Suspension theory

[gone-ot]

...I'll agree "angle" is better wording than "how far" but you can't have an angle without a displacement distance.

[Bicycle Bob]

"I've read here that while perfectly aligned wheels front and back might be good for FE, they generally make for a squirrelly-handling car."

As the lads note, there is a lot to learn about suspension. However, if you are researching it for FE, look for low roll centers to reduce scrub. Steering geometry/suspension geometry and compliance with some pre-load on the steering gear to prevent wander, that still does not have a tendency to toe-out under braking will help. That way, you can run zero toe in or close to it for cruising.

[Frank Lee]

All this toe in'n'out... it's sposta normalize out to zero or darn close out on the road, under loads. RWD vehicles have static toe-in specs cuz the forces the front wheels see try to force them to toe out. FWD vehicles have static toe-out specs cuz when they transmit power those forces try to force the front wheels to toe in. Make sense?

[bgd73]

perfect alignment is for flat worlds.

I finally got an AWD old sube to negative camber in the rear...its freakin mythological in handling.
I had a delta88 that broke both tail ends of its frame, swayed badly...but never burned the tires again...
A tractor trailer with low air bags..its a hot rod, leaning bouncing and pouncing.

if the world was perfectly aligned, perfect alignment would be perfect.

I learned to call a cars appearance advanced or retarded...cambers and toes and suspension struts back forward or up and down...

This does not need knowledge, but repeating...

[CapriRacer]

Atomic,

Some Other Dave hit the nail on the head. Toe Out = squirrelly Toe In = stable.

The trick is to get the smallest amount of toe in without going over.

I wouldn't argue about the nominal (target) value for your vehicle. Rubber bushings are going to have some compliance (movement), so the static setting will not be the dynamic position.

But the tolerance (the amount off the target value) needs to be as little as possible. Since toe is infinitely adjustable, there's no excuse for a car leaving the alignment shop with a toe value that isn't really, really close.

[micondie]

Front drive cars can run no toe in because the power applied to the front wheels to pull the car makes them toe in. On rear wheel drive cars the drag on the front wheels pulls them towards toe out so if your have static toe in you will have less when you are moving, the amount is determined by the amount of play in your front suspension. Factory toe in settings are probably exagerated to allow for wear to prevent going to toe out.

[MechEngVT]

Front suspensions tend to have isolated/bushed control arm/strut mountings at the frame so that the physical suspension has compliance. Steering linkages tend to utilize ball joints with substantially less compliance than bushed joints. Even in a FWD car, the tractive loads will pull the mounting arms forward but the steering linkages will be unaffected, potentially causing toe-out. I wouldn't agree with a blanket statement that FWD cars run static toe-out; it does not seem logical. Quite possibly nominally less toe-in than RWD, but rarely to never static toe-out.

A vehicle with a dynamic toe of zero can still track straight and find the steering center with the right combination of caster, trail, kingpin inclination, and scrub radius (all of which are relatively independent). Usually, but not always, the line of caster passes through the rotational center of the wheel, making caster angle and trail co-dependent. If the line of caster is offset from wheel center this is not the case. Likewise, kingpin inclination and scrub radius (distance between center of contact patch and the ground intersection of the line passing through the upper and lower wheel-end pivots in front view) are co-dependent only for a given wheel offset. Changing wheel offset changes scrub radius independent of KPI.

Running more positive caster helps steering return to center, but increases steering effort and jacking (lifting) when turning, as does high kingpin inclination. Running a zero scrub radius reduces turning effort but would make center feel more numb and a bit squirrely (tire will still only "scrub" when turning, not going straight). Running a negative scrub radius (KPI line intersects tire CL above ground) will cause dynamic toe-out under power (reverse under braking) with FWD. Positive scrub radius will cause dynamic toe-in under power with FWD, and will cause centering under power. Running non-zero scrub radius with FWD would likely make for some horrendous torque steer.

[Frank Lee]

Front drive cars can run no toe in because the power applied to the front wheels to pull the car makes them toe in. On rear wheel drive cars the drag on the front wheels pulls them towards toe out so if your have static toe in you will have less when you are moving, the amount is determined by the amount of play in your front suspension.

[micondie]

For more info try here: Wheel Alignment

[Peter7307]

Originally Posted by Old Tele man

...I'll agree "angle" is better wording than "how far" but you can't have an angle without a displacement distance.

Ah yes very true.

cheers , Pete.