experiences 4link setup slippery tracks?

[BillyShope]

...what IC length and position might give the most front rise?

IC length has nothing to do with it. IC position (height) has nothing to do with it. But, when you divide the IC height by the IC length, then divide the result by the ratio of CG height to wheelbase, and, finally, multiply by 100, you have the percent antisquat.

In other words, it doesn't make any difference whether the IC is 50 inches out and 10 inches up or whether it's 50 miles out and 10 miles up, the effect will be the same.

This is because the resultant force acting on a freely pivotable link must have a line of action which passes through the pivot points. When viewed from the side, the rear axle assembly can be considered as one big link, having pivot points at the rear tire patch and the instant center. The resultant of the dynamic forces carried through the suspension links must then act on a line which passes through the rear tire patch and the instant center. (There are also vertical forces being carried through the springs and shocks, but these can be considered independent of the forces carried through the links. And, these spring and shock forces go to zero at 100% antisquat, anyway.)

An infinite number of lines...each representing one of an infinite number of values of percent antisquat...pass through the rear tire patch. So, if you want 100% antisquat, it's only necessary that the IC be positioned anywhere along that 100% antisquat line. The exact position is totally unimportant.

An extreme example is when the upper and lower links are perfectly parallel. Since parallel lines meet at infinity, it would only be necessary that the links be parallel to the line representing the desired value of percent antisquat. The IC would then be an infinite distance forward and an infinite distance up, but the result would be exactly the same as if the IC were only 50 inches forward.
http://www.racetec.cc/shope

[ccrp]

hmmmmm, judging your words carefully, wouldn't that contradict common believe like it could be read in so many magazines and suspension books?

I don't know how many publications wrote about IC height and its effect although it perfectly makes sense what you say with the IC line and staying on it.

mathematically a 100% AS is a 100% AS no matter where it is located along that line.

now, am I only after a certain AS value or I am after a AS value and specific angle of bottom/upper bar. Let's assume I can get 100% AS with bottom bar angled down, nearly flat or angle up with various IC lengths of course - which one would be preferred or it doesn't matter anymore as we just look at the kinematics of the whole axle/rod assembly?

[BillyShope]

now, am I only after a certain AS value or I am after a AS value and specific angle of bottom/upper bar.

As you know, the IC is determined by the intersection of the link lines. As an exercise, I once did a free body diagram of the rear axle assembly with two very different conditions. In both cases, however, the IC remained in exactly the same position.

In the first case the lower link was horizontal and the rear pivot for the upper link was located at a reasonable height.

In the second case, the rear pivot for the lower link was 60 inches above ground level and the rear pivot for the upper link was 150 inches above ground level.

Remember, the intersection of the link lines (the IC location) was the same in both cases.

The resultant force had the same line of action and the same value in both cases.
http://www.racetec.cc/shope

[want-a-be]

What kind of IC have you been running/trying? How high are you running the IC off the ground? Where are you running the front shocks and the rear shocks at on the settings?

Have you used a jack and made sure that the rear suspension is freely moving through out it's range of travel? Sounds like you may have some sort of binding going on.

Are you running a wishbone track locator? If so,... are you sure it isn't bottoming out some how?

Don

I'd still like to know this information,...just for shyts and giggles.

Don

[ccrp]

there is no bind in suspension anywhere, actually it got a track locator not a wishbone.

shock setting on front Koni struts as far as I remember is 1 (softest) on extension and 5 or 6 on compression. In the rear right 5 compression and 4 left, extension I don't really know as I can't see there at the moment.

here is a pic of rear

[bracketracer]

Looks a little Funny ........Upper 4 link bars are in the lower 4 link holes and the pinion is pointing up Oh
and the anti-roll bar should be in the center of the axle tube also..

When that is at ride height your IC must be in the dirt

[ccrp]

that was the 50% value like I bought the car, yes, IC height was about 3 feet under ground

pls not forget, rear axle is hanging down on the lift on picture that's why ARB looks that way. at ride height it is level

[Dave Morgan]

ccrp,
I have been developing a generic IC location that has been working very well with a variety of cars. I'll get into that in a moment but I'd like to focus on some advice Don gave you. Check for the basics, like bind. Whenever a car does something stupid or unpredictable, bind or flex are the primary culprits.
My generic fourlink setting is simple:
- Place the lower bars parallel with the ground
- Put the upper-rear bars in whatever hole is closest to the axle centerline, which will probably be the lower hole.
- Position the front of the upper bars in a hole that places the IC very close to the center of gravity. This will give you a basic setup that may require some front shock/spring changes and rear shock changes. I'm aware that some may say this setup will porpoise, but I've tried it on low and high nine second cars and a seven second car and it works well.
Again, don't get too focused on the IC positions because it sounds like there are other problems in the car. Find that first.
Sleep well!
Dave Morgan

[ccrp]

Mr. Morgan,

thanks for reply. I checked again and there is absolutely no bind in suspension, all is perfect oprder and moving freely. Car did run a best of 7.08/312kph several times in Mantorp Park/Sweden with same suspension, shocks, wheels + tires sizes and ABR of course. Difference was engine/drivetrain combination, it had a 555 nitroused Shafiroff and 4 speed Lenco and now it sports a 632 14-71 blown BBC with race TH400

difference now is just rough unprepped airfield tracks.

due to a laptop crash I can not longer read my old 4link maps into 4 link analyzer software (which I believe shows your suggestions), thus I need to remap and remeasure my 4 link points and setup coming weekend.

[BillyShope]

Mr. Morgan,

thanks for reply. I checked again and there is absolutely no bind in suspension, all is perfect oprder and moving freely. Car did run a best of 7.08/312kph several times in Mantorp Park/Sweden with same suspension, shocks, wheels + tires sizes and ABR of course. Difference was engine/drivetrain combination, it had a 555 nitroused Shafiroff and 4 speed Lenco and now it sports a 632 14-71 blown BBC with race TH400

difference now is just rough unprepped airfield tracks.

due to a laptop crash I can not longer read my old 4link maps into 4 link analyzer software (which I believe shows your suggestions), thus I need to remap and remeasure my 4 link points and setup coming weekend.

Remember: It's the percent antisquat that's important and NOT the location of the IC. In other words, if a hole combination gives you an IC that's 100 feet in front of the car, but at the percent antisquat you want, go for it! See Page 38 of
http://www.racetec.cc/shope

[sg7365]

Dave Morgans book was great to use.
Chassis set up etc, springs, IC and mapping everything out.

My old car was a ladder bar type system and its hard to get what you want out of a ladder bar system when you run quick.

Got another car about two years ago with a four link(s/g and super street car).
Broke out Dave Morgans book again and I also broke out another book I had bought about five years ago and basically combined them, it was; Jerry Bickels Complete Guide to Chassis Performance.

Did many versions of the IC and IC height
and mapped it out on a table for the best projection.
I highly recommend using this book. It cost a little more than Daves but this might help you.
I've always had someone else do my chassis scaling and after reading this book-it was dead on-what I wanted. Read it cover to cover like you did with Daves book, understanding shock set-up, spring rate, chassis bind, setting a four link, rear end alignment, front shock adjustments-----too numerous to mention them all. And one of the biggest things I've learned is ensuring the chassis is square and true by the plum bob method. One thing I also did was to ensure the engine was plum bobbed to the rear end. Had a lot of fixes to do on that. When it was all done---car ran straight and true. Like Dave said in his book-you'll find out in the burn-out box if it goes to one side or the other. Straight is good.

That track that you run at-does not looked prepped at all.
Your rear end set up with the bars does not look correct and like someone said the pinion looks like it going up.
Hey ccrp-I bought this car two years ago, took it completely apart and wonder how they ran this car. It took 20 months (not rich but have a lot of time) went through everything, replaced so many bad or damaged components or just bad engineered. Learned a lot from Daves book in my early years and those two books are keepers.

[bracketracer]

Remember: It's the percent antisquat that's important and NOT the location of the IC. In other words, if a hole combination gives you an IC that's 100 feet in front of the car, but at the percent antisquat you want, go for it! See Page 38 of
http://www.racetec.cc/shope[/quote]

[ccrp]

it's been soem time but we now have carefully setup front suspension, mapped 4 -link, changed IC to around a 100% for starters and re-mapped 4-link after changing pinion angle.

@ SG, I know what you mean. Same here, went through every little nut and bolt and rod end and after 5 hours on the laser guided setup lift everything is a square, symmetrical as it possible can get, caster, camber, offsets you name it are where they should be and have been tweaked with scales. That should be all in order now.



As last resort pre-loaded left rear tire with about 90lbs on wheel scales. 340kg left rear vs 299kg right rear = 750lbs vs. 665lbs

this is the result now:




comments?

[sg7365]

Billy
I learn something new everyday and you opened my eyes up again and especially your web site and on page 38. I know you hate to hear this but--you are absolutely right in all what you said. I guess its time for me to go back to school and learn some stuff. I am going to read more on your site because you figured all the factors in of the whole car. I've read that before but you put everything in perspective. Now I am no expert but its always good to see someone who really knows what he's talking about and puts it in black and white so the everyday Joe can figure it out.

CCRP-what a car. I don't think you'll have any problems once your car is set up right.
I just redone mine again due to some chassis bind in the front and a little more weight. It was good to see things were all straight and true.
Thanks again for setting me straight Billy S.

Ron

[ccrp]

John, Billy, anyone want to comment?