Toe In / Toe Out, Effect on Handling/Steering Feel

[mechtech]

Many RWD cars of American origin had positive camber specs [a little] ostensibly to load the larger, inside bearing [tapered roller bearings]. Toe in was common to straighten things out, when rolling along.

 

[Gary Allan]

I resurrected this thread because this bothered the crap out of me. Now I reasoned through this and didn't verify anything so let's see if I'm correct about this.


What kind of offset and backspacing do the wheels have in this vehicle stock?? This could be the answer to this nagging oddity.

Let's see if it lights off any bulbs in anyone elses brains here.

 

[metroplex]

I'll take measurements tommorrow. I have the wheels off because I'm changing the diff in the rear end.

 

[Gurkha]

Just have a question regarding this issue, where does 4WD or AWD stand in this, toe out or toe in?

 

[JDP]

A specified toe in or toe out setting is dependent in part on the scrub radius. If the scrub radius is positive or inside of the tire centerline, like most rear wheel drive cars, you need toein.

A front wheel drive vehicle usually has 0 to negative scrub radius and this calls for a toe-out setting.

Like you were thinking Gary, If you change the wheel offset/width relationship or even the tire diameter, the scrub radius may change.

Excessive changes in camber will also alter the SAI and affect the scub radius.

The purpose of static toe-in is to prevent a dynamic toe-out.....and visa-versa.............

JD

 

[moribundman]

quote:

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Just have a question regarding this issue, where does 4WD or AWD stand in this, toe out or toe in?

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Here are the toe numbers for my Audi A4 Quattro:
8' +/- 5' (per wheel)

Compare to the FWD A4:
10' +/- 5' (per wheel)

 

[Gurkha]

moribundman

Thanks a lot for your reply, so am I to assume that 4WD uses more toe in than the FWD.

 

[Gary Allan]

quote:

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Like you were thinking Gary, If you change the wheel offset/width relationship or even the tire diameter, the scrub radius may change.

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This is what made me reason a toe out situation. We frenquently run into "custom" toe settings on Jeeps where you require wheels with less backspacing that alters, as you describe, the scrub radius. Wider/taller tires rub the frame. You're moving the tire outboard and therefore the reactive force on the wheel are modified requireing (typically) more toe in to compensate for the additional force.

In solid axles 4wd applications we have the perception advantage of having fixed camber and therefore can isolate the view a little better. Unless we play with pinion angle (caster) the camber is unchanged.

My thought was that, due to some trend to narrow the profile of the car, Ford employed a deep backspacing requiring a toe out setting to compensate for the resultant reactive force applied by the contact patch vs. the steering axis (i.e. scrub radius).