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 Post subject: Re: Suspension Dynamics.
 Post Posted: Fri Apr 10, 2009 10:24 am 
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I wanted mid 50's for 50% of the wheelbase assuming the car was 50/50 on weight bias.
It wouldn't hurt my feelings if it was high 50's if that's what it takes to get the correct angle/IC height.
I just don't think high 40's will get the job done long term.


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 Post subject: Re: Suspension Dynamics.
 Post Posted: Fri Apr 10, 2009 12:52 pm 
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I'm interested in why the Instant center distance from the rear is important? I know why the height is important, but I have seen 4 bar cars that have an IC length at infinity work just fine. I have seen short ladder bar cars with an IC of under 3 foot preform fine. I have seen leaf spring cars with an instant center the same length as the front half of the spring work also. Not to mention Zlink, where one of your 4 link on each side runs to the rear. And don't forget track bar, ( NASCARS old Chevy pick up version).

I'm all ears but my train of thought now is length don't mean squat. Pardon the pun.

Now I can understand how we could start thinking length means something because it is and was an old chassis tuners trick to put the bottom bar's line across the neutral line at 2/3rds to 3/4rs the length of wheel base, then by just moving the top bar or ride height you could change the height relationship with the neutral line. This made it easy at the track to get back home if you went the wrong way or too much. That and the fact that if someone is getting side wall distortion from hitting hard, only looks at IC, not at rim width , tire pressure or even loading of both rear tires.

Ok, here is a little science experiment to show how IC really works. Get a couple coat hangers, side cutters and pliers. Cut the hook off. Make a straight run for a few inches then a 90 degree bend. Run for a few inches and another 90 degree bend in the same direction, then on one a short run and the other a longer run and another 90 degree bend and a straight run for at least double the run of the second straight run. Place a strip of electrical tape on this last run. This is just so the weight you put on this last run doesn't move. Put some keys or nuts on it on the last straight run. put the starting point on the edge of your bench or desk and slide weight till first run is vertical. At that point there is force, (gravity) the whole thing has a center of gravity. You can alter the center of gravity with weight. Now by moving weight very little you can see what happens to that vertical run that represents your bars. Moving that weight represents the difference in IC height and Neutral line, (based on COG). You can see compression or separation from that vertical run just above bench. Make the other a little longer or shorter. You can even make one scaled to your car. This also has some relevance to transfer of weight due to COG. picture your car hanging off a point on neutral line. Moving weight represents moving COG. The first vertical run will show the action of links when not on the neutral line if leaning. Remember this is about force and it's relationship to COG. Wire should go up around bench and under it. This is simple but for guys like me that need a visual it can help.

Oh that first straight run represents IC so make that longer or shorter.

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 Post subject: Re: Suspension Dynamics.
 Post Posted: Fri Apr 10, 2009 1:28 pm 
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I can't help but think you are using roundy round thinking here.

Round track racing doesn't have a 10th of the torque or tire adhesion a drag car does (forward bite).

I have seen long bar combos and short bar combos on a scale car with a torque wrench applying torque to the axle and there is a major difference.
As your IC gets longer it also gets further away from the neutral line which diminishes anti squat progressively.

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 Post subject: Re: Suspension Dynamics.
 Post Posted: Fri Apr 10, 2009 6:21 pm 
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Bubstr mentioned that 4bar setups can be very effective. The picture shows how they work. Note that the instant center (IC) is an infinite distance forward and either an infinite distance up or down.

The "pushing a refrigerator" analogy is a very poor one. Without going into the kitchen, just picture a ladder bar with the front end attached to the car, but the rear end dragging on the shop floor. It should be obvious that, if you push forward horizontally on the rear of the bar, you'll get a different effect if the bar is short or long. If it's only 20 inches long, you'll push the rear of the car up; if it's 20 feet long, you'll be pushing the rear of the car down. The angle of the bar makes the difference. The force at the rear tire patch acts through the IC and it's the angle of the line through the tire patch and the IC...in side view...that is important. That angle is a line of constant percent antisquat. So long as you keep the IC on a given line, performance is unchanged.

Finally, book publishers have, in this digital age, become very sensitive to the posting of book pictures without their consent. If you haven't requested consent and are willing to risk a lawsuit, you should, at the very least, provide the book title, page number, etc. I wanted to post a picture a couple of months ago and contacted the author. He couldn't have cared less, but the publisher was in control and I can't recall exactly how many hundreds of dollars it would have cost me. Needless, to say, I didn't post the picture.
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 Post subject: Re: Suspension Dynamics.
 Post Posted: Fri Apr 10, 2009 8:07 pm 
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Scott, your right I do think in circle track. I drag raced for around 15 years before I went full time roundy round racing. I went because the money went out of Drag racing. Them first couple years was expensive lessons. Them guys beat me like a red headed step child. I did a lot of things right drag racing but never understood why until I changed over. We are talking 850 HP and 2400 lbs getting hooked on a glob of snot. Or worse hard dry slick. Although you add different forces going around a corner, the laws of physics stay the same. I have been back to the drag strip to help a couple friends, but mostly retired. Trust me, the same things hook a stock car or sprint car up as a drag car. It's just a little easier on a drag car because the traction forgives being off a little.

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 Post subject: Re: Suspension Dynamics.
 Post Posted: Sat Apr 11, 2009 3:33 am 
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I can see the thought behind longer lower IC's. Because we get squat out of the rear, it leads us to believe we are getting more weight transfer to the rear. My train of thought is to watch the front to see weight transfer. As the front rises weight is transferring, whether the rear is compressing or not. The simple fact that if it isn't in front , it can only be in the back. There are only two choices. Compression in the rear only show what you are doing with that weight when it gets back there. I have said before the IC and you spring/ shock are pardners in transmitting weight of the car to the contact patch. You can add tire sidewall into that. The higher IC may not compress the rear, but that don't mean it didn't get and use that weight that was transferred to the rear. Now I can see where you may want to lower the IC value if your distorting the sidewalls, but wouldn't a better faster solution be to stiffen sidewalls with rim width or tire pressure and transmit as much weight as you can, as fast as you can. That is the goal, weight transfer with an undistorted contact patch, as quickly as you can. You can only think this way if you believe that forward force and it's relationship to the COG are what makes weight transfer. To take out the idea that engine torque lifts a car threw links or ladders, think of side bite. You have IC there also. One for front,(control arms are your 4 link), and rear where Pan hard bar is you Link. These don't transfer weight, just determines how you use that weight. COG still transfers weight side to side.

This has been a good topic and even though we seem to disagree, most of the end results and causes are still linked to laws of Physics. A lot of the time our remedy's work, but if we know what's going on, it takes some of the indecision out of it. I am still interested in Shrinkers formulas, and Scott is right the farther out an IC is, if not compensating for the rise in the neutral line, it will be lower. I also see a lot of guys going to lower anti squat values and there may be a good explanation for it, but I haven't heard a good reason yet. These bench racing sessions are not a win loose argument. You can just give your thoughts and let everyone sort it out for themselves. They will win or loose. There has to be more questions and if anyone disagrees with me at least say so, I like my crow warm and well done .

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 Post subject: Re: Suspension Dynamics.
 Post Posted: Sat Apr 11, 2009 8:25 am 
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I had hoped that the picture of the 4bar arrangements would reshape the thinking regarding the forward position and height of the instant center (IC). After all, if the IC can be an infinite distance forward and provide squat, rise, or a neutral condition, why do you worry about whether it's in front of or behind the center of gravity (CG)? And, if it can be an infinite distance high and produce the same results, why do you concern yourself with 15 or 20 inch heights?

The important matter is the angle of the line of action of the force applied at the IC. Or, in other words, the important matter is the percent antisquat.

Do not concern yourself with "inner" forces. The entire rear axle assembly can be considered as nothing more than a simple link, pivotable at both ends. The rear pivot is the rear tire patch and the front pivot is the IC. (To simplify the picture, you might want to consider a ladder bar, where the IC and the mechanical pivot have the same location.) The total force vector at the rear tire patch...the sum of the vertical and horizontal components...acts on a line through the IC. That line is a line of constant percent antisquat. If that line is as the one in the picture...passing through the intersection of a horizontal line through the CG and a vertical line through the front tire patch..., the car has 100% antisquat. (The 4bar pictures act on the fact that parallel lines meet at infinity.)

As Bubstr has indicated, suspension considerations of an oval track car are similar to those for a drag car. Everything is simply rotated 90 degrees in plan view. As Bubstr would tell you, if he wants to increase the push (understeer) of his car, he increases the front end roll stiffness relative to the rear end roll stiffness. One way of doing this would be to install higher rate springs at the front. This increases the load of the right front tire as he turns left. Now, let's rotate Bubstr's car 90 degrees and make the front end the right side of a drag car. It should be evident that, if we want to cancel the driveshaft torque's effort to unload the right rear tire, all we have to do is increase the spring rates on the right side. But, since the right rear spring sees little...if any...deflection during launch, all we have to do is increase the right front spring rate. There's a spreadsheet at my site for just such a change. This requires adjustable coilovers and, since there are not an infinite number of spring rates available, some further tuning will be necessary. This will get you close, however.
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 Post subject: Re: Suspension Dynamics.
 Post Posted: Sun Apr 12, 2009 4:06 am 
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Bubstr wrote:
I'm interested in why the Instant center distance from the rear is important? I know why the height is important, but I have seen 4 bar cars that have an IC length at infinity work just fine. I have seen short ladder bar cars with an IC of under 3 foot preform fine. I have seen leaf spring cars with an instant center the same length as the front half of the spring work also. Not to mention Zlink, where one of your 4 link on each side runs to the rear. And don't forget track bar, ( NASCARS old Chevy pick up version).


This sounds like you're trying to compare a bird cage rear suspension to a 4 like type rear suspension of a drag car. They do not even remotely do the same thing. A drag 4 link transferes load. The Bird cage only induces rear stear. As it's chassis seperates while under acceleration the rear end actually moves foward and rearward depending how each side is set up. The lift bar that is usually ran in conjunction with the bird cage rear suspension is actually what transferes the load in that type suspension. It is actuallt a modified ladder bar imo. I'm not wanting to get under anyones skin here, jus wanting to point out the differences.

Don

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 Post subject: Re: Suspension Dynamics.
 Post Posted: Sun Apr 12, 2009 6:12 am 
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want-a-be wrote:
A drag 4 link transferes load.

Weight transfer is determined by the total weight, center of gravity height, wheelbase, and forward acceleration. The only way any suspension arrangement can affect weight transfer is through a change in forward acceleration.
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 Post subject: Re: Suspension Dynamics.
 Post Posted: Sun Apr 12, 2009 8:50 am 
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Put both bars parallel in a 1.20 sixty foot drag car and get back to me on how it works out. :-$


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 Post subject: Re: Suspension Dynamics.
 Post Posted: Sun Apr 12, 2009 9:47 am 
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Scott Smith wrote:
Put both bars parallel in a 1.20 sixty foot drag car and get back to me on how it works out. :-$


Dayyyyyyyum, short and to the point =;


I am reading all this info and comment from many of you, and what I want to know is, what are the key items needed to make a chassis launch, regardless of wheelbase, tire size, engine power, shocks/springs, 4link, ladder bar and gear ratio?

Here is an example of what I am talking about, or a question I guess, has anyone seen Dan Flethcer's K&N Camaro lately and his wheels up launches? now this is a little extreme for most of us, but that's the class he runs it in, now, what does it take to make any chassis raise the front end 6"-12" and just haul the mail carrying the fronts about 30-60 feet and no upsetting of the chassis?, and cutting a great short time and still having the chassis stable at speed and during the gearchange, and, whether a 4 link or ladder bar system is used, or slider leaf spring setup(or what ever they use with leaf springs)??????? What are the key points of interest in what area's to get the maximum tuning out of each chassis? I know, I know, you can't answer than one because every car is different, but, yet, we are all the same!!!!

What is it exactly that makes a car hook and launch? is it the C/G placement of each chassis, and then where the I/C is in relation to the C/G that makes a chassis haul the bacon? If the chassis runs a 1.20 short time consistantly, should it be messed with? or keep tuning? What is the best for each chassis? I see it as a balance of what each individual chassis has for engine power and gear ratos, and thrust on the tire patch, plus the C/G, AND I/C combined, so in essence, every chassis is dialed in differently, and they have to be because no two chassis's are alike.

So, I guess one question could be for my setup when it is done being built is, where is the ideal C/G, in my example of a 116" wheelbase chassis making over 800hp at the flexplate, and an off bias of weight front to rear say 55%front & 45% rear? how do I make that combo work to get the best short time? Oh, sorry, with a 4 link setup and engine is stock location, not higher, not lower, and in a good sturdy chassis with lots of rubber to grab with? I could give more details, but I am just generalizing with my Elky as an example, and like Barry's Baretta, I would think a 1.20 short time is killer!!!! =D> for his engine power. Am I asking the right questions, using wrong examples, what? I do understand some of the physics of the suspension, and some of the terminology being used, but when you guys start compairing both drag and circle track info, it kind of looses me a little because I don't see exactly what is going on with someone telling me exactly what is going on and when!!!! call me dumb, but my chassis guy said for me to go to the local circle track and watch some of the quicker cars like the modifieds and see how they go into the corners, come out of the corners, and down the straights, and to me, it just doesn't compair to drag racing to see this, yes, it shows weight transfer, this and that, but most of those chassis's are built offset, like the complete rollcage, which if looked at straight thru the windshield is clearly slammed to one side of the car body for a reason, well, if I ever go sideways down a 1/4 mile straight track, then maybe it will help me, but this is where (I) am getting confused with the theory part. We need more LAMEN'S terms here for some of us to pick it up I guess, your input is awesome really guys, \:D/ but trying to decipher this from that, well, I have just wasted another set of tires trying to spin it into my head, but, that's just my opinion ok? It is a very good thread going deep into technology, and keep it up, heck, one of these pages has to make it click for me eventually right?

I just think of little Johnny, and big Susie on the teeter totter and little Johnny just can' quite pick up big ol Susie off the ground yet, and this is the philosophy I think of in terms of weight needed to lift a chassis in the front to get the transfer of weight needed, or to just be shot out of a cannon and haul a$$ down track! No replys needed, it is just soo much info to digest and understand. Ok, done for now, next!!!! ;-)

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 Post subject: Re: Suspension Dynamics.
 Post Posted: Sun Apr 12, 2009 9:57 am 
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BillyShope wrote:
The only way any suspension arrangement can affect weight transfer is through a change in forward acceleration.

I Think perhaps this poster is referring to weight transfer due solely to acceleration, because that's all that statement could mean. A suspension system can indeed increase weight transfer without changing acceleration. Just a ladder bar will do that, the torque lifts the car, you can see it easily on a dyno the front and the rear springs extend. The car gets lifted by the torque arm.

And parallel arms are useless.


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 Post subject: Re: Suspension Dynamics.
 Post Posted: Sun Apr 12, 2009 11:31 am 
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Quote:
I am reading all this info and comment from many of you, and what I want to know is, what are the key items needed to make a chassis launch, regardless of wheelbase, tire size, engine power, shocks/springs, 4link, ladder bar and gear ratio?


It's all relative.
Combo Combo Combo.

You wouldn't want a 350 HP motor in a on the ground tube chassis car with 3.90 gears and a crank C/L of 10"

Just like you wouldn't want a 1100 hp engine in a SS/CA with a 15" Crank C/L and a 5.38 gear.

The high wheel standing SS cars need to keep the rear tire planted with a lack of HP. So they are set up with low starting line numerical gear, high crank C/L and lots of front end travel. As the power goes up the wheel standing goes down because there is more power present to keep the tire planted.

A good example would be SS/AA (The Hemi Darts). Back in the 80s they were on the back bumper. Now they have gotten the HP to a level they leave pretty much on the ground.


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 Post subject: Re: Suspension Dynamics.
 Post Posted: Sun Apr 12, 2009 3:49 pm 
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Scott Smith wrote:
Put both bars parallel in a 1.20 sixty foot drag car and get back to me on how it works out. :-$


Here is how it works. Was 1970 and my first attempt at a 4 link or 4 bar car. You must remember, at that time you didn't see any of them. This was a B/G around 800hp at 2840lbs. My 4 link was actually a 4 bar as upper and lower bar was equal length and parallel. I wouldn't say it would run with today's tech. We had poorer tires and a lot less aftermarket parts, but it ran an 8.90 on a 10.06 record at that time. I copied the suspension from a car and driver mag. It was a Lola or Jag. I just scaled it to the Hemi powered Challenger. This was going to be my world beater. Well first time out the IC was so high, it hopped like a Bunny. I didn't know what I know now and said bars are too short. There was no good way of making them longer and I'm about to take them out and put a ladder bar back in, when a Roundy round racer came by, who I was making bullet proof Pittman arms for, and said lower the fronts. With nothing to loose but some drive train parts from bouncing I did. Still had some rebound in the rear, so I made new front brackets. The front transferred weight about the same in all three locations. While we didn't have 60 foot times then, it's 1/8th mile time really came down, way under National record at the time. 5.60s. So that may not have been a 1.20-- 60, The 4 bar did work. With a little more knowledge at the time, it may have worked better. By the way, this was running a 13.50 hard M&H slick and a 5.13 no spool gear, an untreated asphalt launch pads. The rule then was no locked or welded rears. Front wheels barely cleared the ground and held them there threw 1st and part of second gear. This car made a little over 1,500 dollars after expenses, even building expenses. I was tickled till they did away with the weight to cubic inches class racing. I would have no fear of using that suspension today. It's only weakness was the Watts linkage mount on the tube frame. This would be my choice for a street / strip car today. While it don't have the quite the adjustibility as a 4 link, it won't put as much pressure on brackets going around a corner.

Now before anyone says something about more power or traction, I would just lower the COG to compensate for it. When I ran out of low, I'd move it forward.

I think where I'm not explaining well is IC's are ICs no matter what suspension you get them from. Some have an advantage on ease of adjustment. They do not transfer weight. They only determine how you use that weight. COG transfers weight. When the COG for a car is close, it makes all other adjustments work better.

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 Post subject: Re: Suspension Dynamics.
 Post Posted: Sun Apr 12, 2009 5:27 pm 
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Bubstr wrote:
I was tickled till they did away with the weight to cubic inches class racing.

And this is why I lost all interest in building something after leaving Chrysler and the Ramchargers. Christmas trees belong in the living room, NOT at the dragstrip. Hate 'em!!!
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