ok. lock this if you must. send me to the archives if you must, but i have a nagging suspension setup issue that has bothered me ever since the wai/rr98itr debacle and my own experience with increased rear roll stiffness on my sts car. i will begin at the risk of being banned from h-t forever, or at the least having my posts filtered (see wrx thread) into the blabbering non-sense it probably already is.

ok, for starters, the basis of my reasoning.

1)simply put, weight transfers in a side to side manner (i'm ignoring things like braking and acceleration yada yada)

2)grip is lost at a wheel pair (front or rear) when the amount of weight coming off the inside tire is greater then the amount of weight coming off the other inside tire. (forgive me on my clarity here, i'm not as eloquent as rr98itr)

3)furthermore, the slip angle of the outside tire gets greater as more weight is transferred to it.

a little history: after the wai/rr98itr debacle i finally became convinced that increasing my rear roll couple would make my car rotate better, helping me get some of the time i need to move up from my 3rd at nationals. i changed my setup from 600fr 24mm bar/500rr 22mm bar to a higher rear roll stiffness setup of 600fr 21mm bar/700rr 22mm bar. at the next autocross i suddenly had issues with the inside front spinning coming off hard transitions. i was confused, and for a short while felt that weight must transfer in a pure diagnal direction. however, to follow that logic, all other suspension setup theory would have to be thrown out, and since many of these theories are 4 times as old as i am, i felt that this couldn't be right either. so now i've come to this:

using the excellent math that rr98itr contributed, i'll stick with 1000lbs of weight transfer (its a nice round number) and i'll also use corner weights of 700lbs fr and 450lbs rr. yeah, is idealic, but i'm working on theory here, so numbers to work with are sufficient.

a) our first example is a car with the traditional roadrace setup, using a roll stiffness dist. of 30%fr 70%rr. in this example, the outside rear would take roughly 700lbs while the outside front would carry 300lbs.

b) our second example is a car with the opposite setup, 70%fr 30%rr roll stiffness distribution. this car transfers 700lbs at the front and 300lbs at the rear.

c) our third and final example is a car with a 50% roll stiffness distribution. this car transfers 500lbs at each end.

in example "b", the car will push. why? the slip angle of the outside front is probably way outside its operating range, and if it isn't, it is much greater then the outside rear, not to mention it has taken all the static weight off the inside front. obviously that is very bad for handling.

in example "c", the cars attitude should be rather dependant on alignment angles, varying from push to loose depending on alignment. the car will probably have a tendency to push, agian because the outside front is running at a significantly higher slip angle then the outside rear, but the mechanical grip will be much greater then in "b" since the inside front is still carrying 200lbs, while the inside rear has 0 weight. theory would hold that in most situations the car should be loose.

in example "a", the car is loose. why? the inside rear has no weight on it while the outside rear has 700lbs on it, plus its static weight for a total of 1150lbs resulting in a higher slip angle then the outside front. the catch i've found is this. where does the other 250lbs come from? we only have 450 lbs static weight on the inside rear, so if we transfer 700lbs to the outside rear, the other 250lbs has to come from somewhere. right? (remember, weight transfers side to side) now, there are only two other options available, and since acceleration or deceleration is the only way to get the weight from the outside front, it ain't coming from there. the only other place it can come from is the INSIDE FRONT. hmmmm...... now the problem i ran into makes sense, unless i'm missing something else. now, i'm not sure if this is going to work for a roadrace car. it may be that with a limited slip this is a desired effect. it may also just be my driving style doesn't work with the high rear roll stiffness. i was going to say more, but i got interrupted and lost my train of thought. i'll stop now and see what i get for responses, maybe i'll remember.

nate-who doesn't know why he's posting this if he truly believes it will help make a car faster and possibly smote him.

edit: not that i think this will happen, but don't go changing your setup just cause i posted something that "seems" logical. hell, i could be miles off and too dumb to know it!


[Modified by solo-x, 1:41 AM 12/12/2002]

 

hmmm......silence for over an hour. either i grossly overestimated the attention span we have at this time of year, or i'm so off base in left field that nobody even wants to bother. oh well, i had fun and it passed some time at work...

nate

 

cliff's notes are your friend

 

i have a hard time getting an idea across using lots of words. now you want me to condense it! :apalled:

cliff notes version:

if you go too high with your rear roll stiffness in relation to front roll stiffness, you actually reduce front grip, and ultimately, overall grip.

nate-who felt the long version was an excellent way to waste 2 hours at work.

 

yes but this is at the cost of increased 'rotateability' which allows the driver to apply the throttle sooner, which is ultimately what will reduce lap times.

 

Look, already a reply

 

which is why it might not work for roadrace. i still feel that using alignment, tire stagger, and tire pressure you could still get the car to rotate.

nate

 

and you still reduce overall grip in the process, and can come up with a handfull to drive, IMO. However this could work great for a stock class autoX car where your adjustments are limited.

 

nate-i think alot of the problem with simply apply the roadrace type set-up to a dedicated autoX car is that it tends to make the car very very loose, and on a tight, transition intensive sub-60 sec autoX course that isn't the desired effect...we dont' want to have to deal with things like lift-throttle oversteer and snap oversteer....the best way i've explained to my co-driver is that we want a surgically precise car.....autoXer's want the car to do *ONLY WHAT WE TELL IT TO DO* and *ONLY WHEN WE TELL IT TO DO IT* now, don't get me wrong i'm not saying roadracers don't want this either, because they certainly do to...but not necessarily <sp> to the same degree or even in the same sense

nate, i don't know what you have done in terms of gaining more negative camber but maybe try some adjustable control arms up front, might help you be able to get a truely neutral feeling set-up while also having true neutral set-up (50% roll couple dist)

i also see what you are talking about with alignment specs and tire stagger....get the car balanced, by the numbers, and use the remaining adjustments that are left to be made to dial in/out any push or looseness.

man...you must really be racking your brain as of late....i might be shooting you an email soon as saturday and sunday are my scheduled days to measure and crunch the numbers for my chassis and come up with a starting point.....suspension tuning is fun

 

i like loose. loose is fast, loose is fun. loose is why my car has flat spots on all four tires, in multiple places! the "loose" i got from the higher rear roll stiffness didn't _feel_ right. the front end was vague, turn in sucked, it really just blew. i've driven my car with bad camber links, so that the car was going into positive camber in a hard turn, and it didn't feel as bad as this.

a 50/50 setup does _not_ reduce overall grip. in our example, it keeps 50lbs more weight on the inside front then a 30/70 setup, plus an extra 200lbs on the outside front. you have to remember that a "loose" situation on a car with a 50/50 weight distribution is when the rear wheel pair transfers more weight _off_ the inside then the front pair transfers. increased loading isn't what causes the loss of grip, it's increased weight transfer. if increased loading caused a "push" scenario, increasing front downforce on a car would make it push _more_ not less. standing on the brakes would cause the car to instantly lock the tires.

in roadrace, i think people stay away from this because the outside front is worked harder, making it go away earlier, making a car _really_ slow towards the closing laps of the race. however, if you take TOO much weight off the outside front, overall grip is sacrificed. so really its a balancing act between tire preservation and ultimate grip.

nate