How do the fundamental suspension angles (toe, camber and caster) affect steering effort?

[LMF5000]

By "steering effort", I mean the force required to deflect the steering wheel by a certain angle to the left or right. I'd like a qualitative description of how the three fundamental steering system angles (toe, camber and caster) affect the force needed to deflect the steering wheel of a road car moving at medium speed (~60km/h), assuming no power steering assistance is present.

 

[GregLocock]

The steering effort is dominated by (mechanical trail+pneumatic trail) * ay*vehicle mass*Front axle weight proportion.

While the angles you have nominated may subtly alter parameters in the equation, it'll be slight and dependent on the baseline configuration.

This is easily examined in any competent vehicle dynamics package, and I dare say a good bicycle model would do it.


Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[LMF5000]

Hi Greg. Thanks for the answer.

Doesn't mechanical trail depend on caster angle? I'm not familiar with automotive symbols - is ay the angle of yaw of the wheel?

P.S. I only need a qualitative description of the effects (eg. more positive toe increases/decreases steering effort, and so on). I'm not designing anything - rather I'm troubleshooting an already existing design

 

[GregLocock]

You can alter castor without changing the mech trail, so no, that is not a given.

ay is lateral acceleration.

Looking at your other post, tire pressure is the most likely cause.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[GregLocock]

If you alter the castor of a suspension without changing the upright you'll do 2 things. The first is you'll change the relationship between the steering arm, the steer axis, and the tie rod. That's 3d geometry so I wouldn't expect a general trend, it will be installation specific. mech trail will also be affected. If you increase castor it will increase mech trail for the usual range of adjustment. If the castor exceeds 45 degrees then things get weird, but it doesn't so they don't.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[dynatune]

I'd like to add my 2 cents: at 0 speed, so not at medium speeds, another parameter of the tire, the so called "bore" moment can be sensed in the steering (there is no "classical slip angle" at 0 speed so no "classical aligining torque due to pneumatic trail" and this "bore" moment is also affected by the camber since the camber angle affects the effective contact patch area. Thisis however at 0 speed. Once the car starts to roll this moment disappears.

Cheers,
dynatune,

http://www.dynatune-xl