rear coil over tuning help needed

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BillyShope
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Re: rear coil over tuning help needed

#16 Post by BillyShope » Wed Jul 28, 2010 5:41 am

BillyShope wrote:At 100%, there is no relative motion between axle assembly and the chassis, so spring and shock forces are not important.
Mike Peters wrote:
Anyone want to buy my Afco's? I'm buying me some Monroes :lol:
No shock absorber...whether OEM or aftermarket...can exert a force if the distance between upper and lower mounting points remains constant during launch. And, at 100% antisquat, this is...by definition...the case.

If, however, your car is NOT operating at 100% antisquat, the use of good adjustable shocks might indeed be a necessity for decent performance.

This begs the question: Is it wise to be running at anything but 100% antisquat? A friend...Ed of EdVanced Engines...often made the point, in his posts, that an increase in engine torque usually means extra time getting the rear suspension to act as it did before the engine change. This is certainly true when the suspension is at anything but 100% antisquat. If the rear of the car squats or rises during launch, that extra engine torque is going to make that motion more violent. But, at 100% antisquat, the increased engine torque causes problems only in the area of increased chassis twist.

Unfortunately, the 4link software available makes it difficult to work backwards from a desired antisquat value. (And, one or two don't even calculate the antisquat correctly, putting the 100% line directly through the center of gravity.) That's why I added Page 48 to my site, which gives you the 5 best hole combinations for a given percent antisquat.
http://www.racetec.cc/shope

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Mike Peters
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Re: rear coil over tuning help needed

#17 Post by Mike Peters » Wed Jul 28, 2010 9:46 am

BillyShope wrote:No shock absorber...whether OEM or aftermarket...can exert a force if the distance between upper and lower mounting points remains constant during launch. And, at 100% antisquat, this is...by definition...the case.
Billy, I challenge you to find a car that will remove the shocks with the I/C on the 100% anti-squat line and be held up with springs only for a launch demonstration. You have consistently discounted and ignored all the other dynamic forces associated when launching a car. The pinion acts upon the ring gear, the rear end housing wants to rotate in the opposite direction of the tires but held in place by the suspension links so the force is exerted through them, slicks want to wrinkle, housing wants to drive forward, etc...... Your hypothesis of the I/C being on the anti-squat line and cancelling out all these other dynamics is just flat out wrong. You pretend the housing is a static factor in the equation. OK, here we go again with the asymmetrical 4-link setting. :roll:

If your preaching of the I/C being on the anti-squat line as being the end-all solution for every car that has rolled down a drag strip was true, why is there the fairly well-known fact (unbeknownst to you however) that Pro Stock cars have I/C's that intersect far forward of your idealogical 100% anti-squat line? Warren Johnson is a storied engineer. Did he miss one of the classes you attended? :scratch:

Your continuance to ignore all the other dynamic forces on the notion that an I/C setting of 100% anti-squat is not valid no matter how good it looks on paper.

Billy, read this link please- http://afcoracing.com/tech_pages/4link.shtml

Note where it describes the chassis reaction to bar angles (which you totally discount) and the description of "loose roll steer" and why it occurs. The link provided pertains to dirt track racing and turning under power so the geometry set-up does not apply to drag racing but, the description of physics remains constant. As you have stated in the past, bar angles and bar spreads have no bearing as long as the I/C is set on 100% anti-squat. That would be totally wrong.

You're a grand fellow and conduct yourself with the upmost class and respect. Good for you but, I don't see anyone buying what you're selling. Please tell us of someone subscribing to your 100% A/S I/C or asymmetrical 4-link setting and applying it to their car.
"If winning was easy, losers would be doing it"

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BillyShope
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Re: rear coil over tuning help needed

#18 Post by BillyShope » Wed Jul 28, 2010 3:54 pm

Here's an interesting example of the incorrect information out there on the web. At this site, there are two schematics of a car with upper and lower links that are parallel, in side view, to themselves. In one case, the links are horizontal and, in the other, the links angle up from the rear.

It is stated that forward bite can be increased by angling the links upward as shown. When angled up, it is said that the rear tires then try to drive underneath the chassis during forward acceleration and, in so doing, thereby increase the loading of the rear tires.

Sounds reasonable, doesn't it? We've all done things like use a stick to pry up a piece of furniture while we retrieve the dog's toy. We're very familiar with the forces involved.

But, it's simply not true.

Consider the entire car as it accelerates forward. Dynamically, there's a forward thrust at the rear tire patch, an inertial force acting at the center of gravity, and vertical forces at front and rear tire patches. For a horizontal force balance, the inertial force is equal in magnitude...but opposite in sense...to the forward thrust at the rear tire patch. The vertical force at the rear tire patch (the weight transfer) is equal in magnitude...but opposite in sense...to the vertical force at the front tire patch. For a moment (torque) balance, the forward thrust times the center of gravity height must be equal to the weight transfer times the wheelbase.

These force and moment balances are determined without any consideration of the many internal forces. For instance, the pinion gear is trying to climb the ring gear, the upper links are going into tension while the lower links are going into compression, the driver is chewing gum, etc. All that need be considered are those dynamic forces which develop at the points where the entire car interacts with its surroundings.

So, while there are no vertical forces in the links while the links are horizontal (one of the two cases pictured), the vertical forces necessary for the weight transfer will nevertheless be present, having been carried through the suspension springs. This is, of course, a situation of zero percent antisquat and severe drop (squat) of the rear of the car as it accelerates.

But, what of the case where the rear tires are trying to "drive underneath" the chassis? The illustration shows the parallel links angled up at a severe angle. The slope appears to be greater than the ratio of center of gravity height to wheelbase. Remembering that parallel lines meet at infinity, this would mean that these link lines would be parallel to a line of constant percent antisquat having a value over 100 percent. In other words, the car would have "hit" or "separation" and the rear of the car would rise on launch.

In the case where the links are horizontal, the rear of the car is initially being accelerated downward as it squats. In the case where the links are angled up, the rear of the car is initially being accelerated upward as it rises. In the first case, this would mean an initial rear wheel loading less than that predicted by the force and moment balance of the entire car; in the second case, it would be greater than.

But, that vertical acceleration can't continue forever. As the rear of the car reaches its final position, the accelerations and forces reverse. So, in either case, there's a time of oscillatory loading and then a final loading exactly as predicted by the analysis of the entire car.

Once again, we find that we can't get something for nothing. And, once again, we find that a "reasonable" explanation can be very deceptive.
http://www.racetec.cc/shope

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Mike Peters
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Re: rear coil over tuning help needed

#19 Post by Mike Peters » Thu Jul 29, 2010 9:31 am

Yep. You win Billy. Every top chassis builder in the drag racing world is wrong. Rick Jones, Jerry Bickel, Haas, etc.... Afco, who wrote the mentioned article you said was incorrect yet do tons of real world R & D, is wrong. I'll sit back and watch while you go on to inform them of this epiphany.

In the meantime, I hope you build your car soon or find that struggling team that buys into your revelation. This will topple the drag racing world onto its ear with the Billy Shope "one I/C fits all" tuning philosophy.

Good luck wif dat............ :roll:

As for the original question, in spite of what Billy says, shocks are indeed important and the Aldans are junk. Invest in better shocks that will actually do what they're designed to do. In my opinon, you'll be chasing your tail as long as you have them on the car but, I'm probably wrong. Have you met Billy Shope?
"If winning was easy, losers would be doing it"

ky mustang
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Re: rear coil over tuning help needed

#20 Post by ky mustang » Fri Jul 30, 2010 2:30 pm

Most professional built fast door cars have very little suspension movement at launch , it would have to suggest the suspension setting is close to 100% a/s and the chassis was constructed with the correct cog placement to the available power planned for the chassis would it not ?

If inertia was not completely responsible for weight transfer how would a front engine top fuel car or funny car get enough traction to produce the 60' times they do ? They have absolutely nothing to produce more forward bite. The only thing they can tune with is weight placement by changing the cog , and a clutch. A tf rear engine dragster is the same way , all that frontal length is just leverage replacing weight from the engine being located in the rear.

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Mike Peters
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Re: rear coil over tuning help needed

#21 Post by Mike Peters » Fri Jul 30, 2010 3:08 pm

ky mustang wrote:Most professional built fast door cars have very little suspension movement at launch , it would have to suggest the suspension setting is close to 100% a/s and the chassis was constructed with the correct cog placement to the available power planned for the chassis would it not ?
No, the rear end housing movement is controlled by really great shocks -

http://afcoracing.com/tech_pages/dragshock.shtml
"If winning was easy, losers would be doing it"

ky mustang
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Re: rear coil over tuning help needed

#22 Post by ky mustang » Fri Jul 30, 2010 3:20 pm

I know they got those electric high dollar shocks on pro stockers and I am sure they induce limited tire rotation to work with the clutch , but they also got lead weights stuck in odd places for some reason. Most people are gonna say ballast , but I don't buy it they are set at a certain place and a certain height for some reason. The only reason I can see is to put the cog where they want it. They have a minimum weight and its very easy to build the cars lighter and adjust the cog to make up for the wheel base limitation put on them by the rules.

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Dave Morgan
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Re: rear coil over tuning help needed

#23 Post by Dave Morgan » Thu Aug 05, 2010 12:35 pm

I’d like to begin by offering my apologies for not being here more often. I can’t use the excuse “been too busy” because while I have had a vibrant summer, I should always have time for my friends here. The plain truth is that I don’t enjoy confrontations, yet the time has come for me to confront Billy Shope because his views are far too academic and not nearly mechanical to be practical.
I’ve been living with fourlinks for nearly four decades, using my mind, eyeballs and fingers to figure these linkage systems out. My opinions have evolved as my experiences developed. I was once an Instant Center man, but now lean more to the kinematics of the system. Kinematics is the study of links and is a concept championed (and ignored) by such excellent builders as Ed Quay, F.J. Smith and Don Davis.
I haven’t divorced myself from IC tuning, once the car is moving, this relationship is important at the faster stages of the run. Yet, I feel that at the moment of the launch, when all the implications of torque, inertia and friction are at their greatest value, IC location seems to me to be minimal compared to the effects of the linkage system itself.
So here are my thoughts:
• 100% anti-squat? Are we trying to stop these cars? Or accelerate them? IC location along what I was taught to call the Neutral Line (Billy’s 100% anti-squat line) is a valid concept. It’s been my experience, and the experience of my students, than when an IC is placed on this line, pitch rotation is minimal, but suspension travel still occurs as the entire car rises equally at both ends, much like a Mopar Super Stocker does (man, where those boys sharp!). It’s a bunch of fun to watch these same cars get off the throttle at the top end as one can see how the chassis drops. So I don’t argue that the effect does not exist, I know it does, but it’s not a magic balancing point like Billy says it is. In other posts, he’s mentioned that the car can oscillate fore-and-rear if an IC is at 100%. I’ve run into the same problem anytime I get the IC remotely close to the center of gravity. In extreme cases, one can hear the engine rev and fall, rev and fall, as the rear tires bounce. The drivers can often feel and hear this effect. In other situations, the driver has been unable to notice this “rocking sensation,” but it clearly shows up on data acquisition as it looks like the car has been driving over a very bumpy track. It’s only when you look at the timing of the front oscillations versus the rear, do you see that the car is quickly and subtly pitch rotating.
• IC length is not the be-all element to a fourlink set-up, but it is crucial as it greatly affects how the car handles at the top end (although I sometimes wonder if this has more to do with the bind we place the rear rods end into when we run a short IC.) I’ve played around with this relationship a bunch, especially in the late 80’s early 90’s. You can choose two ICs, each one giving the same anti-squat value and see that the length of the IC does affect the car, even though the anti-squat vales are identical. For Billy to say the anti-squat is all that matters simply indicates to me that he has not taken his eyeballs and fingers under a car, nor to the track to do any tests.
• Finally, during the launch, that first instant when the torque strikes the ring gear, I feel linkage geometry has a much greater effect than IC location and the same is probably true during the gear changes. I’ve played with top bars positions a lot, found they have effects and am lately startled to discover just how important the lower bars are. I’m nearing some conclusions that the lower bars may have a greater effect on the efficiency of the system than the upper bars, which now places me on a fourth evolutionary plane in my own development of understanding these weird four bars.
Anyway, that’s all I have to say right now. Sorry I’ve been gone so long, but I’ll be back.
Dave
Author of "Doorslammers: The Chassisbook"
Drag Racing Chassis Seminars and Videos

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Mike Peters
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Re: rear coil over tuning help needed

#24 Post by Mike Peters » Thu Aug 05, 2010 1:03 pm

Dave, thank you my friend for your insight into this discussion. Glad to see you're out there on the trail sharing your passion. If anyone has the opportunity, do yourself a favor and attend one (or two) of Dave's Seminars. Not only will you walk out of there with a plan on how to diagnose your chassis afflictions but, an understanding on how to correct them.

Dave, I hope you're doing well. :thumb:
"If winning was easy, losers would be doing it"

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BillyShope
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Re: rear coil over tuning help needed

#25 Post by BillyShope » Thu Aug 05, 2010 1:55 pm

Dave Morgan wrote:In other posts, he’s mentioned that the car can oscillate fore-and-rear if an IC is at 100%.
You've got me confused with someone else, Dave. I HAVE said that...even at 100% antisquat..., the rear of the car will wiggle as the front springs extend. But, the whole idea of setting a car at 100% antisquat is to MINIMIZE oscillations and thereby MAXIMIZE traction. That "wiggle" increases in magnitude as you get further away from 100% antisquat.

That tire patch force vector, which has a horizontal component equal to the force pushing the car forward and a vertical component equal to the weight transfer carried through the links, acts on a line which passes through the instant center. It follows that the instant center can be anywhere along that line (which happens to be a line of constant percent antisquat) and the effect will be unchanged. The "out" of instant center location is meaningless without the "up." The ratio of up to out, when multiplied by a constant, equals the percent antisquat.
http://www.racetec.cc/shope

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BillyShope
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Re: rear coil over tuning help needed

#26 Post by BillyShope » Thu Aug 05, 2010 8:17 pm

Dave Morgan wrote:I feel linkage geometry has a much greater effect than IC location....
Dave
As for the significance of the lower link being parallel, let's plug in some numbers and see what happens.

Suppose the lower link is horizontal with a rear attachment point directly below the axle centerline and 9 inches up from the strip surface.

The upper link's rear attachment point is directly above the axle centerline and 22 inches up from the strip surface. The front attachment point is 24 inches forward of the axle centerline and 15.76 inches above the strip surface.

These link lines intersect at 50 inches out and 9 inches up.

Now, we'll assume a 6000 pound force is acting horizontally at the rear tire patch to accelerate the car forward.

The lower link will be in compression. The upper link will be in tension. (For simplification, I'm lumping left and right links and tires together to make the problem two dimensional.) So, the horizontal forces acting at the rear link attachment points must balance. That is, the sum of the tire patch force and the upper link force must equal the magnitude of the lower link force.

In addition to the force balance, there must also be a moment (torque) balance. Taking moments about the tire patch, 9 times the lower link horizontal force must equal 22 times the upper link horizontal force.

It is possible, then, to solve for the horizontal forces at the links' rear attachment points. There would be 10154 pounds directed rearward at the lower link and 4154 pounds directed forward at the upper link.

Finally, there must be a vertical force balance. Since the lower link is horizontal, there is no lower link vertical force component. The upper link is angled down and is in tension, so there is a vertical force component downward which must be equal to the weight transfer experienced by the rear tire. The ratio of (22-15.76) to 24 would equal the ratio of this unknown force to 4154 pounds. This would be a downward vertical force of 1080 pounds.

The force acting at the rear tire patch would, then, have a horizontal component of 6000 pounds and an upward vertical component of 1080 pounds. The ratio of 1080 to 6000, when multiplied by 50, results in 9, meaning that the resultant force vector passes through the instant center located at 50 out and 9 up.

Now, suppose we retain the upper link and remove the horizontal lower link. A new link will be added whiich has a rear attachment point directly above the axle centerline and 100 inches above the strip surface. Yes, it's an absurd arrangement, but useful as an example. The front attachment point is 24 inches forward of the axle centerline and 56.32 inches above the strip surface.

Again, the link lines intersect at 50 inches out and 9 inches up.

The horizontal forces now are 1692.3 pounds at the upper link and 7692.3 pounds at the lower link. The upper link is exerting a downward force of 3080 pounds and the lower link is exerting an upward force of 2000 pounds.

The resultant tire patch force components remain 6000 pounds horizontal and 1080 pounds upward.

In other words, excluding strength and weight considerations, link angles and locations can take on any values and, so long as the instant center location is unchanged, launch characteristics remain unchanged.

Taking this exercise a step further, the instant center can be moved to any other point on the force line of action (which is also a line of constant percent antisquat) and the results will remain the same. Take it to 500 out and 90 up and see for yourself.
http://www.racetec.cc/shope

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Bruce69Camaro
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Re: rear coil over tuning help needed

#27 Post by Bruce69Camaro » Fri Aug 06, 2010 9:42 am

Ok, I gotta jump in here.

I've been reading and reading and reading all this information, but now I have a question ?

Does anyone remember what the original question was and did the guy that posted this question ever get his problem resolved?

Wow, Billy Shoupe is now going up against Dave Morgan, what's next?

Dave is one of the "God's of Suspension's" in the racing world and many know his name.

I never heard of your name Billy, until I came here to this site, but boy do you know how to pick a battle.

This is a good example of why some of the "Big" names don't want to come on a post answers, because there is always someone out there that knows more and has done less.

To the person that I bet, that Billy would have a come back against Dave, you owe me a steak dinner.

Wow......

Bruce
Those who think they know it all have no way of finding out they don't......... :scratch:

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Re: rear coil over tuning help needed

#28 Post by Elkyman1 » Fri Aug 06, 2010 10:47 am

Here's another question,

What constitutes big power? vs. low power vs. serious power? What levels of horsepower can we all use to refer to with this suspension info., 600,800,1000+ power??? When the word serious power is used, I think of 1000hp and above as THAT is some serious power and is very affordable to many racers in this day and age.

Nothing against all you guys that run from 10 seconds flat and slower, but why do you guys have big tires on the rear if you don't need them? I had to go to a bigger tire because I ripped my frame apart, but I hit 9.80's with 10.5 tires!!! with only a lil ol 505 big block and a glide :scratch: I know I don't make serious power but I have never had an engine or chassis dyno session either.

After reading all this info also, kystang made a comment about the fuel car chassis's, and everyone know's they do NOT have to have shocks or springs? Nope, not required my NHRA rules, but everyone below those two class's (T/F & F/C), ARE REQUIRED TO HAVE A SHOCK AND SPRING AT ALL 4 CORNERS OF THERE CHASSIS! Go ahead, check the rules, and if Pro Mod cars could make shocks and springs go away, the would be most likely be called an old name way back when, (AA/Fuel Alterds) because THEY used to be F/C style chassis's and had no springs or shocks, well, some of them had spring's and shocks on the front axle, and rear, but the ones with no shocks and springs in the rear, used rear tire psi as the rear shock and spring.

Dave, I will stay in touch wth you when I get some laps on my Elky, until then good luck and keep your chin up :mrgreen:

John
"The Elkyman"
Looking for 8.90's :thumb:

ky mustang
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Re: rear coil over tuning help needed

#29 Post by ky mustang » Fri Aug 06, 2010 11:41 am

I think there are a lot of racers that think that a particular 4 link / ic / a/s setting will actually pick up the car through leverage and multiply more weight to the rear tires than what the car actually weighs.

If that were the case how wide would the housing brackets need to be on a top fuel / funny car :mrgreen:

I do think I agree with Dave on the bottom 4 link bar (not sure exactly what he is thinking) . I think the overall height of the bottom bar in reference to the cog height has a big effect itself not even weighing out the bar angle.

daves540
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Re: rear coil over tuning help needed

#30 Post by daves540 » Fri Aug 06, 2010 9:54 pm

Bruce69Camaro wrote:Ok, I gotta jump in here.

I've been reading and reading and reading all this information, but now I have a question ?

Does anyone remember what the original question was and did the guy that posted this question ever get his problem resolved?

Wow, Billy Shoupe is now going up against Dave Morgan, what's next?

Dave is one of the "God's of Suspension's" in the racing world and many know his name.

I never heard of your name Billy, until I came here to this site, but boy do you know how to pick a battle.

This is a good example of why some of the "Big" names don't want to come on a post answers, because there is always someone out there that knows more and has done less.

To the person that I bet, that Billy would have a come back against Dave, you owe me a steak dinner.

Wow......

Bruce


I'm still here, thrilled with all the input. I've been trying to get to a Dave Morgan class for years now just never gets close enough to my area.
No I haven't had a chance to get back to the track yet, but hope to on one of the weekends in Sept. I'll be able to post some video of my car launching with 4 different I.C. & A/S settings. Hopefully will generate more input from all.

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