Help me choose a suspension setup

JJ427R

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And people also said the Wright Brothers would never fly.... just keep reading those papers Norm.....
Just think if NASCAR engineers just did everything by looking at what is on paper...
 

Norm Peterson

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I see what you are saying though.... with say a 1g left sweeper, the chassis won't twist enough to benefit from increased torsional rigidity. You might be correct, but I believe there are other factors in play...since all the various suspension components tend to interact somewhat. With increased torsional stiffness, that may well lessen the effect of various suspension pieces 'fighting each other'. I'd like to isolate the torsional rigidity from the rest of the suspension bits.
Actually my spreadsheet does exactly that. And more.

This whole situation boils down to being a series-parallel spring problem.

Chassis stiffness is a spring in the middle of a series arrangement comprised of rear tire vertical stiffness, rear suspension roll stiffness, chassis torsional stiffness, front suspension roll stiffness, and finally front tire vertical stiffness. Suspension stiffnesses are springs in parallel with their companion sta-bars.

Chassis torsional stiffness affects how well the suspension roll stiffness at one end can "steal" roll moment from the other end - this being the basis for tuning a car's handling via springs, bars, and even shocks/struts.


Norm
 

Norm Peterson

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And people also said the Wright Brothers would never fly.... just keep reading those papers Norm.....
Those people weren't engineers, let alone not being engineers doing similar analyses.

I can't explain how engineers think that's different from the way most non-engineers think, I only know that it is different. Maybe that's why you couldn't see the value in me comparing my sheet to somebody else's real-world testing (and coming up with decent agreement).


Norm
 

Pentalab

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Actually my spreadsheet does exactly that. And more.

This whole situation boils down to being a series-parallel spring problem.

Chassis stiffness is a spring in the middle of a series arrangement comprised of rear tire vertical stiffness, rear suspension roll stiffness, chassis torsional stiffness, front suspension roll stiffness, and finally front tire vertical stiffness. Suspension stiffnesses are springs in parallel with their companion sta-bars.

Chassis torsional stiffness affects how well the suspension roll stiffness at one end can "steal" roll moment from the other end - this being the basis for tuning a car's handling via springs, bars, and even shocks/struts.


Norm

Do I have this right. Let's say Norm installs BMR SFC's, welds em in... then starts exhaustive testing.
Let's just assume for a moment that chassis torsional stiffness does increase..and by X%. Is the 'suspension tuning' now way outa wack, no longer optimized, compromised handling, 1-3 steps backwards ? Or is only minor re-tuning required.. like backing off on front/rear sway bar/spring rates /strut/shock adjustments ? After re-tuning, are you then back to where you were b4 the SFC's were installed.... or is the car's overall handling now in a slightly improved state ? How long would it take to evaluate all of this ?
 

Norm Peterson

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Do I have this right. Let's say Norm installs BMR SFC's, welds em in... then starts exhaustive testing.
Let's just assume for a moment that chassis torsional stiffness does increase..and by X%. Is the 'suspension tuning' now way outa wack, no longer optimized, compromised handling, 1-3 steps backwards ? Or is only minor re-tuning required.. like backing off on front/rear sway bar/spring rates /strut/shock adjustments ?
Best estimate I have at this point is that the change in TLLTD (and the downstream effect on handling) is well below the difference that a one hole adjustment on either sta-bar makes. About the same amount of difference that an 0.1 psi difference in either the front or the rear tire inflation pressure (not both at the same time) might make. Yes, I ran the numbers.


After re-tuning, are you then back to where you were b4 the SFC's were installed.... or is the car's overall handling now in a slightly improved state ?
When you force TLLTD back to being the same, and you haven't stiffened either the suspension, or the tires, or even the suspension attachment points, you're right back to where you started.


How long would it take to evaluate all of this ?
This magnitude of change (0.0x%) almost certainly requires somebody with better test driver credentials than I'll ever have. The half-percent stuff I do notice, and that might take a couple of tries. On any given day I can usually keep scatter in lap times on my home tracks down to about a full second, excluding laps involving passing or being held up in traffic. That's what my available datalogs show, anyway. It's not nearly good enough for what your proposed test sequence most likely requires.


Norm
 

eighty6gt

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car feels x way

You want it to feel y way

time makes no difference, materially, esp. on the street.

In general, you are just fooling yourself and adding weight, losing money. I keep parts off the car as much as possible.

Norm is too good for this place.


here's a good race car for you guys to evaluate:


10:00 is where the driving starts.
 

Juice

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IMO, skidpad testing would be the best possible way to measure any change in lateral grip after installing these parts. And it is quicker than doing laps at X track.
 

Racer47

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Norm is too good for this place.

I won't go quite that far :), but do agree with Norm especially on the engr thought process and on the the notion of significant driver variation in non-professional drivers and pretty much everything else he's posted in this thread. He has way more patience that I do for debates like this.

All of this debate is because this isn't real racing, with real drivers, real crew chiefs, real data acq, etc. Its all based on someone trying to justify their spending. Its not based on facts and real results.

If you bought something and think it was worth it, than good for you. But knocking @Vorshlag-Fair or claiming libel is just wrong. Most guys here have never raced anything at any high level. You have no idea what it takes. Fair has posted tons of real info, no one should be knocking him.

Also comparing camber plates to chassis bracing is ridiculous. Factory street car camber and race camber requirements are vastly different.

Lastly, debating with pentalab is pointless. I gave up on this quite a while ago because he simply does not know what he is talking about much of the time. The more technical the debate, the more nonsense he spews.
 

Pentalab

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And people also said the Wright Brothers would never fly.... just keep reading those papers Norm.....
Just think if NASCAR engineers just did everything by looking at what is on paper...


There is a sign up at nasa, that sez.......'one test is worth a thousand opinions'. It's still up.
On a non car related subject, I use mechanical software to design sw hf antenna's for myself, and primarily other fellows. So far so good, it factors in ice and wind loads, gusts, differences in material used etc, etc. Then I discover it doesn't factor in the weight of the various fasteners used, which of course throws the calculated sag data...out the window. Some designs use software designed TQ compensator's. Great, except it places the tq comp in the wrong place, by almost a ft, which means I have to manually shift it's position, which in turn throws the entire design outa whack.. and the fix for that mess is for me to trial and error the design tweak. It's being re-written as we speak.

I also design HV DC power supplies for specific applications. I use software from the UK..it's used world wide. Been tearing my hair out the last 4-5 months as data results are goofy and obscured, unreliable, and dubious, but only under certain constrained conditions. I contact the fellow in the UK, send him a 1/2 doz files of my results. He concurs, then proceeds to explain how he found the limitations of his software. We both came up with a temp work around, which is a major pita. So version 3 is currently under development. Why the anomaly's were never discovered b4 is beyond me. Actual tests and measurements by myself and a few others, confirmed the software glitchs.

The last electronics eng book I bought, peer reviewed to boot, I found 38 mistakes in it, mostly silly typo stuff, the rest are tech in nature. But the damage is done, and lotsa design flaws have since resulted from the various errors. There are 2-3 more software design programs I use on a regular basis, that also have limitations, but I have managed to find a work around for them, and know what to do, to fool the software, to get around the various issues.

So I get a bit leery when computer simulations are run. Some of the mech software I have been using since 1991 was touted as the ultimate thing since sliced bread. Fast forward, and 9 revisions later,
they almost have it right. Then I found more stuff, where the formulae was wrong, stuff that was squared, that shoulda been cubed. You get the picture. It's a real piss off, esp with > 400 hrs wasted
over the last 4-5 months.
 

JJ427R

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Those people weren't engineers, let alone not being engineers doing similar analyses.

I can't explain how engineers think that's different from the way most non-engineers think, I only know that it is different. Maybe that's why you couldn't see the value in me comparing my sheet to somebody else's real-world testing (and coming up with decent agreement).


Norm
My whole point has been exactly what you just said, you are basing your opinion of the matrix brace on some papers and on "what you think" as an engineer. You are looking at this completely from an engineering standpoint. As I stated before you have not tried one, so to dismiss what myself and other people who have tried them have said on this forum is complete bs. If you were to try it and then come back and say you noticed x amount of whatever, I'd give you a lot more credit, but that is not the case here.

But knocking @Vorshlag-Fair or claiming libel is just wrong
but it's ok for him to come on here and knock other vendors huh, and criticize those who don't agree with him.. I'm not knocking him, I'm just stating facts.
 

Pentalab

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All of this debate is because this isn't real racing, with real drivers, real crew chiefs, real data acq, etc. Its all based on someone trying to justify their spending. Its not based on facts and real results.

If you bought something and think it was worth it, than good for you. But knocking @Vorshlag-Fair or claiming libel is just wrong. Most guys here have never raced anything at any high level. You have no idea what it takes. Fair has posted tons of real info, no one should be knocking him.

Nobody is trying to justify their spending, far from it. Some stuff works, some stuff barely works, some stuff is very subtle. Some stuff has zero effect. I have read all of Fair's postings, all of em. Informative reading. However, I don't see anywhere where he welded BMR sfc's into place, evaluated them, then arrives at the conclusion that they are a wasted effort. If he did do that specific test, I missed it, my apologies. As far as piling on weight with various lightweight CM braces etc, I dumped a lot of weight when the AL DS got installed, so it comes out a wash, moot point. Right now I just want the jacking rail capability, that's it. IF the perceived handling marginally improves, that's a bonus. If not, nothing lost.
 

Racer47

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I'm not knocking him, I'm just stating facts.

Well the facts are that he has set several track records and set fast times in many nasa tt events in addition to building race cars for many other drivers. Real racing experience and testing trumps mid level hdpe driving.

He could choose to add braces and claim big benefits in an effort to sell more product or he could state the facts as he sees them based on race results. His integrity to not promote fluff parts is commendable. Many places sell parts just because guys will buy them regardless of actual benefits.

I highly doubt that any brace is worth an honest 2 secs a lap on anything, even an old fox chassis.
 

Norm Peterson

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My whole point has been exactly what you just said, you are basing your opinion of the matrix brace on some papers and on "what you think" as an engineer. You are looking at this completely from an engineering standpoint.
You can't understand structural behavior from any other standpoint than structural or possibly mechanical engineering. And without being willing or able to understand structural behavior, your attempts to describe the benefits of this bracing as providing 2 seconds/lap benefit solely on a structural/mechanical chassis basis are utterly without basis.


As I stated before you have not tried one
Not the KB piece, no. But I have done a little fabricated car chassis stiffening myself, directly, so it's not that I have zero 'real-life feel' for such things (like you seem to think).

Some of that has been strictly repair in nature, but there's also some 'stiffer than OE repair' and 'adding supplemental chassis stiffening' in my background to go along with that. I'm not afraid to crawl underneath any of my cars with a MIG-welder gun.


so to dismiss what myself and other people who have tried them have said on this forum is complete bs.
I am not disputing or dismissing anybody's lap time improvements, so I'd appreciate it if you'd quit implying that that's what I'm trying to do here. I do know a thing or two about driver confidence and how that can affect lap times.


Norm
 

Norm Peterson

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So I get a bit leery when computer simulations are run.
Series-parallel spring problems like this one are as basic structurally as a series-parallel DC circuit with six or eight individual resistances is in the electrical world. I think we can conclude that the theories and equations were ironed out decades ago. Before my time, even.

Perhaps if I pulled up all of the individual stiffnesses (easy enough) and turned them into an analogous DC electrical circuit (shouldn't be all that tough) you'd see this more clearly.


Yes, I get the concept of adding something like a jacking rail for its stated purpose, while figuring that any other benefits - no matter how large or small - would still be improvements.

But somehow I doubt that any of the supplemental bracing vendors are giving much credit to driver confidence as one of these side benefits. Maybe they're not giving any credit at all, and as a result hardly any of their customers think it's of any importance either. Doesn't even cross their minds.


Norm
 

Pentalab

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Series-parallel spring problems like this one are as basic structurally as a series-parallel DC circuit with six or eight individual resistances is in the electrical world. I think we can conclude that the theories and equations were ironed out decades ago. Before my time, even.

Perhaps if I pulled up all of the individual stiffnesses (easy enough) and turned them into an analogous DC electrical circuit (shouldn't be all that tough) you'd see this more clearly.


Yes, I get the concept of adding something like a jacking rail for its stated purpose, while figuring that any other benefits - no matter how large or small - would still be improvements.

But somehow I doubt that any of the supplemental bracing vendors are giving much credit to driver confidence as one of these side benefits. Maybe they're not giving any credit at all, and as a result hardly any of their customers think it's of any importance either. Doesn't even cross their minds.


Norm

Points well taken. I still can't wrap my head around the fact that one tire is still on the ground...with the other lifted off the ground....... vs both coming off the ground, when the brace is installed. On the face of it, it appears the torsional rigidity (with braces installed) has increased by more than a bunch. Esp on a car that weighs aprx 3700-3800 lbs. Roughly assume 1k lbs on each front..and 900 lbs on each rear. That's a lot of corner weight to lift XXX inches, off the ground. I'll find out soon enough this spring. At $118.00 on sale for the steeda jacking rails, ( steeda.com), it's really a cheap jacking rail solution for myself. Unless somebody else comes on here, (esp Vorshlag) who has installed / welded in BMR / KB SFC's, with detailed data, we should consider this thread closed.
 
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JJ427R

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You can't understand structural behavior from any other standpoint than structural or possibly mechanical engineering. And without being willing or able to understand structural behavior, your attempts to describe the benefits of this bracing as providing 2 seconds/lap benefit solely on a structural/mechanical chassis basis are utterly without basis.

I never said that it was all brace for the decrease in my lap times and no driver change, all I'm saying is you are not giving the brace enough credit.
I do believe by now at 57 years old I know my own ability as a driver...

I'm not an engineer and evidently don't know what one thinks like, but I very much understand control and feel of a car, probably more so than most as I drive solely with hand controls and no feet involved...
I could feel a very significant difference in the handling and ride after the brace was installed and did notice a significant difference in my times, even after 5 years of driving my car on track.
Structurally I noticed a significant decrease in flexing when I jack the car as mentioned earlier.

Thank you for giving me the driver credit for the decrease in my times.

At this point I'm with Pentalab and I call uncle on this thread....
 

Norm Peterson

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Structurally I noticed a significant decrease in flexing when I jack the car as mentioned earlier.
Points well taken. I still can't wrap my head around the fact that one tire is still on the ground...with the other lifted off the ground....... vs both coming off the ground, when the brace is installed.
There's a bit of an illusion and stuff left to the imagination going on with that demonstration, like there seems to be when it comes to just about any forum topic that gets involved with structural strength and stiffness.

In this no-brace case the other front tire is already very close to being lifted clear of the ground. All it takes is enough more torsional stiffness to finish unweighting it, and this can be estimated. Probably not with 500 ft*lbs/degree vs 550 ft*lbs/degree resolution, but I think such an estimate is more than good enough to show that the demonstration didn't need 5000 ft*lbs/degree more stiffness either.

Here's another look, from a slightly different point of view than I was using in post #34.

Let's say your no-bracing case left the other side tire 1/4" compressed (probably a high estimate, but strongly dependent on exactly where you did your jacking). That's about 400 lbs still on the contact patch based on tire stiffness being constant. Now add enough chassis stiffness to just barely take all of that 400 lbs off the contact patch - any further lifting cannot reduce that tire's loading any further because you're down to zero. So your bracing caused a 400 lbs force reduction and a 1/4" displacement change taken over about 2.5 feet (half the track) - and about half a degree of rotation. This gives 2.5 * 400 ft*lbs for half a degree, or about 2000 ft*lbs/degree. Still less than 10% of the OE chassis stiffness, when even a 50% increase hardly alters the TLLTD at all.


FWIW, "handling" in a more general sense might really be part car, part driver, and a little bit the "road" you happen to be driving on.


Norm
 

Norm Peterson

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I'm not an engineer and evidently don't know what one thinks like, but I very much understand control and feel of a car, probably more so than most as I drive solely with hand controls and no feet involved...
I could feel a very significant difference in the handling and ride after the brace was installed and did notice a significant difference in my times, even after 5 years of driving my car on track.
Let me think on this some more.


Norm
 

JJ427R

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Like the Sopranos and Godfather: "Just when I think I'm done they pull me back in"

Yes I would like to clarify that as well, I was talking jacking RF and the RR comes off the ground, not the opposing front.

Prior to MB and jacking rails, if I lifted RR wheel I could lift the rear of the car several inches and the RF tire would still be on the ground, after braces not the case you lift the RR the RF comes up same time, that amount of flex is no longer there.

There's a bit of an illusion and stuff left to the imagination going on with that demonstration

If you still think that is no change and the braces make no difference, you are definitely the one with the illusion and imagination going on....
 

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