froggy47

So just to be clear in general automotive terms is POSITIVE like the angle on the front of a chopper bike and NEGATIVE like the front wheels of a shopping cart?



So vettes have negative.

Last C5

You've got the positive and negative right, but vettes usually run a positive castor of 6.4 deg to 7.4 deg. or thereabouts when you're done getting camber you want.

froggy47

Wow really, like a chopper!

Thanks.

So to increase caster on one side using UPPER SHIMS ONLY where do I move the shims?



Found more, positive means lower bj is ahead of upper bj.

dbratten

To increase caster you need to move the upper ball joint back. To do that you add shims to the front of the UCA and/or remove shims from the back of the UCA. It is just the opposite when working with the lower control arm.

--Dan

froggy47

Thanks Dan, mine is close to where I want it but I think a .5mm or 1.0mm shim will make it spot on.

Then I'll go ahead & set my camber where I want & so on.

Once you have that "differential" in the shims done and you keep that differential, the caster should remain equal, no matter where you take the camber, yes?



Video will be up tonight.

dbratten

I believe so. I only adjust the UCA and leave the camber plates set to max on the LCA. On top, I set caster with washers so they can't fall out and then drop in shims to adjust between low and high camber settings.

A note about washers, if you go to the hardware store you can find a wide range of thickness (.060" - .105") in the same 3/8" washer. I've mic-ed and marked a bunch and can fine tune with these behind the dog bone to set caster.

For shims, I went to 1/8" from the local tire store and can place up to 5/8" on longer studs that I also made. This will take the camber from zero to -3.5. I keep all five shims in at all times and vary between how many are behind or in front of the dog bone. This way the nut doesn't move much when making adjustments.

--Dan

mrr23

image from my website showing caster. basically it's a line drawn from the upper ball joint to the lower ball joint. if the top is behind the lower it is positive. it is ahead, then negative.

mrr23

to add caster only without affecting camber, you would add shims to the front of the arm and remove the equal amount from the rear.

mrr23

so long as you add/remove an equal amount from both sides, then caster won't be affected.

froggy47

Check out my video posted yesterday if you have a chance. I show some McMaster Carr shims that are marked & uniform thickness to 3 decimals.



I should do that with the washers & get back a lot of 2mm shims.

dbratten

I'll check it out but to be honest I can't tell the difference in half a degree let alone three decimal places. At least not in autocross.

--Dan

froggy47

Me either, I was just saying the shims are marked as to thickness to 3 decimals. Never saw shims that each individually was labeled with thickness.

63Corvette

Froggy please let me offer a bike based view of caster, or self centering, or trail, as it is commonly called on Bikes.
If you draw a line down the steering axis and mark where that line hits the ground. Then drop a plumb line down intersecting the centerline of the front hub. The second line must hit the ground BEHIND the first line. That distance is called "trail" or kingpin inclination, or caster, It encourages/requires the steered wheel to follow the aiming point, or "self center".
If, on a jump, the rear wheel hits first, then the front or steered wheel will always come down with the correct geometry and self center....in the forward direction.
If however, the bike lands on the front wheel, AND the rider/bike combination is tilted too far forward, THEN the line of the steering axis will hit the ground BEHIND the centerline of the front wheel, STILL promoting "self centering", BUT now causing the front (steered) wheel to try to turn completely around (like a shopping cart caster)...............and in the process, usually depositing the rider (catastrophically) on the ground, sometimes with the bike on top of him. I use this rather graphic illustration because it helps people remember what happens when a "caster" self centers

froggy47

Thanks!

mrr23

kingpin inclination and caster are not the same angle when referring to cars. this is kingpin inclination or steering axis inclination

mrr23

for those wanting a "cheat sheet" on how to make camber and caster adjustments to their car, i made these up years ago for my employees to use.

froggy47

Good technical clarification. Thanks!

froggy47

Yep, that's the ticket. Thanks!

Looks like my handwritten data sheets.