From what I have been able to glean a Watts at the bottom of the upright serves as a trailing arm.
A watts at the top of the upright is an anti-hop device.

Someone will be along to correct me if I have this wrong.

Thanks for the responses guys.


Tyrellracing - 

Does the Jag setup have the wheelhop problem because the upper end of the spindle/carrier is not tied down well enough (no UCA)?  That seems to be the case with the simple upper arm on the T-bird version too.


About your K/A watts link addition, 

If you mounted the upper pivot point equally far from the wheel hub as the LCA mounts, then wouldn't you basically be eliminating the signature K/A parts of the deal?  Taken together with the existing forward longitudinal link, the wheel's up/down path with would come out as roughly a straight line when viewed from the side.  (Maybe not straight vertical, but a straight line.)  

I'm not trying to criticize what you did, I'm just trying to understand it.



I am in the process of designing & building my own IRS right now.   It's more of a DIY than a modified version of any single OEM setup.  I really like the watts-type setups that move the wheel backward during squat & twist the hub for anti-dive during braking.  But I am struggling to come up with a layout of hub carrier & links that do very much of that.  

Basically, I can't put much curving & rotating in the hub & carrier's movements because of the packaging limitations of the whole thing.  The squat/dive action depends on the upper longitudinal link being mounted right near the hub, and the lower link being far below it.  The hub & wheel rim dimensions don't allow for very much of either. 

I've picked apart some online photos of Duane Carling's KA setup.  Even there, I only see perhaps 11" of total spacing between the upper & lower link, and the center of the hub is perhaps 3" below the upper link.  When I map out those movements on paper it isn't very impressive.  Is this really what all the fuss is about?   The hub & carrier's travel paths are still hardly curving & rotating at all in the big scheme of things. I wonder how it could be worth the trouble compared to more traditional common IRS setups.  I get the feeling that even a plain vanilla twin-A-arm setup moving the hub in a straight line would be capable of almost identical results in the real world (street cars), if you threw in a few degrees of permanent caster like the Jag setup has.  


Any other thoughts on all this? 


 

If you go through all the different types of rear suspensions you will find that all of them have a change in toe with travel. Some are much worse than others. The new 5 links used now by Chevy, Porsche,and a few others are the closest to a perfect suspension I have seen so far. Very nearly no change in toe and what it does have is in a beneficial direction. The KA suspension actually has toe change in the right directions but the change during compression is too dramatic and when extended is too little to help. Keep in mind that suspension was designed for narrow bias ply tires. When ever you design a suspension you start with the tires and wheels and work your way in. Not like most people do and go backwards.with the tire selection as an after thought.

Putting the lower control arm at the angle the xj6 uses works fine with a low hp/weight ratio. Add  more than twice the hp and reduce the weight by 1000 lbs and you will have wheel hop. I did not eliminate anti squat entirely. I reduced the angle from aprox 3 deg to about 1 degree. Anti squat/ lift under braking really is not that huge of a concern on a car that has excelent shocks and is balanced(sorted out). Those charistics are from the relm of crappy shocks and loosey goosey rubber mounted suspensions running bias ply tires. The kind of car that you can wag its tail by turning the steering wheel back and forth at speed. I am a machinist and the steel was free at work from the rem bin in the saw shed. While I was converting back to the Jag set up I went to larger vented 12 inch rear rotors and used helsey hays 4 piston calipers that came off the frount. This was the secondary reason for making new inner mounts. The pivot had to move down to clear the rotor. . I also made half shafts from 1 ton Chevy truck drive shafts getting rid of the heavier solid Jag units. Tube drive shafts are easier to cut to length than the old solid ones were. The set up is narrowed from the jag width. When I shortened the solid jag axles they kept cracking so they had to go. When ever you weld a torsion loaded solid shaft, cracks are inevitable. The solid Jag rear brakes were insufficient for stopping once I made 6 piston calipers and 14 inch rotors off an Escalade for the front. I had to increase the swept area as well as the distance from center at the rear to get the brake balance back up with the front. Confusing I know. Years ago when I was running a 9" rear I used under ride traction links that attached to 6 inch long lever arms welded to the bottom of the axel tubes. The other end attached to the front spring eye mount bolts. The resulting angle produced nearly 90% anti squat. The car hooked up great but the unsprung weight sucked. My 67 shelby is set up for road racing not drag racing so having a heavy rear axel weight really made the cornering suck on bumpy roads. .

Last edited by tyrellracing (8/23/2016 1:40 am)

        
The only possible benefit that I see for a 5-link (instead of double A-arm) is that you can get more creative with the wheel's movement path in the side view.  That's what I started this thread in attempt to hash out; what the ideal side-view movement path is.



21st-century sporty cars all have big grippy tires.  The body motions are all pinned down with heavy swaybars & shock valving.  It works, but it's a different kind of chassis from what I'm putting together in general. 

I AM wanting to build a softly-sprung car with small tires.  15x8 wheels & street radials.  Rubber bushings & ball joints.  Ride height is on the tall side for a sporty car.  

The front end of the car has strong "stabilizing" geometry from the factory:  The front UCA has a big anti-dive angle.  The front roll center is about 6" off the pavement (which seems kinda high to me).  I've been thinking that continuing this general outlook on the rear end would produce a well-sorted & predictable street car.  Use heavy stabilizing geometries in my IRS design.  

I'm thinking of making the rear roll center around 9-10" high.  Yeah, I know that sounds like skyscraper height.  But the RC on the stock Hotchkiss leaf setup is around 14-15" so it's still a big step down.  The car has a longish wheelbase too.  If I set the rear RC below 9-10" then the overall front/rear roll axis line is virtually parallel with the ground.


The motor is a big-block V8.  There is no hope of hooking it up very well and I'm okay with that.  I just want to lead-foot around on the street comfortably.  The rear end preferably doesn't squat into the ground upon throttle inputs.  And no big wheel-hopping.  Ideally, when you give it gas, the car either launches smoothly forward or else the rear tires spin.  The goal is a factory-style IRS for this kind of muscle car during about 1975-1995.  I want to use modern hub bearings & CV's instead of Corvette/Jag half shafts, but that's about the only big departure from OEM style.  

     

Last edited by thedude (8/23/2016 6:11 am)

I have set up cars for road racing for years. In my experience it is best to go soft on the springs and get the best shocks money can buy. All sway should be controlled with bars not the springs. I worked for a spring company that bent all of the sway bars for Quickor. I made gazillions for my self too. Then I discovered torsion type sway bars and never used a bent to fit bar again. I have made a few for my self over the years. Cutting splines on the high carbon steel is a "I used a word I shouldn't have" but worth the effort. The torsion type bars I like are gun drilled. This makes them much lighter and stronger for their size. a win/ win deal.
As for roll center heights. I have seen sooooo many people really screw up cars by moving the roll center where they think it should be before they ever drove the car. I believe in leaving things like that alone until I drive the wheels off the dam thing and analize exactly what is needed. The only exception to this is during set up then I look the suspension as a whole to figure out the roll cuple. Or the line that goes through front and rear roll centers. This is critical and must be done with knowledge of how roll centers affect the suspensions f/r then as a whole. I dont mean to get all Zenn on you. but thats how I do it. If I am changing a existing design I make only one or two alterations at a time so if something goes terribly wrong I can easily track it down. That becomes impossible after you have redesigned the wheel and have to look at the car as a whole to figure out the problem it never had before.

Last edited by tyrellracing (8/23/2016 6:28 pm)

I have the entire set up still. It would be easy to get those lengths for you. Its 1 am so it will have to wait until tomorrow. The upper mount on the bearing carrier has 1/2 inch holes on 1 inch centers. All of my links used heim joints so they all had one inch of adjustment on each end.The trailing link had to be replaced due to length issues but I saved the two original links. They are all stainless and looked pretty sharp. I made threaded ends and welded them in at work where I could use their stainless wire. Then I turned them full length so all of my work was invisible. I agree with your assessment of the design in theory but the actual way the first iteration performed I couldnt really feel the dramatic  anti squat I was expecting. However it did deliver far better grip than the jag xj6 ever did with out wheel hop. In all fairness I beat that K/A set up pretty damn hard. I also used two adjustable coil overs per side. The engine could overwhelm the tires so easily in my opinion the anti squat would have been more pronounced with better tires and alot more traction. As I recal the original K/A design used non adjustable leading and trailing links. The inner mount of the LCA was all the adjustment that design had. For exact numbers I will have to find my original drawings with all the pivot points layed out at 1/2 size. What platform are you putting this under?

Last edited by tyrellracing (8/24/2016 1:47 am)

Dont those use a four bolt mounted front spring eye hangers? Seems to me they did. If so, you couldn't have chosen a better candidate for the conversion. The obvious leading links mount there and the lower differential stabilizers mount there too. Having removable mounts would mean the custom mounts would be removable and the conversion could be reversed back to stock if the cars value was an issue for resale. You said you were going to use a big block, B or RB? I have built some sh@t kicking 440's and 383" when I was a younger man. Back when I was in college a friend of mine had a 440 4 spd cuda. I did the majority of the rebuild on his engine after we blew it up drag racing. When it was done it could do 10's all day long. That isnt that big of a deal now but in 83 it rocked.

The 400 is a rendition of the B block with a bigger bore than the 383. Those 400 make fantastic foundations for strokers. Smaller than the 440 with the potential to be bigger than the 440 internally. All I was getting at was the springs can be removed with the spring eye hanger leaving this reinforced pad for building a new custom bracket for supporting the leading link as well as the triangulated lower differential support mount. That is how the K/A was set up but on the mustang you run into trouble getting the diff support hitting the frame rail preventing it from fitting into the front spring eye mount. A custom bracket must be made to attach the diff support to. I extended the bolt through the frame so the diff mound could be held at the correct location sandwiching the frame. This was no easy task because the rocker is in the way of a long enough bolt to fit in.  You will not have this problem. I am aware that your platform has other short comings but they are sum what minor. That said. It sounds like a fun project !
 

Last edited by tyrellracing (8/26/2016 7:25 am)

I agree with all your mopar thoughts. The older 60's=70's mopars are very ridgid for any car of that era. When any one talks about big block mopars they immediately go to the HEMI.  The hemi is good but their too big too heavy and no one has any spare parts for them. If you have one and want to rebuild it, you will spend as much as you would building three 440's.   The 413's 426 wedge, 440's and 383,400's are the un known step children that were forgot in the shadow of their hemi relative. However, any one that knows engine architecture knows there is a mountain of hp lurking in them engines just waiting to get out. There are few special tricks to make these engines scream. It just takes common sense and machining know how. Too bad they did not get the ink and popularity they deserve..

The only reason most American cars of the 60's didnt come with an IRS is because live axles are cheap and can be made to hook up better. Drag racing has always been more popular than all other kinds of racing because it doesnt require driver skill until you advance well above stock vehicles. If you can stomp on a throttle, you can drag race. As for rubber, I agree and disagree. The rubber makes the suspension too compliant. In the front it allows the tires to go out of alignment in corners. At the rear it allows the vehicle chassis to shift off center causing excessive body roll. This is all for the quality of ride by nullifying harshness. The effect rubber has on the handling of most vehicles could be summed up as handling like a row boat in heavy sea's. Todays vehicles have a more harsh of a ride because its safer than a row boat like an old caddy. Being able to drive around a problem is safer that being big enough to survive the impact. You cannot put antilock brakes on a suspension that is too compliant. It just creates problems that the brakes cannot overcome. The Jag rear was designed to be entirely solid mounted. If you look at how Jag took a good Dana built and shipped design and turned it to mush by mounting the carriage in rubber. Speaks for its self. Jag compromised handling for the elimination of ride harshness.The early mopars used torsion springs. The only way these can work is by placing them at the pivot point. This puts them at a mechanical disadvantage. A coil spring properly placed as close to the wheel as possible will support the same weight at 1/50 th the spring weight and size. The early geometry is archaic. The caster/camber curves were based on bias ply tires and will not perform optimally with modern radials. Wide radial tires do not require the camber gain that the old bias ply tires did. You cannot expect good results by just slapping modern tires on to an ancient suspension with its bias ply geometry. Entirely new camber curves are required to make these modern tires work the way they were designed to. 

Last edited by tyrellracing (8/27/2016 9:04 am)

The bump steer issue is not a t bar issue but rather across the board. All rear steer cars had some bump steer. Mustangs were terrible. Some of this had to do with Ackerman angle. They made the tires turn different angles so when moving slow there would be less scrub. All the manufacturers built in under steer. They knew the tires available would get people killed if they made cars that steered neutral. The AC cobra, some Ferrari's,lotus and very few cars sold in the sixties didnt have bump steer.  Basically all rear steer with recirculating ball steering boxes have some bump steer. It wasnt until NASCAR started using full tube frame cars did any one actually make a good rear steer suspension. Shortly after that they all went to front steer. The stock mustang suspension is a prime example of a real pile of excrement. The coils over the top of the upper control arm over loaded the unit body in a weak area of the front structure because the springs sat at the center of the A arm the spring seats were heavily loaded.. Ford put braces on the towers but that wasnt enough. Shelby put an export brace and a monty carlo bar on the towers to trianglate the support but that was a bandade at best. To support 250 lbs a 600 lbs spring was required.. Then the UCA's inner pivot was in the wrong place and induced under steer. Because of this pivot location was too high the inner bushings took a serious beating and failed frequently tearing huge holes in the strut towers. The Ackerman was never quite right so the more you turned the tires the more exaggerated the toe out got. This was to the magnitude of 8 degrees toe out at full lock. The least amount of bump steer I was able to obtain was 4 degrees toe from 6" bump. That is pathetic.  The manufacturers really didnt try to make good suspensions back in the 60's They all did crap like this. The car buying public didnt know any better so it was the status quoe. I worked with the Mustang suspension until I could not make the bad design work any better. I had raced with this handicap for many years and knew I could do better. Thats when I discovered Griggs racing suspensions. I scaled their GR350 racing suspension from images on their web page, made an exact copy and have been happy ever since. Front steer power rack and pinion fully adjustable upper and lower control arms, Very nearly zero bump steer. Tuneable camber curve. Coil over shocks attached to the LCA at the lower ball joint. Adjustable track width (3") each way. Pluss I made my own 3" drop spindles and 6 piston calipers. It out performs the old mustang suspension like you cannot believe with out going for a ride. Google Griggs racing and you will find the suspension I plagerized. All of my numbers were from my racing notes. I own a hunter alignment computer. Mine predates their lazer machine but still produces good numbers. I have owned it fifteen years now and am competant of its proper use.

Last edited by tyrellracing (8/27/2016 4:24 pm)

   
Yes I'm aware of rubber's consistent hardness.  

The OEMs do a lot of different stuff with bushings.  Putting strategic holes in the rubber, using thicker or thinner layers of rubber on the same diameter of bolt, etc.



At first I was trying to figure out what THE bushing application is that everyone uses.  (Mustang-II? C5 vette? etc.)  But everybody is trying to eliminate the bushing compliance, not keep it.  Nobody has any advice on picking rubber bushings.

I've been thinking of using 73-81 Camaro front end bushings.  The dirt oval racing world loves 2nd-gen Camaros so they should be on the aftermarket's radar.  The bushings are big enough for the job and simple enough to incorporate into custom-fabbed parts.  The leading & trailing end of the front LCA used two different thicknesses of the rubber layer (allowing two options for stiffness).  

But I got a few of these Camaro bushings from a local parts store and they don't seem very well-made.  The sleeve hole for the bolt isn't perfectly round.  I dunno if this should bother me or not.  

I'm also thinking about Fox Mustang bushings.  A classic Charger is a much heavier car than a Fox but it might work for places where I need a smaller bushing.    

If you have any other suggestions I'm listening.

 

Last edited by thedude (8/27/2016 9:31 pm)

(Whoa, I just now saw your last comment from weeks ago)

A single curb or pothole can cause a very expensive day when there is nothing but metal between the wheel rim and the car's frame.  That issue alone is enough to make me want some cushioning.  It's less of a desire for comfort and more like a plain old durability thing from my POV.

I totally get why nobody likes bushings on the track.  Different situation from public streets.  


The OEMs seem to mainly adjust bushing hardness by bushing size.  Bigger = softer.  They seem to design more softness for wheel movement in the front/rear direction.  For lateral movement they are less generous with the rubber.  I'm following that plan. 

Between 2nd-gen Camaro bushings and Mustang-2 stuff, I think I've got the bushing thing worked out now.  Fingers firmly crossed.  And toes.  

 

Last edited by thedude (9/18/2016 12:06 am)

tyrellracing
I'd really like to hear about your KA suspension project. I'd like to do the same thing for a 65 Rcode tribute project. What hub carrier did you use? What center section? Did you make your own LCAs or did you find some that would work?