http://www.racetec.cc/shope/index.htm

some light reading is in order

 

I was on that website reading for about 3 hours last night before I posted this thread. I was baffled w/ information. I was hoping someone could dumb it down for me. I understand the terms IC, CG, and AS but I need to figure out how to achieve these numbers and where I need to set up my car. I understand the bottom bars need to be level or slightly down and the separation between bars need to be around 12" in back and 6" in front. I can do all that but want understanding of what changes the car will make when the bars get moved? How much preload do I put on the top right bar?

 

I understand the bottom bars need to be level or slightly down and the separation between bars need to be around 12" in back and 6" in front.

Just to clarify: This was NOT from my site.
http://www.racetec.cc/shope

 

Do you have a ARB if not start there it will make it a lot simpler for you.

LOL @ Billy

You should be starting at or just above 100 % anti squat and adjust from there not just a static bar adjustment.

 

Instant Center window of opportunity for most cars.. 46" to 60" out and 4 to 8 inches up..

I tell people to start with the rear spread as close to 12 inches as possible, use the bottom hole for rear lower mount, keep the lower bar close to 1/2 to 1 degree down in the front (no more than .375 lower in front than rear), make the front spread around 7.5 inches.. Start there and see what the tire wants from there...

 

Instant Center window of opportunity for most cars.. 46" to 60" out and 4 to 8 inches up..

I tell people to start with the rear spread as close to 12 inches as possible, use the bottom hole for rear lower mount, keep the lower bar close to 1/2 to 1 degree down in the front (no more than .375 lower in front than rear), make the front spread around 7.5 inches.. Start there and see what the tire wants from there...

Based on your post, dropping the bottom bar down one hole in back and two holes in front would get me closer to those numbers. Would it have the same effect if I moved the top bar up one hole front and rear and the bottom bar front hole down one?

I will try to get 100% antisquat and the instant center from 46" to 60" out and 4 to 8 inches up (but from what?). What about the preload and adjustment in top right bar and adjustment in the anti roll bar? Sorry for the newbie questions but ya gotta learn sometime right?

 

"Up" is a term from the ground plane and UP this many inches ( the ground under the tires)

 

So 46 to 60" out is the intersect point and 4 to 8" up is measured from the ground to that imaginary intersect point?

 

Yes.

Assuming equal angles, the difference between moving the bottom bar down two holes, vs moving it down one and the top up one would be the IC height from the ground.


The best explanation I ever got was from my ol' man. - Take a 10' piece of pipe and set one end in your belly button; you're going to pick up the opposite end. Is it easier to pick up from the ground or from on top a table? Is it easier to pick up while holding 1' out from your belly or 2'?

 

get the 4 link wizzard or a program like that. it will help out tons.
you can make the adjustments on the computer and print out every option avalable.

 

Just curious, what formula do you use to figure out the intersect point of the two bars? Also, would this setup work better on the street as well?

 

You can use graph paper using every block as 1 inch so you can calculate every change, I'm not sure what computer program will do the same. The more HP the further out you will tend to go. I was testing years ago with a small block Beretta. I moved my intersect point to just under 40" which was great for pictures, 3 ft wheelstands straight as an arrow going 8.80's 20 years ago.

 

Jeff, I'll give you a call this Saturday when I'm working on the car. Thanks, for the phone number.

Billy, as far as my passing notes in Algebra 2 class... No not really, I just have a bad case of CRS (can't remember sh!t) LOL

Thanks for all the replies. I'm confident I will be able to get this suspension working with your help!
-Chris

 

Here's a post from another forum:

I'm tired of waiting. Let's bust some more myths! Specifically, these 3:

* Lower link angle is, in itself, significant.
* 4link spread affects weight transfer.
* Instant center distance forward is, in itself, significant.


Consider a competition 4link. To simplify the calculations, rear pivot points will always be directly above or below the axle centerline.

"Out" will always be the horizontal distance forward from the axle centerline and "up" will always be the vertical distance from the strip surface.

The lower link is 6 inches up and is horizontal.

The rear pivot for the upper link is 20 inches up.

The instant center is 50 inches out, which means that, since the lower link is horizontal, it is 6 inches up.

The thrust (horizontal force) at the rear tire patch is 3000 pounds.

The lower link would be in compression and the upper link in tension.

The slope of the upper link is 6 minus 20 over 50 or minus 0.28 . This means that the vertical force component, acting in the upper link, would be 0.28 times the horizontal force component. Since the lower link is horizontal, this would be the only vertical force acting against the vertical force at the tire patch. In other words, this would be the total weight transfer carried through the links.

For a horizontal force balance, the horizontal force carried through the lower link, less the horizontal force in the upper link, must equal 3000 pounds. For a moment balance, 6 times the lower link horizontal force must equal 20 times the upper link horizontal force. This gives us 2 equations and 2 unknowns. Solving, we get an upper horizontal force of 1286 pounds tension and a lower horizontal force of 4286 pounds compression.

So, the weight transfer carried through the links is 0.28 times 1286 or 360 pounds.

Now, we'll discard that lower link and install a new link above the upper link. In other words, what was the upper link is now the lower link. This new link has a rear pivot which is 100 inches up. No, it can't be built, but it CAN be calculated and the results will be interesting. Since the instant center is still 50 inches out and 6 inches up, the slope of this new link will be 6 minus 100 over 50 or minus 1.88 .

Total vertical forces will now be 1.88 times the upper link horizontal force downward less 0.28 times the lower link horizontal force upward.

The horizontal force balance remains the same, but the moment balance is now 20 times the lower link horizontal force less 100 times the upper link horizontal force. Solving, we get an upper horizontal force of 750 pounds and a lower horizontal force of 3750 pounds.

So, the weight transfer carried through the links is 1.88 times 750 minus 0.28 times 3750 or 360 pounds. That number sounds familiar, doesn't it?

But, we're not finished. A line through the tire patch and the instant center is a line of constant percent antisquat. So, let's move the instant center out along that line. We'll move it to 500 inches out, which would mean that it would be 60 inches up. We'll return to the original link arrangement: A lower link with a rear pivot 6 inches up and an upper link with a rear pivot 20 inches up.

But, for the link lines to intersect at the new instant center, the slopes have greatly changed. The slope of the upper link is 60 minus 20 over 500 or 0.08 . The slope of the lower link is 60 minus 6 over 500 or 0.108 .

Total vertical forces will now be 0.108 times the lower link horizontal force downward less 0.08 times the upper link horizontal force upward.

The moment balance is as it was for the first case: 6 times the lower link horizontal force must equal 20 times the upper link horizontal force. Not surprisingly, the horizontal forces are the same as in the first case: 1286 pounds tension in the upper link and 4286 pounds compression in the lower link.

So, the vertical force is 0.108 times 4286 pounds downward less 0.08 times 1286 pounds upward or 360 (there's that number again!) pounds downward.

So, the weight transfer carried through the links is the same regardless of extreme changes in lower link angle, 4link spread, or distance out to the instant center SO LONG AS the antisquat percentage remains unchanged.
http://www.racetec.cc/shope

 

Billy I have seen you post this a few times.. and again.. it is some pretty cool mathematical exercises.. but when it comes right down to it.. The link location in relationship the the centerline of the housing, even with the same IC, changes the way a race works, look at any ProStock car form the early 80's then look at one from the mid 90's on and you will see a drastically different looking set of brackets, they lowered the mounting for both the upper and lower mounts and increased the available rear spread.

Now why would this have been necessary if the only thing that matter is the IC?

Now here is where I think the Math becomes a problem..

As a race car launches.. there is a push through the lower bars and pull through the upper bars but there is a transition to where there the pull from the upper bar decreases and moves towards pushing..

How much that is? I dont have a clue.. Does it matter if we know how much? Nope, as long as we know how to position the bars to make the car work properly..

 

Now why would this have been necessary if the only thing that matter is the IC?

It was "necessary" because someone along the line came to a false conclusion. When adjustments are made solely by changing the upper link angle, it is impossible to retain the same antisquat percentage. Someone made a change in rear spread while changing the IC out, got a performance improvement, and said, "Aha! The car likes that rear spread."

The performance improvement was due to a change in antisquat percentage, NOT a change in rear spread.

As indicated, the rear spread can change...as an example...from 14 inches to the ridiculous value of 80 inches, but the vertical force carried through the links remains EXACTLY the same IF...and this is the hooker...IF the antisquat percentage remains the same.

...but there is a transition....

There is no "transition." It is physically impossible for the upper and lower link forces to change disproportionally during the launch. Force and moment balances must always exist and these balances are determined solely by the geometry.

This was not a mathematical exercise. Mathematics is simply a tool used in the analysis of a situation existing in the real world.
http://www.racetec.cc/shope

 

I would agree and for the same reasons and I am sure that math will work for that too, I use Billy's sight as a theory and follow it as relitive not literal. however it always comes back to math and what your tring to get to, and get around which maybe more important

 

this is a cool thread,,Thanks Billy for your patience and time!!

 

One of these times I would like Billy actually HELP one of these guys get their cars to work better, instead of speweing the same ol bs.


I agree with the others on this thread, get the IC between 50 and 60 out, 3 to 6 up with a slight down angle on the bottom bar and let that focker eat. :rock:

Then take a ton of video and show some of these guys the data and fine tweak it from there

Good luck

 

Actually if you follow what Billy says, its VERY helpful. Its just over alot of peoples heads so it goes in one ear and out the other. This is not his fault. He is actually very helpful and will even spend his time on the phone with you, even about a crazy setup that has never been done.

Good guy in my book.

 

Billy we will just have to agree to not see eye to eye..

I do know you have ALOT of information that is very helpful to many racers, and I applaud you for that..

But there are alot of things that the theories just do not work on when actually aplied to a functioning race car..

 

Well, we couldn't scale the car this weekend but I did take some measurements and moved the bars to what sounded close to what we discused in this thread. I moved the top bar to the top hole on the axle (19" from the ground)and the fourth hole from the top on the chassis (15.125" from the ground). I also moved the bottom bar to the third hole from the bottom on the axle (7.75" from the ground) and the bottom hole on the chassis (7.625" from the ground). This is .3 of a degree down.

The rear bars spread is now 11.25" and the front spread is 7.5". The right top bar has one flat of preload, the pinion angle is 1 degree down and the anti sway bar is in the neutral position. The WB is 108" and the cam centerline from the ground is 17.775".
Are there any problems with this set up or is there a better set up?

According to Billy's charts I'm way off or I did something wrong??????????
Thanks, Chris

 

Is that enough information to tell me what my IC is and how many inches "UP" it is at those settings?

 

Well, I had to make a couple of assumptions, but Page 13 yielded an antisquat percentage of 63 and up and out of 7.4 and 70.7 inches. I wouldn't call that "way off," but I'd try to get the antisquat closer to 100%.
http://www.racetec.cc/shope

 

I think I will drop the top bar in front one more hole (That will give me 61.7" IC according to your page 13) and go from there.

Now what about the front... How much toe in and tip in at the top of the tire? This is a strut front end so I may be limited.

Thanks again for everyones help.

 

That will give me 61.7" IC....

Of greater importance, it will increase your percent antisquat.
http://www.racetec.cc/shope

 

Your toe should be around a 1/16th of an inch in. You want zero bumpsteer, so you want that to stay the same when the tires come off the ground. What struts do you have on the front-end, stroke of strut, springs, travel limiters?

 

Your toe should be around a 1/16th of an inch in. You want zero bumpsteer, so you want that to stay the same when the tires come off the ground. What struts do you have on the front-end, stroke of strut, springs, travel limiters?

I have HAL struts with 3" of travel and 350# springs (no limiters"). To get the front end off the ground I had to raise them so I only have 1/2" of up travel and 2.5" down. That gives me 4.5" of ground clearance. I may have to lower it a little. At ride height the tops of my tires are tipped in around 1/4" inch. There is no toe in according to the tape measure. I may have to put it on a alignment machine. (Thanks for the offer Randy) The next time I will get to the track is on the 23rd. I'm hoping to get some testing done at Jackson. Hopefully I can get down the track straight.

 

Billy gives out very useful info TT. I don't mind helping you out at the track sometime also.

I have a friend that sets up all our front ends and double checks rearend squarness on a computerized alignment machine here local. Its will even tell if your housing ends are on straight , check bump steer , etc. I can hook you up with him if your are interested.

 

Have you made a fullscale drawing of your four link? It takes some time but having your intersects in full scale will make your adjustments easier to understand and make. a car with that power level should be between 50- 60 inches long and around 3-6 inches up. I know thats a big spread but it will get you in the ballpark. having a full scale drawing (fully plotted) will show you whats available. hope this helps. are you near lewisberg? i have a friend there thats very well versed in setting up high horsepower cars. I can get you with him if need be.

 

I'm hopefull that my current settings (IC-59, 7.5" up and 77% AS) will be good this weekend but how would the car react if I dropped the front top bars down one more hole to (IC-48.5, 7.5" up and 94% AS). Just curious how will I know when to make that adjustment? What will the car be doing or not doing?

 

whats the car weight on front, and back ? put bottom bar level with ground and make the intersect point of the top bar at the place were 55 to 60 % of the weight is from the back

 

Unfortunately I have not had the car on the scales yet so I don't know the percentages. I'll just have to try it out at the track.

 

That front spring is entirely too heavy. You need something in the 200 to 250lb range. You're going to need that stored energy.