Application specific suspension.....

[SN65]

OK... I typically keep to my own posts, my own topics, my own threads. Something I have been reprimanded for.

That being the case, I have been following other threads and trying to add my two cents when I think I can be of help.

In doing so, I have noticed one thing. People don't seem to ask many questions about the proposed vehicles application before they comment on a thread.

Maybe I am missing something here. Maybe it is generally understood that if they are posting on this site that the car is intended for road racing or a road racing type application.

Is this true?

Also, even if this is true, I would think that there should be more questions asked than comments made.

For example. there is another thread in this section asking about the best suspension, but no one asked any questions about the fellows car. Maybe everyone knows this guy and his car and his intended use, but I had no clue.

Is a watts link always better than a panhard bar? Maybe yes, maybe no. Depends on the application.

Shouldn't we find out at least some basic information before we make any recommendations?

[parsonsj]

Bob,

You're right. Intended application, budget, fab skills, toolset, etc. are all relevant questions that apply to the basic (and oft-repeated) "What suspension should I use" question.

In general, though, most assume that members who post here are looking for insight and help for road-racing, autoX, and street performance. This is Pro-Touring.com, so it's a reasonable assumption. It's an exception when someone asks about drag racing suspensions, other than to ask how their ladder-bars will work on the street or some such.

jp

[SN65]

As I look through more and more posts I am finding that the more experianced person posts at least some data about his intent. It is the newcommer that askes questions witout at least some prelem explanation.

OBTW, congrats on SEMA. Is this going to be your first time displaying there? Your first time with MagnaFlow?

[Marcus SC&C]

Bob, John pretty much hit it on the head. The primary focus of this forums is to bring the performance of older muscle cars up to par with modern performance cars. Your SN65 project fits right in. The hardcore cars take things another step and are basically a cross between a modern road race car and a vintage musclecar. There are a lot of questions to be asked and it`s hard to cover all of the countless details in a discussions forum "Post It Note" format. You may notice I often tell folks to just call us if they want to so we can cover things in much more detail. That said forums like this one are still an invaluable resource and a great sounding board for ideas and combinations. Another useful tool in the box. Mark SC&C

[mpozzi]

I'll always ask about the intended use of the car in question unless it's specified in the thread . . .

Makes answering questions that much easier.

Cheers,
Mary Pozzi

[parsonsj]

As I look through more and more posts I am finding that the more experianced person posts at least some data about his intent. It is the newcommer that askes questions witout at least some prelem explanation.

That's a good insight. And it goes right along with maturity levels as people grow up.

OBTW, congrats on SEMA. Is this going to be your first time displaying there? Your first time with MagnaFlow?

Thanks! Yes, it will be my first time with SEMA. The folks at MagnaFlow are great to work with, and I'm really looking forward to the show.

jp

[ss dave]

Bob and jp I really appreciate your thoughts and comments in my thread. Bob was the first to question my set-up and goals and made some insightful suggestions: Take it slow, and change things one at a time, amoung other more specific suggestions. In the future when I post I'll be more specific about my app and goals, probably save alot of time! However I found that posting a general thread gets alot of different ideas and comments and allows me to pick up on things from many directions and philosphies. I've learned alot and its all good! Others will be asking these same questions in the furture and will benefit from these posts. I did a search and could not find exactly what I wanted, until the last couple days. It sure beats bugging people on the phone; and they reply because they're interested, have a good comment and the time. Thanks again for the insight, I'm still weighing options and the thread was PRICELESS!

[SN65]

Bob, John pretty much hit it on the head. The primary focus of this forums is to bring the performance of older muscle cars up to par with modern performance cars. Your SN65 project fits right in. The hardcore cars take things another step and are basically a cross between a modern road race car and a vintage musclecar. There are a lot of questions to be asked and it`s hard to cover all of the countless details in a discussions forum "Post It Note" format. You may notice I often tell folks to just call us if they want to so we can cover things in much more detail. That said forums like this one are still an invaluable resource and a great sounding board for ideas and combinations. Another useful tool in the box. Mark SC&C

Hi Mark,

Thanks for the kind words. The SN65 project is still rolling along, but, as many on this forum have pointed out, is old news. It is a shame that most people could not look past the factory apperance of the car and see the unique things we did to the unibody structure.

But that is going to be the drum I beat for a long time.

:bsjerk:

In order for all the cool suspension and engine packages to work properly, you need to look at the chassis or in most cases with 60/70 muscle cars, the unibody structure. If you do not invest some time and effort towards improving the overall structure first, all the fancy drivetrain and suspension components will not function to the level that they were designed.

[High Plains Mopars]

Very true, to make accurate recommendations, the specific intended purpose is very helpful. However, I also agree that the intent of the forums here are already fairly clear and we can make the assumption that improved performance is the goal of most questions.

I also see a vast majority of cars built this way are never intended to be a "maximum output" application, nor will they ever be driven in a manner where that level of performance is required. So long as they look better, perform better, and/or use the latest go fast tricks, the vast majority are satisfied. Maximized performance within the confines of a rule set usually isn't the goal here.

Honestly now, there is no road racing equivilent to bracket racing and scca rules are so restrictive that almost any pro-touring style car would be put in a class so high that it would be uncompetitive in most cases. So most "pro-touring" style mods are inteded to be primarily for driver pleasure. As such, fully maximizing the performance of most peieces is not always necessary for most drivers. They just need to be better than what they replace.

[Marcus SC&C]

Bob,a really well thought out and executed performance car is never old news,not in my book anyway.
You`re right the chassis itself is often overlooked. There has been some good discussion here on the topic though. Subframe connectors,firmer/solid body bushings/subframe bushings and cages are fairly frequent topics. Not too many people beefing up the unibody itself although that certainly has a lot of merit as well. I`ve done some of that on Mustangs,box Novas and Ramblers in the past myself with good results. Frankly most folks just don`t think about it much. Mark SC&C

[SN65]

Bob,a really well thought out and executed performance car is never old news,not in my book anyway.
You`re right the chassis itself is often overlooked. There has been some good discussion here on the topic though. Subframe connectors,firmer/solid body bushings/subframe bushings and cages are fairly frequent topics. Not too many people beefing up the unibody itself although that certainly has a lot of merit as well. I`ve done some of that on Mustangs,box Novas and Ramblers in the past myself with good results. Frankly most folks just don`t think about it much. Mark SC&C

Hi Mark,

Thanks for the kind words.

It is kind of sad that, as you say, "...most folks just don`t think about it much". Maybe it is because they don't realize just how weak the original unibody designs were/are. Maybe they think that updating the basic mechanical assemblies will be enough. Maybe they are scared to attempt any structural modifications. Maybe they just don't care....

I think that people are blinded by the fancy engine, brake and other mechanical assemblies that they are bolting onto their project car. It is fun shopping for the pretty wheels, etc. There is no glammer in chassis modifications. You can't see a chassis modification. You can't show it off to your freinds at the local cruise night.

The unibody / chassis is where the whole "pro-touring" proccess should start. Unfortunatly, those who don't invest any time or effort into the basic structure of these old muscle cars will never know what they are missing.

[parsonsj]

The unibody / chassis is where the whole "pro-touring" proccess should start. Unfortunatly, those who don't invest any time or effort into the basic structure of these old muscle cars will never know what they are missing.

That's true. I remember going through turn 1 at Road Atlanta with David Sloan (my passenger) shouting "My next car has to have a full frame!".

Torsional stability and reduced body flex makes the suspension engineering a lot easier. When you know that any movement of the suspension is just due to the suspension (and not the body moving) it allows better tuning.

Now ... that being said ... I think it's doubtful that handling differences are measurable without the resources of a full-on race team behind you. Us engineering geeks are intrigued and interested, but there aren't any hard criteria or feedback. We're talking ass-o-meter differences, with all of its confirmation bias problems, which makes these exchanges hard to have in a meaningful dialogue.

jp

[High Plains Mopars]

Now ... that being said ... I think it's doubtful that handling differences are measurable without the resources of a full-on race team behind you. Us engineering geeks are intrigued and interested, but there aren't any hard criteria or feedback. We're talking ass-o-meter differences, with all of its confirmation bias problems, which makes these exchanges hard to have in a meaningful dialogue.

jp

I disagree. A parking lot, a permission slip, a stop watch and a friend are all thats needed. I also think any track any were would be willing to rent you an afternoon for verification, and many have skid pads available as well.

However, even with that effort, there is still a lot of "paper engineering" going on by the masses that isn't necessarily bad. If Detroit Speed tests and verifys their products, it is reasonable to assume that even if you don't exactly duplicate their application, simply using their parts will generate at least a percentage of their results as well. This means someone is at least starting to look for, and understand the importance of engineering.

That is what I was alluding to earlier. Most enthusiasts aren't looking for optimization, they simply want it to be better and easier, and better looking, than it was originally. Optimizing the stock stuff is a butt load of work. Buying a new subframe and bolting it on is easy. As an example, lets look at the trans am cars from 1970. These cars were the pinnacle of stock class racing handling then, and are still pretty hot stuff even today and can turn laps that are still sizziling fast. They all used optimized stock suspensions. Many pro-touring cars of today would still be hard pressed to keep pace with a 37 year old race car, even with a hydro-formed subframes, three links, coil overs, 14" brakes and 17" rubber.

Similarly, the tubular suspension, welded seams and braced sub-frames of most pro-touring cars would put them in an outclassed position in any scca meet, which is probably the closest thing to regular guy racing most of us can come for a handling application.

But I agree with Marcus, those of us who know the time, energy , and effort that goes into optimization will never overlook a well thought out and engineered car, even if it is less flashy than the many other sittnig around it. However, I suspect we are the vast minority of the pro-touring subset of the whole automotive hobby. But come on, is that really any different than society as a whole? In general, society is a lot about looks ahead of function. Just watch any episode of a reality tv show to confirm that.

[gt1guy]

Just thinking about the flood of subframes for a moment. How many companies do you think actually test and verify the product? I've seen more than a few that look like it would actually make the car handle worse. Ridiculously short control arms come to mind. It seems today the end user really needs to be on his game, just to keep from getting burned.

Kevin

[parsonsj]

I disagree. A parking lot, a permission slip, a stop watch and a friend are all thats needed. I also think any track any were would be willing to rent you an afternoon for verification, and many have skid pads available as well.

I really doubt that you can measure the difference bracing your unibody makes with a skidpad or parking lot autoX. So you go out there on Saturday morning, run your stuff, then weld in some flex reducers and go back out the next day and see if your time is lowered? I'm skeptical the average guy will be able to see or measure any difference beyond normal sampling error ... I could be wrong though.

jp

[High Plains Mopars]

Okay then. How about XV's four post test rig results? While mopar specific, it does demonstrate the differences in effective unibody reinforcement that just a few pieces can have compared to stock. For a mopar, this is only 5 pieces; 2 subframe connectors, 2 shock tower braces, and one radiator support yoke. They also translate how this hard evidence stacks up against lap times and skid pad testing, in this case, that equals a significant seat of the pants as well as stop watch difference.
http://www.xvmotorsports.com/enginee...on_process.cfm

[parsonsj]

That's what I'm talking about. Genuine data with a chassis jig, load cells, and a disciplined approach. XV seems to be taking the sort of engineering approach that will result in verifiable and repeatable results.

It's just not something the average guy is going to be able to do. The message there is that Mopar guys have a real resource with XV, and one should talk with them about chassis stiffening.

The rest of us need somebody to do the same thing with GM and Ford bodies and chassis.

jp

[gt1guy]

You don't measure tortional rigidity on a 4,5, or 7 post rig. It's done a completely different way. Anyone, at home with just a few tools, can measure the rigidity of thier chassis, and the changes that modifications do. As far as the "shaker" rig goes. It was the topic of this months Chassis Newsletter from Mark Ortiz. Hopefully I can paste it here. It's long. I think it worked.

Kevin

October 2007

Reproduction for free use permitted and encouraged.

Reproduction for sale subject to restrictions. Please inquire for details.

WELCOME


Mark Ortiz Automotive is a chassis consulting service primarily serving oval track and road racers. This newsletter is a free service intended to benefit racers and enthusiasts by offering useful insights into chassis engineering and answers to questions. Readers may mail questions to: 155 Wankel Dr., Kannapolis, NC 28083-8200; submit questions by phone at 704-933-8876; or submit questions by e-mail to: [email protected]. Readers are invited to subscribe to this newsletter by e-mail. Just e-mail me and request to be added to the list.


WHAT EXACTLY ARE SHAKER RIGS FOR?

Over the past few years I have seen and heard about all of the developments with 4-post, 5-post, and 7-post shaker rigs. However, it seems that most articles focus on the technology employed by the latest and greatest rig rather than what type of results the rig is going to yield. My question is this, when teams test on a shaker rig, what exactly are they going to get in return in terms of results (i.e. lateral and longitudinal G forces or something else)? Also, maybe even a better question, what is it they are testing for (i.e. is there a way these rigs measure “grip” in particular) and what type of testing regiment is going to be employed? For instance if you are a team that is on a limited budget and can only afford to put your car on the rig once per year, do you put the car through a generic set of accelerations and simulated corners or do you try and tune for something more specific or maybe even a particular track? And lastly, at the end of the day how do you know what was the better setup (if there isn’t a way to measure “grip” specifically)?

Shaker rigs are an example of street driving improving the breed for racing. They originated in passenger car development, and were later applied to race cars. The original objective was to explore the car's response to excitation at the wheels, in a more controlled and observable situation than could be achieved on a test track. Improving handling wasn't the main goal. Engineers were more concerned with isolating frequency-sensitive effects that would impact durability and noise, vibration, and harshness (NVH). Does a portion of the roof or the floor pan resonate at a certain frequency? Are there brackets or ducts that buzz or might break? Does anything rattle? At what speeds and frequencies do the wheels "dance", and does this agree with calculated natural frequencies?

Early shaker rigs had posts only under the wheels, and the sprung mass was allowed to do whatever it wanted to do in response to excitation at the contact patch. It soon became apparent that it would be more desirable to allow the contact patches to float both laterally and longitudinally, so that the track and wheelbase could vary with suspension movement, without having tire scrub fight the movements. A fifth post attached to the sprung mass allowed the car to be anchored horizontally


while all four contact patches could float. The car still needed either an anti-rotation feature in the fifth post, or some other mechanism, to constrain the car in yaw.

This was good for replicating highway driving, but it was impossible to explore suspension behavior in conditions of sprung mass displacement caused by aerodynamic loads, banked turns, or pitch and roll due to longitudinal and lateral acceleration. To reproduce these displacements, three posts were attached to the sprung mass. Conveniently, three posts also constrain the car in yaw, without any additional devices. With this addition, it is possible to reproduce any combination of suspension displacements that the data acquisition system may have recorded on-track, or that an engineer might imagine.

Importantly, this does not mean that the rig reproduces all the forces acting on the suspension. The posts only move vertically. The rig cannot apply or reproduce any horizontal forces. It also cannot measure any horizontal forces. Therefore, we cannot measure grip at all. We also cannot reproduce loads and frictional influences in the suspension that result from horizontal forces at the contact patches. We do not even know vertical wheel loads with any accuracy, because horizontal forces at the contact patches affect these.

This last phenomenon is particularly significant in stock car rear suspensions, and in any suspension with large geometric "anti" effects. (Stock car rear suspensions, and most beam axle suspensions, have ample geometric anti-roll.) With formula cars, where there is modest anti-roll and anti-pitch, the wheel load values on the 7-post are closer to reality, but still not highly accurate.

I am referring here to individual wheel loads. On the rig, we do get reasonably accurate total loads for all four wheels, and for the left, right, front, and rear wheel pairs. It's the loads for individual wheels and for diagonally opposite pairs that are inaccurate.

Even though we do not read accurate individual wheel loads on the shaker rig, we can get a reasonable comparative evaluation of how much these loads vary dynamically in the excitation conditions that we test. What we are after is minimum load variation. We cannot measure grip itself, but we do know that variation of normal load is bad for grip, and minimizing such variation will improve grip.

This is true for two reasons. First, if the tires unload for any significant length of time, the car is limited by whatever grip the tires have at that load. If the grip limit at that load is exceeded, the car will break traction, and once traction is broken it is hard to regain. A slide, once initiated, tends to persist.

Second, even if we are dealing with load variations over small time spans, so that vehicle inertia masks the intervals of low load and grip, we do not fully recover during the highly loaded periods what we lose in the minimally loaded periods. Why? It's our old friend, load sensitivity of the coefficient of friction. Adding 100 pounds of load doesn't help as much as losing 100 pounds of load hurts.

So we try different combinations of shock valving and springing, and we try to minimize load variation at the wheels.

I was asked recently how you valve shocks based on suspension displacement traces provided by data acquisition. I had to reply that I don't know of any way to do that, and I don't know anybody who claims to be able to do that. However, with the use of a 7-post rig, we do at least have a means to make gains by trial and error.

There is another kind of test rig that does let us look at the effects of horizontal forces at the contact patches. It's called a kinematics and compliance tester, or K&C rig. Until recently, only passenger car manufacturers had these, and nobody was offering testing by the day or hour to racers. There is now a K&C facility available to the motorsports community, just up the road from me in Salisbury, NC. It's called Morse Measurements. The people who run this facility are friends of mine, so I'll give them a plug. They are at www.morsemeasurements.com or 704-638-6515.

What the K&C rig does is grab hold of the frame of the car, and then apply horizontal loads at the tire contact patches. The sprung mass can be kept from moving, and the changes in wheel loads measured that way. Alternatively, the sprung mass motion can be controlled to keep the total normal force at the contact patches constant and we can measure the displacements and load changes that result. Roll and pitch moments are applied to the frame, based on an input sprung mass c.g. height. Individual wheel horizontal forces are applied based on estimates, which in turn are based on tested or estimated tire properties and calculated wheel loads.

We then see from the test results whether our estimated wheel loads approximate those produced in the test, and we may want to adjust our contact patch forces and do another iteration on the rig.

There are other tests on the K&C rig as well, including simply cycling the car slowly in heave through its suspension travel and measuring the camber changes, contact patch scrubs, and wheel loads, with the contact patches allowed to float horizontally so that all horizontal forces at the contact patches are eliminated. This test can be done on either a K&C rig or a 7-post, so it can be used to compare the agreement of the two types of rig.

What the K&C rig does not do is move the chassis fast. The 7-post can load and move the chassis at racing speed, but only up and down. The K&C can load and move the chassis in all directions, but only slowly. At this writing, there is no test rig that moves and loads and measures a car in all directions at once, at realistic on-track speeds. And even the low-speed testing done on the K&C rig uses estimated or assumed grip levels at the contact patches.

We do have a test that does measure grip: the skid pad. It measures average grip over a lap, by stop watch, or over smaller intervals, using accelerometers or other sensors. Of course, we have difficulty observing the car during testing, because the car is in motion rather than on a test rig. And the grip measured is only on a particular surface, on a particular radius.


We thus have three useful methods of testing, all of which provide useful comparative measurements, but none of which allows us to fully replicate track events in a controlled environment. I could even say we have four methods, if we include wind tunnels, or a much larger number if we include component testing devices such as tire testing machines, shock dynos, and engine dynos. But so far we have no device that really puts the car through its paces in a manner that replicates in full what happens on the track, on a stationary platform where we can safely watch and measure it. The best we can do is look through a number of windows, each of which affords a view from a different angle, and use our mind to try to put these glimpses of reality together.

[SN65]

You don't measure tortional rigidity on a 4,5, or 7 post rig. It's done a completely different way....

....SNIP

Testing for differences in torsional ridgity is similar to testing engine modifications on a dyno. Dosn't really matter what dyno you use (as long as it is the same dyno for every test) and what the nunbers are, it is the changes in the numbers, as modifications are made) that tell the story.

Yes, I know that the test bed we use on our mustang is not the same that is used for testing torsional ridgidity on a NASCAR chassis. But if we keep the setup the same on every test, we can measure the change and determine if any improvements have been made.

On our primative test bed, we have measured a reduction in torsional deflection of more than 1". We went from 1.3" of deflection on a stock unmodified chassis to less than .25".

Tell me that this type of change, regardless of the suspension components used, will not be noticable in both the seat of the pants and also at the track.

[parsonsj]

Tell me that this type of change, regardless of the suspension components used, will not be noticable in both the seat of the pants and also at the track.

Bob, who are you asking? Or is the comment rhetorical?

jp