Steering Kinematics

[VicenteMMOS]

Hello.

I've been searching this forum for some time now, looking for an answer to this doubt I have, but with little success, so far. The closest I got was at a thread about Ackermann, where Pat mentions that the important thing is that when trying to have a certaing Ackermann percentage, it's enough that the relative movement of the wheels with respect to the ideal kinematic steering condition would be satisfied despite of things like having the tierod at the same plane of a suspension controlling arm, having the outer tierod ball joint aligned with the intersection line of the center of the rear axle and the projection of the kingpin (hope to be making myself enough clear). My big doubt related to this subject is about a program that I'm working on Excel for the kinematics of the vehicle. I have basically found every other hardpoint, but those of the tierods. And so, I want to know how much freedom of choice do have for those. Is it enough to have the tierod linkages aligned with the wheel's instantaneous center? Do I also need its inner connection to be colinear with the suspension arms linkages (in order to minimize bumpsteer), or is it enough to have the same y coordinate of these while having different z coordinate? What are the effects on the steering when the car hits a bump but the steering wheel isn't at neutral position? I mean, I had learned before that placing the rack aligned with the control arm's hinges minimizes bumpsteer effects. But I believe that's only true when the steering wheel angle is zero. What about otherwise? It wouldn't be always true then, in my opinion. Is it relevant?

[VicenteMMOS]

Hello.

I've been searching this forum for some time now, looking for an answer to this doubt I have, but with little success, so far. The closest I got was at a thread about Ackermann, where Pat mentions that the important thing is that when trying to have a certaing Ackermann percentage, it's enough that the relative movement of the wheels with respect to the ideal kinematic steering condition would be satisfied despite of things like having the tierod at the same plane of a suspension controlling arm, having the outer tierod ball joint aligned with the intersection line of the center of the rear axle and the projection of the kingpin (hope to be making myself enough clear). My big doubt related to this subject is about a program that I'm working on Excel for the kinematics of the vehicle. I have basically found every other hardpoint, but those of the tierods. And so, I want to know how much freedom of choice do have for those. Is it enough to have the tierod linkages aligned with the wheel's instantaneous center? Do I also need its inner connection to be colinear with the suspension arms linkages (in order to minimize bumpsteer), or is it enough to have the same y coordinate of these while having different z coordinate? What are the effects on the steering when the car hits a bump but the steering wheel isn't at neutral position? I mean, I had learned before that placing the rack aligned with the control arm's hinges minimizes bumpsteer effects. But I believe that's only true when the steering wheel angle is zero. What about otherwise? It wouldn't be always true then, in my opinion. Is it relevant?

[Drew Price]

You're correct, when the steering is turned the tie rod ends may not remain in the same plane of movement as the arms. It's up to you to figure out how much them not being in the same plane is acceptable, and how much that will effect bump steer (if that's something you're trying to control).