Does rear upright need a caster angle and a kingpin?

[firasf1dream]

Because the track rod determines the toe gain/loss while the suspension articulates. The track rod does what the steering rack does without the steering part. If you attach the track rod further or closer to the upright relative to the upper arm you change KPI.

From my bit of knowledge, once you determine the kingpin you can not change it. What can be changed is the camber and toe

[godlameroso]

Because the track rod determines the toe gain/loss while the suspension articulates. The track rod does what the steering rack does without the steering part. If you attach the track rod further or closer to the upright relative to the upper arm you change KPI.

From my bit of knowledge, once you determine the kingpin you can not change it. What can be changed is the camber and toe

KPI is locked in by the mounting points of the arm to the upright. So if you change where the arms are mounted to the upright you change KPI. Granted not really possible once you have a finished upright.

[Mchamilton]

Caster isn't something critical on the rear end of any wheeled vehicle except for fork lifts that have the steering linkage in the rear. The closest thing I can think of is KPI and that's pretty much determined by where you stick your track rod.

How is kpi determined by where you put your track rod?

Because the track rod determines the toe gain/loss while the suspension articulates. The track rod does what the steering rack does without the steering part. If you attach the track rod further or closer to the upright relative to the upper arm you change KPI.

i think youre incorrect. KPI is the angle of the 2 points about which the steering acticulates from the forward view, nothing to do with the track rod.

[godlameroso]

How is kpi determined by where you put your track rod?

Because the track rod determines the toe gain/loss while the suspension articulates. The track rod does what the steering rack does without the steering part. If you attach the track rod further or closer to the upright relative to the upper arm you change KPI.

i think youre incorrect. KPI is the angle of the 2 points about which the steering acticulates from the forward view, nothing to do with the track rod.

The steering rack is the track rod in the front. Steering articulates along the KPI, which is dependent on where the joints of the steering rack attach to the upright.

[firasf1dream]

Because the track rod determines the toe gain/loss while the suspension articulates. The track rod does what the steering rack does without the steering part. If you attach the track rod further or closer to the upright relative to the upper arm you change KPI.

From my bit of knowledge, once you determine the kingpin you can not change it. What can be changed is the camber and toe

KPI is locked in by the mounting points of the arm to the upright. So if you change where the arms are mounted to the upright you change KPI. Granted not really possible once you have a finished upright.

You're right if it still is in design stage, but I was talking when the upright is on the car

[Greg Locock]

KPI is a tiny effect on the rear suspension. I wouldn't fret about it. Rather like the castor angle, it is a compliance effect on the rear, and you are more concerned with lateral steer compliance and SAT steer compliance and perhaps camber compliance, than these second order effects. The compliance based steering axis basically cross couples toe and camber, which could be evil, except that the toe angles are so small that the effect is usually ignored.

Sadly I don't know of a free K&C program that includes compliance effects, partly because nobody cares, and partly of course that you never know what the bush curves are. And if you do, you need to know how compliant the body is at that point. That's why modern suspensions tend to have slightly odd looking layouts - L arms instead of wishbones. Then we can talk about having a stiff bush as the pivot, and the NVH bush at the end of the L. The rate of this is soft, and we can measure it easily.

[firasf1dream]

KPI is a tiny effect on the rear suspension. I wouldn't fret about it. Rather like the castor angle, it is a compliance effect on the rear, and you are more concerned with lateral steer compliance and SAT steer compliance and perhaps camber compliance, than these second order effects. The compliance based steering axis basically cross couples toe and camber, which could be evil, except that the toe angles are so small that the effect is usually ignored.

Sadly I don't know of a free K&C program that includes compliance effects, partly because nobody cares, and partly of course that you never know what the bush curves are. And if you do, you need to know how compliant the body is at that point. That's why modern suspensions tend to have slightly odd looking layouts - L arms instead of wishbones. Then we can talk about having a stiff bush as the pivot, and the NVH bush at the end of the L. The rate of this is soft, and we can measure it easily.

So you mean I should have a 0 KPI ? for castor I did not put any caster here it was 0
about L shape do you mean F1 cars ? can you define wishbone against L shape ? because from my modest knowledge I think wishbone are the A arms no ? except without the line in the middle of the A

[Greg Locock]

KPI doesn't matter, 0 or 15. F1 uses A arms not L arms.

[firasf1dream]

KPI doesn't matter, 0 or 15. F1 uses A arms not L arms.

ok thank you