Spindle Design

[elmariachi]

Just did a search and looked over a lot of pics of spindle designs and have a couple of questions:

1) Should the point where the tie-rod/steering arm attach at the spindle fall in line with the kingpin angle - or in other words should you be able to draw a straight line through all three: the upper spindle mounting point, stearing arm mounting point, and lower spindle mounting point? It would seem having all three in line would reduce or eliminate bump-steer (or does it even make a difference and the only important points are the upper and lower a-arm pounting points at the spindle with proper kingpin inclination). My thinking is you want all three to more or less follow the same arc as they move up and down.

2) what is an idea camber number for playing in the dirt? I've heard 2-3* negative camber is good.

3) should the lower a arm spindle mounting point be in line with the stub axle?

[minibajaman]

1) Doing as you say is correct, and makes things simpler. However if you want to put Ackerman geometry in your steering, then the tie rod connection would no longer be in line with the kingpin. Bumpsteer can then be eliminated by tuning the rack location and distance between inner tie rod ends.

2) Usually most people shoot for 5-7 degrees of negative camber at full compression. I set mine with 0 at full droop, so I have about 2 or 3 deg at ride height.

3) It can be for increased ground clearance under the a-arm, but it doesn't have to be. Mine is under the stub axle for increased arm length and reduced angle of the spherical bearing mounts, but slightly decreased ground clearance.

[elmariachi]

Originally Posted by minibajaman

1) Doing as you say is correct, and makes things simpler. However if you want to put Ackerman geometry in your steering, then the tie rod connection would no longer be in line with the kingpin. Bumpsteer can then be eliminated by tuning the rack location and distance between inner tie rod ends.

I forgot about ackerman. In one of the posts by Rorty he states that ackerman in the dirt has no real effect one way or another. I guess this is what prompted my question. I was looking over his spindle design and his tie-rod attachment point is way out at the spindle (but still not in line with the kingpin attachment points). I also saw other spindles that had the tie-rod attachment point closer to the center of the car (presumably for ackerman).

Originally Posted by minibajaman

2) Usually most people shoot for 5-7 degrees of negative camber at full compression. I set mine with 0 at full droop, so I have about 2 or 3 deg at ride height.

My thought was 0* camber at ride height was ideal (more tire contact patch to the ground, but may be you want more contact under compression like when going around a turn ).

Originally Posted by minibajaman

3) It can be for increased ground clearance under the a-arm, but it doesn't have to be. Mine is under the stub axle for increased arm length and reduced angle of the spherical bearing mounts, but slightly decreased ground clearance.

I read somewhere that the lower a-arm should be in line with the stub (or is it the lower shock point should "point" toward the stub?). I was doing a lot of reading last night and all the stuff I read (kingpin, ackerman, camber, caster, etc) created
more questions than answers.

[evan]

Suspension design is all compromises. Stability vs agility, travel vs pitch/roll control, understeer vs oversteer, corner entry vs corner exit, anti-dive/squat vs compliance, best handling on hardpack vs loam vs sand. There is no correct answer, just some principles that are better suited to us. My standard advise is to read a few books (namely "engineer to win" by carroll smith) and thoroughly understand suspension dynamics before you start cutting / welding / milling. Also make provisions for adjustment. (i.e threaded hiems @ a-arm allow static camber / caster adjustment)