[robrobinette.com]

It's a simple calculator site for converting inches to degrees and the other way 'round. But it also allows you to take tire diameter into account too, which can make it handy more for truck people that like to change tire sizes.

Use it at your own discretion. If it creates more headaches than it cures, ignore it the next time.

Paul

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Re: Alignment specs. conversion
Posted by: 66vairman ()
Date: December 06, 2021 12:31PM

Frank DuVal Wrote:
-------------------------------------------------------
>
Quote
66
> If you start with 0 degrees caster and 0 degrees camber, the spindle will always be parallel to the ground
>
>
> No. sad smiley You have made a not true statement. The only time 0 caster and 0 camber give a parallel to ground spindle at all times will be with a Steering Inclination Angle of Zero, as Joel says. Never will a Corvair have a Zero SIA. Just look at the ball joint spatial relationship. SIA is typically around 6.5°
>

Ah Frank I never said that, you are quoting someone else. Yes I know about the steering inclination angle works.

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Re: Alignment specs. conversion
Posted by: wittsend ()
Date: December 06, 2021 03:50PM

CoCoCo Wrote:
-------------------------------------------------------
> Well, this could just be adding fuel to a fire,
>
> [robrobinette.com]
>
> Paul

Actual, no (for me). It only reinforces what I said previously. The linked website illustrates that:

1. The toe angle (as opposed to inch measurement) is what is important. Granted you can get an accurate inch measurement but one needs to do the math first knowing the proper angle and the tire diameter.

2. That the inch measurement becomes larger with a taller (or smaller with a shorter) tire. Thus unless you use the same tire size as the manufacture used, the inch measurement is not going to be accurate with different tires.

3. The website author states that measuring at the tread (largest diameter) is the "norm." By what authority he states that I don't know but it makes sense. There is a reason the tire diameter is an input variable in the calculator.
Prior I had stated "measure where..., rim, ...tire...???" I was being somewhat facetious when I stated that speaking more to the ambiguity used by some as a measuring point rather than rational measuring points (meaning at the tread, at the tires foremost front and back points).

I simply entered this discussion because when the toe question gets asked most look to the manual (based on a singular, specific tire size and relative to tire technology of the 1960's). Tire technology, tire size and intended preference of driving likely make that measurement less applicable today.
Added I have this vision of someone crawling under their car with a tape measure and as high up as the suspension and body/frame allows (a limiting allowance) makes measurements at the front and back of the tread that is not at the outermost area of the tire. Thus as a rough example; their 1/16" toe is more than likely closer to 1/8."
In the end the mentioned variables of technology, preference and even the car in motion as opposed to static likely makes these setting only "close" anyway. As it is my Mazda daily drive has a range of acceptability for toe and it goes to either side of zero!

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Re: Alignment specs. conversion
Posted by: RobertC ()
Date: December 07, 2021 11:13AM

MattNall Wrote:
-------------------------------------------------------
> I searched!!!GG
>
>

I guess I should add the caveat:

These specs (LM) ARE NOT the stock LM specs listed in the manuals.

They correspond to:

Front

Toe-in 1/16"
Camber +1/2 degree
Caster +3 degree

Rear

Toe-in 3/16"
Camber - 3/4 degree

I have used them for 40 years.

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Re: Alignment specs. conversion
Posted by: Jonathan Knapp ()
Date: December 08, 2021 10:46PM

Frank and Joel are right. My attempt at a verbal simplification was clumsy. The spindle would only stay parallel to the ground if what I call the kingpin angle (or what I think Frank is calling the steering inclination angle) was 0. That is to say that the spindle was exactly perpendicular to the line through the upper and lower ball joints. With a positive kingpin angle (as on a Corvair), the spindle does go through an arc as the steering moves the spindle from lock to lock. At either full lock position it points down toward the road surface slightly compared to the wheel-straight-ahead position. Thus kingpin angle is also responsible, along with caster, for partially contributing to recentering after turning.

The effects of positive kingpin angle on camber during cornering, however, are undesirable from a performance point of view. Positive kingpin angle makes the outside wheel gain positive camber and the inside wheel gain negative camber. This is the opposite of what is desired for keeping the tires in contact with the road surface during the body roll that occurs in cornering.

Every suspension design is a compromise, of course. The general point I was trying to make earlier about changes in caster remains true, however. Increases in positive caster counter the undesirable effect of kingpin angle on camber change during cornering. Positive caster accentuates negative camber gain (or decreases positive camber gain) on the outside wheel. It accentuates positive camber gain (or decreases negative camber gain) on the inside wheel. Both of these tendencies are desirable for the goal of keeping both tires in full contact with the road surface (especially if you have wide wheels and wide, low-profile tires) during the body roll that is induced in hard corning.

See the second paragraph after the diagram in this article on suspension.

Jonathan Knapp
Wheeling, WV
'66 Corsa Autocrosser

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