Compromises!

51t · Jan 10, 2003

What of the following (and any I missed) would be the most to least important? Assume it will be for a autocross STS car with some road course (solo 1 but non competitive) use.

Center Of Gravity
Track Width (max +13mm)
Suspension Travel
Suspension Compliance (soft/stiff)
Weight Distribution (corner weight)
Oversteer/Understeer/Neutral Characteristic
Whatever I am missing...

ZXmurph · Jan 10, 2003

I'm a bit confused as to what your asking...

in regards to how these characteristics are may be
adjustable in a given vehicle or ?

They ALL can be interelated to an extant so it's difficult to list an order of most to least important when one can profoundly affect another....

a cool discussion will follow however

[ 01-09-2003, 09:33 PM: Message edited by: ZXmurph ]

51t · Jan 10, 2003

That's the thing. One thing affects another and usually in a negative way. If you (or I) are going to build a race car there is going to have to be compromises. What factors do you give the most weight to? Is a low center of gravity worth the sacrifice in suspension compliance?

MichaelXi · Jan 10, 2003

51t,
Define your starting point.
Are you referring to your Focus, or "any given car"?
That may at least give a STARTING point for opinion on what would offer the most improvement for your application.

[ 01-09-2003, 10:19 PM: Message edited by: MichaelXi ]

OmniFocus · Jan 10, 2003

I'm still a tad confused, but above ANYthing, a neutral handling characteristic is important.

In an all out racecar, there aren't many compromises as far as suspension setups.

The compromise lies in the use of a car for both a track car and a daily driver... Or if you wanted to look at it this way, a Focus is in itself a compromise over say... a Miata with a nice COG and perfect weight distribution. The very idea of racing a Focus is pretty much a compromise.

Look at the Grand-am Focus on the other hand... Just about the only compromise on such an all out racecar is what is required by the rules and the fact that you have to fit a cumbersome driver somewhere inside the car. The spring rates, shock settings, bar settings, brake bias, tire compound, etc. can all be set to ideal for a given track. Other items such as what is on your list, (COG, Track, Travel, compliance, Weight Disti, handling), have all been defined in a no (or little) compromise fashion.

So... The same idea applies. The very idea of running under STS rules is another compromise. You must sometimes pick less than ideal parts or a less than ideal car to compete within the rules. Even within these rules however I'd say that a neutral car is STILL your #1 objective. If you can maximize grip and have neutral handling, then the rest of the stuff on your list will pretty much fall into place. You can begin to work on the challenge of getting by with what you have to work with.

Now.. back to the COG/suspension travel bit. If you race on glass smooth surfaces, then it is acceptable to start with suspension geometries that are pretty much ideal WRT camber, toe, and ride height... as long as you have enough spring to maintain these while racing. This is FAR from ideal, but if you take a look at the dominant street prepared or prepared cars, you'll see that this has been established as the most competitive layout. So yes, it is acceptable (not ideal) to improve ride height at the expense of suspension travel... as long as you aren't driving along on your bumpstops. The compromise with racing any street car is that all of these cars started life as something that could have been driven to work on a daily basis... so as an ideal race car, the platforms pretty much stink... but we can make them work.

I assume that to attain all the goals of the best possible setup within class guidelines that you need a certain amount of money... which I imagine is probably the driving force for you developing an ordered list? Of course, it would be great to address ever piece of the list, but since money doesn't grow on trees, it is necessary to put parts in order. What might be a better thing than a list of handling/car attributes would be a comprehensive list of every part available for a Focus that is STS legal... and then put THAT in order!

[ 01-09-2003, 11:54 PM: Message edited by: OmniFocus ]

MichaelXi · Jan 10, 2003

"What might be a better thing than a list of handling/car attributes would be a comprehensive list of every part available for a Focus that is STS legal... and then put THAT in order!"

Now that I've started a new job, I'm Workin' on it!!!

51t · Jan 10, 2003

The main goal for me here is to 1) establish an order of presidence for dynamics. Being it either autocross or road racing. 2) What's worth giving up for more of another (eg. compliant suspension vs. body roll vs. ride heigh + many others). 30 To learn more and 4)just get an interesting converstation going.
Assume it's a daily driver car. Should not matter what type. Everyone should be striving for the same thing. Also assume the ultimate goal is to make this daily driver into a track only car. I'm not including weight reduction because it's not an option in STS and it's a given in road racing.

As it stands right now your saying:
1. Neutral Handling.
2. Low center of gravity
3. ?Suspension Travel?
4....

Another example of compromise is:
Lowering springs = lower COG = higher spring rate = no compliance (understeer?) on bumpy surfaces. What's more important the compliance or the COG?
What other compromises are there? Larger anti-roll bar = less body roll = terminal understeer.

[ 01-10-2003, 01:07 AM: Message edited by: 51t ]

51t · Jan 10, 2003

As for STS we have
Shocks/Struts
Bushings
Brake Lines
Brake Pads
Rotors
Anti-roll bars
Stress bars
Front Camber Plates
Rims
Tires
UDP
Air box
Can't think of anything else

MichaelXi · Jan 10, 2003

"What other compromises are there? Larger anti-roll bar = less body roll = terminal understeer."

WRONG.
Here you need to just study some more. Maybe someone here can recommend some specific good books.
A larger FRONT roll bar can result in more understeer, but a larger REAR one will result in more Oversteer.
BOTH Larger, in equal percentage, will remain equally neutral, while reducing body roll.
In this case, however, you are reducing the independence of the suspension, which is why some prefer to go w/ Stiffer springs w/o too much increase in sway bar sizes.
There are too many things to take into account to address it in a single post....

[ 01-10-2003, 01:38 AM: Message edited by: MichaelXi ]

OmniFocus · Jan 10, 2003

Originally posted by 51t:
Lowering springs = lower COG = higher spring rate = no compliance (understeer?) on bumpy surfaces. What's more important the compliance or the COG?
What other compromises are there? Larger anti-roll bar = less body roll = terminal understeer.

<font size="2" face="Verdana, Arial">Spring compliance by itself doesn't have anything to do with understeer/oversteer. It is the ratio of the spring rate F/R that influences this factor. You should strive to keep this number at least as "good" as a stock Focus... or preferably shift it more toward the rear (in order words, stiffer rear in relation to the front than a stock Focus would have)...

Same goes for bars... Big bar only means understeer if you install just a big front bar... a properly matched set would be just perfect. If I were going all out, I'd start with 21/22 F/R bars, and probably go to something like a 22/24... I'm just guessing. Sure, a MASSIVE front bar would ultimately take more weight off the wheel with the most grip... and could also cause you to lose some suspension independence... But that is why I wouldn't use totally massive bars.. especially in the front.

There is a lot of mentality that body roll is really evil.... well, truthfully it isn't great, but if you have a fairly compliant contact patch on your tire and enough negative camber to counteract it, then you can get by with a lot more body roll than most people would expect. Given the amount of pitch and roll my Focus has, it sure doesn't *appear* to handle as well as it *feels* like it does.

Okay... So lets say I was designing a car from the ground up...

My first priority would be to keep it neutral handling. The second would be to determine how much travel I will need based on the compliance of the springs I've chosen... The softer the spring, the longer it will travel for a given load.... after that I'd choose the appropriate damping needed for that spring and the weight transfer of the chassis. Throughout the entire design process I will try to keep every part of the car as low to the ground and as close to the center of the vehicle as possible. I would arrange the vehicle peripherals such that the corner weights are equal diagonally.. or equal on all corners if I've attained a perfect 50/50. (Equal should include a driver.) The track width? I'm not sure how I'd go about determining that beyond having the widest track possible without resorting to some strange Akerman effect.

So... What I think I'm trying to say is that it is tough to put those on a list in order, because they are all interconnected... Like you say.. a "compromise"... But I wouldn't look at it as a compromise.. View the entire car as a system and you'll be better off... It either handles good, crappy, or somewhere in between... If you are truly "improving" one characteristic, then there shouldn't BE any compromise.

So... regarding a Focus... if you REALLY want a list, I would rearrange it like this:

1) Neutral Handling.. accompanied by maximum grip.
..a) suspension compliance... enough to keep the tires as flat to the pavement as possible.
..b) suspension travel... enough to ensure that for the chosen suspension compliance, the travel is long enough to stay off the bump stops except in extreme situations.. (Potholes, etc..)
..c) COG.. as low as possible given you've met the previous two requirements...
..d) Corner weights... This is basically all about being neutral while turning left AND right...
..e) Track width... wide... but on a Focus this is really more for tire clearance than a handling effect. Too wide will also create scrubbing problems, as the left and right wheels do not turn at the same rate... which is to accomodate the larger turning radius of the outside wheel... But if you mess with track without moving the pivot points, then the wheels will be traveling in the wrong arc for the given direction.... Basically with a Focus, if it fits inside your fender wells, then you shouldn't have to worry about it.

So... That is my list. A), B), C), D), and E) are all required to Achieve the ULTIMATE goal... which is 1)

51t · Jan 10, 2003

Perfect. That's what I wanted Omni. Being more specific and saying the focus works best on conditions x with such and such settings is well beyond most of our cash flow (testing many different products in the same conditions). I understand it's about making the best educated guess possible with what is available. But now I can say product X gives me this benefit which outweighs this negative.

rheacer · Jan 10, 2003

Balance grasshopper and the rest will follow....
Feel the car...be the car....
I vote F),D),C), A&E) are REAL similar, B).. Wait, that's what Omni said. I agree but would add,"and practice practice practice". You can acheive F through double throwdown unobtainium magic widgets, or just balance what you have. Proper alignment, Best tires you can afford,Tire pressures, Urethane swaybar bushing on rear, rubber on front, GOOD shocks and struts/ springs, , swaybars, Gonna need a cage in there for SOLO I- that will help compliance. That's the list I would work off. Did I mention practice?

teamDFL · Jan 10, 2003

After deleting about half a dozen post in this thread before posting them, I think I can finally say what I want in the proper manner.

Go slowly. While it is really tempting to rip off every suspension part and do all your modifications at one time, you end up with a car you hardly know. My advice, is that none of the criteria you listed (or any of the ones others have added) matter in the least if you are not comfortable driving the car. You make the car fast, not the parts you throw on it.

I am not trying to turn this into a "zen and the art of drving" thread, nor am I trying to discourage you from making changes to the car. What I want to make sure that you understand is that you, the driver, must always be comfortable for a change to be effective. There will come a day when you will be able to handle that super-trick triple adjustable suspension you dream of. But an honest answer to the question "Is that today?" can save you some grief and maybe make your arrival at that point come faster.

ZXmurph · Jan 11, 2003

Originally posted by teamDFL:
Go slowly. While it is really tempting to rip off every suspension part and do all your modifications at one time, you end up with a car you hardly know. My advice, is that none of the criteria you listed (or any of the ones others have added) matter in the least if you are not comfortable driving the car. You make the car fast, not the parts you throw on it.

<font size="2" face="Verdana, Arial">My brother from the other coast! I could not agree more, and would even add that if modification are not done concurrently with available venues and/or instruction to quantify and benefit from the changes.....you're re-learning a "different" car each time, instead of progressing in steps.

Case in point- I've tried to condense 15 years of driver/car development with Vdubs into one year with the Focus. Through opportunity, I've had multiple set-ups in the new car but changed before I could possibly say I was "wired" with any of them. Now the biggest set-up change I've made to my car, has come right at a two to three month layoff from any venue to get it wired. I feel I'll be re-learning a "brand new" car, instead of just pushing a new capability further. No doubt the car is fun and capable....but I would bet anyone I would beat myself in it, in an old Rabbit dialed for H-stock...the one that I spent time as a DRIVER with instead of a wanna-be hair-splitting chassis tuner from hell.

take your time going faster....

51t · Jan 11, 2003

Well, since this thread has deteriorated into the
"learn to drive" hole so many threads do I will tell you of my overall plan. I have 2. The first is to slowly modify my focus for 1)autocross use (STS) and 2) fun daily driving over the life of the car. Maybe from 2 to 3 years from now. My other goal is to highly modify over a 5 year period a soon to be aquired stock Pontiac turbocharged Firefly (78 hp here I come). Hopefully making it into a full time track car. Starting with modifications that also qualify me for STS class. Once complete moving on from there to track use.

teamDFL · Jan 12, 2003

Originally posted by 51t:
Well, since this thread has deteriorated into the
"learn to drive" hole so many threads do.

<font size="2" face="Verdana, Arial">Sorry, then I didn't explain very well. My point was that all the factors you mention contribute to the overall capability of the car, but you need to make sure that you can still recognize what the car is doing. I have been in a car that was way above my ability level, and it sucks.

To that end, I would put suspension travel as the most important. A car that has bottomed (and therefore has an infinte spring) rate is very difficult to control. Now do you see?

51t · Jan 12, 2003

I understood what you said. Make a step, learn it, make a step,learn it, make a step learn it. I by no means think I'm some gifted F1 diver that can go and do 3 laps and say "I want this and this changed" then kick ass. I understand I need to learn each aspect of a car to get the most from it. It's just I am looking for opinions on car dynamics.

teamDFL · Jan 12, 2003

OK, then here is my .02

Weight distribution is difficult to make major changes to, so you may as well scratch that from the list. Sure you can get adjustable perches and corner weight, but in all honesty, I cannot tell the difference from perfect 50-50 on the cross weights and the 48-52 that was there before I rolled on the scales. As for front/rear and left/right, that is a lot of work.

CoG and suspension stiffness go hand-in-hand if you aren't doing a major re-design. You must up the stiffness significantly if you lower a large in order to avoid bottoming. I will assume you know of the consequences of an overly stiff car, so while a low CoG is great, don't get carried away.

Track width can help, but as I am a big "feel first" guy, be aware that different offsets can mess with the feedback of the car. This subject has been covered before, and no-one has come up with a conclusive answer as to what happens. Murph can send me his OZ's anytime for back to back testing!

So that leaves understeer and oversteer. And while you are going to complain, that is more a driving issue than anything else. Unless you do something freakishly stupid in your modifications, the Focus is always going to be a relatively neutral car that a competent driver can get to respond in most any situation. That said, it will take extensive testing and money in order to determine how you should set up the car for your personal driving style. But, in terms of handling, as many others have already stated, this is the whole enchilada. All the others are just steps on the way to getting the car to be its fastest.

51t · Jan 12, 2003

Thanks TeamDFL for the input. It's much appreciated. BTW what's with the OZ crono's and track width? Just asking because that's what I am currently running (not in the winter).

teamDFL · Jan 12, 2003

Most of the OZ fitments are 42mm offset so 10.5 from stock. So if you were talking 13mm total, you are over, but if you ment 13mm per side, you are fine. I have offered many time to Murph to take these hideous destroyers of suspension geometry away from him for free and he has never seen the light.

Compromises!

51t

ZXmurph

51t

MichaelXi

OmniFocus

MichaelXi

51t

51t

MichaelXi

OmniFocus

51t

rheacer

teamDFL

ZXmurph

51t

teamDFL

51t

teamDFL

51t

teamDFL

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