History Rear suspensions (from the past)

Andy, here is a picture of the C-Type rear suspension: http://i78.photobucket.com/albums/j89/BillyShope/C-Type.jpg
I doubt very much if this suspension ever came close to a production car. It was highly asymmetrical and it was pointed out to the engineer in charge (after the LeMans win) that the braking would be adversely affected. Apparently fearing lawsuits, such a design was immediately set aside and work was concentrated on an IRS, as was used in the D-Type.

 

If I am understanding what I see in that C Jag design, the rear suspension is lateral torsion bars with spring plate trailing arms, similar to VW Type I & II rear suspension, but applied to a live axle.

What characteristics of the illustrated suspension adversely affects braking?

Ray

 

Perhaps I'm not seeing this right, but my first reaction is that if the aim is to balance out engine torque, the offset distance is critical. The problem is that of the other two variables, the car's mass is pretty much constant but the torque the rearend sees varies between very wide limits. What exactly are the circumstances under which you want to balance out engine torque?

As some of you know I'm partial to the DeDion axle, as it makes this problem go away while behaving exactly like a live axle in most other respects.

 

The rear end set up will balance the engine torque vs the rear end side to side loading at any load. I drew up a really crude sketch as a friend had ended up with a chassis I built. I was at a swap meet with him and was trying to explain how it works. The numbers are just made up for simple math. I know it will be hard to follow but start in the middle of the page with the engine/trans torque and work back.
I see there is some concern about stability and excess reactions. I guess it is more of an art form and experimentation to get to a good design. I have been at this for more than 50 years with zero problems. I have never had any odd antics from the rear ends. They have always been predictable and stable.
I will go take measurements from the roadster so there are real numbers.

 

Hmmm, Billy;
I wasn't actually asking for computations to done for me, using data points from my cars/etc. I was hoping for a work-thru example (like, say, one you already did for yourself in the distant past) to follow, understand exactly what was being discussed, & be able to extrapolate into version(s) for my particular circumstance(s). Guess I'll find some book somewhere (maybe it's already in the 3 or 4 I now own. The original comments just don't sound familiar.) that has examples in it, or forget it & use what I can work with.
But thanks anyways. .
Marcus...

BTW, Thanks Andy. Seriously.

 

There are three trailing links. The bottom two are attached to the torsion bars. The top one is offset to the right and in tension during forward acceleration. This is the one that adds extra loading to the right rear tire and causes the rear tire loads to be equal. During braking, that same upper link is in compression, causing the rear tire loads to be unequal when there is an absence of driveshaft torque.

 

I didn't bother to go through your math, Andy. You've got the right idea. I would only say that you're short on the ladder link. I'd make it as long and as low as possible. Remember: The early funny cars with ladders had very long ladders.

 

Sorry, Marcus, but I'm at a loss as to how I can help you further. Just go to the example I gave you, plug in your own numbers, and calculate the offset.

 

Yes, if you want to exactly cancel out the driveshaft torque, the offset is critical. However, drag racers throw on an ARB, preload their chassis, and go racing. No, this isn't the way to do it, but that's how it's done. Of course, they end up with something that is a bear to drive! Yes, I also like the DeDion, but, today, the better solution is the IRS. The essential thing to remember with the IRS is that the 100% antisquat line passes through the center of the wheel and not the tire patch.

 

If you're really interested in the testing of an automobile suspension and if you own or have access to Race Car Vehicle Dynamics, I would suggest you read the section on "constrained testing." This discusses the testing of suspensions during cornering, but the same principles can be used to test suspensions during forward acceleration, and you don't even need to start the engine! If we were to discuss it, that would take a new thread, of course.

 

With all due respect to you, your experience, your education and your obvious engineering background, most of us do not have that collective smarts at our mental disposal. That is the reason many have asked for a pictured example to work backwards from. You have taken a lot of time explaining things but I'm a dipshit I suppose because all the words add up to just that, words. A simple picture of what you have been discussing would be of tremendous help.
At this point though, I'm gathering that you would rather not show a picture and instead just talk about engineering principles. If point B is the case I would imagine people that could really benefit from your experience will tune out. I know if you are encouraging people to refer to Race Car Vehicle Dynamics then I am in the wrong thread.


Sent from my iPhone using H.A.M.B.

 

I actually found that a shorter bar is better. I started out using the full length 50 Olds bar. I found a shorter bar gave more anti-squat and more traction at launch. I did bracket race both the Chevy 11 and the 32 Ford. I never needed a posi track. I ran 30" bars. Both cars launched great.
I have a friend who is an active drag racer now. He tried to use the design in his gasser. He leaves at 8 K. He had trouble building a bar strong enough to take the launches. He went back to dual ladder bars. I thing they are more flexable and maybe don't grab as well. As Wayne-O metioned, The Mustang did not work out as it did not have a frame and it tried to push the passenger floor thru the roof.

 

I will draw some pictures tonight.

 

Many thanks Andy! I really want to know more about this and appreciate anything visual.


Sent from my iPhone using The H.A.M.B. mobile app

 

Baloney!! You've got smarts I wish I had. As I worked in a shop owned by a friend who built race cars, I put a Pinto front suspension and Toyota engine into a Sprite. When it came time for the disk brakes, my friend gave me the brakes, expecting me to install them. I simply couldn't do it. He had to have his son do it for me. Yes, I've rebuilt engines, Muncies, and rear ends, but my knowledge in that area doesn't compare with yours. Stop your belly aching and just dig in. Andy has given you a sketch of his work. If that's not enough, and you have the opportunity, just sit and study an early Ford or Chevrolet. I'm certain you have the imagination to consider the housing enclosing the driveshaft shifted to the right a foot. Then, imagine that driveshaft, in its original location, having a U-joint at each end. There! That wasn't so hard, was it? Anyone with the imagination to build a race car can do it.

 

Andy, I can understand your goals in a street car can be very different than those building a car for the drag strip. You like the violence of a short ladder. I tend to be more sympathetic to the needs of a drag racer. When you're dealing with cars that do the first 60 feet in less than a second and a half, everything has to be done smoothly, though it looks like it's anything but smooth. Please don't misunderstand! I still tip my hat to you as one who truly understands the capabilities of a car with a single ladder bar.

 

Some sketches.
I show the design used in my roadster and some others.
There is also the design that carries the spring load on the left thru and not have the right side see the small moment caused by the spring behind the axle.

 

Andy,

thanks for the drawings!

Ray

 

I'm still waiting to see something magic. At least all this smoke has lead me to believe there is some ancient mystical knowledge. It's like trying to pin down WTF ancient secret knowledge Rosicrucians actually possess. If any.

So far I see a P&J ladder bar and a version of 60's Galaxie suspension.

 

It is magic.
It balances the load on the rear tires and eliminates body roll from engine torque plus is simple and is compact and is free to move without binding.
What features do you need?

 

Yes, Andy is correct. No magic to it. And, if I can stretch your imagination a step further, a 3link can be considered to be the instantaneous representation of that ladder bar (or housing). The advantage to instantaneous centers is that the pivot point can be placed on the 100% antisquat line, meaning there will be no squat or rise on forward acceleration.

 

The same applies to the DeDion: the zero-squat or 100% anti-squat line passes through the wheel centre. The interesting thing to consider is what happens to that line in the real world where there are bumps etc., because the instant centre migrates with vertical suspension movement. I think a longer virtual arm, i.e. instant centre far forward, would give a more forgiving arrangement. I'm not sure if that'd be easier to achieve with a higher or lower line. You would still use the line through the tyre patch to determine what happens under braking, unless you've got inboard brakes.

The problem with IRS is that ideal camber recovery in roll isn't ideal for launch, and vice versa. You'd ideally want constant camber in launch (e.g. trailing arm) but a fair amount of camber recovery in roll (e.g. unequal-length control arms). It becomes a factor when you recognize that a decent amount of travel is too useful a thing to give up, instead of making the suspension work, as per Colin Chapman's gripe, by not letting it do so. I'm not sure if it can be achieved without making the system partly non-independent, as for instance the Dax system does, and you end up with a complex arrangement of linkages to make a wishbone suspension act like a solid axle.

Then there was the Trebron system of the '70s, which used two separate roll centres:

It's all oriented to road racing, and doesn't really give the pitch-soft characteristics you would want for a daily driver or a drag car.

 

Here are some pictures of my 3 link setup that Andy and I designed for my roadster around 10 years ago. It uses '36 bars for the lower link. The first pic is how the lower bar mounts to the axle on the drivers side. Same thing on the passenger side. There is a large rubber bushing in mount tube that lets it move without binding. Second picture shows the pass side where you can see the upper third arm. Third pic shows the pass side where the links mount to the axle. I originally used the crappy urethane bushed ends you can purchase through any hot rod shop on the upper arm.. They only lasted a short while. Replaced them with industrial rod ends. You can also see the tube with the rubber bushing in it. The last pic shows the front of the lower link and how the upper link is connected to the lower link and the Chevy II type rubber bushings in a tube Andy mentions. I have close to 20K miles on this setup and it works great.

It is not so much magic but sound engineering principles. And it is simple. Andy needs to be given credit for thinking out of the box and doing something different.

 

I have yet to see any proof that complete cancellation of squat and rise is in any way antithetical to goals associated with racing not associated with drag strips. I realize there are a lot of "suspension freezing" stories floating around and I view them as nothing more than "old wives' tales." They simply cannot be supported with calculations. And, incidentally, the manner in which a woman's bra opens proves that you drive on the wrong side of the road.

 

Ladder bars!!! finally a subject I know well and I have already done a drawing on how to set up. I am very much into Gassers not street freaks and own and race a ladder bar Gasser. My sketch and description will help explain to anyone seeking more traction by using the ladder /Lift bars and torque pinion climb to jam the tires into the track . I know nothing about a single ladder bar set up but maybe for a lowered car that corners rather than drag races it may work . I will post my drawing later today.


Sent from my iPhone using H.A.M.B.

 

here is the sketch of how to setup a gasser ladder bar for maximum traction. This mainly pertains to drag racing with traction issues .
setting the bars above the imaginary center of gravity causes the rear tires to try and drive under the chassis. This lifts the chassis and creates the opposite reaction pushing the tires downward towards the track . if the instant center lift point which is the very front of the ladder bar regardless of its length is below this line then the rear tires try to drive over the chassis which causes the chassis to squat in the tires to move away from the track. Yes I know that some people think that want to car squats this is a good thing. Well maybe in a lightweight car with the giant wrinkle wall slacks a squatting car will still crank out a good 60 foot time ,but generally with an adequate size tire chassis lift is good. for every action there's an equal and opposite reaction in this reaction equates to improved traction! Ihave experimented with raising and lowering the bars on my 46 Chevy sedan delivery and with the bars sitting in the lower position at the front mount the car never hooked up. No lift no squat just neutral. so I raised the infant center up considerably and immediately The tires hit hard and pull the front wheels up for the first time. also found a great deal if you years ago on some double adjustable AFCO Shocks and this really allowed me to fine tune for street or strip. Another suggestion I have for anybody building a gasser the plans on dragracing I would suggest putting a torsion splined anti-sway bar in the rear. this is mandatory if you are putting out any serious horsepower as it allows the chassis tonight with and keeps even weight transfer to both slicks. One Final suggestion if you have a leafspring car is to put floaters to stop the binding caused from the dissimilar arch and length of the front leaf pivot and the front pivot of the ladder bar. Without some form of slider or floater pro vision there will be binding and parts are going to break or crack ...most likely where the ladder bar brackets are welded to the housing . If anyone is interested I have drawings for that also which will save a lot of words trying to explain. Do not think for a moment because they did not run floaters or sliders in the 60s that you don't need it we just did not know about it back then. you might get away with it on a drag race only car but if it's a street strip car you can forget about it ..parts will crack and break!!! I know from experience.


Sent from my iPhone using H.A.M.B.

 

for some reason my sketch will not post. It says error contact administrator ?


Sent from my iPhone using H.A.M.B.

 

Sent from my iPhone using The H.A.M.B. mobile app

 

I agree with you that there is little sense in designing for anything but zero-squat, as far as it's practical. There might be some argument for a tiny bit of pro-squat under braking, but the amount of forward weight transfer you'd save is splitting hairs.

I seem to remember there being an excellent explanation of launch geometry on an old website of yours. It cleared up a lot for me at the time. Is it still somewhere on the Internet?

I got to thinking about IRS, camber recovery, and zero-squat. I think you'd agree that with zero squat a car will always launch at the same rear ride height, and if you get the rear-wheel camber on an IRS right at that ride height it doesn't really matter what the camber does elsewhere in its travel, at least for launch purposes.