froggy47

So now that I know how to do it (see other thread), I ended up with +8.0 both sides.

What do you guys like for your track/autox cars & what is the plus/minus on having more (higher #) or less (lower #).

A guy I race with has a highly modded Boxster & tells me he has +11 /+12 ish. He also comes out of corners and literally lets 2 hands off the wheel & car straightens itself out. He is fast too, figure top 10 times of event.

So discuss, bear in mind that the number for autox may be different than track. Lots of hairpin/button hook turns in autox, not so much at Sebring/Daytona

ErnieN85

Basics of caster more is better for high speed stability, if you get too much you can get impact shimmy where the wheels will go from left to right while going straight........ back it off too much.
the more caster you have the higher the steering effort will be. This may be the limiting factor for auto cross.

mfain

Remember that caster is a "dynamic" entity. For most modern cars, caster will increase with compression. Caster causes increased negative camber on the outside tire when the wheel is turned, and decreases negative camber on the inside tire - a good thing. For a track car I shoot for a caster setting that is 2 degrees higher than kingpin inclination angle (KPI) AT FULL COMPRESSION. So with 7.5 degrees KPI, I dial in 9.5 degrees with full suspension compression. For my car, that gives me about 7 degrees of caster at ride height. In the photo below, this left front (inside tire in a left turn- suspension jacked up to full compression) went from -2.2 degrees of camber when pointed straight ahead to +3 degrees at 28 degrees of left turn (an extreme turn angle for the track). The right (outside) tire went from -2.2 degrees of camber to -3.8 degrees. This is with 9.5 degrees of caster at full compression. Suspensions designed with high caster gain with compression have one advantage in that you can reduce static camber so the wheels are flatter on the ground when pointed straight ahead - great for braking. Then, you gain the desired camber when the nose is forced down (braking or aero) and you start your turn-in.

froggy47

Thanks Ernie, steering effort seemed good yesterday, no high speeds in autox so I guess I would not want more, plus running 315 in front, I suppose that's increasing steering effort some.

froggy47

Thanks, I am a sponge, learning.

andersnor

8 degrees front?

froggy47

I believe that is what the screen is saying, looks like a nice racy alignment.

AND0

Pros and cons to everything....
How much caster is enough? 8 degrees? 11? 5000?

Downside of caster is the weight jacking effect of the outside wheel lowering the ride height and the inside wheel raising with increasing steering input.
Since the axis of the spindle is leaned back, when you turn the wheel, as a matter of geometry, it pivots upwards away from the ground, and the inside wheel does the opposite, it pivots down towards the ground.
This results in a detrimental dynamic change in the ride height up front putting more load on the outside wheel. The front end is basically "leaning" away from the turn. At some point the trade off for the dynamic camber improvement won't be worth it.

So how much is enough? In "Tune to Win" Carrol Smith says about caster "How much is ideal has to be played with." and of course he is correct, because it will be different for every corner, as well as different in the separate phases of the corner.
Corner entry blending from braking to turning will want geometry different from the relatively steady state middle and the corner exit. A course with more fast corners with small amount of steering input will want different geometry from a course with slow tight turns and lots of steering.
Best you can do is the old stand by. Pick a set up and test it using good data acquisition and analysis. Then try different settings and see where you gain or lose.

froggy47

thx

froggy47

Guess I'll leave it, feels good street & track.

RX7 KLR

I have typically always gone with minimum available caster... With most of my past experience being "Stock" (Street) classed cars adjustments were limited. Negative camber trumps caster, and since most every A arm car I have worked on lost camber when you dialed in caster we always went for the minimum setting - which is still typically 4.5 to 5 degrees. Even as I changed to classes with more suspension modifications we stayed in the 4-5 degree range because I didn't like the weight jacking. On the FWD road race car excessive caster sucked, made it so hard to turn, and hurt the ability to put power down on corner exit. On our C5 CAM-S car we only have 5 degrees.

froggy47

Thanks Jason, on the c6z I can get plenty of neg. camber, even with the stock lower eccentrics. Are you saying or thinking if I adjust to +7 or +6 caster it'll take away my negative camber, I would not want that. So maybe I stay with +8?

Froggy

cpt11gs

When you add shims to increase the castor, you are decreasing the camber. I do my adjustments like Jason, remove all the shims to get max camber, and then just make sure caster is somewhat even, but I don’t need to make caster identical, just not enough off to make the car pull to one side.

Chris

froggy47

Well , I'm confused. I have "always" been told, and it worked that way on my car, that the caster adjustment (add subtract the same shims) did not change camber.

So, I did that on my car and it did not change the camber. Within margin of how close I could read the bubble.

So much conflicting opinions/facts/ whatever on caster.

Ugh.

cpt11gs

Bob,

That’s not a conflict. You still have the same number of shims when you do that. What I meant that when you add shims *from no shims at all*, you are decreasing camber. What I do, and Jason said the same thing, is remove *all* shims to get maximum camber. If that’s still confusing, I can show you at the next event.

Chris

froggy47

OK I think we are just not describing in total what my adjustment procedure is.

1) Kick out the lowers to max neg.
2) You end up with over 4 negative
3) You add UPPER shims back to get to what you want equal shims all upper front 4 bolts (or studs if you converted)
4) Then you start moving from front to back upper or back to front upper to set caster (camber remains the same) Total "value" of all upper shims never changes just forward or backward positions.

Seems to work, as I rechecked camber after caster was "equaled" and within my ability to read a bubble it was perfect. Driver side = pass side. Car straight as an arrow down an uncrowned road (if you can find such).

YES?

cpt11gs

Bob,

Your method will work fine. The difference is that mine, and other Corvette's I've worked on, I've never seen 4 degrees negative with stock parts. If that's what you have, then your process is fine. In front, mine with max out lowers, and all shims removed is barely 3 degrees, and maybe a bit less. The lower the ride height is, the more negative camber you would have, so yours may be a bit lower, or maybe you are just lucky.

Chris

froggy47

I was a little surprised that the eccentrics gave me that without going to the special camber kits. It's not lowered (by me anyway). I can tell it's higher than my c5z by some.