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Old 11-08-2013, 11:39 PM   #1
raamaudio
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Default Performance, real, not so real, balance in the middle?

So much for spell checking, please disregard my errors as the meat of this has some very pertinent info for those that want to know more about handling, and in reality safetly, than just posing for the camera or the local parking lot showdown....

I see so many posts with pictures of car so severely compromised I just had to write this up. I love to make a car look really great and have lowered dozens for over 46years now but sometimes the extremes I sell give me the shudders when I know what is going on in the real world of driving such vehicles.


I took the time to write the info below as I hope at least some of the members here read and consider this information as I really care about this subject a great deal. I have studied the best books from real race engineers and and implemented and track tested all of the best principles that do not change, they work on all cars, all the time.

Of course some, I hope many, here know this but some obviously do not know or just do not care but maybe I can help a few understand the differences in looking fast and being fast, being fast being far more fun to me than looking fast.

On my own 332ti project the car will be set for the proper ride height so the suspension geometry is the best I can make it, vice slammed and having the car act like is has two wheels as so commonly occurs, overly lowered simply puts nearly all teh weight on the two outside tires, if those are skinny tires on ultra wide rims, you have very little real grip, simple physics. For those that go for style over substance that is OK with me but I have spanked many such "faster" looking cars on course that were simply to low to work right.

I want as much tire for the least fitment issues I can make fit, rolling front fenders is pretty easy and can gain quite a bit of room. Rears are another story, triple layered metal, I have cut it all out and welded in or molded in flares, at least a full day of hard work and I want to skip that if I can. I might end up cutting it all loose, rolling the stock body work out as far as I can then welding in to fill the gap.

Camber, caster, toe, roll center, roll couple, spring rates, roll bar settings, lowered unsprung weight, etc...I have studied and used these for decades and always setup my cars to maximize them.

Stretching tires to fit, that is one thing that bugs me a great deal, more than super tall wheels just to be tall is number two or three as heavy wheels and tires are a huge performance killer. Super wide wheels with skinny tires does not equal performance, it is style only. The perfect stretch, determined by the actual tire in question, is to have some to help support the sidewall, to much or to little reduces grip or precision, either of which makes you slower and/or more prone to making mistakes or simply breaking parts, road hazard issues......add in a slammed car with severely compromised geometry and you are reducing your performance hugely as well as inducing safety issues in many cases.

I have had fun against hundreds of such setups in my 46 years of modding and driving modified cars. Everything is best when in balance, period, there is nothing else that matters to me except the balance of the whole car and that includes how much power I add to it.

With the 300HP and a 2750 lb car I am building, which is more than enough for me, those that want more that is cool, been there and done that before most here were born, I need some serious grip in the rear and front as well for cornering as this car will see serious track time on dozens of tracks driven flat out. I am going to stick with street tires to keep the speeds in check a bit though as I have not driven most of the tracks I will be on one time only in most cases and the tracks have many close guard rails(Armco is the older and often used name in racing)

I also want to keep the car as stock looking as I can outside, I always like stealthy cars, why I have kept my license all these years and cheap insurance rates though hundreds of thousands of fun miles under my belt

If you want to truly be fast then you must use proper geometry and rim width support for your tires, lower unsprung weight as in wheels, tires, brakes, etc...lower rotational weight is very important as well, these are some of the golden rules of racing and all apply to the street as well.

Those that have severely lowered cars on super skinny tires on super wide wheels, have fun, following well behind and dropping out of site of this old man

Sincerely,
Rick

Last edited by raamaudio; 11-08-2013 at 11:47 PM.
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Old 11-13-2013, 04:09 AM   #2
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Great post. I too like a balance between "stance" and usability. I still appreciate the eye candy of a slammed car though.
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Old 11-19-2013, 06:12 PM   #3
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While I do agree with your general sentiment, there is a strong argument that the "balance" might not be as conservative as many believe.

For example, natural frequency. 2.0-2.5Hz up front and ~10% higher in the back is a pretty well backed number to shot for by every suspension engineering book out there. However, in types of racing that have very high transition rates (autoX), most of the guys winning are actually higher than this range. This is also ignoring cars with heavy aero work that can generate considerable down force but that can be very pitch or roll sensitive.
There is a reason for it too and while the softer suspension might be ideal, depending on the car, going to a higher spring rate (natural frequency) might allow you to lower the car further before you have issues with the tire running into things. Ultimately, it's the tire here driving this as well because if you are taking this approach, you have also likely tried to stuff as much tire as physically possible under the car. You can only do so much within the rule set to fit a wide tire on a production based car, so often upping the spring rate lets you get away with a little extra meat under the car without having to raise it up.

I'm also not sure why you say a lower car ends up with all the weight on the outside 2 tires when that is also true with a higher car. At the theoretical limit, all of the weight is on the outside 2 tires due to the center of gravity being above the roll center. For a production based car, that's the reality, the center of gravity will (and should be) above the roll center. The difference between a lower car and a higher car here though is the lateral load that is required to put all that weight on the outside tires. A lower car, at the same lateral acceleration rate will actually distribute the weight more evenly and will not transfer all weight to the outside tires until a higher lateral acceleration rate.

Bump travel is often where an overly lowered car really has problems. The car might only have 1 to 1-1/2” of bump travel before slamming into a hard suspension travel limit. In this case, absolutely, the car is too low. But the alternative here is to shorten the shock bodies so you get that travel you need. Then after that, you likely run into the tire running into things. It’s one thing after another...

However, I will take a lower stiffer car that has adequate bump travel and poor roll center height (but corrected bumpsteer) over a higher car with an “ideal” roll center height. Getting that adequate bump travel is the key though and where it becomes difficult on a production car. Thus, there are definitely limits to what works. It is just my opinion though that roll center height should not be the number 1 concern here.
1. Adequate bump travel
2. Proper steering geometry (bumpsteer)
3. Maximize tire grip
4. Lower Center of Gravity
5. Proper roll center and suspension geometry


Wheel width and stretch is all about the tire used. Some tires simply do better with some stretch. The R-S3 for example has a soft side wall that kills steering feel. Put it on a wide wheel (top of the recommended wheel width or just slightly more) and the tire actually gets to be very responsive without having to raise tire pressure way up. Other tires however perform better on a wheel that sits in the middle of the recommended range. It all depends on the tire.

As for beating guys on overly lowered cars, the reality is, it's probably driver ability more then anything else. I see guys with stock EVOs nearly taking FTD against national champions at local autox events. A decent car (in autox) can do very well when put in the hands of a great driver against even a great car in the hands of another good driver. The car often in this case is a secondary item in determining who wins.

Last edited by 03whitegsr; 11-19-2013 at 11:00 PM.
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Old 11-19-2013, 06:50 PM   #4
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Clarification may be needed here

My post was aimed at those that simply do not know better or just do not care but we all pay for this one way or another.

I have a special thought for the stance car with his buddy and their girlfriends running around at speed not even realizing the added weigh effect, which is huge.

Unfortunately few understand the basic concepts, if we start talking about motion ratios, frequency, actual aerodynamics, we are getting way over most everyone's heads.

We also have center of gravity, weight distribution, easier to understand but seldom considered.

I love lowered cars so make them as low as I can go and still have proper geometry which just part of the equation of setting up a care properly.

Simple physics, go past a certain point the roll center changes dramatically and causes far to much weight transfer to the outside tires, it does so very rapidly, easily, etc...and thus less overall grip.

I have read all the great books and tested this personally and found with just a tad more height I could make a huge improvement, when going by real measurements of all the critical issues.

A car to low for proper geometry will loose grip.

Springs to stiff or to soft will loose grip unless on a glass smooth surface.

Dampers to stiff or to soft can be an issue as well. Sway bars are the last thing to use for tuning, to much, to little, loose grip.

Skinny tires overly stretched, loose grip compared to more contact patch and easily ripped off the rim, really loosing grip.

Too much power, loose grip as well.

Do all the above and then add a bunch of power, a disaster waiting to happen.

The main focus of my comments are the "stance" cars with little regard for anything but looks. If you want to be fast you put looks where it belongs, lower in priority, you can have both but not to the extreme I often see.

Build a car to maximize the handling for all the uses it will need it for and then go have some fun, it that means creeping along over every little bump, driveway, etc and parking it to be seen, cool, just do not pretend you are fast and drive it like that and end up hurting others doing so.

I have seen far more issues with stance car drivers than any others and we all pay for their behavior in higher insurance rates, costlier tickets, more rules(more limitations, etc)

If you really want to have it all then then learn how to setup a car properly, make it adjustable easily, set it for the type of events you are going to do and then drive it accordingly, I have done that for decades, still do

Rick

Last edited by raamaudio; 11-19-2013 at 06:57 PM.
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Old 11-19-2013, 07:16 PM   #5
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You guys are blowing my mind. I understand most of it except for the stuff about the weight on the two wheels and the roll center stuff.
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Old 11-19-2013, 08:12 PM   #6
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From another post, not the last member:

A bit of stretch is almost always a good thing, especially on soft sidewall tires, I agree completely. The exceptions are when tires are designed to be on a narrow rim due to some class rules like the cantilever Hoosiers I had on a 7" wide rim, the tread was over 9" wide but worked very well.

-----------------------

The roll center is a bit hard to express but easy to see when drawn out, it is simple a lever.

The line between the inner and outer points of the suspension needs to aim up towards the center of the car, when lowered it aims down. When you take that combined with the center of gravity there is a large leverage force placed upon the outside tires transferring nearly all the cars weight to them.

With most of the weight transferred, by leverage, to those two tires you then have basically just two tires doing nearly all the work.

Then add in bumps which cause the tires to loose contact to a degree, can be quite significant, you have very little left to keep the car on the road.

-------------------------

On another note, bump steer. That is an effect caused by lowering the car but not the steering linkage accordingly where it attaches to the steering knuckle. Now when you hit a bump, more so when turning, it will change the direction of the tire a bit, not what you want to have happen under a high g load, one side of the car can be steering differently than the other side(some of that is designed into the suspension, akerman effect but that is another subject as well)

-------------------------

So, compounding unstable steering, shifting the load to the outside tires, smaller than optimal tires, less than ideal suspension travel so hitting the bump stops at times, you create a very unstable car at speed in corners.

-------------------------

The is one simple word that best covers all of this and in fact everything in life.

Balance, the more in balance, the better everything is.

--------------------------

When I setup a care I take the utmost care to balance out everything possible to the best overall effect and then add in power in a balance way to compliment the car, not overpower it.

Making a car work on the street and track and be livable takes some effort but it can be quite rewarding, like passing a full on STI race car at the local road race track in a daily driver Forester XT that is on street tires, I really did that

Why? Because the car was balanced(and had $30k in mods that I did to it yet it looked nearly stock and got 28MPG)
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Old 11-19-2013, 11:25 PM   #7
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The suspension has a certain amount of "bumpsteer" built into it from the factory. This is done so the tire toes in slightly as it travels away from the normal ride height. Think of it like an upside down U on how it behaves at stock height. Compression or extension from stock height and the tire toes in. At stock ride heights, the geometry is centered up so the bumpsteer is minimal under most circumstances (your on top of the upside down U).

Once you lower the car though, you generally end up deeper into the curve, you are now sitting on the side of the U. Instead of only a minor amount of bumpsteer around ride height, it can be a decent amount. Basic body roll motion now means it steers the wheels differently as one side is in compression and the other in extension.

This problem is compounded when adding camber and caster as now the outer/upper pivot points are in different points than originally intended so now the pivot points for the steering arm are no longer in the right positions at the ride height.

As far as roll center height, it doesn't change how much weight goes to which tires. That is dependent on track width, center of gravity height, and cornering force. Roll center does determine where the load goes int eh suspension components as well as jacking/anti-jacking forces. It has a ton to do with how the suspension moves (which controls contact patch) so it is important, but it doesn't control how much weight is on the tires.

I won't argue that ideal geometry wouldn't be great on a heavily lowered car. If we were designing a car from scratch, we could have better control over the geometry. Unfortunately, we have a strut/trailing arm suspension car and both of those suspension types suck for geometry. That hasn't stopped a LOT of fast BMWs over the years though. Even those heavily modified cars I bet still had less than ideal geometry despite the massive amounts of money poured into the programs. That's just the reality when dealing with production car based suspension systems.

Regarding the stance kids though...who cares if they figure this out? Let them crash their brains out. If they were interested in going fast, it would take them all of about 10 seconds to figure out they are doing it wrong. Stanced or not, it's been my experience that those type of kids manage to be stupid and crash the car regardless of the tires being stretched or the car being too low.

Last edited by 03whitegsr; 11-19-2013 at 11:37 PM.
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Old 11-19-2013, 11:55 PM   #8
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I guess we differ a bit on the importance of roll center effect. I am not an engineer, I just have read most all the books written by top race engineers and they always place a lot of emphasis on it and I have tested it and found it did have a very big change on lap times. The books I have read all talked about the leverage effect of loading the outside tires with nearly all the weight.

It is only a part of the equation of course, they are all important and I do agree, starting from scratch, well, we would most all be running double A arms if we had our choice instead of making a lower cost, easier packaged system work like struts, which can do quite well, look at Porsche!

I seldom see mention of roll couple outside of text books though, another important but lesser issue than some, in some ways that is.

I am hoping at least some of the stance crowd sees this type of debate and reconsiders what they are really doing, just following the crowd. It might be a smaller crowd than what others do but it is still a crowd and ran by marketeers for profit, not to enlighten anybody

Same as any fad, it may start with some individual doing something different than the rest but soon it becomes a fad for profit. I have always tried to live my life doing my own thing as much as I can, not led around be a nose ring like most tend to even if they think they are being different.

As mentioned it is the certain type of vehicle owner and certainly not all stance enthusiasts but many, that cause us all trouble in numerous ways, it is not just about them, it is about us. Before stance, just overly boosted Civics, etc....I have seen massily powered cars without stance but no suspension, brake, safety, etc upgrades and seen some kill people and have been hassled by the police just because I had a modified car.....so it does effect me and others.
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Old 11-20-2013, 06:36 AM   #9
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Default Perfromance, real, not so real, balance in the middle?

So what wheels are all the weight on? The outsides of all four? Or do you mean the drivers side wheels? This is a very cool thread. I'm learning a lot of stuff.

Edit: oh I see what you mean now. In cornering you basically throw the load either which way on the two outside tires. Leaving the other ones almost useless. Interesting. I'm not saying I'm one of the typical stance guys. I'm not a mindless idiot. I do enjoy the way the cars look though. Wouldn't ever do it to mine because I enjoy driving and having fun. With those you practically have to always creep around. Now I can't stand the camber thing though. A little bit can look nice but they get ridiculous with it sometimes. Anyway I like this topic! Very good info here. Before this I knew little about suspension setups. Now I know a bit more!

Last edited by Breticus; 11-20-2013 at 06:46 AM.
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Old 11-20-2013, 04:41 PM   #10
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With regards to the 318ti specifically, the roll center height (relative to the chassis anyway) doesn't change as you lower the car in the rear. It's not until you start changing the inside pivot to adjust camber that it starts to change roll center.

The biggest problem with lowering the trailing arm rear is that you end up DEEP into the toe curve. I would bet good money that the competition 323ti used in the 90s likely went to a shallower trailing arm angle specifically to deal with the toe gain, and not camber gain issues.

Up front, take a look at the ride height of my car. The front control arm pivots are flat with the ground at that height. The car can be lowered a decent amount before the roll center goes under ground.

That said, I don't think the actual position of the roll center is nearly as critical as how it moves around. When the instant center starts going out to infinity or the roll center starts crossing back and forth across ground level, that I feel is when the real issues come up.

Also, we are talking static roll center here where the roll center migration is more important anyway. What's the roll center doing as the suspension articulates non-symetrically as the car rolls under corner loads?

But in reality, I doubt any race team cares about roll center in modern motorsports. A forced based model and a 7 post shaker rig is the answer. Not static roll center diagrams.

Last edited by 03whitegsr; 11-20-2013 at 04:44 PM.
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Old 11-20-2013, 06:01 PM   #11
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I'm going to be going full coilovers all around does changing the rears to true coilovers change anything?
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Old 11-20-2013, 09:33 PM   #12
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It can improve the amount of droop travel you can have when using stiff springs as you can use helper springs.

Pretty sure going to a full coilover in the rear often leads to cracked upper shock mounts though as the shock tower wasn't really meant to carry the weight of the car, just the loads seen by the damper. Not sure how well the shock mount on the trailing arm really holds up either as it was also designed to only carry damper loads and the mount is only a 12mm bolt in single shear.

Also, if you are trying to fit a lot of tire, the larger OD of the coilover might be a problem since it reduces tire clearance.
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Old 11-20-2013, 09:45 PM   #13
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I see some talk about natural frequency; is that the same as wheel rates that I also see when talking about suspension tuning?

Does anybody have setups worked up for specific applications on the Ti?

For example, I want to autocross. Is there a recommended lowering, spring rate and anti-roll bar diameter to keep the natural frequency at 2.0 Hz?
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Old 11-20-2013, 10:01 PM   #14
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I was considering rear coilovers as well and the first thing I did was start designing a brace to fortify the shock towers, I would not do it otherwise.

Since I decided to not go real low and also have 700lb springs to help with hauling two big dogs and stuff for sightseeing, haul the groceries, quite a bit of weight all the time and they would be good for the track I could live without coilovers.

I have had many sets including a custom $8500 set of Ohlins, $7000 Motons, etc...I am a big fan of coilovers but sometimes they are not the best option for our needs.

---------------

Every car is setup differently, tire and wheels different weight, how you drive, many many factors there is no one size fits all when it comes to this stuff. Best bet is research those that have used this particular car in a particular class and won championships then work from there.

Or call somebody like Ground Control and see what they recommend, I went to them because they know what they are doing, know BMWS, and have a great setup for a reasonable cost.

Then I can tweak it if needed.

----------------

Sticky tires are the biggest handling gain you can ever have, then making the car and the driver use them right comes up next.

Seat time, seat time, seat time, will make you faster if you do it right as well, get some instruction unless you are fast already but most are no where nearly as fast as they think they are

----------------

All this upper end tech talk is fun but most is not of real use unless going to extreme levels and have the seat time and talent to really dial it in no matter how well you can do the math.

----------------

A BMW is a magical car to start with, not many things needed to make them incredible and well beyond what can be imagined by most, a nice simple setup will make the car do wonders as stock they are pretty amazing.
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Old 11-20-2013, 11:01 PM   #15
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I was going to buy the kit from GAZ along with their rear shock mounts designed specifically for the true coilover. My friend and I are also making front and rear strut braces out if quarter inch steel. I wouldn't think they would break. D: you make a good point about the bottom end though. I think it'll be okay though. They change the spring rates lower as well when going to a true rear coilover.
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