<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LX4CYL &raquo;</TD></TR><TR><TD CLASS="quote">Longhorn PCA Auto-x? Whne was this, and why wasn't I informed? here I am sitting here going through withdrawals for not having been to an AX for the past couple of weeks! </TD></TR></TABLE>

You can always check my calendar here for most of the Central Tx events: http://www.dmcknight.net

 

The tire lifts because you have decoupled the rear tire from the rear wheel pair roll stiffness. The body is still rolling and the inside rear has already reached maximum droop travel. A big rear sway bar(bigger sway bar limits droop travel)/more rear rate (transfer weight off the rear faster) will only make this worse, the inside rear will lift sooner and higher and cause even more understeer. The rear tire lifts, and the roll center moves to the instant center of the outside control arm(s) (and then to the contact patch of the tire when the suspension becomes fully compressed). So at this point you've transfered all the load off the inside rear tire.....and the outside rear tire is already generating its maximum amount of grip, so where does all the load transfer too? It goes to the front axle pair. Its common knowledge that a wheel pair generates its maximum amount of grip when the load is evenly distributed between the two tires on that axle, so when you add the load you lost from the inside rear (and remember the outside rear can't generate any more grip!) then the front wheel pair loses grip = understeer. The best setup is that at maximum steady state grip (every turn has some steady state in it no matter what is said) the inside rear is just barely becoming unloaded/still ON THE GROUND!!!


Basically you want a high enough front spring rate to keep the inside rear tire from lifting off the ground. And on my SE-R we have a high enough rear roll center that the roll stiffness achieved with a 22m rear bar and anywhere from 200 to 250lb spring is enough to jack the inside rear tire off the ground. So a stiffer rear setup would only make it worse.

The only solution to rear wheel lifting is either drive slower (now who would want to do that?) or more front spring.

For instance, at the last National Tour event, the winner in STS was running 850f/750r and no rear bar and I can guarantee you that the inside rear never lifted and from what I've heard the car is really really loose. Nate might comment on it and help provide some insight

 

if i didn't know better i'd almost say that was written by me. one correction though, i am using a 23mm rear swaybar. i'm in the middle of some skidpad testing that has indicated that at the very least the 14mm stock rear bar is needed, but that the extra stiffness of the 23mm one might not.

 

Damn you and your laws of physics Nick

Interestingly enough, I am running the sort of setup you're describing; 500f/600r with a stock Si 15mm rear bar and a 22mm DA Integra front bar. I just don't understand how you get the car to rotate with a front-stiff setup though other than alignment and staggered tires. My car understeers just slightly, and I've been considering taking off the front bar to make it a little more loose and also to help keep that inside wheel from spinning without an LSD. From what you're describing, my car would understeer more?

 

hehe yeah Nate, I pretty much copy and pasted from the last time you answered that question (its just easier that way )

Kent, is your car understeering? Or is it wheelspin because of not enough rebound damping? Thats the biggest problem I'm running into, a driver can pretty much dial out all understeer (unless its a stock class car) and I just can't put the power down because the front wheels just hop. I can explain F/R bias with the suspension on my car but obviously the suspension is much different than your car so I'll reserve comment until Nate gives his input

 

in my experience, an understeering car will have more problems with wheelspin then one that is loose. make the car looser and you'll naturally reduce wheelspin.

disconnecting the front bar does seem to reduce wheelspin. however, we already know that post rear tire lift off there is no more weight to transfer across the rear axle, so just like stiffening the rear of the car would have no effect mid-corner, softening the front will also have no effect as far as load the on the three active contact patches is concerned. you will, however, increase your roll angle (bad from outside front tires desired camber perspective, good from the outside rear tires increased decambering... see scott, i DO care about that tire! ) and likely hike the rear tire higher in the air. raise the cg, increase total load transfer for any given cornering force, which would raise the cg more, and so on and so forth. where would that additional load transfer happen? you guessed it, the axle we least want load transfer to happen on.

so what is the net result of disconnecting the front swaybar? worse case scenario the car feels looser (decamber outside rear more then outside front) and if we assume my first observation is correct might even have less wheelspin. however, since we are rolling the chassis more and raising the cg higher our total grip may have actually decreased (another thing that could lead to a feeling of more grip on the inside front) and the package as a whole is slower. i think this worse case scenario happens a lot more then anyone knows. probably because even though the whole package is slower, it turns faster lap times purely because it is looser, allowing the driver to unwind the wheel earlier, accelerate earlier, and have a higher average speed. imo, that is easy to do on a track car when 70% or more of your lap time is spent on a straight.

front rebound is a wonderous thing. it can really diminish that nasty inside front wheelspin thing. i've got some insanely stiff front shocks on my car. the soft end of my adjustment range is half way up the SPSS3 adjustment range. i use 75% of the adjustment range most of the time. front rebound tuning is another topic all together.

what's so wrong with using the alignment to fix the balance? i don't run tire stagger, even though i've figured out a way to do it while using the same compound tires on both ends. my alignment isn't even that aggressive anymore. zero rear toe, ~-1* rear camber, something over -2.5* front camber. are you afraid of throwing away grip? if it's any consolation, the STX EF i've been helping to tune is knocking down over 1g steady state on street tires that aren't even shaved. that car is running 800/700 with stock swaybars on both ends. front camber is whatever we got from lowering, rear camber is about the same as what i run. (this car is even running toe in on the rear and it's not quite as loose as my car but gets away with it because of the quaife.) once you've done all you can to stick the front of the car, who cares what you have to do to free it up. i prefer camber over toe though, much easier to drive and very responsive to rear tire pressure changes. (my car was too loose at the last event. i dropped rear tire pressures from 40psi to 38psi and it was too tight. 39psi=perfect!)

nate - shouldn't post this late at night because he rambles too much

 

Sounds pretty radical Nate. How do you predict it'll work against the legion of more "conventionally" suspended Civics at Nationals?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by jzr &raquo;</TD></TR><TR><TD CLASS="quote">Sounds pretty radical Nate. How do you predict it'll work against the legion of more "conventionally" suspended Civics at Nationals?</TD></TR></TABLE>

needs a better driver.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by solo-x &raquo;</TD></TR><TR><TD CLASS="quote">if i didn't know better i'd almost say that was written by me. one correction though, i am using a 23mm rear swaybar. i'm in the middle of some skidpad testing that has indicated that at the very least the 14mm stock rear bar is needed, but that the extra stiffness of the 23mm one might not.</TD></TR></TABLE>

This is a thread about killing cones Nate. Get with the program