thoughts on kingpin angle

[stanglou]

in reading chassis engineering by herb adams, i was interested in his claim that with excessive kingpin the tire tends to flop from side to side, and run up the edge of the tire as it is turned. I thought about it for a while and wondered how much of this logic applies to radial tires. if i am running a radial tire with a 9.4 inch section width is there an advantage or disadvantage to running a lot of kingpin. my design will probably be in the neighborhood of 10 degrees to get zero scrub. any thoughts?

[baz67]

A small amount of scub radius is not that bad as it helps with the steering feel.

With a steeper KIA you may not be able to run much static caster due the the caster induced camber when the wheel is turned. Intitial turn in may suffer because of it. What about camber gain due to the greater difference in UCA to LCA ratio. I guess it depends on your design.

[chicane67]

https://static1.pt-content.com/images/noimg.gif

[dennis68]

You wuss Tom...gonna wait it out huh?

Limit KPI to under 12*. At 10* how much SR do you intend to have? If you intend to make that radical of a change how about changing hub depth to decrease scrub?

[wally8]

10 degrees is probably fine and a decent way to go.

I'm inclined to go the same way as Brian though. A little scrub radius for feel is a good thing. Some like a little heavier feel than others so it's a bit of a trade off, like everything. We talked about this a little in another thread but I would also trade zero scrub radius for track width.

I suppose that my A4 has pretty much zero scrub radius (I don't know, I'm just going by eye. I could be way off) and it definitely turns in nice and corners pretty well. I've also driven cars that had 4+ inches. You can definitely tell there is something going on there.

After talking it through with Katz and others in the other thread, I was thinking of designing around 1.5 inches of SR. Maybe 1 inch and I could add a spacer if I wanted. My experience is that 2 is still a reasonable number at least for what I was doing.


Wally

[Mean 69]

A good power steering system will mask scrub very easily. That said, I still feel that minimizing (or making a small, reasonable number such as suggested here already) is very important. Further, I think it is a really difficult thing to confine, it really depends A OT on the rest of the suspension design and what you are trying to accomplish with it. If this is a first go at a design, I'd stay pretty close to what others are using. Modelling with a suspension program is super valuable.

Mark

[stanglou]

for my design i can easily get zero scrub with under 10 degrees Kingpin. the reason i am going for zero scrub is because i am not going to have power steering. the weight ratio on the car will be about 60-40, so i really want to decrease steering effort as much as i cam. my cambur curve is good in pretty much any design, without too much caster change and side scrub. i was also worried about tire wear induced by the so called running up. it sounds like i should be ok though. thanks for the input

louie