steering geometry

[Nishantsrm]

Hi!!!this is nishant raj , member of team participating in Baja International(south-africa) from India.
i just wanted some help on how to decide the correct position of rack housing on the frame such that to have minimum feedback and steering effort along with other essential requirements of a proper steering..
also how to find out steering effort required at steering wheel if rack-pinion gear ratios, steering wheel dia, lateral displacement of rack to both ends are known????? kindly reply as aoon as possible...

[Nishantsrm]

Hi!!!this is nishant raj , member of team participating in Baja International(south-africa) from India.
i just wanted some help on how to decide the correct position of rack housing on the frame such that to have minimum feedback and steering effort along with other essential requirements of a proper steering..
also how to find out steering effort required at steering wheel if rack-pinion gear ratios, steering wheel dia, lateral displacement of rack to both ends are known????? kindly reply as aoon as possible...

[J.R.]

Steering force and feedback etc is mostly determined by your tyres properties. I think Baja is mostly done by benchmark (haven't done Baja, but thats the impression that I've gotten) for steering systems. Your suspension setup has a lot to do with feedback, more + caster = more steering effort, etc, etc. I think our baja team said theirs got pretty heavy around +12 deg, but they didn't have any offset behind the wheel center.

To get a general idea on force feedback, you can estimate your tyres lateral force at the peak, I assume something around ~100-150 lb for the outside tyre, (this is a pure guess) at the tyre, set up an beam balance, knowing that your a-arms and steering link are supporting the "beam" that is your tyre/wheel, and then solve for the reaction forces in each member. The you have to do some dividing/ multiplying of the rack ratio (did it a while ago, but didn't fully understand how it worked), to transform that link force into a torque, and then given the steering wheel diameter you can back out driver force. A big component you'll be missing is aligning torque though, and I have no clue how to estimate that.

All that being said, I would just make the car and adjust the caster to reduce/ increase steering effort, and use the behavior of this years car to change next years. W/o the tyre data, its going to be tough to get an accurate feel for steering effort through calculations.