More Positive Caster

[christophe]

If this was done properly, you should find an equivalent shim under the upper inner front A arm. Otherwise, I would expect extra wear on the busing and suspensions pins. This is not a ball-joint suspension.
In any case, you'd better do a full geometry checkup before getting back on the road.
Nice day to all.

[StudeB]

If this was done properly, you should find an equivalent shim under the upper inner front A arm. Otherwise, I would expect extra wear on the busing and suspensions pins. This is not a ball-joint suspension.
In any case, you'd better do a full geometry checkup before getting back on the road.
Nice day to all.

Egghead alert... math lesson: One can take the above a step further by visualizing the three sides of a triangle formed by (1) the frame mounting surface, (2) the inner pin, and (3) the shim at one end. The angle formed between the frame and inner pin should be the same for both lower and upper mounts to avoid binding during suspension travel. The distance between mounting holes is greater for the lower pin, less for the upper. So, for the same angle, the shim used for the lower pin will be thicker than that used for the upper pin. One can determine the shim thicknesses needed by knowing the distance between pin mounting holes, choosing a caster angle, say 2 degrees, and then calculating the tangent of 2 degrees. Divide this result by the distance between mounting holes to get the shim thickness. The following link shows the simple trigonometry. https://www.mathsisfun.com/sine-cosine-tangent.html You can probably find an online calculator to do get the tangent of any angle. One more bit of eggheadedness, then I'll go away. This method for getting the shim thickness works because the caster angle is small, 1-3 degrees, or so... because we are assuming a "right triangle". It really isn't, but I think the small angle let's us neglect this detail.
Rich G

[48skyliner]

I am amazed that one degree or so of castor change could be very significant. When I designed my Stiletto three wheeler, I surveyed a lot of production and some race car specs, and the castor and camber were all over the map. I just picked some numbers out of the air and designed it with 10 degrees steering axis inclination, 5 degrees castor and no camber. It drove pretty well, but got a little twitchy at high speed. We recently did some adjusting and shortened some of the arms to get 10 degrees castor, and now it drive noticeably better at speed. I don't think one or two degrees change would have made much difference. Of course all the joints are Heim joints, so there is no issue with the joints binding. I am running zero toe in.

Is the stock Studebaker suspension very sensitive to toe in?

[t walgamuth]

I think toe in does not feel like much of anything. Toe out though will cause the car to twitch around on the street and require a lot of attention to your steering. I like minimal toe in for the street. For autocross I like some toe out to help the car turn.

[PackardV8]

I am amazed that one degree or so of castor (sic) change could be very significant.

Yes, in general, when all the components are new and correctly adjusted, the OEM Studebaker suspension works well. What it doesn't do is track straight down the highway at high speeds. So yes, when a front suspension has zero or slight negative caster, changing to one degree positive is a very significant improvement in high speed stability.

Is the stock Studebaker suspension very sensitive to toe in?

Yes. Alignment, caster/camber/toe, are critical or a Stude will eat front tires like popcorn.

jack vines

[StudeRich]

I am amazed that one degree or so of castor change could be very significant./Cut/

What is important to note here is that, ONE Degree of Positive Caster would be THREE and a Half Degrees more positive than the stock NEGATIVE 2 1/2 !

And of course, will steer like a 5 Ton 1949 International Truck or Tractor with manual steering!

[PackardV8]

What is important to note here is that, ONE Degree of Positive Caster would be THREE and a Half Degrees more positive than the stock NEGATIVE 2 1/2 !

And of course, will steer like a 5 Ton 1949 International Truck or Tractor with manual steering!

The older Shop Manuals do say -1 to -2-1/2, but that's for wimps, bias ply tires and standard steering. JMHO, but any car with PS and radials and the '61-and-later cars Shop Manual says -3/4 to +3/4 (zero preferred)

It's moot, as very few Stude kingpins can actually get adjusted to zero, and positive caster is mostly wishful thinking.

That's where the shims under discussion came in, trying to drag those old kingpins into the modern era, even though the stock parts were never designed to go positive.

jack vines

[Mike Van Veghten]

Just a point of question.
Why all the desire of positive caster ?
My ol 59 Lark had plenty of "self centering" in the steering. Which is...mostly what pos. caster does, right ? Hell, my, 4dr., inline six cylinder 54, has plenty of "self centering" in the system. My Lark WAS originally a power steering car...but no more, and the 4dr. is full manual.
While it's obviously not specifically from positive caster...the action IS there.

To me, handling wise, the BIG PLUS would be to attain a little negative camber with the steering wheel turned. THAT, would be a huge improvement in the handling of the Studebaker.
But yea, we've talked about that a bit. Nothing good comes easy..!

Mike

[PackardV8]

Well, all we can know is Studebaker Engineering thought it necessary to redesign the kingpins to take out that two and a half degrees of negative caster. All the later (approx '62 - '66 and Avanti into the '80s) kingpins were designed for zero caster.

jack vines

[t walgamuth]

Tilting the steering axis back creates negative camber on the outside wheel when cornering too. Mercedes typically uses 7 degrees or more, making the cars track down the road excellently. 4 degrees is pretty good and a lot of cars will not adjust to more than 4 or 5.

[wittsend]

I'm all for a "positive caster." I mean when a man throws his line in the water he should be hopeful he catches some fish.

Seriously, there are billions of shopping cars around the world that prove that negative caster is also self centering and stabilizing. It would seem that zero caster would produce the least "straight ahead stability" and the least "wheels return to center" capability. Thus if you have a negative caster and can't get beyond zero I'm thinking you are not gaining anything desirable moving closer to zero be still stuck staying on the negative side. Is my logic off?

[PackardV8]

Seriously, there are billions of shopping cars around the world that prove that negative caster is also self centering and stabilizing. It would seem that zero caster would produce the least "straight ahead stability" and the least "wheels return to center" capability. Thus if you have a negative caster and can't get beyond zero I'm thinking you are not gaining anything desirable moving closer to zero be still stuck staying on the negative side. Is my logic off?

Yes, your logic is definitely off. You're confusing trail with caster. The interaction between caster angle and trail is complex, but they both aid steering: positive caster tends to add damping, while trail adds feel and returnability. The shopping cart has a great deal of trail, but obviously somewhat confusingly to you and others, it has no caster.

jack vines

[wittsend]

Thank you for the correction. I had erroneously assumed the upper pivot point of the shopping cart swivel mount and the wheels axle were a line that created caster. Many caster illustrations are with McPherson struts the emphasis simply on the upper mounting point being ahead of or behind the axle. Thus likely how I came to my wrong conclusion.

So, if the one looks at the bicycle, the arc of the fork would generate trail (or perhaps in this illustration "lead" given it is going forward) but the angle of the fork mount is what creates caster. Did I get that right?

[Mike Van Veghten]

Like motorcycle front suspensions.

The have both "caster angles" in the steering head, AND "trail"...depending on where the axle is mounted in the fork tube. Some "ahead" of the fork center, some "on center", some "behind center". Just depends on what the designer wanted out of the action of the suspension.
Like Jack basically says, "trail" is is often mistaken for caster.

Mike

[wittsend]

From: https://en.wikipedia.org/wiki/Caster_angle

"The shopping trolley/cart setup has a great deal of trail, but (somewhat confusingly) no caster."

Wikipedia make it a point to acknowledge the confusion..., so I must not be the only one. Now I need to go back and read Fred Phuns book again. Haven't done so since my Datsun 510 days back in the 70s. Maybe this could make Simon Whistler's "Today I Found Out" on You Tube.