Caster, SAI, Steering and Camber

[7thgear]

not to take away from what you have said, i would just like to point out that we all shouldn't be using F1 cars as examples because those cars rely on speed for grip. As that guy from top gear showed us, if you drive an F1 car slow, you'll spin)

a much better comparison would be to keep track of WRC, or better yet, what the Group A guys do. Not only because they are as close to our every day cars but because they actually end up running across conditions we would see in our daily commutes and occasional track excursions.

[Draco-REX]

Originally Posted by 7thgear

not to take away from what you have said, i would just like to point out that we all shouldn't be using F1 cars as examples because those cars rely on speed for grip. As that guy from top gear showed us, if you drive an F1 car slow, you'll spin)

a much better comparison would be to keep track of WRC, or better yet, what the Group A guys do. Not only because they are as close to our every day cars but because they actually end up running across conditions we would see in our daily commutes and occasional track excursions.

True, but suspension setup for low-traction environments (i.e. dirt) is far different than high-traction environments (i.e. tarmac). We could look at Aussie V8 Supercars. They're big, heavy, and often run on road courses converted from public roads.

I was using F1 as an example of suspension design in a near optimal environment and how even they have to make compromises.

[7thgear]

Originally Posted by Draco-REX

I was using F1 as an example of suspension design in a near optimal environment and how even they have to make compromises.

i'd argue that the suspension design in F1 is far from "optimal", they have great limits on their car and a lot of their design is often a big compromise of mechanical grip (what 99% of us are after) in favor of aero grip (which 99% of us don't experience)

[Draco-REX]

Originally Posted by 7thgear

i'd argue that the suspension design in F1 is far from "optimal", they have great limits on their car and a lot of their design is often a big compromise of mechanical grip (what 99% of us are after) in favor of aero grip (which 99% of us don't experience)

Not to veer off track here but..

Mechanical grip is still very important in F1 because they can't generate massive amounts of downforce in slow corners. The success of Red Bull in F1 is due to both advanced aero AND mechical grip. The RBs are capable of maintaining speed in the slow corners and putting the power down on exit.

If anything, the increased reliance on Aero means that the suspension needs to be as optimized as possible since any body movement will reduce aerodynamic efficiency.

But all this is off topic for this thread...

For our cars, keeping an eye on SAI and IA might not be a bad idea, as the charts above show, it isn't something to worry about. For someone wanting to minimize IA, they would want to get as much of their front camber from the bolts as possible. This lets them stand the strut up more, reducing camber gain.

[7thgear]

Originally Posted by Draco-REX

Aero means that the suspension needs to be as optimized as possible since any body movement will reduce aerodynamic efficiency.

i think you and me have different diffinitions of the word "optimize"

think for a second what the biggest component of the suspension system is going to be to "eliminate body movement," it starts with the letter S....

then factor in how controlable roll and gravity centers are in an F1 car.

The two must overcome very different challenges, and while the physics is teh same, the real world applciations are noticably different.

Like i said, if you want to replicate precise control and insane grip of race cars in your daily, then look no further than Group A or WRC.

F1 are built from the ground up with very minimal concern about accomodating a human body... let alone cargo, haha

anyway...

[mike156]

All this theory overlooks one big thing... How much tire can you put under the car?

Using the lower strut mount for camber means less tire clearance. Thus you have to use lower offset wheels. Now your scrub radius starts to climb...

As always, pick a tire and set the suspension up around the tire because the tire drives EVERYTHING. What is the best compromise for one tire width and type is going to be completely different then another tire.

[Draco-REX]

Originally Posted by mike156

All this theory overlooks one big thing... How much tire can you put under the car?

Using the lower strut mount for camber means less tire clearance. Thus you have to use lower offset wheels. Now your scrub radius starts to climb...

As always, pick a tire and set the suspension up around the tire because the tire drives EVERYTHING. What is the best compromise for one tire width and type is going to be completely different then another tire.

I'm running 265s that way.. There isn't much need for more than that with this car.

[Wepeel]

Originally Posted by yzarc0g

What sort of issues with the ADK? What else would you recommend to get .5 degree of positive caster?

I agree, just light variation from stock is preferrable.

They had some issues with the bushing separating from the inner sleeves... they had a few revisions of the design and I'm not sure if it ever became reliable. If you search for ALK on the other subaru forums there's some info there.

The only other way you can get caster is via an adjustable strut top, like a camber plate that is tilted to provide some component of caster change or one that has some already built in.

[Wepeel]

Originally Posted by mike156

All this theory overlooks one big thing... How much tire can you put under the car?

Using the lower strut mount for camber means less tire clearance. Thus you have to use lower offset wheels. Now your scrub radius starts to climb...

As always, pick a tire and set the suspension up around the tire because the tire drives EVERYTHING. What is the best compromise for one tire width and type is going to be completely different then another tire.

It goes the other way too - you'll have spring interference with the chassis if you try to get too much camber from the strut top. And just like with wheel/strut interference, coilovers improve the situation.

With coilovers there's a good bit of room - seems people can run a 275 Hoosier on a 42 offset wheel.

[autobrz]

let's say stock caster is 5.6* and on the track, the max wheel angle is maybe 7*? According to your table, the camber gain from caster is -0.68*

If I increase the caster 2* to 7.6*, the camber gain from caster at the same wheel angle is 7*sin(7.6*)=0.93*

So adding 2* of caster adds a max of 0.25* of camber gain over stock. It also means, I can run 0.25* less static camber and have the same alignment at the slowest corners. In your opinion, is that worth the price of the adjustable caster front control arms to just gain 0.25* camber? I haven't played with camber in that small an increment to know if it's even noticeable.

[7thgear]

you guys keep forgetting to add in angle changes due to body roll.. lca tucks in, top of strut rolls out.. also forward tilt under breaking and backward tilt under acceleration... shit matters.

[ZDan]

Originally Posted by 7thgear

you guys keep forgetting to add in angle changes due to body roll.. lca tucks in, top of strut rolls out..

No, it will continue to gain negative camber in bump pretty much beyond the reasonable limits of suspension travel. McPherson struts do NOT start losing negative camber when the control arm "goes past horizontal". The control arm has to go past perpendicular to the strut line of action, typically ~15 degrees or so past horizontal, before it stops GAINING negative camber with bump and starts losing it. This point is usually outside the range of usable suspension compression.

[7thgear]

Originally Posted by ZDan

No, it will continue to gain negative camber in bump pretty much beyond the reasonable limits of suspension travel. McPherson struts do NOT start losing negative camber when the control arm "goes past horizontal". The control arm has to go past perpendicular to the strut line of action, typically ~15 degrees or so past horizontal, before it stops GAINING negative camber with bump and starts losing it. This point is usually outside the range of usable suspension compression.

not what I was talking about

*also please note that what you say maybe true for the FRS, but not for all macstrut cars... the VW Golf in particular pretty much starts off with the arms above perpendicular..

anyway here is a photo of my stock VW back when I didn't have any facial hair

as you can see, the outside wheel not only has to deal with the geometrical movements of the suspension, but also the relative re-positioning of the chassis pickup points in space..

ie, for a proper discussion... chassis roll MUST be taken into account

[TouchMyHonda]

So much info