ride height effecting the i/c

will lowering the rear of the car (ladder bar with coilovers) decrease the i/c ? therefore dercreasing the intial hit ?

Your limited with what you can do with a ladder bar set up, in the past lowering the rear on my car was always detrimenta to making it hook betterl, it gets into more than I can put into words on a computer screen..........I'm sure Dave will come along and explain in a lot better detail.

IMO the fox cars have the crank centerline real high in the car and this is a tough one to overcome without lowering it further.........which is a PITA.

Honestly Nick in your situation and considering I don't see you running a class such that does not allow them.........and your wife bought you a nice new set...........PUT THE DAMN WHEELIE BARS ON IT LOL!!!

Nick lowering the rear of the car will lower your ic height and change the angle of your a/s line.

This will raise the amount of weight on the top side of your a/s line and reduce the amount on the bottom half of the a/s line when force is applied by the rear tires. The weight on the bottom side is what your suspension is pushing against and causes the load to be placed on the tires , the weight on the top side rolls over on to your suspension.

bruno wrote:will lowering the rear of the car (ladder bar with coilovers) decrease the i/c ? therefore dercreasing the intial hit ?

Less initial hit leverage doesn't necessarily mean less hook. Lowering the I/C might make the car hook less, or it might hook harder, it just depends on what it really needs & how far off base the current setting is now.


If this is really about the recent double wheelstand/crunch pass it boils down to the fact that (A) you were throwing decent power at the rear tire hitting/planting it hard, (B) the car dead hooked, and (C) the car climbed the ring gear. But before you make a big "swing a hammer at it" change like moving the I/C around, my question is what have you done as far as fine tuning goes? Have you first tried all of the usable rear shock/front strut valving settings? Have you worked through the usable air pressure ranges? I guess what I'm asking is have you truely done a decent amount of testing/adjusting, or are we really talking about a limited number of hits before the double wheelstand/crunch pass happened?

Once you start getting into these kinds of "instant" power level increases that nitrous can deliever on a car that can dead-hook, you have to make a choice........riding out big wheel stands, or inducing some "tire rotation/wheel speed/getting up-on the tire" (or whatever you want to call it) or reducing power. Sure you can try to "calm" the inital hit on the tire some by moving the I/C around, but don't forget, you still have decent "at launch RPM" nitrous power also hitting/planting the tire too.

At some point with this "instant power" and a dead hook car you might even reach a point where you have the suspension adjusted as calm/stiff as it can go and it still wheelstands big cuz you're still hitting/planting the tire hard with engine/nitrous power. At which point you still have to decide.....wheelstand, or wheel speed, or reduce power.


So it's time to make some choices.......

(A) ride out the wheelstands (that means DON'T lift at the top then stab it again on the bounce).
(B) try to adjust in some wheel speed (more/less air pressure, tighter shock/strut valving, ballast on the nose, etc)
(C) put the fukin wheelie bars on the car and induce some wheel speed.
(D) reduce "at launch" power numbers (less total nitrous, delay nitrous with digi-set box, less initial launch timing curve w/digital 7 box)

I guess I'm thinking about this differently. How about increase power off the transbrake to help increase wheelspeed? I do believe utilizing the gear retard could help with this and possibly using a different gear ratio.

whatbumper wrote:I guess I'm thinking about this differently. How about increase power off the transbrake to help increase wheelspeed?

That is another possible option he could try.

But I sure as hell would have wheelie bars on the car before trying more launch power just for the safety factor (although adjusted higher than normal so they are less likely to effect/mask what effect more launch power has) just incase increased power happened to make it wheelstand a lot higher instead.

good point. we went from 4.10's to 3.70's to help with dead hooking to increase wheel speed.

I have a question. A rear suspension utilizing "ladder bars", is the most forward attaching point the I/C? If on the same "ladder bar suspension", moving the most forward attaching point up or down (bracket permitting) simply change the I/C or just the height of the I/C?

Dave.

Moving it up or down will change the ic length a very little amount because the axle centerline moves in an arc through its travel . The height setting will change most but it changes the line of force from the tire contact point through the chassis.

Its not the angle of the ladder bar in relation to being level with the earth that makes the difference, its the relation to the chassis center of gravity that does. Power is the biggest influence on how it works that's why if it dead hooks and has enough torque to wheelie it still will no matter how far from the starting line the car is.

Changing the ic to induce spin is just hoping or planning that by the time tire friction causes it to hook the torque level will be low enough or falling so it does not wheelie as bad and the leverage of the wheelbase will keep it down.

One must also consider the bar is pushing the car forward as well as trying to rotate upwards.............

richter69 wrote:One must also consider the bar is pushing the car forward as well as trying to rotate upwards.............

That is a good point, bottom bar angle (it's self) can have an effect separate from I/C placement.

The angle of the bottom bars on both ladder bar & 4-link (and eventually the line of force angle through the I/C) can sometimes have some unexpected results on the 3 action/reaction leverage forces related to/through the I/C (aka lifting the nose up, planting the rear housing down, & driving the chassis forward).

My friend's ugly Willys (and before when it had a camaro body) has been hampered for years with a limited selection of usable I/C choices all with the bottom bars pointing down at decent angles because the previous owner had for some damn reason cut off 1 top hole & 2 or 3 bottom holes off the housing brackets. I know they cut the top bracket hole off to gain some more housing/chassis clearance (and that's understandable). But cutting off the bottom holes was just a bad idea causing nothing but problems.

This real steep bottom bar angle caused the car to in effect drive the rocker panel/body/chassis down into the ground (at the chassis bracket) instead of forward after the initial hit separation & thus wasting time. This effect wasn't really suspension/chassis "squat", but was more the effect of the sidewalls remaining compressed & wadded up longer from the initial downward force of bottom bar's steep angles. This also kept the tires mosly dead hooked longer & hurting the 60ft every pass regardless of chassis settings & launch power numbers.

Fast forward to about a month ago after new taller/longer full height housing brackets have been installed on the rear end and the result is like night & day. Even though the I/C now is still in about the same place as before, the more favorable bottom bar angle drives the car more forward now after the initial hit separation instead of more downward. This has resulted in more usable launch wheel speed & the rocker panels aren't hitting the ground while basically changing nothing else (wheelie bar height, I/C placement, shock settings, etc, etc are all the same as before).

The bracket change has also given me back a bunch of air pressure adjustment to work with on the car. Before with the steep bar angle I was having to use a lot more air pressure than other similar cars were using (we were pretty much stuck with the 8.0 to 8.75 lb range) as a way to try & reduce the amount the slick sidewalls were compressing/over wadding/dead hooking. Now with the more favorable bottom bar angle I have been able to back the air pressure back down to the 5.5-6.5 lb range other cars are using.

bruno wrote:will lowering the rear of the car (ladder bar with coilovers) decrease the i/c ? therefore dercreasing the intial hit ?

bruno, if I may make an attempt to somewhat give you my summary relative to your post.

On a ladder bar suspension the I/C is pretty much set during the construction of the ladder bar's length. Lowering the car's rear ride height may offer a slight increase of the I/C's height fractionally. If the rear ride height is lowered and the forward attaching point of the ladder bar remains the same, the of "line of sight" from the axle housing to beyond the ladder bar's forward attaching point would raise, but only by fractions. The axle may experience more load from the car, although the axle may tell you it's now carrying a bit more load, it would be hard to document IMO. Another note, the vehicle's ride height should be set/used as a tool to provide tire fitment issues, aerodynamics and last, personal preference.

I've seen and heard many people looking under a car, seeing an extreme angle of the lower bar (ladder or 4 link) and assuming the suspension is set to do a certain job, hit hard or soft. The best way to understand your suspension, is to measure all suspension points with the car on a flat surface and at rest. Transfer all measurements on a wall or floor at actual dimension. Move the intersect points around on your drawing, it will explain what each and every move of the your suspension's attaching points and how it will effect your car. Also you will know every answer to your suspension questions.



Dave.

LivermoreDave wrote:.... Lowering the car's rear ride height may offer a slight increase of the I/C's height fractionally.......

If we're talking about lowering the car while the ladder bars stay bolted in the same front chassis bracket holes as before lowering, then I think you mean to say the I/C's height would be lower (closer to the ground) not higher. So keeping the LB front rod-end in the same hole but lowering the car 1" closer to the ground (at/around the chassis bracket hole area) would lower the I/C aprox 1" closer to the ground.

Doing the same thing on a 4-link car (lower car/chassis a given amount, but front rod-ends stay in same holes as before) should also lower the I/C a given amount as well. But how much the I/C is actually lowered depends on what holes (hole spread/bar angles) were originally used. On a 4-link car where the I/C length is roughly double the length of the 4-link bar's center to center length (say aprox 22" vs 44"), lowering the car a given amount at the front 4-link chassis bracket could result in the I/C being lowering somewhere around double that amount. But again that's depending on spread/bar angles, the actual I/C heigh might be lowered more or less than double. In this example the I/C length should also shorten up a given amount as the car is lowered with the same holes being used as before lowering.

bruno wrote:will lowering the rear of the car (ladder bar with coilovers) decrease the i/c ? therefore dercreasing the intial hit ?

The front locating point will not move mechanically. The axle housing will also remain the same at rest. This new adjustment (lowering) will now during dynamic reaction allow more weight to the rear axle and at the same time lift the I/C higher, fractionally..... I think? If the I/C has no involvement in the "initial hit" after the lowered stance, the weight transfer should, ya think? Consider the forward ladder bar attaching point as the axis.

Now I'm more confused,
Dave.

The I/C on a LB car can be called a fixed (well.....during the pass anyway) mechanical rotational axis point. And as mentioned before it effects 3 action/reaction leverage forces with it's placement, lifting the nose up, planting the rear housing down, & driving the chassis forward. So the I/C placement will always have some effect on the "initial hit" energy/leverage. But the total amount & direction of energy/leverage generated-released from this point (over a given period of time) is not set in stone just because the I/C might be sitting in any one given place.....the shock's extension/compression valving also has an effect on the speed at which this energy is released.

So you can hit the tire harder/softer by moving the I/C around, but you can also do the same thing by adjusting the shock extension valving tighter/looser to adjust the "hit" harder/softer as well (and don't forget adjusting "at launch" power numbers is also another initial hit "tool" too). So no one adjustable factor controls 100% of the suspension's actions. A balance must be found between all the factors that control the "hit/plant" energy/speed the tire sees (available "at launch" power, suspension leverage, suspension dampening, stored/compressed spring energy, etc, etc). You can also adjust the suspension's speed/action "after" the initial hit, during the "recovery" period, (controlling stuff like loading the sissy bars harder/softer, and thus staying "up-on" the tire/wheel speed sooner/later) with the shock's compression valving. Adjusting the compression valving is also a useful tool for controlling how the slick follows the track surface down course on rough/bumpy tracks.

It is possible to adjust the rear shock extension valving so tight on some cars (with Santhuff & Koni anyway) that it in effect makes the car think the I/C is much farther out as the tight valving slows the speed of the suspension's initial hit way down. On fresh Santhuff's setting the extension valving even farther (to "full tight") can in effect make some car's act/work as if there is in effect no suspension I/C point at all, as if it was a solid suspension in the rear.


On a 4-link you can't technically call the I/C a fixed mechanical point as it is not a mechanical point, and it is not "fixed" as it does move around some amount as the suspension moves.

Again, it all boils down to a balancing act between many different adjustable variables. No "one" individual component or "one" individual suspension geometry factor "does it all".

Sorry bruno for taking what some would believe a simple question (original post) and dissecting it with a microscope, but the skinny of it all is a bit more than skin deep! I do believe after all has written, dilly and I are near the same page.

Dave.

LivermoreDave wrote:Sorry bruno for taking what some would believe a simple question (original post) and dissecting it with a microscope, but the skinny of it all is a bit more than skin deep! I do believe after all has written, dilly and I are near the same page.

Dave.

and we all learned something too!

The first half of Nick's original question does have some simple answers.

..."will lowering the rear of the car (ladder bar with coilovers) decrease the i/c ?"...

Assuming we're talking I/C height only & the front rod-ends stays in the same hole as before........

Height in relation to the ground.................................................yes.

Height in relation to the slick contact patch.................................yes.

Height in relation to "fixed" un sprung chassis points/landmarks........no.

Height in relation to the car's C/G...............................................no.

Is the C/G height also lower in relation to the ground.....................yes.



But unfortunately there is no "one" simple answer to the second half of Nick's original question ...... "therefore dercreasing the intial hit ?"...... there's just too many other variables that also play a part. It also kinda depends on a person's definition of "initial hit"

If "initial hit" refers only to the suspension's first initial action/reaction leverage, (downward force at the housing centerline and upward force at the I/C point) & the resulting suspension separation & compression of the slick into the track surface..............then theoretically yes.

If "initial hit" is used as a reference to the slick's physical amount of initial traction.....then that's an unknown until tried because of too many other variables.


To be honest Nick, a racer shouldn't even be thinking about moving the I/C around anyway (using whatever method) until he has FIRST done some shock valving testing over a number of passes & adjusted through the entire "usable" shock adjustment window (every "click") . It makes no sense to blindly swing a bat at I/C choices until you first use the shock valving to help shine a light on the direction the car might want/need the I/C to be placed. The fact is your current I/C setting might actually be dead-nuts perfect for the car, but just requiring some fine tuning with the shock valving adjustment. Only more testing will tell.

Very informative thread Dave .