Suspension Stuff.........Again!

[BillyShope]

Our car has the IC located static at 35.55" forward and 7.5" above the ground. It has 155% anti squat.

So, your center of gravity height is less than 15 inches? That's very good! Back in the days of the Ramchargers' C/A, we were forced to go the other way. But, with today's tires, I don't think you can get the car too low.

What I'm asking people to think about is if you draw this supposed 100% line as a line related to the height of the CG at the position of the front axle and you go and move the front axle without moving the CG then why should you have to adjust the 4 link?

Here's why: Suppose you moved the front wheels forward by, say, 500 inches. (I think it was you who mentioned the use of unobtainium. I prefer toasted marshmallow.) Anyway, there's no weight involved in this move. So, the weight on the front wheels is reduced to almost zero. Nearly all of the weight is on the rears. We'll assume the 4link adjustment is not changed. This means the force vector has a slope equal to the center of gravity height divided by the original wheelbase. For a moment balance, the product of center of gravity height and forward thrust must equal the product of that portion of the weight transfer carried through the links and the wheelbase. But, that original angle of the rear tire patch force vector requires more vertical component (weight transfer) than the newly positioned front wheels are capable of supplying.

I wouldnt advise running a different 4 link setting left to right side, that forces the axle to twist, binding up the suspension.

On the other hand, a symmetrical adjustment results in unequal tire loading and a loss of performance.
http://www.racetec.cc/shope

[Beretta]

Beretta, would you share your hole locations? The ones you put into the 4link software? If you don't want to make them public, please PM them to me. They won't go any further.
http://www.racetec.cc/shope

Your going to have to wait till tomorrow as 4:30 am comes quick...

[Ken0069]

I just checked the IC setup on my Camaro and I'm 54" out, 5" up and 49% antisquat. Wheelbase is 108", car weighs right around 2450lbs wet with 1240lbs on the rear tires. Cam CL is about 18" and my SBC engine's #1 plug is about 5" behind the front axle CL. Leaving it's got the front tires about 6 inches off the ground for about a cars length and a half. Checked some time slips and I've been 1.18 in 60ft at Roxboro which is the "norm" for that track. We did some 1.20s at the track at Natural Bridge a few weeks back in the heat.

While I was looking in that program, I counted 6 different settings that I had tried before I settled on this one.

[shrinker]

Shrinker there is no possible way to move the front axle forward and not change the cog location .The wheel base change is very significant. If you have a 40lb front axle / strut assembly say 40" from the current cog of the car and then move it to 50" its a decent size change.

I realise that there has to be a structure to hold the wheel, Im just eliminating the weight of that structure for the purpose of the discussion as Billy pointed out. And the body is a sprung mass the Front hub is not. We are talking about 4 link reaction to the body.

Nearly all of the weight is on the rears.

Yes But the CG is still located say 50" forward of the rear axle. All that has changed is the weight sharing of the axles not the CG location. The inertia still comes from the CG.

This means the force vector has a slope equal to the center of gravity height divided by the original wheelbase.

Disagree, because the force vector is not related to the wheel base, the 4 link is a force that is centralised at wherever the IC point is and that vector causes reactions at the CG location. Nothing at all to do with the front axle location.

But, that original angle of the rear tire patch force vector requires more vertical component (weight transfer) than the newly positioned front wheels are capable of supplying.

thats not a problem because virtually all the cars weight is already on the rear axle when the front wheels are 500 feet ahead.
Yes you can only transfer the weight that is available on the front wheels but if the rears got it all then you dont have to transfer much do you? So when the rear's got it all then you dont have to have the IC located where it is. You can put parallel bars in the 4 link and get zero lift. You will still have all the weight you can get on the rear wheels because its already there.

[ky mustang]

Shrinker there is no possible way to move the front axle forward and not change the cog location .The wheel base change is very significant. If you have a 40lb front axle / strut assembly say 40" from the current cog of the car and then move it to 50" its a decent size change.

I realise that there has to be a structure to hold the wheel, Im just eliminating the weight of that structure for the purpose of the discussion as Billy pointed out. And the body is a sprung mass the Front hub is not. We are talking about 4 link reaction to the body.

Ok i see this example is make believe , but I think the front axle/ strut tire etc is part of the mass sprung or not , but that is just me. I will get out of this conversation getting to technical for me

[BillyShope]

This means the force vector has a slope equal to the center of gravity height divided by the original wheelbase.

Disagree, because the force vector is not related to the wheel base, the 4 link is a force that is centralised at wherever the IC point is and that vector causes reactions at the CG location. Nothing at all to do with the front axle location.

My bad. I should have explained that I was assuming the original wheelbase car had 100% antisquat. As you say, the direction of the force vector has nothing to do with the wheelbase EXCEPT when you're making this assumption. With no change in the 4link setting as the wheelbase is lengthened, the force vector continues to pass through the instant center with the slope determined by the original wheelbase.

But, that original angle of the rear tire patch force vector requires more vertical component (weight transfer) than the newly positioned front wheels are capable of supplying.

thats not a problem because virtually all the cars weight is already on the rear axle when the front wheels are 500 feet ahead.
Yes you can only transfer the weight that is available on the front wheels but if the rears got it all then you dont have to transfer much do you? So when the rear's got it all then you dont have to have the IC located where it is. You can put parallel bars in the 4 link and get zero lift. You will still have all the weight you can get on the rear wheels because its already there.

Yes, you can always put the instant center anywhere you want. But, I'm still assuming you want 100% antisquat with the longer wheelbase. This means the angle of the line passing through the rear tire patch and the instant center MUST be reduced. Otherwise, you're going to have a terrific moment imbalance. You've still got the same vertical force at the rear as with the short wheelbase, but nothing at the front to balance it. The rear of the car would pop up like a balloon.

You can put parallel bars in the 4 link and get zero lift.

Yes, parallel and nearly horizontal. They would still have to be angled up with a slope equal to the center of gravity height divided by the sum of 500 and the original wheelbase to reclaim the original 100% antisquat.
http://www.racetec.cc/shope

[Elkyman]

UN-FREAKING-BELIEVABLE, WHAT THE HECK DID I START OR START BACK UP

You guys, I am not asking for the magic spot on MY chassis, I am just trying to understand what does what like most of us bracket races need to know, and how it (SHOULD) effect our chassis's like Ken said, although it probably sounds like it huh?.

Something to think about with my chassis, with the same engine as now, in Sept of 2007, on a cool crisp 58 deg. Sat. morning, first pass with my car that day was magic for me and if felt like no other pass since. I launched the car and it just floated up, I never felt the front suspension stop traveling, nor did I feel the ground when the front end came back down, and it went say ohhh, 3-6 feet out. That was my best pass ever now I found a bad ARB over time, and was just beating the living crap out of my 10.5 soft sidewalled Hoosier's but boy did they hook. Air bags, 12 way only shocks in the rear and I had 3600+ lbs of sled going 9.90's at 135+mph, now how much power does it take to run that kind of number in that heavy of a car???? I had a I/S about 45" out, and say 8-10" off the ground at the time but had NO idea where my C/G was at all, and that height is a guess.

Now, I have bigger tires, same trans and engine, just a set of tires and now a 4 link suspension with really good shocks and springs this time around, so in therory, I should be able to, set my 4 link up to say 45-48" out and about 8-10" off the ground and go for it and it should be very similar to the stock 4 link GM suspension right? I would think maybe so but have no experience with my 4 link yet, none

Also, the front to rear weight bias was a little heavier before than now, so I now have only 166lbs more in front than the rear, so how much more weight transfer will it take to get my chassis to launch the same or a little bit better than that one day? I have no clue but I am going to try like heck to find that spot before I croke in life.

I try to investigate things before I try or buy them to optimise my end result and not waste too much money and time getting the result I want. This is why I ask these questions on what people run for a setup so I can at least have some info to look at, and think about, read more and then make my best call for a setup, and that's it. I know I will struggle with this suspension, and I am willing to pay for it in time and sweat and blood, but I am like other guys out there, I need to see it and then I can understand it, and that's just me.

So when Billy mentions to try and get the I/C on the 100% A/S line or as close to it as possible, and then other's mention there I/C's and how level and low there bottom bar is, I know there I/C is no where near there 100% a/s LINE, JUST CAN'T EVEN COME CLOSE TO IT!!! UNLESS , like Barry and others that have full tube chassis's and are as low as they can go with everything, I just can't see how a low and down in front angled bottom bar can give a high A/S % in any chassis and I guess this is where I am not getting it. If I seem like a dead horse, quit beating me then on this subject, and I will just have to figure and realise it myself with testing and logging notes down as always.

You guys really have some great knowledge and info. I will give you all that, and it is not an argument at all, just opinions with paper vs. actual, that's it and I think Math never lies and it proves itself every time. I always sucked at math too

One more thing about my combo is this, it will be able to launch 1000rpm's higher, and just be right under my stall of the conv. now instead of 3600rpm limited by tire size so will I have MORE power for the bigger tires, or not enough?, I know I should have enough if and when I spray another 150-200hp of nitrous thru it!!!

Great info, don't mean to see heads bang together though, so wear helmets

ps, the pic of my Avatar on here to the left is the exact pass I was explaining.

[Ken0069]

FYI on the front tires off the ground, I never know how high they are nor do I feel mine touch back down either. I find this out via the video that Pit Bitch takes of almost every pass.

[Slowpoke]

I have to ask, if you have 2 cars (let's just say 800 hp, 2500#, 4 link, bracket car) set up with everything else the same, except one has 4" X 32" slicks and the other has 16" X 32" slicks, would you still have the same 4 link positions? If not, how would you adjust the suspension to optimize the traction for the different tires?

Lots of good info coming out of this discussion,

Thanks

[Bubstr]

I have to ask, if you have 2 cars (let's just say 800 hp, 2500#, 4 link, bracket car) set up with everything else the same, except one has 4" X 32" slicks and the other has 16" X 32" slicks, would you still have the same 4 link positions? If not, how would you adjust the suspension to optimize the traction for the different tires?

Lots of good info coming out of this discussion,

Thanks

Don, You have come across something here that may clear a lot up about link setting. If you changed nothing but tire size the link settings would still be the same. Don't get me wrong. A 4 inch tire won't hold what a 16 inch tire does. This is the traction component of the balance of power. cog and traction. The link adjustment won't fix this. You need to adjust power and COG to match your traction. The real speed secret is the balance of POWER, GOG and Traction. Link settings are only a smidgen of the traction component. Link settings seem to be there and because they are hard to understand, everyone thinks there is magic there. I really believe that most that run lower IC settings do so because high ones are harder to fix with other suspension components.

Now think. What would you have to do to make the 4 inch tire work the best it could with power and COG for a 16 inch tire?
! lower power= LOWER LAUNCH rpm, Higher gear, Change Power curve of engine.

2 Raise and or move COG to the rear.

3 more rim width to stop tire distortion.

You see these three things have more effect than any link setting. All three are in that magic formula to a balanced race car.

[BillyShope]

...I just can't see how a low and down in front angled bottom bar can give a high A/S % in any chassis and I guess this is where I am not getting it.

Remember, it's the intersection of the link lines that defines the instant center location. So, if the front pivot for the lower link is sitting on the 125% antisquat line and the upper link is pointing at that front pivot, the car would have 125% antisquat regardless of the angle of the lower link. Yeah, that's a ridiculous angle for the upper link, but the point I'm making is that it's not too difficult to get a high antisquat number with an angled down lower link if you're willing to accept a short instant center.
http://www.racetec.cc/shope

[Beretta]

Can't see how a short IC will work with a high hp car...

[shrinker]

Yes, you can always put the instant center anywhere you want. But, I'm still assuming you want 100% anti-squat with the longer wheelbase. This means the angle of the line passing through the rear tire patch and the instant center MUST be reduced. Otherwise, you're going to have a terrific moment imbalance. You've still got the same vertical force at the rear as with the short wheelbase, but nothing at the front to balance it. The rear of the car would pop up like a balloon.

See that's where we differ. You say there is still the same vertical force at the rear, YES I agree and what i think your not seeing is the CG is still located in the same place in the same distance forward of the IC and therefore the inertia from the CG is identical. The inertia from the CG is not related to the position of the front axle. It's related to where the force is occurring and that's the IC. So if you don't change the CG or the IC locations you wont change the inertia or the physics. I don't know how to explain this any other way. But all through the Universe forces act upon Centers of Mass not extremities of an object. As you know the extremities of an object add together to form a single point of mass, Mass has inertia and the inertia of any point on an object can be considered to 'combine' into one singular point called the Center of gravity. So when you push on an object, its reaction occurs as though all its mass is infinitely small and at that one point, the CG. So when you push on the body of your car with your 4 link you push on it at the concentrated mass point, the CG. The reactions are due to the Force application points and there relationship to the CG.
So if you build a silly wheelbase car with the same CG location and the same 4 link in a static position then its initial reaction will be the same.
If a Force is applied to a CG in the same vector then the result is the same. Billy, you are saying that not to be true,are you not? I think you must be saying that, because your saying its necessary to alter the 4 link to achieve the same anti-squat just because you have moved the front axle even though the CG is still in the same place.

I have qualified the discussion by stipulating the 4 link at a static position. In reality the suspension moves etc and that alters the IC location but were not trying to complicate things were trying to keep it simple so we can analyze why Billy and I differ.

if you have 2 cars (let's just say 800 hp, 2500#, 4 link, bracket car) set up with everything else the same, except one has 4" X 32" slicks and the other has 16" X 32" slicks, would you still have the same 4 link positions?

You can run any 4 link position you like it depends on your available traction verses torque applied. Assume now that the 14" tire cant hold the torque at the snap of the throttle, so you have to move the IC closer. When you move the IC closer you generate more upward lift at the IC point. That translates into downward force on the wheel. Just imaging the IC as a short torque arm like a ladder bar. So what we can do is lift the amount of weight that is present in the car at that point. To figure out what I mean but haven't said very well figure this out. Move your rear axle forward to where the IC is, now re weight the car and you will get lots more weight on the rear axle and much less on the front. So now your rear tires can support more power. If your torque is enough you could lift the body up enough with torque so that you could remove the rear springs. In reality that doesn't happen because the acceleration weight transfer still goes down through the springs. Anyway don't get caught up in that.
I have explained details about our car and why it is done that way. If you watch the you tube you can see the car do exactly what i describe. It has to be that way to perform as fast as it does. If its setup with the 4 link on say 100% it goes slower. It even breaks traction at high speed on some tracks. It doesn't have enough rear weight on the available tires for the power. To solve that problem I adjust it the way I do. Its not conventional but it works for our problem.

Now if your 14" tire is breaking traction say 5 feet out from the start line then you have a different problem to solve. Look at it this way, if you set a short IC you will snap the diff down at the launch and gain some traction but once the car starts to accelerate the angle of the lower bar becomes very important. the lower bar has very high compression forces in it, say 6000lbs for example. the top bar only has maybe 600 lbs force in it. its possible to get the top bar to zero, Lets say it is zero just for now. So what's pushing the car now? Its just the bottom bar and it forcing that chassis connection with a force of 6000 lbs at some angle. The angle is the angle of the bar. So what is the angle of the bar when the diff is separated from the body? You have to know this because that force is pushing the car forward and UP. It's a force vector that's way below the CGH, thus creating a torque at the CGH and that torque is reacted to the diff via the springs. Oops whats happening to the springs now? Are they compressed, relaxed or not moving? If the springs have moved then the 4 link is different geometry and its doing different things too . I work it all out that way.
So with this car that has zero load in the top bar and 6000lbs in the bottom bar if the bottom bar is level with the chassis rail and its the only thing pushing the car then there is going to be zero upward force. So your 4 link isn't doing what you thought it was. You have to realize that the force vector from the IC constantly changes it's angle. It changes its amount and it changes its angle. So its a very complex problem to solve as some numbers.

[shrinker]

Can't see how a short IC will work with a high hp car...

Hi Beretta, We have a 900 hp car. it makes 900hp on the track it goes 8.17 at 168.8MPH and it weights 2400lbs and it's auto. So plug that into some calculators and they will come up with around 900 hp. It pulls max 2.7 g off the line but usually does around 2.45 on the Sydney track (not a good track that one i hate it. it got different traction on different concrete blocks as you go down track. A terrible surface).

It has a short IC but we use hard springs, 200lb/inch rate and soft shockers. 180lb /inch at 21" shaft speed. These shocks are not drag racing shocks. They are a Carrera shocker for the front of a Speedcar. They are 50/50 rating. By using soft shockers the diff movement is fast and by using harder springs than most drag racers the suspension movement distance is kept less. Its the spring that supports weight and its the springs rate that determines the suspension position dynamically.If we used a soft spring, say a 95 LB/inch spring the body separation from the diff would be twice as much as it is with the hard spring so the 4 link would move more and things would change more. We have tried conventional drag racing shocks and springs according to the experts in the car over the years. Nothing is as fast as what I use. We constantly try other stuff too, it always comes back to the way I do it now.

By using a high spring rate the suspension movement range is reduced and the 4 link forces are more stable and predictable. The front and the rear springs of the car are all the correct length to go to complete relaxed state of spring without topping out the shocker. That makes the car stable under 'chute because the chute pulls the front wheels of the car off the ground on deployment. Also setting the front springs so that they are zero pre-load at full droop makes the weight transferred from the front to the rear a smooth progression. If you have the front springs with some pre-load in them when the shock tops out the remaining weight is an instant transfer to the rear and it causes a fast geometric change to the 4 link etc (due to the soft shockers) and bounces the tires. Its all a blend of actions.

[BillyShope]

Can't see how a short IC will work with a high hp car...

By no means am I recommending a short IC. There are too many problems with differences in ride height. I was merely pointing out that high antisquat values can be achieved with an angled down lower link.
http://www.racetec.cc/shope