UBJ, LBJ spherical linkage bolts inline with kingpin?

[method55]

Must the UBJ and LBJ spherical linkage bolts always be inline with the kingpin or is it possible to pickup the discrepency with the misalignment in the spherical?

Just having issues visualizing I suppose.

Any information would be greatly appreciated!

Thanks.

[method55]

Must the UBJ and LBJ spherical linkage bolts always be inline with the kingpin or is it possible to pickup the discrepency with the misalignment in the spherical?

Just having issues visualizing I suppose.

Any information would be greatly appreciated!

Thanks.

[Sathersc]

I've always visualized it as the UBJ and LBJ center points define the KPI, and the ball joints allow the misalignment with the bolts to occur. If you had static ball joints, keeping the bolts in line, your a-arms would bind, and the entire idea of a camber curve goes out the window. If you're having trouble thinking it out, you could always draw it up in a CAD program to help you out. Aurora even provides 3D drawings of all their bearings online. I import them as assemblies, rebuild them with sensible part names, and they work just like the real thing.

[Brian Evans]

You can put the bolts in the same axis as the king pin angle, or another axis, or at 90 degrees to the axis (bolt horizontal-ish, not vertical-ish). What you need to do is understand the range of motion you will require in bump, droop, and steering motion, and design to accomodate those motions. For me, I tend to start with the bolts at 90 degrees to the suspension arm. That gives equal range of motion in both constrained directions, which may or may not be what you need, but it's a starting point at least. The king pin axis angle is kind of irrelevant, which is not to say that you might not end up with the bolt at the same angle.

Brian

[method55]

The reason I am asking is front uprights need to be able to turn about the axis between the UBJ and LBJ (rhetorical question), right now the setup is so that the the kingpin is through the UBJ and LBJ sphericals. However, the bolt that connects these joints to the upright is not on the same axis as the kingpin.

It sounds as though as long as the misalignment of the sphericals is great enough to account for this, all SHOULD be fine?

Best,

Eric

[Brian Evans]

As long as the sphericals don't bind, they will be happy. That isn't to say your design will be of course, but steps in the right direction are good...

It comes to mind that there is no reason why the axle should fall on a line between the upper and lower ball joints. That would be interesting to think about. I understand that one of the leading DSR's has the upper ball joint leading the kingpin axis...

Brian

[Drew Price]

Brian,

Do you mean leading the spindle axis? How can the upper balljoint lie ahead of the kingpin axis when it (and the LBJ) forms the kingpin axis?

Forgive me if I am missing something,

Best,
Drew

[method55]

I'm confused as well as I thought the same.

[Brian Evans]

I explained it wrong - in this case the axle spindle is behind the king pin axis, not in line with it.

sorry about that.

[Drew Price]

Do most of you put the spindle axis on the kingpin axis? Is there any reason to do this? Moving it off simply seems to be an effect of playing with how much mechanical trail you are designing for, and how much caster angle, which could put the axis (plural) skew.

So I guess the question is do you have the axis intersecting?

Best,
Drew

[D J Yates]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Drew Price:
So I guess the question is do you have the axis intersecting? </div></BLOCKQUOTE>

No reason why they have to intersect. It's exactly the same situation as with offsetting the kingpin axis in the front view, the center of the wheel will move vertically as it steers about the kingpin axis, leading to caster jacking. I noticed a bunch of F3 cars lifting their inside wheel whilst being pushed around the paddock, which i figured might be due to offsetting the kingpin axis in the side view, wkether it's a good thing or not i don't know. It's all a compromise with achieving the desired camber gain, steering feedback and caster jacking.

[BBolze]

ohhh, you mean caster offset.

yeah, I think most everyone has caster offset.

When you design this assembly, you pick a scrub radius, Kingpin angle, mechanical trail, and caster angle. Seperatly of eachother.

How long you make the hub and where you put the balljoints laterally inside the wheel is going to sort your packaging to get the scrub radius and kingpin angle you want to work.

For caster, lets assume your running 13" rims so axle height typically 10.5 or 11 inches. well, sin(7)*11 inches gives a mechanical trail of 1.34inches. well that's very very large when compared to the typical change of pneumatic trail... what that means is, not much steering feel and feedback going to the driver. Obviously then you need to move the UBJ and LBJ longitudinally within the wheel to hit your mechanical trail target.