Where is the article that Ed from ED-VANCED ENGINES go?????

Old 08-17-2011, 11:16 AM
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Default Where is the article that Ed from ED-VANCED ENGINES go?????

I am looking for all that info that Ed wrote for the moderators back in March of 2007 about 4 link basics, anyone know where or how to get to it? I want to send a friend to read it all, thanks.

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Old 08-17-2011, 11:47 AM
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You have a PM.
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Old 08-17-2011, 12:40 PM
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Old 10-26-2011, 06:51 PM
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Send it to me please at [email protected]. Thanks, Frank.
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Old 10-27-2011, 09:02 AM
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Originally Posted by md80drvr
Send it to me please at [email protected]. Thanks, Frank.
Email sent. You may need to check your junk email file. I sent it from my yahoo email.
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Old 12-13-2011, 07:24 PM
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have been looking for this myself, been sitting / rebuilding for the last two years, and now about ready to start assembling again, please let me in again
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Old 02-03-2012, 01:40 PM
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Well ,seems everyone wants a copy. I too would like a copy to compair to what ive been doing with my 4 link. Maybe ill learn something new, cant hurt right. Please send to ([email protected] ) Thankyou
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Old 02-03-2012, 04:12 PM
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How about I just repost it.

That'll be $29.99 from everyone that reads it and $49.99 if you copy it.
Now don't try to short me 'cause I can see you through your web cam.

PS. Don't spill that coffee cup on the keyboard!
:wink: and you sir need to clean that desk off!

Posted: Sun Mar 25, 2007 3:57 pm Post subject: 4 Link Basics. Theory & Help Instructions

I was asked to make this post here, by one of the Moderators.
Previously I had begun this on another board and it got too large. I have since added quit a bit more to it.

Introduction to theory and descriptions.
Part 1

My first and very real suggestion to you, and to all racers is to buy some books on basic racecar chassis design and adjustments.

I will post three of the links to sources, which may be helpful for you to purchase. You will discover that if you research and read writings by different authors and builders, that they all do not use the same theories or the same terminology.

This can get confusing if you do not understand that some of the different terms are describing exactly the same thing.
Examples are;
Tire or chassis Separation = Anti-Squat = Tire Hit.
Negative separation = Squat = Not enough tire hit.
Neutral Line = Line of Theoretical Instant Center

Many years ago Alston Engineering, Chris Alston, developed his own theories and his ways of explaining. He also sold many chassis training tapes and also conducted chassis schools all over the country and the students came out with words and theories and descriptions which were different than what the other chassis men like Don Ness, Willie Reils, Don Hardy, Wolverine (Tom Smith), Ron Butler, Gateway, Paul Peyton, were using. Those guys used the same terminologies that Most of the older guys like me were used to, so we were all talking on the same page. We all could actually talk and discuss suspension tech on the phone and the other person knew what each other was meaning.

This is not Trashing Mr. Chris Alston, far from it. He has contributed much into racing suspension and chassis from where we all were years ago. Were it not for his clinics and schools, it is likely there would still not be many good chassis shops around. I give him thanks and appreciation for what he has brought to us all.

Now there is so many different ways to explain theories that I too get lost in their explanations. I have still never seen any benefit to using the Percentage of Rise theory. Yes it does work once you can figure what is your theoretical Percentage of Rise. None of the theories take into consideration the individual car's power differences or gearing differences etc. So to me it is all fictional or loose theories of what is an actual "Squat/No Squat/Anti Squat Line". No matter what fictitious percentages you call it the bottom line is you are still moving your Instant Center, up or down or forward or backward, just like we have been doing for ages. [Note; this is only my opinions.]

Now days, many of the chassis builders are using the words originally started by Chris Alston, and also some of the Chrysler Engineers, and now being frequently used by many who were schooled in them, and later picked up by Dave Morgan and others. It uses a theory called "Percentage of Rise" and the words of Anti-Squat". Anti-Squat is easy to understand.
"Percentage of rise is not so easy". The theoretical perfect Percentage of rise isn't.

You can make either theory to work and to work right but I am more familiar with just using the Imaginary line of theoretical Instant Center (similar to Chris Alston's and others' Neutral Line. or the lower but, Parallel running imaginary, Squat/Anti Squat/No Squat Line than I am with using the Percentage of Rise, to explain things. I also can add that as big as Alston Engineering is that they have never had a Pro Stock car using their designs to ever be a winner or champion to my knowledge.. One time many, many years ago, they had a ladder bar car owned and run by the Yuill Brothers, that did win one Pro Stock race. However they did also do some great work on Dave Riolo’s car when it was first re-done years back and it worked very well. So you can do whatever you wish with that piece of worthless info. .


ETC Racing Programs



Tim McAmis chassis plotting software.
"Chassis Master"


Jerry Bickel Chassis plotting software.
"4 Link Wizard"
Plus get and read this treasure book;
Complete Guide to Chassis Performance Manual
"The Chilton Manual Of Drag Racing"


Dave Morgan
BOOK: Door slammers: The Chassis Book
Door slammers Chassis Tuning Package
(some good info here and some bad info too)



There are basic similarities when adjusting Ladder Bar suspensions, but you can only adjust Instant Center to be moved either up or down.

It is very beneficial for you to know or to learn just what happens when you adjust or locate any component of your rear suspension by using basic laws of physics. Also know and remember that with a 4 link that all suspension angles, measurements and adjustments rapidly or instantly change the moment you begin the launch applying forces of torque. Then it is almost as if the right and the left are seeing different adjustments because of the change in bar angles as the right rear tries to lift inside the right fender.

Anti-Roll Bars;
Anti-Roll bars do help a lot but they are another integral part of the entire rear suspension equation that needs to work in a balanced force with all other components of that rear suspension. Each piece is as critical as any other piece. Always remember that Anti-Roll Bars were not intended for adjusting Pre-Load. They are not named Pre-Load Bars, They are named Anti-Roll Bars, but with a few factory suspension cars like the Chevelle, Malibu, Cutlass etc and Mustangs the Anti-Roll bars can help when spring adjustments are not enough, and any bar adjusting would upset the rear alignment. On all other cars it is my opinion that they should always be adjusted to be neutral. I do not believe that Anti-Roll bars can be any benefit with a correctly set up and adjusted Ladder Bar car. I know there are many who disagree. There is no stronger torsion bar than a rear end housing if it is welded and is braced.

The other theory which is more commonly used is more simple in description and establishes a theoretical ideal "Point of Instant Center" or "Neutral Line" that uses an imaginary line from the rear tire contact point center that will be diagonal to the actual point of the car's real center of gravity. This is what we will use.

The Percentage of rise theory moves down below the actual center of gravity and then draws their imaginary
line to the tire contact point. For this article I completely will do away with Percentage of rise except just to talk against or to
compare to it.

Percentage of Rise (PR)
Anti-Squat (AS)
Neutral line (NL)

These are all words phrased in Chris Alston's Chassis Classes years ago and are now used by some shops that were trained in using them to describe what was taking place in suspension settings.

What happens when Torque hits Rear End from Driveline;
Know and understand that anytime torque is applied that your left rear tire will be trying to push down and your right rear tire will be trying to rise looking from the rear of car. All cars in any kind of racing or activity will exhibit this twisting motion if there is any form of friction coefficient existing between the tire rolling surface and the ground/track/road. The tendency will still be there to twist the rear with torque even with no tires or wheels. It is when you start to hook that it really shows up.

If your rear end was not attached with brackets, when the drive shaft rotates in the counter-clockwise movement (looking from rear of car), the entire rear end assembly would rotate counter-clockwise like a propeller if it were suspended in the air and had room to move. The drive shaft rotates in the direction that engine torque is applied to it. Even attached with bars and suspension it still wants to rotate.

Always keep in mind that As greater torque is applied the rotational force will be greater so as power increases the car will want to pull to the right, which we counteract by suspension preloading in adjustments. If doing any bar preloading do know that even only 1/2 turn is an extreme adjustment from neutral load position. We usually preload bars in increments of portions of a nut flat when we are close. 1/2 of a flat can make a car go straight that was trying to veer to the right. Too much bar preload will pull us to the left and quickly can get us into the wall.

Corner weight adjusting methods;

Physically moving weight
adjusting weight preload with springs or spring adjustments
adjusting preload with 4 link or ladder bars
adjusting preload with an anti-roll bar (not preferred).

A lot of times what is considered to be an ideal weight bias on the corners with car sitting in a shop is not close to ideal weight bias during launch and going down the track.

Funny thing about weight bias and preload;
What can make a straight launch can also cause some down track problems and unequal unloading while stopping. There has to be a balance of what launches good, drives good, and stops straight.

To further complicate it all is that the more power you launch with the more the car will drive to the right, so we add preload into the right rear and the left front to act as a counter force.

To make it even trickier is that if you have a car just right to launch good and stop and drive good, and you lose power or reduce tune-up etc, then the car will drive to the left.

The higher the horsepower is, the trickier it all gets.

Bar Pre-load ecample;
How many of you noticed that when Jeff Naiser was sorting his car out and running in the middle of the pack and at times not qualifying, that then his car was always driving initially to the left and would then get straight further down track. BUT when he was finally able to get his full power to the track and ran his string of low 4.50's and 4.40's that his car launched and ran and drove arrow straight. You see, his car was set up to run the number. When he was off on power it drove left. How could they have known what preload would work best when the car was able to do full power? Several reasons. Good educated guessing with much 4-link experience with that same car and lower powered engine. The first few times out the car ran and hooked pretty good and gave then indications of what to expect with it. Robert Fulmer is a very good suspension man.

Ladder Bars or 4-Link;
I personally prefer a 4-link set up to anything, IF I am the one doing the tuning and adjusting. If not I usually do a different suspension set-up so customers can make simple changes. Ladder bars are very simple and are easy to teach a customer how to adjust and when to adjust them.

Truth is there are many racers using 4 link that really have not a lot of understanding of physics and why to adjust what. I have seen racers adjust bars up and down going far too radical of a change pretty much with all adjustments. After I saw a question and answers to those questions in a Forum between two different owners of Pro Mod cars that were professionally built and I saw that the answer given could cause a serious crash is when I began writing this.

Most of the time minute adjusting can make huge differences. Simply a small change in rear ride height will alter the bar angles and the active point (Actual) of instant center. Slightly moving the front of the bottom bar and top bar down (lowering actual instant center, and at same time not moving it forward) can at times make a big difference in a car that tries to lift the left rear of the car like in a barrel roll, and also can help to keep the front tires from lifting as quick. This applies to cars with equal length bars. This quickie rule of thumb does not apply equally to cars with two different length bars. The effect will be similar but the Instant Center will also move rearward at the same time.

Contrary to what many of your chassis shops will set and their adjustments, what you really want is in most instances the bottom bar will be near to level while under hard torque and full acceleration, not when the car is sitting still with no torque applied. Sitting still it will likely have the front of bottom bar lower than the rear of the same bar, by just a few degrees.

Bottom Bar on 4 Links;
If the bottom bar is close to level before the launch and the left front side of car is rising and the tire is planting lifting the rear, there can be a very negative effect called "Barrel Roll". That is because with all the suspension movements the bottom bar on the left can end up pushing upward and the bottom bar on the right side is pushing downward. Oops! Can you say Whoopie!. Animal Jim's car was a good example of this, also Charlie Bucks, car exhibited that trait. I also had one that did that until I changed the bottom bar. Simply lowering the actual point of instant center, which would also place the bottom bar in a downward angle, can help eliminate this. Anti-Roll bars now also help this. If lowering Instant Center is the only desire in change while keeping actual distance of Instant Center the same, you must move both bottom and top bars the same amount in the same direction. You can also move the rear of both bars up one hole if it looks close to the same IC length when you plot it out on paper, computer or however you plot out your suspension positions. There are now computer programs that can help you quite a lot as I mentioned earlier in this thread.

If you will look under any top 16 Pro Stock car you can notice that the bars usually have not been in more then two to three different holes even from the very beginning. Most of the adjusting between the holes comes with the initial base lining while the car is new. Once a good overall baseline is found, most other tuning and adjusting to differing track conditions is minimal. Even slight adjusting changes make a big difference.

Bar Spread Bar Mounting Locations;

Someone asked about rear bar mounting positions and if it is important. on another board.

Yes it is but in my opinion at times some people make too big a fuss over bar spread in it's priority of importance.

A correct set of rear 4 link brackets will measure shorter from axle center from top bracket holes and longer on bottom for bottom bracket holes.

This is because of mechanical reaction time of top vs bottom and because of mechanical force or leverage of top vs bottom which is a multiplying factor of how much torque gets appied to either bottom or top bars.

A correct rear 4 link top bracket will also have holes for adjusting Starting at bottom hole forward of vertical axle center and each additional hole will be farther from horizontal and verticle center of axle housing. Meanwhile at the bottom the bottom bracket will have all adjusting holes to be in a straight vertical lineeither at vertical center, but usually slightly forward of vertical center.

The longer leverage at bottom will react quicker but not as much immediate force. The shorter leverage at top will react slower but with much greater instant force.

So yes' It is important.


Shocks for Drag Racing

I feel that good quality Double Adjustable shock absorbers are one of the most valuable suspension tuning aids there is and is money well spent. Cars running quicker than a 9.00 in the 1/4 really need them.
Side Note;
Coilover shocks well suited to street usage (no brand names) are not Drag Racing shocks. Shocks, and the good shocks that are primarily designed and built and tuned for Drag Racing absolutely will out perform any designed and built for the street coilover shock. You can still use the Drag Racing shock on street/strip vehicles though.
The 90/10 shcoks were designed to hook a 500 to 600 horsepower car on 7 inch wide old school tires on old tracks. hey in my opinion have no place on any modern day Dag Car including in the Stock Classes. Better ways to get better weight transfer when it is needed and not have to deal with the nose in the air position all the way down the track catching maximum wind resistance. Check the Stock Suspension Section.


The Chassis design software by Bickel Race cars & QuarterMax, should help you to understand better and to see on your computer what can change and the reaction when even small changes are made in bar adjustments.

I cannot tell you in a forum how to adjust the suspension of your particular car. No one can.

This will end the introduction to 4 link basics. Next are instructions to find your car's Center of Gravity without scales.
Cont --> to Part 2

4 Link suspension basics

Cont from Part1

Finding Car's Center of Gravity;

IN part of this section, I shall try to teach you how to determine what your actual front to rear weight distribution is by using stuff you already have, without having to go pay a chassis shop to scale your car if you are on a tight budget or there are no scales near you. Of course you are better off to scale the car but we have not always had individual wheel scales in drag racing so here is an old fashioned method that has worked for years in some of the baddest cars there was.

With 4 wheel scales it is easier to find the center of gravity and center of balance. You take the instructions I gave and use them in reverse to find where it is from the front to the rear. So if you know the total weight and the weight on each end then you will be able to calculate the percentages on each end with that info. Then you just use your wheelbase and figure for example 45 % of weight on the rear translates to 45 % of your wheel base from the rear would be the center of the car so that should be the balance point.

Write all of this info down so you will keep it in a log. Any adjustment changes you will write down and the results of them always.

where is your actual center of gravity of the car.

What is your actual wheelbase

what is your rear tire diameter

Place a weight in the driver's seat equal to the weight of driver. Load fuel tank, water reservoir and make the car balance the same, as it would be weighted while at the starting line.

get two jack stands. (I actually even place short angles on them so there is an actual point instead of the larger top of jack stand).

Now you will think I am nuts.

You are going to balance the entire car on only two jack stands, one on each side. Do not give up. The car will perfectly balance. Mark that place with a piece of thin "3M FinishLine Tape" (Buy at Paint and body supply) attached to each side of your car in a level vertical line. That is the point of front to rear balance of your car. Good to write this down by measuring from balance point to the center of both front and center of rear wheel hub.


Make a mark where a level vertical line is at the center of balance, to the ground or floor. Mark a level vertical line where the rear-housing center is. Mark a level vertical line where the front hub center is. All of these three vertical lines will be used to determine your actual front/rear weight distribution.


Measure your exact wheelbase from center of rear housing marked vertical line to center of front hub marked vertical line. Write it down.


Divide the distance measured horizontally level on the ground/floor from the rear housing center to the vertical level line that is at the car's point of balance by the measured wheelbase. That will = your rear weight percentage or percentage of weight on the rear wheels. Write it down.


Divide the distance measured horizontally level on the ground/floor from the center of front hub to the marked vertical line at car balance point by the measured wheelbase. That will = your front weight percentage or percent of weight on front wheels. Write it down.

Lower car to the ground and bounce it a few times to get it to be at normal ride height.

measure from ground level to center of camshaft. That should be close to the height of center of gravity. Write this measurement down.

At the exact place previously established as the car's balance point, at the height of the center of camshaft, will be your
theoretical point of center of gravity of your car. Mark that spot on the door or fender by crossing two thin pieces of tape in an
X. Take a picture of side of car with tape on it.

Measure all the discovered dimensions, including the measurements from front axle and rear axle to that place where the car
perfectly balanced. Write all this down in a notebook to keep.

With someone helping stretch the thin tape from the place you determined was the center of gravity of your car, in a downward angle to the bottom and center of where your rear tire is contacting the pavement. This will be the Theoretical Instant Center line (Neutral Line). You will keep this imaginary line in your mind forever once you begin using it. It is only a point of reference for you. Take a pic of tape positions on car from the side.

Take a picture of the side of your car with the tape showing the angular line from the bottom of rear tire to the place marked to show cam height at the balance point that we are calling the car's center of gravity.

That imaginary line is to be used as a reference as theoretical "Line of Instant Center". Some call it "Neutral Line". The actual (or active) point of instant center is the actual point where a straight line extended from your top bar and your bottom bar will intersect in an imaginary line looking like a triangle shaped like a Ladder Bar.

Use the narrow 3M Finishline tape, which you will find at auto paint and body supply houses or paint stores. If you use a magic marker, or pen or pencil to mark on your car you will have a nightmare removing the marks. Finishline tape will stick on and will easily peel off.

Place the 3M Finishline tape in a vertical level line on the car at that point of balance. Which is easier when you have scales to weigh the ends with. At the camshaft ht place a piece of the 3M Finishline tape in a horizontal line at camshaft ht. That X where the two pieces of tape cross should be your Center of Gravity of the car. That is Center of Gravity. That is not where you want your Instant Center. I use Center of Gravity as my reference point for pretty much everything related to suspension adjustments.

Adjust Instant Center & WHY;
As you move your actual instant center further forward or below that Theoretical "Line of Instant Center" (Neutral Line) (It is an imaginary
angled line, where you had your tape) The rear suspension hit will decrease, but the front will have a tendency to rise on it's suspension. Likewise, If you move your actual "Instant Center" back or up toward the Theoretical "Line of Instant Center", the rear suspension hit will increase.

As you move your actual or active Instant Center point forward of the Imaginary line of Instant Center (Neutral Line) you will promote more front suspension lift and less rear tire hit.

As you move the actual or active Instant Center to the rearward you will give it more tire hit and greater rear suspension reaction and less front suspension lift.

As you adjust for increased rear tire hit, you will be at the same time be adjusting from less effect of actual bar lift in the front.

When you adjust for decreased rear tire hit, you will at the same time be adjusting for more effect of actual bar lift in the front.

If you reach the Ideal, as the tires hook the car will rotate on the rear axle and will also try to lift the front, as the car is moving forward.

Hopefully you will know that a low torque engine will be needing more adjusted Hook or Tire plant than will a high torque BB car. As the power level at launch increase you will need less and less adjusted hook in your suspensions. Sounds strange but that is the way it is.



Contradicting my words;
That simple explanation is and can be misleading. Best example is the old Chevy factory 4 link. According to suspension theory that car should be very wheel stand prone, because the point of actual instant center is far forward in front of the car and is also below the Theoretical Line of Instant center. Problem is it is so far to the extreme forward that only a tremendous amount of power with huge tires to hook could possibly get it up. That car's factory tendency is to actually lift the rear tires under hard acceleration is the reason it squats. Only changing the upper bar angle to a lower front position, or moving the front of bottom bar up or the rear of bottom bar down, will give major rear tire hit on that car. Now you could also make a way to change the forward and/or rear lower bar mounting position and in essence end up with a factory but modified adjustable 4 link. Lol. Rear shock dampening control is needed after making any extreme bar angle changes to that style of suspension. You can also help those cars by lowering the rear ride ht. That does change the bar angles some.

There is so much more to say but there is just not enough room in a forum to get much deeper than I have.

Times past in suspension adjusting & plotting
In the older days we used to draw out all the dimensions I just discussed on a shop wall or on a shop floor to plot out the different bar angles. Now you can use computer programs. I do still do it to scale on a piece of paper though when no computer is present. Actually by now it is pretty much in my head of what to do based on results observed by Video Camera seen in slow single frame advance or with data provided on shock travel. In really extreme bad conditions watching the car can tell somewhat it needs, but be aware that things are happening quicker than your eye can see. Best is a video shot at an angle covering whole car from left rear corner. A good quality video shot from left rear at an angle will tell you much when play back one frame at a time.

Please try to learn as much as you can about this subject if you are tuning your own 4 link. It can get dangerous if you go too extreme.

Also remember also that after your run the 4 link adjustment and rear components are also important. You do not want severe rear suspension unload when you back off it either. When you cross the traps you do not want to hit the brakes and experience severe rear suspension unload or if you pull a chute. We may later get into using the actual car's center of gravity calculated at speed to determine where to place the chute tether attachment point.

One other point to make.
If you set your preload with a top bar do not get wild and crazy. Before you set preload with all weight in the car you should be able to easily slide the front bolt out after removing the nut. One top bar will be used to set and adjust pinion angle. The other will be used to adjust preload to preload the left front/right rear weight bias. With this adjustment a little can make a big difference. 1/2 turn of bar pre-load is extreme.

If you are using the top right bar to adjust pinion angle, the top left bar will be your pre-load bar. In this example you will
lengthen the top left pre-load bar to pre-load weight to the left front and right rear tires. Be careful just a 1/2 turn of pre-load makes a huge difference. Usually even a fraction of a nut flat can be noticed in your handling.

If you are using the top left bar to set pinion angle, then the top right bar will be your pre-load bar. To jack weight in
pre-loading using the top right bar you will make it shorter. Again just 1/2 turn is a huge difference.

Bottom bar length adjustments are used only to center the rear in alignment with the chassis

The rear and the front springs should be no stronger/heavier than what is needed to support the weight of the car while sitting at starting line. With strong and fast cars rear double adjustable shocks are a must.

How do we know if we have the correct spring rates;

To begin with we need to understand tha the spring in a drag car has only two functions.

Support the weight of the car up to the starting line.
Give as smooth of a ride aas possible while going down the track.
Possibly a third function is to support the additional weight during weight transfer.

If you can not adjust lower spring adjustment enough for there to be 75% maximum, to 62.5% minimum of the total shock travel inside the shock while car is sitting at rest with all weight in it including driver, you have the wrong springs for the car.

Usually a 2900 to 3000 lb car will want between a 130# to a 145# rear spring on it, but that is never absolute. I know Outlaw 3,000 lb cars working well with 150# springs even. You can not go by just the rear weight to guess what springs you need. Too many other thing figure in, such as the exact shock mount placement in relation to center of axle, Shock mounting angles if any,

You let the car tell you what it wants and you can do that without ever going down the track. At all times you want to keep enough compression available for car to sink on shocks some when front weight is transfered to rear by wheelstands and/or accelleration forces which shove a bunch of weight to the rear even if no wheelstand. You also need enough compresion to allow a good smooth ride down the track. Bottoming or topping a shock out is a sure fire way to unload tires and if at high speed to crash.

Support car on all 4 wheels so you can get under it. Disconnect anti_roll bar on one side (if equipped) just to be sure it is not interfering. adjust the bottom spring adjusters all the way even on both sides, doesn't matter right now how high or low. Measure how much of the shock ram is sticking out of the shock. If more than 50% of the total travel is outside the shock, you need to adjust spring adjusters down so that you will only have appx 25% to 37.5% of the total shock travel sticking out. If you can't and at all the way down on adjusters, that means the spring is too stiff. If you have adjusted the lower spring adjusters as high as you can and you still can not get at least 37.5% to 25% of the total shock travel to stick out of the shock, that spring is far too light and the shock will bottom out while lanuching and while going down track when it encounters any sort of bumps.

The more rear travel the shocks have available the bettter it is to tune. At one time people were using shocks with 5 inches total travel in the rear. That does not allow much room for any error. 6 inches is far better and over 6 inches is even better. Problem is that the longer travel shocks do require more room to mount.

I will use the 6 inch travel shock as my example;

Ideal will be 1.500 to 2.25 inches of ram inside the shock I can not accept anything else if I am tuning the car.

This tolerance does allow it to work with more than one spring rate spring becuase of the lower spring mount adjustability.

I do believe I will be adding this into my 4 link article at Racing Junk. I did touch on it but not this much.

Hope this helps you.

Oh' A ladder Bar car will need to hit the tires a little harder than a 4 link car will becuase of the difference in how they work.

If you are also expermenting with power adders etc. Know this, no matter how crazy and backwards it wiill sound. The more you increase power to the rear wheels the less suspension action you want front and rear.
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