Steering feel wheel offsets and scrub radius may be sleep provoking for some

Does anyone know what the stock scrub radius is typically for a 246 or 308 Dino? How does it compare to say a 911 or other sports car?

I now understand that with ABS cars the scrub radius is very small to avoid the steering wheel being jerked from your hand with differential ABS application, but was wondering how the #s actually compared from ABS to non-ABS cars.

Ferraris have also often described as having a dead on center feel - would that be because of carrying minimal scrub radii? I have also read that steering feel (and especially kickback) are directly proportional to scrub radius. So, if I wanted to increase steering feel, could I do that by changing the wheel offset with spacers? I haven't read where this would change the steering response however.

If camber is controlled by lower A-arm mounting shims, wouldn't changing this also change scrub radii (although not much) ?

My many thanks as I learn about front suspensions.

best
rt

Add more caster if you want more feed back. Additional caster will also give you more neg camber gain when the wheels are turned into the corner.

"Ferraris have also often described as having a dead on center feel"

This is due to the front toe setting. Effectively, front static toe-in causes both front tires to generate a small inward pushing force. When one tire is disturbed (traction-wise) the other tire pushes the car into the disturbance (understeer). Once the tires are turned enough that the toe-in on the inside tire is removed, the outside tire then pushes the car in the direction indicated by the driver at the steerign wheel. This 'feels' like a dead zone on center (assuming caster is balanced, and wheels equally weighted). Want to enliven the steering, take some toe-in out. Already too lively and want more calmness on the straights, add more toe-in.

"So, if I wanted to increase steering feel, could I do that by changing the wheel offset with spacers?"

Caster and toe are a lot easier to manipulate. These cars are very sensitive to suspension alignment. Suspension alignment (and corner weighting) can make these cars only drivably by racing drivers on one end of the scale and at the other end your grandma could drive the car all day long. The question is:: what do you want the suspension to do? Cruise down the road effortlessly, or attack corner after corner dancing with the devil in the clear moonlight? BTW you can't have both at the same time!

"If camber is controlled by lower A-arm mounting shims, wouldn't changing this also change scrub radii"

No, the scrub radius is controled by the ball joints and the hub. The line passing through both ball joints intersects the road at the scrub point. This is the point where steering movements of the wheel/tire rotate around. The distance from this point to the center of the contact patch (in the horizontal direction) is the scrub radius "length". The shorter it is, the less kickback in the steering system.The distance from this point to the center of the contact patch in the longitudinal direction is the caster scrub. The longer the caster scrub, the more force self centering force generated (until the traction envelope is exceeded).

You want little scrub to minimize kickback (through harsh roads or through ABS activity), but you want a useful amount in the caster direction for at-speed stability.

Mitch,
You have it correct when you ask "What do you want the suspension to do". Toe changes will change how the car feels on turn in. But, as stated,this might not be the hot deal with ABS. Caster uses the weight of the car to cause the wheel to return to center by weight jacking diagonal weight from the inside front wheel to outside rear wheel. I would try increasing castor first to see if it would give the desired effect that Russ wants.
Russ,
What do you want the car to do. Prior posts with you seem to go towards the performance side with the lose of streetability.

Bob: rturner ask about the dead center feel.

Caster deals with the amount of feedback when the steering wheel is off center
Toe deals with the dead zone while the steering wheel is on center.

True, but the effect of more caster would be felt sooner and stronger as you "leave the dead zone". Driven many race cars and some Ferrari's and never really felt a Dead zone. Is the car tracking true by itself due to toe settings and has some play in the steering system, that causes the dead zone to be felt until the play is taken up and the steering system finally causes the car to steer? Interested in this dead zone, has to have a reason. Your thoughts,,,,

Mitch,

you beat me to it....I decided to study this thread, but only when I had time and a "Pad & Pencil" to put everything in geometrical proportion for study...

I'm wondering about the 'dead zone' myself...there should be a point on center where the car will go stright by itself depending on road surface , but could still be "steered" with one finger generating R or L movement.

Gotta be a pretty small point think that might be what we are talking about. Might even depend on which finger we are talking about. On rack and pinon steering, they do wear the rack at the center point creating more clearance(play). could this be a source. We have shimmed the racks for zero play on center, but it will be to tight when turning and in extreme adjustments the rack would not return to center quickly. Fun stuff, but still worried about JRV with his pad, pencil, and finger.

Got it, Slip angles, could the dead zone be the slip angle of the tires due to toe in?
Hey Russ, nice going, JRV is walking around with his pencil, and my headache is coming back