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Just a broke down engineer here.
SO I gotta ask: "You boys gonna hug now?
"Reckon we got sum metal ta cut...
This has been enjoyable from the sidelines and a lot of good info past.
I know I'm smarter for it! Thanks for smiling!
Cheers - Jim
OH - And thanks to DAY for letting it play out too!
Last edited by phantomjock (1/25/2012 4:40 pm)
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Heck,
TR has all the answers.
From him I learned the 427SC was a pig. The darn thing weighed a whopping 2,350 lbs.180 lbs. more than the 289 @ 2,170 lbs. and it only produced a measly 170 more HP. With an all new heavier frame tube. A major mistake I'm sure Shelby would have never made if TR were there. Hell, what was he thinking building a 2,350 lb.car! What a boat! How much does your car weigh? Next he will dispute the numbers I took off Shelby's page.
Then again, he can figure out a bolt circle on an oval. DO YOU KNOW WHAT THAT MEANS? I didn't think so, neither do I. He could be Shell's oval bolt circle maker maybe.
I learned to never question OZ, OZ knows all.
Here is an example of I don't know what by OZ. A question directed at me.
"I guess the most important point I have to say is: I am writing about a running driving vehicle that I have had finished! The Jag Irs has been done since 2010,the T5 conversion has been installed for over 9 month. I drove it to work all last summer. with out any problems If the paint were done. I would be driving it daily still.
You have yet to explain how a vehicle that has such high roll stiffness that body roll in is nearly non existent could provide roll steer of any significance."
OK, so you built a car with an IRS that features roll steer. But you stiffened it up so much, you can't even see the benefit of RS. You use the car as a daily driver as you say, dodging pot holes! Who is not making sense?
As I had told you, RS seems to be good for street cars but not racers. He put those stiff azz springs in, that are suited for racing and put it on the road. CHANGE THE SPRINGS OUT! Soften it up like a street car. Then check back dude.
He also builds a performance car with roll steer and he writes this. Post #27
I get how this can induce roll steer but my question is.... Why would you want to induce roll steer in to a performance cars suspension?
How would you approach others? Maybe saying,
Hey I did my install unfortunately I've stiffened my suspension to the point I am not seeing any benefit to having RS. I can't pull enough cornering G's consistently to even really shake it out. Maybe I should have not pursued this RS idea from the beginning. I'm driving this beast in traffic, dodging pot holes. And I told you about the idiots on the road right. The ride is really rough. I may need another daily driver. Maybe I should soften her up?
But not OZ he has to propose the question like I'm the idiot. LOL!
I mean really, is that funny? That doesn't include all the snide remarks he has made also.
Just follow this thread I tried so hard to be nice, he never took the clue.
PJ, he keeps on trying not to understand my point that he could have toe out due to design. Yet he posted himself half the answer I gave him.
From #3
I always understood that in order to create anti-squat on a IRS the wheel travel when viewed from the side could not be perpendicular to the road surface. It had to be angled so that as the tire went down it would move forward and as it went up it would move to the rear.
OZ if your inner pivot of your LCA is fixed and your rear wheel goes back, AS YOU SAID! The LCA goes back at the outer pivot with the wheel, with that, possibly toeing out. Unless you have enough angle in your upright pivot points.And I'm sure you do. Hello!
You need to apologize, every time you have insulted me and questioned me you were proved wrong.
Ralphy
Last edited by Ralphy (1/25/2012 10:02 pm)
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PJ,
Maybe people like hard arguments.
People have been signing up pretty heavily in the last 2 days. We also have about 46 newbies since the 10th month last year. With a total of 131.
Ralphy
Last edited by Ralphy (1/25/2012 10:12 pm)
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TR, I try to read your posts. Sometimes they are long. When I have responded to you I have always tried to be sincere and also question. I try to interpret what you say and do not say. I will even read the text more than once, trying to comprehend what anyone is trying to say, before I respond. I don't think you ever explained your measuring the RS. So I tried to draw an answer out of you. You did bite, however you seemed angered assuming I thought you were ignorant maybe. That's your issue. It sounded like you may have never taken the opportunity to get numbers. Pier has not at VetteMod, nobody blasted him. Hell you and Pier accomplished your mission. I and many others here are looking for answers. Because we are not where you are. I applaud your work. But if you want to do anger, I can do anger also. Can you take it down a notch? Comprehension in a conversation is more visual than any other factor. We were taught this at work by professionals. Here we have no visuals, so typing people are easily able to misconstrue. I'm not here to compete, but learn. The camber rod comment is an example, really? Was that needed? I know I was part of the cause for you to say that.. At that point I was baiting your anger. Go back through this thread and you will see I was always trying to be polite, till I had enough.
I get this feeling you are looking for recognition and respect because of your accomplishments. I never patted you on the back nor anyone else, but we all know. Hey he did it, you have it. At least by me.
Peace!
Ralphy
Last edited by Ralphy (1/26/2012 7:00 am)
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TO WHOM IT MAY CONCERN
I dont care
Last edited by tyrellracing (1/31/2012 5:30 pm)
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TR,
Your digging yourself a new hole now, I see.
Now your suggesting we don't believe you have a T5? And also now including Daze? OK.................................
Are you reading anything here? Are you also blasting Daze?
This was between you and me, not Day.
When a person starts posting, lay down your money. My first thought, that sounds like a teenager. How old are you?
Hmmmmmmmmm...........
So when you started directing posts and mail at me. I sensed maybe you had some animosity toward Day. Now it looks like you do.
I never brought up doubting you have such a car. Or did this work. But now that you went this way, I am beginning to wonder.
Ralphy
Last edited by Ralphy (1/26/2012 7:04 am)
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So if your not a teen. One last question, tell me what you see in each picture?
Last edited by Ralphy (1/26/2012 7:04 am)
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WHERE IS YOUR CAR RALPHY
Last edited by tyrellracing (1/31/2012 5:34 pm)
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OK,
I have a hard time following these tidbits you posted. You stated an IRS develops much less anti-squat than a solid axle, Which is very true. But then you said the Jag IRS develops so much anti-squat that it jacked you car up several inches. A Jag at my guess has a maybe 6 degree inclination at most.
Now this gets better, so you went with the T5 design and you said you now have a lower trailing link at 25 degrees. You have increased the anti squat angle up to 6 times, at least a multiple of 4. And now your saying you have reduced this jacking effect and all is sweet roses. How does a 25 degree angle give you less anti squat than a 6 degree angle?
I'm going to throw the BS card again on you. Saying Your Jag configuration jacked your car several inches up under acceleration. As you stated a truth an IRS creates way less anti squat.
In another post you ragged on a Jag design blasting how they wheel hop. This, at the Cobra site has been discussed quit a bit. Most these guys are running a raw dogbone with no support. The main culprit is no support from above the half shaft. That's where Mickmates upper Watts Link comes in. I'm not 100% sure how well it works, but Mickmates Watts Link seems to be quit popular. Day and I have spent a bit of time on this, he and others here have even talked with Mickmate. And I believe one member here ordered Mickmates upper Watts Link.
It don't add up TR!
And if you want to see my car it's here,ask Day. I could direct you to the thread, but why should I make it easy on you. Go find it hot shot.
Another point you keep posting BS about is that race suspensions do not move. When I was young I pitted on an asphalt oval track car. We would put white grease on the shock shafts to visually see how much motion each had. Back then that was the only way you could measure. The right front had almost 2" of travel. That's 2" of jounce not total travel. And get this the car had a train spring on that corner, no lie. And before you post some other derogatory BS, the car won 2 track championships at Berlin Raceway in Michigan. In the Super Late Model Division. So go blow your smoke elsewhere! Maybe when you drive your imaginary car like grandma you see in your mind no travel.
You say post the pics? My pics are here. Post yours, I never said before, you don't have a car. You brought that on your own Skippy. Sounds like maybe your premeditating being called out to produce any pictures. You brought it up. Hmmmmmmm........ maybe you don't? LOL!
Oh another thing, the picture you directed me to similar to what you have. That you acted like I was clueless to. I posted that pic, I knew what you had.
Ralphy
Last edited by Ralphy (1/26/2012 12:01 pm)
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Take a chill pill guys, then get back to work. You're acting like a couple of bitchy little girls.
JB
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TR,
Your had, in three weeks you went from an all Jag suspension to a KA suspension. But the KA as you said you have been running for what a year?
You posted this on 01-02-12
As for the broken Jag parts, I am running a 408 cleveland stroker engine with a 4130 crank, H beam rods, CHI heads that produces somewhere in the neighborhood of 575ftlb torque in a 2875 lb car with a posi and 3.25 gears in a rear robbed from a XJ6 , spank the crap out of it every chance I get and even with wheel hop have yet to break anything. May be the drag radials provided too much bite or the parts were fatigued and had micro cracks before they were installed in the cobra. After all I think I am correct in stating that none of us know just how violent of a life the jag parts we are using had before we began to molest them. It could be someones grandma drove the car its entire life back and fourth to church or it could have been the
you posted this on 01-03-12
I agree with you Ralphy. I had my brother do a finite element analysis of the LCA in the hope of getting to the bottom of my wheel hop issue. He is one of Boeing's chief engineers and has full access to their incredible computers. His team of engineer's are in charge of cabin pressurization. He told me the biggest reason the Jag setup produces wheel hop is in the forged steel weldments at each end of the tube on the LCA.. The arms at the inner pivots have serious loading issues. They wag alternatingly up and down allowing the hub carrier to rotate about the approximate tube center line under heavy acceleration or braking load. The gussets I welded there do little to reduce this flex .The tube its self is more than ridged
Oh my then you post this, what 2 days ago?
All I can say about Anti- squat/dive is you hit the nail on the head. The design that lifts the rear under acceleration will pull down under braking and will be as effective at one as the other. Doing so is the proverbial two birds with one stone. However when the brakes are mounted outboard the rotational force on the K.A. linkage has an even more dramatic effect on the anti dive. I still have my brakes mounted in board so I do not fully take advantage of this. I was torn between unsprung weight and anti dive. Reduced weight won.
The K.A. suspension modifications I made to the Jaguar IRS had virtually no effect on the ride quality or the lateral grip. It only stopped the wheel hop.
Wheel hop aside, I noticed no difference at all in how it performed so If I have built in roll steer its too small to be concerned with.
From a standing start, it is slower than the old 9 in.
The problem with lies is keeping your story straight and you made that mistake. You went from wheel hop to no wheel hop in three weeks and two different setups.
Ralphy
Last edited by Ralphy (1/26/2012 12:50 pm)
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Sorry ;-) I've been itching to use that phrase and you guys gave me the perfect excuse. Brought to you, courtesy of Sam Ash.
JB
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Ralphy;
The free body diagram is closer but since the two links work as a pair and I made my Upright adjustable, There is no forward movement of the axle when viewed from above when the suspension moves. If you look at the T5 hub carrier it has a short attachment point just above the axle for the trailing arm. When I made my Hub carrier I extended the upper mount and gave it two additional holes. The top hole is the same distance from the axle as the lower mount. There fore it does not drag the axle center forward when moving vertically. As I have said all along Its a watts link and I made it adjustable so I can go either way. My rear mount bracket has four holes vertically spaced every .5 inch so it is adjustable . My lower control arm has a threaded heim that adjusts the track width and camber. This obviously provides 10 times more camber adjustment than the shim method the Jag had. I have aprox. 10 degrees of toe adjustment in and out at the LCA's I learned long ago to make suspensions adjustable. One of the things you seemed to take for granted was my latitude of adjustment . In short I did not estimate any thing, you assumed too much.
Last edited by tyrellracing (1/26/2012 5:36 pm)
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Ralphy
Where Did you get the idea I only had three weeks? I havent responded to this forum since 2010. I had the K.A. in place from the first posts when i got my new pass word to re enter the site. Where do you get this stuff? What differential do you think I am still using? The Jag Salisbury case with Dana 44 Posi carrier and gears. That came out of a XJ6 Jaguar. I am also using the Jag half shafts,. Hub carrier bearings, stub axle's bearings for the LCA in the new hub carrier . The Diff. is the most likely part to be ripped to pieces from torque The LCA mounts un bolt and I made new ones that bolted back on the same location. That was the extent of the K.A. conversion for the diff.
Why havent we seen your Cobra yet. I would think that as prolific as you are as posting you would be proud of your own ride. You always post the work of others, Why haven't we seen any of your own?
The leading link has the least influence of the two link's over axles fore and aft movement. I made my Hub carrier adjustable so as I indicated before the axle is centered between the two link attachments so it doesn't move
forward or rearward when its in motion vertically.That is why and I say this again. The toe chart does not apply.
My brother did the finite element analysis in2010 and I got the flash drive with all the computer generated images and related information at his 50th birthday party October 8 2010.
Last edited by tyrellracing (1/31/2012 5:44 pm)
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Ralphy
Funny how you ASSUME.. Yes I had actually had three set ups. In as many years....First the 9 inch ford Hotchkiss drive with a watts link, under ride traction bars, 4 piston caliper disk brakes and a Detroit locker. Then the Jag , And last the K.A. T5 Then sorting it all out, 100 different alignment settings, four shock valving changes and ,three spring rate changes.
With the Klaus Arning set up I made dozens of small changes last summer in an effort to gain more weight transfer and better grip. The wheel hop did not go away magically when I installed the T5. Some adjustments made the hop go away and when adjusting for weight transfer it came back
As is the usual practice I had to sort it out with trial and error, keeping notes in my log book and breaking down problems to their basic elements This should not be a new concept to any one that has sorted out a race car before. Haven't you?
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There is anti-squat then there is USABLE anti squat. The live axle with say 80% anti squat will use the axle housing rotation to start a chain of events that lead to enough friction to launch..First torque applied drive shaft will try to rotate the axle housing in the opposite direction as the tires. Then this rotational force path goes to the two lever arms extending downward from the axle housing tubes. The rotational force now has a lever arm that through a rod connected at 90 degrees will convert the rotational force to a linear force that will be applied to the frame of the car just ahead of the leaf spring mount. Depending on where the C of G is in the car ans where a tangent line through the traction rods is in compairison to this C of G will determine % of anti squat. Now the force is pushing up on the frame of the car and this in turn applies a.greater force downward on the tires while lifting the cars body at that instant. This chain of events so far may have taken a half second. Slamming the tires down to the asphalt through the use of reactive force is the key to getting useful anti squat and it is a delicate balance! Too much anti squat and the rear of the car can thrust so hard it can bounce the tires right off the ground. Too little and insufficient grip will spin tires. You must get the tires to grip well enough in that instant before weight transfer or you will never get the weight to transfer. This is the meaning of useful anti squat. Its all in the first instant of acceleration. If the anti squat is correct for the vehicle, The tires will maintain grip as their loading is increased from a lever arm's downward thrust to the near 100% of the vehicle weight transferred to just the rear tires!. If everything has gone as it should in the first second and a half then the nose will raise with it as weight is transferred from all four tires to just the rears. This is the moment of success because now two full seconds later it is all up to how much power you can get to the road surface to maintain weight transfer. The balance is different from car to car and when done right is impressive. Too much or too little will result in wheel hop or tire spin.
Now With the live axle, The housing rotation is used as a device to slam the tires down to the tarmac. With an IRS you cannot ever get this effect because the rotational forces are all kept locked to the vehicle's frame. Their has yet to be a device that will plant the tires with enough force to get enough grip before WT with an IRS. The methods of anti squat on a IRS are sum what passive. The downward force applied to the tires from the most common method of IRS anti squat is way too little thrust to get the grip required . Almost enough thrust always ends up in wheel hop. Reducing anti squat will always end in wheel spin and neither will ever gain sufficient weight transfer to launch. Until someone develops a method that can generate enough downward thrust with a IRS, traction will continue to be a problem. Their are exceptions.... RACING SLICKS! If you can get gooey enough tires then to hell with anti squat and weld the axle to the frame and go. You can make any thing hook with slicks. But for dot approved highway tires you must have usable anti squat. Or spin tires when accelerating hard.
Ralphy:
One last thing. I spent a great deal of time refining the antisquat on my car before I changed to the T5 linkage. If you had read up on the T5 you would have known that the original used the same differential as the jag unit but with outboard brakes. The original used the same wheel flange type and hub carrier bearings as the Corvette of the period. Using all the drive parts from the Jag only made sense since I had them and Vette parts are not cheap. With that information you can understand how with the T5 I can still break Jag parts. Its only common sense. I am human and will make mistakes however you are getting carried away with mud flinging. The word you were looking for is CONTINUITY. I have done so many little adjustments to the T5 in the last year that I am not surprised that I may have had a break in continuity. But in reality. Those breaks did occur. The T5 did with refinement stopped the wheel hop. And in my effort to gain anti squat and subsequent tire grip I found new ways to make it wheel hop. So wheel hop happen with both the Jag and at different points the T5. But I always had my notes to fall back on to correct any issue I created..
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Ralphy:
No pissing . just something of interest and the origin of the over weight pig statement.
I used the term overweight pig to describe the 427 Cobra not from my own opinion but from a quote in Ken Miles biography. Do you have any Idea who this man was? He was Carl Shelby's best friend, and was the driving force in Shelby racing program. He was with Carl from the beginning when Carl won Le Mans Ken was crew chief. Ken won the lions share of the races and championships for the Shelby team. He was a incredible driver by any ones standards. It was noted in the biography that during a points race in California with Ken starting on the pole he humiliated the rest of the field really bad by lapping the entire field twice before the half way point in the race. He had a particular dislike and feud with the Chevy drivers and crew so with the extended lead he took an unscheduled pit stop so he could get a drink of water and make fun of the Chevy pit crew . Carl was not amused and told Ken to get his ass back out there. He went on to win the race with the same two lap lead over the entire field when the checkered flag dropped. He did this in a 289 powered Cobra. Ken was unstoppable in the Little cobra. He was well aware of the writing on the wall that Chevy was to release the Aluminum ZL1 Vette soon. that put an end to the 289 Cobras supremacy. Enter the 427 Cobra. Even though Ken could still win in the 427 he disliked it terribly and wasn't shy to say so. Nearing the end of the 67 road racing season Ken Miles was killed in a 427 Cobra during a practice session. Carl was distraut and was quoted to say that with out his best friend and driver the car biz wasn't fun any more, so he quit racing and building cars soon there after. In 68 he sold the entire Shelby company and rights to the name to Ford motor co. Up till then all shelbys were assembled at his rented hangar at the LA airport. In 68 it was all moved to Detroit. .
Any how that' where that came from
Last edited by tyrellracing (1/27/2012 5:57 pm)
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TR I for one appreciate the very well written description of anti-squat above as it was exceptionally easy to follow. Should you see fit at some future time to elaborate on other aspects I expect that would be quite a benefit to those of us still struggling to follow exactly what goes on with the IRS and the forces involved. What we need are nice clear descriptions like that. So anyway, thanks.
Jim
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I will echo Jims post on that TR.
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Does any one have any ideas on how to improve the anti-squat on IRS suspensions? I have worked with the inclined type like the Viper and the Jag uses with little success, I have played with the convergent angled control arms with about the same results. This would be the million dollar invention to find a method of generating the anti squat characteristics of a live axle in a IRS.
I have a sand dragster that has a long travel Goulstrand suspension that provides 24 inch wheel travel. It started as a single seat 350 cc Honda pilot. Then I stretched the rear to accept a 3.0 l sho engine and Subaru WRX transaxle. converted it to long travel suspension and use 16.00-15 competition paddles.
The engine was enlarged by boring and stroking it to 4.0l Then balanced the rotating and reciprocating parts and had the cam's re ground. . This required custom cam follower "buckets" to take up the gap of the smaller base circle.I adapted a toyota Supra distributor to attach where the cam sensor once was. Then I put a blower from a 3.8 t-bird on it making 8 lbs boost. The little thing makes 410 hp at 8k rpm. The vehicle weighs in at 1035 wet . Sand drag racing the track is 100 yards for safety reasons. Only 300 feet long but that's enough for this thing to hit 81.949mph. in 3.821 seconds This thing is on the rear tires and the wheelie ski the whole 300 feet! On rough sand drag strips a well engineered IRS is MANDATORY. A person might think that with 16 inch wide paddles traction wouldn't be an issue. Well that's what I use to think and its dead wrong. Paddles with out anti squat will not bite into the sand rather they will skim over the top 2 inches. With a good anti squat they will dig in 10 to 12 inches and the volume of sand being roosted is a form of jet propulsion rather than traction in the common sense. The paddle tire displaces a greater mass of sand than the vehicle weighs combined with friction equals rapid acceleration.
I raced it from 00-06 and it has been the reason I have gotten so involved in IRS design. The light weight and high power makes getting it to stay on the ground tough. I have snapped the ski and flipped it on the starting line twice. I have tried semi trailing arms, trailing arms, and variations of SLA in angled then convergent, then combined. I have hundreds of pictures on film that I can scan as well as the old rusty toy sitting in my driveway that I can take new pic's of. I will scan some pic's this weekend and download them to this site. This vehicle has been my dynamic test platform for years. I have put so many different attachment points for IRS's on it that I had to replace some of the frames tubing. A picture says a thousand words...
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Seems like a lot of combinations have been tried. Didn't try Front Wheel Drive yet? Just kidding...
I guess launch weight transfer is the key to getting the paddles into the surface.
Have you seen "Shopes's" site yet? He has a few pages on weight tx and a few on anti-squat.
I'll let you go over there and poke around. Careful for his calculators - he sometimes uses an unconventional axis reference system.
The picks will be fun to see too.
Cheers - Jim
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Phantomjock
All the top fuel rail dragsters I have seen have either welded in or bolted in rear end housings. Funny cars will more often have the conventional 4 link. The only reason I bring this up is They are describing a rail dragster. Dont you think having the axle housing bolted to the frame would make the anti-squat discussion pointless?
With that said.... Cool site with good information. Not much that can be gleaned for the IRS though.
So, what do you think would work to improve tire adhesion before weight transfer? With out sand bags!LOL
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So, what do you think would work to improve tire adhesion before weight transfer?
bigger (longer) contact patch - Think a long set of paddles - nearly entire wheelbase .
Uh oh been done--TANK!
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Okay I really am totally new to this IRS stuff. So please bear with me and call me a dummy if I miss the mark. What Im reading is all potential of lift is lost if the RA center is rigidly mounted? I know how a live axle works, so to gain any lift the center section would need to be mounted a little loose and pick up the torque of the drivetrain say off the bottom of the pig? Eventually this potential is transmitted to the outer end of the LCA and then the trailing links might get something to work with if it can get by all the twist and such lost in the design of the LCA . Unless I am missing something , the stock Jag set up has this figured in with the cage mounted on rubber to some extent. I am looking at this right now as only straight line hook up and when you guys get into the road racing geometry,, well Im out in right field there or maybe even on the bench. back to my point ,, if lift is the goal , my thinking is things have to be loosened up a bit and go for transfer points that are further ahead on the vehichle. Please keep in mind also Im looking at this from the straight frame set up I have going and not having the RA buried up into the car. Did I make any sense ?? So instead of designed to bind Im seeing something has to give..lol
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Mental lapse here, can't seem to recall what RA means. Oh well.
Seems to me that the only time you want anti-squat is for straight line acceleration. For a sand rail that seems to make perfect sense and I can see the need for an exaggerated effect, but coming off a turn where you're already balancing tire adhesion against the throttle the anti-squat is going to lift the body and you can forget about any thoughts of an early apex. If it's aggressive enough it could throw you right off the course. And since that is the type of driving I do mostly, I don't indulge very much in efforts to get more anti-squat. For my purposes, maximum cornering ability is much more important, and to me this means as nearly as possible, keeping all four contact patches squarely on the road surface and moving in the correct directions. Normally this means the rear tires are going to track inside of the front tires and the ackerman angle is going to be correct for both front wheels. So I question the intended function of rear wheel steering or toe-in. Why and when would rear toe-in be an advantage? When would it be a disadvantage? How big could that advantage potentially be, and how much effort is really justified in a real life effort to use it? Wouldn't toe-in cause the tires to fight each other a bit thereby incrementally decreasing cornering grip? I can see it working in hard straight line acceleration to offset bending forces from application of acceleration forces, but the rest of the time it seems like there would be no advantage to it and at least a potential grip disadvantage as well as increased tire wear.
Same for rear steer. Is the idea to steer the rear wheels to the outside so they track more nearly in the path of the front wheels, thereby more nearly equalizing the load front to rear on the suspension, or do they track to the inside? If to the inside doesn't this point the nose of the car to the outside of the turn, requiring the front wheels to be turned further? If to the outside doesn't this increase the radius of the turn averaged between the front and rear of the vehicle? In either case, what is the advantage? I'm not sure that, "makes the car go faster" is an answer. If the idea is to make the rear of the car track on the same radius as the front a much sharper steering angle is needed than what is commonly used so if that is not the intent, why bother at all? Basic questions I know, but fundamental ones that have to be answered before a realistic assessment can be done.
As far as the anti-squat is concerned, the first primary consideration seems to me to be that you have to define your IRS type. With the Jag where the stub axle is the UCA there is a very considerable level of torque being applied to the LCA by the forces of acceleration. The distance between the axle bearing and the LCA outer pivot is such that this torque is delicately counterbalanced againce the counter-rotational torque of the pumpkin. The hog's head raises it's snout, the upright pushes it down, and the counter torque in the system is nicely balanced out. This is great for a road course but of course there is nothing left to generate jacking force to plant the tires.
By contrast the IRS with a separate top link splits this torque balance relationship, bypassing the LCA and transmitting the acceleration force directly to the chassis or body, and applying the counter-torque through the pumpkin mounts into the chassis or body at a different point. Clearly if jacking is desired this is the most promising route to obtain it, although in the earlier example it would be possible to alter the upright length to shift the balance and I may return to that later.
Understanding at this point that the initial acceleration forces are what is acting on the upright, rather than counter-torque, it is clear to see that traditional jacking strategies are working in the wrong direction, as they seek to use the counter-rotation of the axle housing to lift the body, whereas with a proper top link it is a linear force. This can be converted to a vertical force by proper geometry of of the longitudinal locating links, and I suspect this is what was done in the later Corvette suspensions, so for more aggressive jacking the practical approach might be to simply amplify what was done there. In which case, longer links may be required to dampen oscillations which could result in wheel hop.
This does not address the counter-torque of course, which is being applied directly to the chassis and therefore requires stronger mounts than for instance, what Jaguar used. This force will act in the conventional manner tending to rotate the body about the center of gravity but will otherwise provide no jacking force due to the solid or resilient mounts, and even if movably mounted the pumpkin has no means of transmitting vertical force to the road surface. The only way I can see to use this counter-torque to jack the car would be to allow the pumpkin to rotate and then redesign the LCA and UCA in such a way that this rotation relative to the body results in a jacking effect at the upright, such as by locating the axle centers behind the rotational center of the pumpkin mount. The distance behind it would determine the jacking force and distance. The easiest way to do this would be to mount the pumpkin on a pivot and provide a means of moving that pivot forwards in relation to both the pumpkin and the car body. This is assuming of course that the coil-over attachment points move with the pumpkin, because they would be responsible for transmitting the vertical component.
Now back to the Jag setup, if the upright critical length from bearing to pivot is shortened, less offset to the counter-torque is generated. If longer, additive torque is created. If the LCA is removed altogether and a suitable UCA is substituted, counter-torque is essentially doubled. I think you can see where this is going.
"Doc"
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JB, I think rear axle, RA?
Digz, a lot of anti squat ability is lost on a IRS. Due to as you say the differential/ center section, being solidly mounted. The pinion tries to climb the ring gear, cauing the housing to want to rotate opposite of the wheels. This energy can be directed and used through suspension mounting angles.
With an IRS you still have forces at the wheels pushing the chassis forward. Proper angle of suspension links will still give some AS.
Think that's right.
A top fuel dragster I guess would have none.
Now as JB points out the AS will have negative effects cornering.. The same forces as he says that create the AS, will push up or pull down, accelerating/braking on the chassis from the trailing link point. The further outboard or angle of the link, the greater the effect.
A double wishbone IRS with zero AS angle would also be very neutral.
Ralphy
Last edited by Ralphy (1/29/2012 3:55 pm)
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Am I thinking right that it would be a positive castor on the LCA would induce AS on acceleration then? And if so how much do you think a person could get away with before it would mess up the handling on normal road driving ,say hitting a swell or dip in the road or wouldn't it ? I'm leaving out the effect of the trailing arms in this scenario for now. I can visualize if both sides moved equally it might not make a difference, but if 1 side goes up that would move that side back in relation to the other inducing a dog track type of thing? Sorry Im still trying to get used to the terminology on all this. 
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Digz, yes and that's a good way to put it, Castor. Although castor or caster, I've seen both spellings, is used as the difference between the upper and lower control arms.
Here is another point with this angle of the LCA. You bring up hitting a bump. When the suspension is jounced/bumped, having AS anti squat actually decelerates the rear wheel a bit. Temporarily slowing the speed of the rear wheel. This will soften these irregularities in the road. Plus it elongates your wheelbase which is good for cornering. When the suspension falls into a hole the opposite happens. So many tradeoffs in any change. I saw this point mentioned on another board once.
Dogtrap? Are you referring to the dirt track suspension toeing out the loaded wheel, over steering When cornering you have a dominate side of a chassis. That's the outside/loaded side. Toe is all controlled by the geometry designed in. That's what's great about an IRS. You can design a IRS to be toe neutral, toe in or out. On asphalt or typical street cars you rarely want the rear to toe out or over steer. This is an issue with my C3 Corvette design, it toes out. The C4 Corvette is designed to toe in.
This is to me, are the right steps to a good swap build
1. Get familiar with all the different aspects of all the IRS designs. Know what they do and don't do. Factory bone yard units and aftermarket.
2. How can you alter the unit design? Know what the changes will or should do as best to your abilities.
3. Determine how your going to use this car. Street, competition, street/competition, show, replica, etc...
4. Now pursue your direction based on this, plus how much $$$$ you have.
Ralphy
Last edited by Ralphy (1/30/2012 12:21 pm)
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One thing I have always ran into is the fact that there is no such thing as a perfect suspension design. In every design I have studied, I came to the same conclusion, Most have their strong features yet none have benefits with out penalties. Or perhaps a better way to look at it is all suspensions have compromises of some kind involved.
The best that can be hoped for would be to design a suspension that has as many of the benefits as possible for your particular application while minimizing the undesirable side effects that come with the benefits.
It is always easiest to lay out a suspension design on paper than it is to transfer this information to a three dimensional vehicle frame with the desired accuracy. Very few cars are perfectly square when new. With use and abuse that only gets worse. The best time to lay out the suspension on the vehicle frame is when the frame is still in the fixture of the CNC machine during its manufacture. After that, generating the same accuracy gets tougher. Add twenty years of bending , twisting and work hardening and it gets even tougher, Add forty years of the same abuse plus rust and grime and it makes you ask weather the gain will be worth the effort? Full frame cars will almost always have it easier than unit body due to their rigidity and ease of separating the frame from the body.. Just a late night thought.
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TR,
Isn't that true in life? Pro's and con's, trade offs? What little college I had, I was taking some economics courses. The term I still remember, Opportunity Cost.
Ralphy
Last edited by Ralphy (2/04/2012 6:10 am)
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