I guess its time I chime in here and clear up this with a little fact that is missing......."TIME"

Thats right ..Time. The time that flex takes to absorb and redistribute. The "absorbstion" and the "redistribution" are not 50/50 either and can vary greatly with vibration damper bleeding. Kind of like you would see ripples in a swimming pool disipate- some bounce off a wall and rehit themselves canceling while others extend acorss other directions.

Back to the point? While all this is going on (time) we have no idea how to gauge the spring rate of the chassis flex and how it is absorbed and then reapplied. It is no zero loss, because some of it deflects laterally until it demenishes.

I will give LS SIX the award for this comment-"You'll never be able to tune the suspension accurately when the platform is essentialy a giant variable rate spring with no dampener. "
So with that, lets go to the question of "How do we measure this flex and if it helps with SFC's".....

...one SIMPLE answer. You add SFC's to any third gen and the suspension balance will make the car go loose. That alone shows how much flex based on how loose it goes and how much adjustment must then be made to tighten it back up to balanced state.

How on gods earth are you going to predict chassis fatigue that is undampered and constantly changing. Chassis metals are not made of the same properties as spring coil metal. It does not have the recoil and damper properties to return like spring material does. It is not predictable in time sequence nor in virbration bleedoff qualities and will always cause a flexing chassis to yeild unpredictabilty in flex and recoil squence as opposed to a firm flex free chassis that yeilds predictablitiy and articulation through proper dampered spring fequency suspension geometry.

Now Lastly- back to the reply I quoted above- the loss of forward motion. There is a great affect on forward motion when it deals with the load placedd on the tire sidewalls when the chassis weight hits them and how hard and how long..... and how much bounce and recoil and frequency...again "time".

Dean

 

A properly installed cage no matter how many points may just save your life but they dont add any rigidity at all unless specificaly designed to do so, wana see fem printouts showing just how flexable a nascar cage is? Look it up it's amazing and they have many more tie in points than any streetable cage will.

I had an answer to this but vetruck got it all then some



As driver the result was a more stable and responsive vehicle that he is now better able to drive near the limit, thats all the PROOF anyone should need.

Yes he THINKS it handles better and that reflects drivers confidence and generaly results in a faster car. Some drivers may be willing to keep going long after the chassis has ceased to give reliable feed back to the driver and no longer responds to a given input with consistant action but thats certainly not the way to go fast, especialy if you want wo win steadily.

 

Dean,

I know that you run SFC's on your Camaro (though it's hardly a typical car). That said, let's cut to the chase. Would you, being a suspensionist and thirdgen guy, recommend SFC's as generally a good idea or not for thirdgen cars?

JamesC

 

My car has no roll bar/cage in it. It's been deep into the 10's with 1.51 60ft's... No frame connectors and It's also a t-top car. I've been doing this for about 5 years now and have absolutely no stress cracks any where on the car.

I'm not saying subframes are a bad idea but for people to say you "need" them or else the car will fall apart I can say from personal experience that they are incorrect.

 

Yes, A very good idea.

1st modification recommendation good? probably not, but one of the top 5 in my modification list to any third gen.

Best picks in modifications that are bang for the buck-

1) tires
2) shocks and struts
3) Strut mounts- these wil make the struts damper better as well as add to steering response and perciseness.
4)wonderbar- preventative chassis support for weak steering box area
5) SFC's to reduce chassis metal fatigue. Every year and every mile that goes by, the chassis suffers more and more from chassis metal fatigue. The car will eventually strat to fall apart, nuts and bolts rattle loose, it just looses that new car feel more and more as the years go by.

I personally think it would be a great test if people could compare two perfectly maintained New vehicles identiacal other than the fact one had all brand new stock componants on a 20 year old unibody chassis that has suffered from 200,000 miles of road fatigue. I can gaurantee (without facts though- just from the gut and experience)that people here would be amazed at the difference in new car feel between the two chassis's.

I see the subject of top fuel drag cars came up earlier in this post. To elaborate a little more on what I do know about them, they do have a usage life until the teams dub the chasiss' to have too much fatigue to be any good any more. Yes, the top fuel chassis does flex the first time they are used, but this gets worse with each run until the toss it and go to the next new chassis. Teams with years of history and multiple cars like John Force (Who my kid brother went to HS with one of the daughters out here in Yorba Linda) keeps extensive charts on chassis useage. They have it down to a science when a chassis is done by- after a certain amount of runs they deem it unpredictable and useless. Force keeps all of his old bodies, but trashes the chassis. you should see the collection of bodies he keeps on display at his racing facility. I used to be around Robert Hieght every year when I used to run that car show I did years back called Thunderfest in Covina California. Dave "TheVoice" McClelland would host announce it and Height would do guest appearances. I had the rare opportunity to sit in his top fuel funnycar once when they fired it for the crowd. Talk about scaring the crap out of me just sitting in the cockpit starring at that that beast motor rumbling the entire chassis apart along with my eyeballs 3 feet in front of me--holly crap- You would be nuts to drive one. Now with that said I have been 8.48 @ 178mph in a 8.90 car with throttlestop issues...whoops, but the 100ft mark full throttle blast was much hader than the line launch when that throotle stop kicks in. ..and this is peanuts to a top fuel funnycar.

Dean

ps- I am just a no name guy that has had a very blessed life in who I have met and what opportunities I have been allowed to do through my personality and knowledge of cars. It is merely a hobby though. People often ask me why I never did anything professional in the car industry, I just was never around that end of the business, only as part of the hobbyist. Jus tthe time I was gearing towards a little business side of things in life, my divorce happened- maybe someday..time will tell.

 

Not to pick at your list Dean, its great, but pricy upfront.

1) Good tires cost alot and thats not just for the tire, that most likely includes a new set of wheels. Now albeit, my definition of a good tire is somewhat stringent. I wouldn't want anything less than a Goodyear Eagle F1 All Season on my car @ $220 a tire and Italian made Pirelli P-Zero Summer only tires being near the top of my list @ $350 a tire. Now either of those tires would require new wheels and the only good option Ive found that is reasonable are the SLP ZR1 17x8 wheels at $600 for a set. Because I plan on driving my car in the winter, I want the Goodyears, but I don't have $2000 for new tires and wheels atm.

2) Same goes for shocks & struts. The Bilsteins I'm looking at are $300 a strut in the front and $100 a shock in the rear. And while you're at it, change the springs. I'm looking at the stock replacement Moogs as a budget item, but Eicbachs would be one of the better options.

3) Strut mounts are a must, no questions asked. J&M or UMI mounts seem to be the best for our cars, but they are $220 for either set.

Otherwise, the rest is cheap. Although I would recommend SFC's before everything else. That way you aren't tempted to drive the car hard and further exacerbate problems.

 

OK then- let me make a comparison point:
I will spend all $220 a tire on 4 tries on my factory 8x16 wheels. Thats your $220 per tire (which I agree is a tire of great caliber for street use) so this nets $880.

Now someone else buys some crappy tires at $100 each and spends the other $440 on crappy semi performance shocks (or whatever else you decide)

i will bet big money that my car with only the great tires and nothing ewlse will beat your SAME car with crap tires and so-so shocks with the same $880 to spend.
Although I have body roll all over the place, I am geting throttle traction, brakng traction and lateral traction that exceeds the money you spent on average shocks and crappy tires.

Now, so goes the same for the next $800 I buy Koni Yellows. You spend $1680 on ANYTHING else you like, any combination of things... anything. Just match me dollar for dollar on the SAME CAR and I guarantee my choice of great tires and great shocks will beat any other parts combinations you can come up with.

Do not skimp on tires and shocks. People just do not like them because they are not so much of a purchase "looks wise" to make the undercartraige look col like all those so called flashy red parts under the car [Did I mention I hate red parts..., they only impress people that do not know what they are looking at. ]

Dean

 

Let me make a "REAL IMPORTANT" point here-

After you buy tires, the next purchases all which add up to alot more that what those tires cost when you start figuring weightloss, soild swivel bushings, etc etc on all those tubular poarts that really add up, they are all in the effort to make a tire contact patch to the ground of an average 75% to gain to an average of 95% all the time.

I would rather take 75% of a great tire compound contact patch, than 80-85% of a crappy tire compound to start with.

I hope this makes sense, becasue it is probably the most important thing I have ever written on these boards.

Dean
ps- that and don't get married!

The main focus on every single suspension modification you make is to try and maintain equal chassis load on all four tires evenly. Lets say a car weights 2000 lbs, divide that by 4 and you have 500 lbs on each tire. Lets say those tires at 25 psi have a contact patch of 6 sq inches. stagnant. Now you hit the brakes from 80mph and enter a corner 3 seconds later at 40mph with the *** up in the air turning right, the weight distribution is now loading the tires 600LF 700RF 300LR 400RR. The LR is domed contact patch of 4sq inches, the outside front RF is overweighted and mashed with a squashed contact patch of 8inches exceeding it design.

remedy? controll the chassis weight better- quick fix? increase front tire pressure to reduce tire quash at a cost of straght line steady state traction which is not a big problem untill you are coming off a corner exit under thottle- the higher psi smaller contact patch willnot grip as well as the lower psi larger patch. There are give and takes. Suspension mods help reduce these give and takes and make a chassis weighting more stable at all times and thus keeping the tire contact patches more equal ly sized and weighted. You never want all the car's weight on 3 tires, 3 tires will over heat 2000lbs faster than 4 tires will overheat that same 2000lbs.

Think of every suspension mod as a aid to tire contact patch at all times. Its all about the tires.

 

Awesome thread! Super informative

 

I 100% agree with what you said Dean. It definitely is cheaper in the long run to spend your money the right way the first time around.

 

If you take nothing else from this post, at least take that advice.

 

Chris, I would be curious to hear any critisizm from you about my thoughts on chassis metal and its dispation of absorbed flex and the "time" it takes to do that in variables. Do you feel what I wrote is accurate? I try not to claim to be any expert where I am not, it is just theory on my part but I think what I say has validity. I feel the chassis can and generally deos bleed off energy different than it is absorbed.. unlike a coil spring made of good quality memory metal designed for repeated cycling that is pretty much balanced in coil and recoil time when undampered by the shock.

 

Well, I was hoping Norm would reply because he really has a whole lot more experience and background with structural than I do but I'll try to address what I can and maybe he'll chime in and tell me I'm wrong or add info.

The structure isnt going to absorb anything, ideally. If it is absorbing energy, its getting permanent deformation. If you refer to Newton, the action of something like a bump is going to have an equal reaction. I believe its entirely possible for the forces transmitted into the body to do really weird things though, because the body itself is not a constant of any sort like a spring or a shock would be. You are absolutely accurate about that. Often times when analyzing a structure you have a flexible component, and then something that is considered completely inflexible (not completely true, but anyway) and that is really what you want with a car. You want the car to be 'inflexible' for all intents and purposes, so that you can accurately determine what its reaction is going to be via the springs and shocks, and maybe tires and air pressures. However this is not the case with thirdgens, the body is quite flexible and as I've stated a million times there is evidence of this in the body of the cars. They show all sorts of damage over time, and its not always (or maybe ever) the result of something like a poor weld. That may in fact be an issue, but there are larger things going on. You have to keep in mind it was never GM's intent to make the body structure as stiff and as sound as possible, they were more concerned with stamping panels and spot welding them together and getting the cars assembled and sold. The design priority of a solid structure was very low on the list. Maybe in 91 they started to show SOME concern when they started using structural glue for panels. Today that is not the case, and this should be quite apparent if you were to go drive a new Camaro. Having driven thirdgens new on multiple occasions (and I mean NEW, 4-6 mile cars) the new Camaro is worlds apart in body stiffness.

I'm certain with enough time, money, and stupidity you could in fact "accurately" model the body of a thirdgen and determine what sort of spring and damper it is, but its not something you can fix or change easily or with any consistency. If you do something to make a change to that spring, then you get to spend more time, money, and stupidity to remodel the entire chassis. I cant, at the moment, think of anything that would be more pointless in life than to try to model the chassis of these cars. The smartest thing to do would be to do what you can, within the rules you may be bound by (SCCA ESP comes to mind) and within reason, to stiffen up the structure and lessen the basically unknown response its going to have when twisted and bent. Shocks and springs are essentially known values that are easily changed and you can easily gauge, and the body of these cars is really a complete unknown that is not easily changed (not to what you may want) and is going to transmit forces as it sees fit. In a dynamic situation where tires are being loaded differently, at different times... your guess is as good as mine or anyone elses what the body is going to do with those forces.

Now, I will again go back to a story I once told and pretty sure I mentioned above (and I'm pretty sure I did not mention names either) about what the FACTORY did to some cars used in competition, namely road course cars. They ventured over to ASC and took some of the convertible SFC's and attached them to coupes to give them what really was an unfair edge. They riveted them to the body, undercoated them, and called them "factory installed" to play within the rules. In reality, actually they were even though no real person could get a car like that. And this is not some hearsay nonsense, I personally know and talked to the guy that worked at the plant that did this to some cars. To me, that says an awful lot if the factory and the race teams involved were interested in and spent the time and possible rule infractions to install the somewhat flimsy vert SFC's to coupes... and that is totally ignoring my own personal opinion and experience with how flimsy these cars are. They're not as bad as a 66 Mustang, but they are no prize either. Maybe its not a "necessary" item, but its going to help irregardless of what anyone says. The line in the sand is drawn between where it becomes more useful than the cost and weight of installing them and that really is up to the person who owns the car to determine. It will help extend the life of the body, and will make it stiffer. It may make for a faster car both in a straight line and in curves just because its more consistent and predictable, for a driver that can use that extra bit of ability because they can push their car to its limit. The rest of us that are not in that league, the added stiffness and less squeaks and rattles is worth the price IMO.

 

I think some very smart people here have gone a bit off on a tangent lol, first of all if the body is being flexed it is considered work and is consumming energy. Even when the chassis recovers you do not get 100% of the energy back. A percentage is lost in the proccess of transferrance as it always is.

Second the issue isnt so much the loss of energy through chassis flex it's the loss of control due to chassis flex. Just like having LCA bushings that are too soft or worn excess chassis flex allows movement at the wheels that as has been said already cant be predicted. Direction of energy and control of torque reaction during the first moments of launce are critical to getting consistant low ET's. It dosnt matter if you get all the energy the chassis absorbs back down the track because un like what has been supposed here it dose not equal forward motion.

By the time the chassis relaxes and relaeses the energy it stored as a big tortion spring during launch it has already cost you a strong hole shot and the way in wich the energy is then released dose nothing to help the car accelerate.

 

I dont think the loss you are referring to is of any significant amount. If it was, it would be like bending a paper clip (not just deformation but heat as well) and the car would break in two.

Edit:
Reviewing an old book of mine that apparently I've forgotten most of, and in doing that:
I'm going to disagree with that statement, entirely. As I suspected, and from what I can remember in reading this way too complicated nonsense in the book, is that if the deformation is in the elastic range then the forces are transmitted back to wherever that member is connected. It is not until the plastic deformation area, where the displacement becomes permanent (that would be a crack in your sheetmetal) that there is any loss in the energy cycle. I guess the simplest way to explain that is the work you're referring to as being done is not being absorbed, it is being transmitted via internal stress and as long as the material is within its strength range and does not yield, it transmits this force either back or to a fixed location and resumes its original shape. If the work done becomes a loss, the work had to accomplish something to dissipate that energy. In the case of only the steel of the body, that would be deformation or a break.

The "time" factor that Dean referred to above isnt really incorrect from what I recall. This is getting way too in depth even for me (especially since I apparently forgot a lot... thankfully), but with the dynamic motion of the body (you have 4 points of contact (tires) for movement, all can and probably should be assumed different and random) you have harmonics and vibration entering the realm and these factors could alter the time it takes for the reaction forces at each of the 4 locations to respond to the action (bump) they were subjected to originally. I'm seeing that and vaguely remembering that in studying the response spectra charts for earthquake motion. We (our 3 student grad class) also actually modeled a car to calculate the response over time (using methods we learned from structures subject to earthquakes) from a non-randomly shaped 'road' with known values for damping (shocks) and springs. So not a completely foreign concept, but its been put in the memory banks and hopefully for my sake to never return anytime soon.

 

Checking in on vacation.

Long thread, still not one shred of data posted.

I'm kind of surprised that otherwise smart people believe that just driving two different vehicles (i.e. a new camaro vs a thirdgen) can give a human being the information he needs to isolate one thing (such as a stiff chassis) as the reason the car feels different. Never mind the myriad of things in the long chain of mechanical parts that ultimately reach your feet, hands, and behind. From the steering wheel, seat, seat mounting, bushings, suspension tuning, NVH... if it were as easy to isolate things by just driving the car, OEMs and race teams wouldn't spend so much time and money on data aquisition.

Madmax, when you quantify something you determine, indicate, or express the quantity of something. That is what they were trying to do in that article with the mustang. In this case, the decrease in chassis flex. So I'm quite happy with my choice of words.
You could quantify the change in performance by driving it but it would still involve trying to precisely measure the changes you've made.

As far as top fuel dragsters go, they purposely build their chassis to flex to go faster. You can look around online and find images of these cars bowing upward on a pass. If they were built to be completely rigid they would have a hell of a time hooking up. I suppose in an engineers world where there aren't as many variables as reality, you could say that a completely stiff chassis would be faster since when you bend something you are generating heat and that heat is lost as energy regardless of whether or not the metal returns to its original shape.
In the real world though there are so many other factors to consider that looking at that is like trying to figure out if the car is faster after you vacuum out the interior.

Anyway, at the end of the day, still no one has quantified any difference with any of the SFCs in a static type of test or road holding differences. Some people have attempted to qualify differences with SOTP observations but that's not hard data unless you have numbers. I don't doubt the chassis may be stiffer but that doesn't mean it will be faster. I point to the top fuel example and to racing Karts too. A completely stiff go kart would suck.

 

You havent posted any data either, other than garbage collected irresponsibly, so I am not real sure what your argument to the contrary is other than a personal opinion with zero background in structural or dynamics.

A stiff chassis does not resonate, vibrate steering columns, dashes, and give awful feedback through the steering wheel. Tell you what, you want some evidence? Roll your window down, and stick your finger between the door and the door jamb on the back side of the door near the handle. Then go drive it up that road of yours, tell me how your finger feels afterwards.

Post proof.

As far as data, look harder. A quick search I found the following, not a thirdgen again of course but anyway
http://www.pro-touring.com/forum/sho...d.php?p=610601 (take note of #1 and #5 on the list, and think about why)
http://www.stangnet.com/mustang-foru...7-coupe-4.html

As with anything else concerning structural items, how and where they mount, and how and where you conduct your testing is critical. Seems that someone found out how much difference the location of the load matters, and how it shows where areas are weaker than others.

 

Let me list some simple facts off of what hgas been said.

Stiff go kart chassis does not have suspension, thuis the wheel contact patches are directly tied into the anlge of the chassis in dynamic motion. Go karts depend of caster to lift the inside rear wheels in order for the kart to rotate. A super stiff go kart chassis is ideal on a perfectly smooth surface. A little soft one is good for a tad bit of flex helping keep the three wheels on the ground (yes I said 3 wheels) They turn on the tow fronts and the outside rear. Too much flex and the cart would nopt lift pressure off the insisde rear and would be a bitch ro try and rotate.

I sated a fact about top fuel dragsters. I have had first hand conversations with several teams about this (I am fortunate enough to hang out in the private sponsor suites at the Winter Nationals- I have a great shot of Michael Anthony and I last year- you know, the guy from Van Halen that now owns Bonspeed) ANyways, hanging out up there I get to chat to various crew members and the occational driver also. They do IN FACT change the chassis' after a certsin amount of runs because their aquisition shows the frames begin to flex excessively more than they can allow for consistancy. Some teams are going through two chassis a season if they are never wrecked.

Along with my famous quote, "Even a square block of titanium will bend ....if Mars lands on it."
Let me equate, "Any chassis will flex when you torque 8000+ HP to it." Their is the old thing call power to weight ratio. As long as they are keeping the Driver cockpit, Motor, and rear drivetrain assembly rigid,(where all the weight lyes) the front of the long nose of the car can pretty much flop where it wants to because it really does not have a affect on the rear wheel traction when it is off the ground. All they are tryiong to do is have it long enough up front to reatin nose leverage weight no tto lift too much to loose steering, but even steering is questionable.......I WOULD NOT DRIVE ONE OF THOSE THINGS---- You aim it, shoot and pray for dear life! ...And hope to god nothing breaks 'cause when it does you die.

 

This was posted on this site before for a different discussion, but what I'd like to point out is the stress diagram on the page, its the colored chassis drawings a little ways down.
http://www.bmeltd.com/Dragster/tubulartales.htm

Note the areas in the back that are all blue. Without even bothering to explain what all the colors generally relate to, the stress is noted by color. If its all blue, where are the weak areas that are designed to flex? They just are not there. Thats all the evidence you should need that any story about being designed to flex is complete nonsense.

 

.

 

Oh sure, anyone that learned from a book or a school or someone with a lot of expertise must be stupid. Great counterpoint.

Find anything to back up your previous statements yet? Without facts, its just an opinion. Everyone has one of those.

 

Well if you want to get personal about "credentials", I would say you really don't have any either. Having degree in civil engineering degree doesn't qualify you an an expert on race car chassis construction. I can call up a friend with a degree in mechanical engineering and he really is no more qualified either. The only thing I see is that a degree is something people hide behind in the absence of facts. If some type of formal schooling were a requirement to know anything then some of the greatest inventions in the history of mankind would have never been invented. In that regard I would say it's a liability since people who are formally schooled are very much "inside the box" thinkers.
Me? I'm just an aircraft mechanic and I see the effects of flex every day I work when I repair stress cracks in aircraft. I have repaired probably over a thousand stress cracks and I have developed a pretty good idea of where stress concentrations are in a structure since I don't do so bad in finding these things during inspections.

Well of infinite stiffness sure but I'd like to hear of a chassis with infinite stiffness.

So you are saying the mounting points on all these components are all of infinite stiffness? You have accounted for their construction and have determined that the components themselves are not at fault?

What would that prove? you call that data? Is that the kind of data that is considered valid for a masters thesis? I hope not.

I'm fully aware that the chassis has flex, do you know if the car will be faster with that flex or not? You don't. Not until you test it. And when you do, maybe it might be faster or slower depending on the test conditions. So you better test under all conditions.


http://web-iml.jou.ufl.edu/projects/...k/chassis.html

"The flex of the chassis allows some of the energy of the launch to be absorbed which helps the dragster gain traction"


took about 5 secs to find those two. Better email that team and that website and tell them they are headed for disaster

Thanks for the links, that's more confirmatory evidence for what I suspected (and posted earlier); that the a and B pillar + roof structure + tie in to the chassis are where the most bang for the buck is

 

Well, I don't have a master's degree in engineering or anything else... But I've been playing this Hot Rod and race car game for a lot of years. I do know that a 3rd Gen with frame connectors, improved suspension and bushings, a 6 point or better roll bar (or complete cage),solid mounted engine and transmission, and a few other parts and pieces will be faster, more predictable, and more consistent then a stock 3rd Gen with equal horsepower and torque....

Facts and data??? I don't know of many people with the time, money, or facilty to acquire all this data. Common sense and years of experience will often be as good or better then a head crammed full of book smarts and data. A well balanced combination of book smarts and motorsports experience is, IMO, the ideal combination!!!!

 

Since this thread got so off track from the original posters question, and has been answered in one reply or another, Im putting this to rest.