Ideal anti squat for PT triple purpose car

[MrQuick]

Hey all,


We are building a 3 link for a Camaro and we are looking at upper link placment and the question has finally come up.

What would be the ideal anti squat % for a pro touring car that will see alittle bit of everything by mostly road course.

It looks like LD is at 65%. I thought I had the AME numbers but I can't find them at the moment.
Past builds (stock car recipe) have been about the same and come to find that it would not be optimal for this particular car. Center of gravity is WAY different.

I am looking at making it adjustible from 55-80% I am starting to steer more in the 75-85%. Thoughts?


vince

[MrQuick]

crickets....:idea:

[Gitter Dun]

How do you rate or figure anti squat percentage?

[LSx_88_Ciera]

How do you rate or figure anti squat percentage?

Source (http://www.modified.com/tech/0512_sccp_making_it_stick_part_4/guide.html)
Calculate anti-dive, anti-lift and anti-squat

1) Find the center of gravity The calculated center of gravity (C.G.) usually ends up 15 to 20 inches above ground-a few inches higher than the plane of the crankshaft-in a typical sedan. The horizontal location is approximately a foot or so forward of the middle of the wheelbase on a front-engine, rear-wheel-drive car. On a rear- or mid-engine car, it's a foot or so aft of the middle of the wheelbase. On a front-wheel-drive car it is about even with the driver's seat. Draw a vertical line from the C.G. to the ground.

2) Find the instant center
Calculating anti-lift and anti-dive requires finding the side-view instant center for the front suspension. Anti-squat calculations require finding the side-view instant center for the rear suspension. To find either instant center, draw lines through the suspension pivots of the upper and lower control arms at their attachment points to the chassis. On MacPherson strut cars, draw the upper line from the upper strut mount perpendicular to the axis of the strut. These lines should converge somewhere in the middle of the car between the wheels. This intersection is the side instant center.

3) Find the percentage
Anti-dive, anti-lift and anti-squat are expressed as percentages of the C.G. height. Draw a line from the center of the tire's contact patch up to the instant center intersecting the line from the C.G. to the ground. This line represents the force vector where the acceleration or deceleration force acts on the mass of the car. To calculate the percentage of anti-lift, anti-dive, or anti-squat, compare the overall height of the C.G. to the distance between this intersection point and the ground. For example, if the force vector intersects the line between the ground and C.G. at one-quarter of its height, the suspension has 25 percent anti-dive.

[MrQuick]

I like to use Billy Shopes spreadsheets. Very helpfull.
http://www.racetec.cc/shope/tim.12.htm

http://www.racetec.cc/shope/tim.17.htm

http://www.racetec.cc/shope/tim.39.htm


I understand 100% will get you brake hop. Not good on a road course.
65% is pretty low. Might not be too good accelerating during/out of a turn. I don't want to run a decoupled upper so I guess I will have to experiment a bit more.

Vince

[parsonsj]

Vince, somewhere between 50 and 65 would be the place to start. Vehicle weight distribution, driver habits, tire size, and even the race course can all affect what the right value should be.

jp

[BillyShope]

First, a procedure for determining percent antisquat has been given which is incorrect.

The horizontal location of the CG is unimportant for determining percent antisquat of the rear suspension.

Instead, the vertical distance from the ground to the intersection of a line through the rear tire patch and the instant center by a vertical line through the front tire patch, when divided by CG height and multiplied by 100, yields the percent antisquat.

(The source of the incorrect posting can be found online, but I would recommend an accepted reference, such as the Millikens' Race Car Vehicle Dynamics. Amazon's price is, I believe, a bit lower than the SAE price.)

As for the original question, 100% is optimum for dragracing, so I would suggest 2 forward mounting points for the "odd" link, with one of them providing 100% and full cancellation of the driveshaft torque and the other closer to 50%.
http://www.racetec.cc/shope

[MrQuick]

The horizontal location of the CG is unimportant for determining percent antisquat of the rear suspension.



thank you...
horizontal as in distance from rear axle centerline correct? Thats interesting. So we just need height and not exact location...makes that easier.
I was planning on 3 adjustments or maybe a tube slide clamp.
Thanks again guys.

Hey John!!

Vince

[MrQuick]

...thank you too Sean.


vince

[Gitter Dun]

Source (http://www.modified.com/tech/0512_sccp_making_it_stick_part_4/guide.html)
Calculate anti-dive, anti-lift and anti-squat

1) Find the center of gravity The calculated center of gravity (C.G.) usually ends up 15 to 20 inches above ground-a few inches higher than the plane of the crankshaft-in a typical sedan. The horizontal location is approximately a foot or so forward of the middle of the wheelbase on a front-engine, rear-wheel-drive car. On a rear- or mid-engine car, it's a foot or so aft of the middle of the wheelbase. On a front-wheel-drive car it is about even with the driver's seat. Draw a vertical line from the C.G. to the ground.

2) Find the instant center
Calculating anti-lift and anti-dive requires finding the side-view instant center for the front suspension. Anti-squat calculations require finding the side-view instant center for the rear suspension. To find either instant center, draw lines through the suspension pivots of the upper and lower control arms at their attachment points to the chassis. On MacPherson strut cars, draw the upper line from the upper strut mount perpendicular to the axis of the strut. These lines should converge somewhere in the middle of the car between the wheels. This intersection is the side instant center.

3) Find the percentage
Anti-dive, anti-lift and anti-squat are expressed as percentages of the C.G. height. Draw a line from the center of the tire's contact patch up to the instant center intersecting the line from the C.G. to the ground. This line represents the force vector where the acceleration or deceleration force acts on the mass of the car. To calculate the percentage of anti-lift, anti-dive, or anti-squat, compare the overall height of the C.G. to the distance between this intersection point and the ground. For example, if the force vector intersects the line between the ground and C.G. at one-quarter of its height, the suspension has 25 percent anti-dive.

Wow, need to get this into the archives so that I could flip back to it sometime when I have time. Awesome!!

[ProdigyCustoms]

Triple purpose car! Not that is a thought right there. I am going to get right on it!

As John mentioned, 60-65% is where all the GOOD G Machine suspensions are shooting for. As Billy mentioned, 100% is perfect for the drag strip, but none of the pre packaged G Machine systems are capable of that 100%. In fact I am not sure you can get 100% AS out of a 3 link system that has 65% AS.

Were it me, I would get the ideal 65% G machine setting and get as much antsquat for drag racing as you can. I would rather deal with too little AS on the drag strip then too much AS on the road coarse.

Or think up something else completely, Hum!

Let us work on that for a couple minutes!

[MrQuick]

Good show Frank. I think if you are starting from scratch you could make predetermined adjustment points for all rear links to get that type of range. I'd be happy with a 50-80% range. Acceleration hop is easier to deal with than brake hop. Both stress suspension parts equally I believe.


Vince

[BillyShope]

Although 100% antisquat is ideal for dragracing, many (most?) dragracers prefers values greater than 100%. They like the idea of an initial "hit" on the rear tires as the rear of the car starts upward on launch. What they don't realize is that, as the rear of the car approaches its uppermost point, it is unloading the rear tires. In short, an oscillatory loading on a friction surface is to be avoided.

With two mounting points for one of the links, there is no excuse for accepting a value less than 100% for the occasional outing at the dragstrip (and, of course, total cancellation of the driveshaft torque). The other mounting point would provide antisquat closer to 50%.
http://www.racetec.cc/shope

[ProdigyCustoms]

I have something to show you Billy.

[zbugger]

I have something to show you Billy.
Eeeewwwww.....:barf:

[BillyShope]

Eeeewwwww.....:barf:
I didn't get it either until I saw the "four zero seven." He's evidently only 10 or 15 minutes away (ProdigyCustoms.com). I'll call him tomorrow.
http://www.racetec.cc/shope

[XLexusTech]

Well if thier is a new suspension in the works of at Franks......

DO tell Frank :-)....... I am lookin for a triple threat option .... Isnt everyone :1st:

[ProdigyCustoms]

Well if thier is a new suspension in the works of at Franks......

DO tell Frank :-)....... I am lookin for a triple threat option .... Isnt everyone :1st:

Lets define triple threat?

Autocross

Road Coarse

Drag Race

That is my idea of triple threat.

Oh Man I wish I could talk about this!

Wait a couple more weeks! I have something. Things are fixin to change in a BIG way!

It is almost UNFAIR!

[ProdigyCustoms]

I didn't get it either until I saw the "four zero seven." He's evidently only 10 or 15 minutes away (ProdigyCustoms.com). I'll call him tomorrow.
http://www.racetec.cc/shope

I am in Apopka.

I am at the shop today working on the project I want you to look at.

Call me anytime.

[Bryce]

I have my 3 link designed, I just need to start building. My anti squat will be adjustable from 50-150% with a ton of adjustment points.

Horizontal parrallel lowers for the street/autoX/road course (if I ever make it out to one)

then the lowers and upper are adjustable to obtain a variety of settings. To fine tune.

[ArtosDracon]

I have my 3 link designed, I just need to start building. My anti squat will be adjustable from 50-150% with a ton of adjustment points.

Horizontal parrallel lowers for the street/autoX/road course (if I ever make it out to one)

then the lowers and upper are adjustable to obtain a variety of settings. To fine tune.


Sounds similar to mine except I have the just the upper link adjustable in four positions providing ~63%-~90%.

[Greg from Aus]

Frank stop that cat from Meowing or it will get out of the bag:ssst:.

Greg

[Bad Bird]

I'm not so sure that it is large ~100% anti-squat values that cause brake hop. Rather, it is the typically short SVSA (side view swing arm) lengths that often go hand in hand with high values of anti-squat. If converging lower control arms are used, you can have high anti-squat AND a long SVSA.

[BillyShope]

I'm not so sure that it is large ~100% anti-squat values that cause brake hop.
'Fraid it is. The resultant of the dynamic forces acts on a line passing through the rear tire patch and the instant center, so it doesn't matter if the instant center is close to the rear axle or an infinite distance forward and up. You still get to go to the hop.
http://www.racetec.cc/shope

[parsonsj]

The resultant of the dynamic forces acts on a line passing through the rear tire patch and the instant center, so it doesn't matter if the instant center is close to the rear axle or an infinite distance forward and up. You still get to go to the hop.Correct.

The simple way to think of this is that the more a-s you dial in for max acceleration the less rear tire you have for max braking. 100% a-s means (almost) no rear tire for threshold braking. Ordinarily, for street and road racing you'd go halfway, to 50%. Since the front brakes do most of the work for braking, and the rear tires do all the work for acceleration (in a rear drive car), values larger than that can work. That's why 65% is a good place to start.

jp

[silver69camaro]

It is almost UNFAIR!

Ha, funny Frank.

[MrQuick]

ruuroooh, I see Matt's here....I think I see where Frank's going.

Would you say "unfair" or "highly competetive"?

Thanks for the additional info guys.

We are figuring 50-85%, see if we can work with that.

Vince

[BillyShope]

We are figuring 50-85%...

Vince
I'll let Frank reveal his baby, but I will say that you'll have the full 100% available for dragracing AND the 50% (or whatever you want) for the twisty stuff.
http://www.racetec.cc/shope

[ProdigyCustoms]

Bill, Your number was not on my caller ID. Call me

[Bad Bird]

Correct.

The simple way to think of this is that the more a-s you dial in for max acceleration the less rear tire you have for max braking. 100% a-s means (almost) no rear tire for threshold braking. Ordinarily, for street and road racing you'd go halfway, to 50%. Since the front brakes do most of the work for braking, and the rear tires do all the work for acceleration (in a rear drive car), values larger than that can work. That's why 65% is a good place to start.

jp

Interesting. What is the advantage of having a long swing arm in side view? I hear 48-60 inches bandied about quite a bit.

Bill, I have a quick question that I posted over in the asymmetric 3-link thread on CC. You've been loads of help so far.

[BillyShope]

What is the advantage of having a long swing arm in side view? Minor track surface irregularities and ride height variations have less effect. http://www.racetec.cc/shope

[terryr]

If you had a front upper mount that could pivot up and down at command you could have both ways. I thought about it but had no deep need for it.

[ArtosDracon]

If you had a front upper mount that could pivot up and down at command you could have both ways. I thought about it but had no deep need for it.

The issue with a pivoting mount would be that when on a pivot the mounting point would move forward and backwards as well, either necessitating a change in bar length else it would alter pinion angle.

[BillyShope]

Long swing arm just gives leverage.... jp Afraid you're getting into the "urban legend" area, John. There's no "leverage" involved. A link can only support a dynamic force which acts on a line through its pivot points. Perhaps this is best understood when considering parallel upper and lower links. These would place the instant center at infinity and provide "infinite" leverage. http://www.racetec.cc/shope

[parsonsj]

I said it badly, didn't I! :) A 4 bar (which you've described with parallel upper and lower links) has an infinite SVSA and no anti-squat.

Sorry for the misdirect. I'm retracting my "leverage" statement. Yikes!

jp

[BillyShope]

A 4 bar (which you've described with parallel upper and lower links) has an infinite SVSA and no anti-squat.
jp
Don't mean to hassle you, but you're giving me excellent opportunities to teach, and I'm as much an educator as an engineer.

Actually, the 4bar provides no anti-squat ONLY when the bars are also parallel to the track surface (horizontal). If they're angled up with a tangent equal to the center of gravity height divided by the wheelbase, they provide 100% antisquat. This is because parallel lines meet at infinity.
http://www.racetec.cc/shope

[parsonsj]

You're right: I was assuming parallel to the road surface, which is what you want for neutral roll-steering characteristics. It never occurred to me that one would angle the bars up.

Can you calculate a real-world situation for a 4 bar that would provide 100% A-S? What angle up? Say with a 20" bar?

As far as hassling me goes, no worries. It's hard enough providing good tech here in this forum environment without one of the moderators getting sloppy and reaching into his urban legend toolbox. :)

jp

[ArtosDracon]

I don't have the calculators handy, but I can tell you that the new Ram Trucks, standard duty only, have a parallel(in plan view) four link that is not perpendicular to the ground at ride height, though I'm not 100% sure that the links are parallel in side view, it would be one application where for the sake of load hauling you would want higher(90%) AS.

[BillyShope]

Can you calculate a real-world situation for a 4 bar that would provide 100% A-S? What angle up? Say with a 20" bar?
jp
Thank you for your understanding, John.

The bar length would have nothing to do with it. If the center of gravity height was 16 inches and the wheelbase 100 inches, the angle tangent would be 0.16 and the angle would be 9.1 degrees.

Yes, this would provide slight roll oversteer, but not more than many production cars.

Since there is no linkage binding while cornering with a 4bar, it is ideal for a street car. And, aesthetically, many...including myself...find it very appealing.

Unfortunately, those who market 4bar kits...such as Art Morrison...do not offer any means of angle adjustment. In my opinion, they're not tapping into that segment of the market with drivers who occasionally run at the strip, but also want no linkage bind and long life on the street. With adjustability, the 4bar can duplicate the performance of a 4link.
http://www.racetec.cc/shope

[parsonsj]

The bar length would have nothing to do with it. If the center of gravity height was 16 inches and the wheelbase 100 inches, the angle tangent would be 0.16 and the angle would be 9.1 degrees.Excellent! I learned something today. I realize the bar length doesn't matter for the mathematical calculation of A/S, but a 20" bar running up at a 9* angle will intrude on the rear seat, I would think. That's what I was wondering about when I said "real world"... as in the the real world of packaging it in a vehicle.

Very cool.

[BillyShope]

...but a 20" bar running up at a 9* angle will intrude on the rear seat....
Ah, but remember: You can either raise the bridge or lower the river. The rear location of a 4bar is not important, so you must include the option of a lower rear mounting point with the angled bars. Yes, ground clearance must also be considered, but a compromise can usually be reached.
http://www.racetec.cc/shope

[silver69camaro]

Unfortunately, those who market 4bar kits...such as Art Morrison...do not offer any means of angle adjustment. In my opinion, they're not tapping into that segment of the market with drivers who occasionally run at the strip, but also want no linkage bind and long life on the street. With adjustability, the 4bar can duplicate the performance of a 4link.
http://www.racetec.cc/shope

Bill, we've tried it in the past with negative results. PM me for more info.

I'm considering doing a four-bar with a medium SVSA for our next bolt-on chassis, but we've had problems with adjustability in the hands of a customer - so it would probably be a fixed design. Really, a guy could simply punch a 5/8" hole in the bracket if he wanted some AS. But we also have other suspensions that serve that purpose.

[MrQuick]

Ah, but remember: You can either raise the bridge or lower the river. The rear location of a 4bar is not important, so you must include the option of a lower rear mounting point with the angled bars. Yes, ground clearance must also be considered, but a compromise can usually be reached.www.racetec.cc/shope
On our current project we have created a lot of space at all 6 mounting points to facilitate a fairly wide range of adjustment. I just need a hard number to start from then go from there. We will consider the actual range before any thing is finalized. Its all math from here.


Bill, we've tried it in the past with negative results. PM me for more info.

I'm considering doing a four-bar with a medium SVSA for our next bolt-on chassis, but we've had problems with adjustability in the hands of a customer - so it would probably be a fixed design. Really, a guy could simply punch a 5/8" hole in the bracket if he wanted some AS. But we also have other suspensions that serve that purpose.
Could it be as simple as punching a few more holes and a set of adjustable links?
I believe it could be done a lot easier with your 3 link set.

Vince

[terryr]

The issue with a pivoting mount would be that when on a pivot the mounting point would move forward and backwards as well, either necessitating a change in bar length else it would alter pinion angle.

Depends where you put the pivot.

[BillyShope]

This is quick and dirty, but I think it's clear enough. This is the extra bracket, solidly attached to the axle housing, that would be needed to make the 4bar adjustable. With the front bracket solidly attached, the original 4bar rear bracket would need only one hole for adjustment.
http://www.racetec.cc/shope
https://static1.pt-content.com/images/noimg.gif

[ArtosDracon]

Depends where you put the pivot.

No it doesn't. If you have a pivoting arm of any length at any angle, when the primary arm pivots a secondary arm attached to it is going to move. With a fixed point on the opposite end the secondary arm will either force movement in what it is attached to, or one of the arms is going to have to change length.

[MrQuick]

correct, you will have to either change the length or change the rear mounting point in conjunction with the front also when we are talking about link angles.


Looks like we have our range of 45-130% with the combination of upper and lower link mounting points. Its a good thing I made the lower plates rather large.


vince

[BillyShope]

A correction to my comments accompanying the picture in my last post:

In order to maintain and adjust pinion angle, it would be necessary to have TWO holes in the original 4bar rear bracket.

***************

This is NOT the form of adjustment which Art Morrison tried with their 4bars as reported earlier in this thread. They chose an adjustment which destroyed the parallelism between the bars. This parallelism is necessary to avoid link bind. I'm still hoping some 4bar supplier will provide an adjustable version. There is so much potential in this design.
http://www.racetec.cc/shope

[terryr]

https://static1.pt-content.com/images/noimg.gif

[MrQuick]

Terry, is that large black circle the tire?

Might need some help with labeling.

vince