I still plan on drawing up Twin Turbo's design but I am not going to do the 5 bar to my car this year. For now the 6 link design suits my requirements.

Mark.

 

Mark,

I really like what you are doing here. One big problem I see tho is with the 'static' drawings. It appears you believe that the half shaft angles downward to the outside when the car is at normal ride height. I know there are several articles that say it should be that way or level, but if you are setting your car up to go around corners, the number one consideration is the center of gravity, which means you must lower your car. On my car I am running 26 in tires and the top of the fender lip is 27.25 I beleive, and my half shafts are angled up to the outside. If they were angled downward as in your drawings, the rearend would be way to high. Not only that but it would mean the camber change would reverse as the half shaft passed the horizontal on compression. Of course the new design might eliminate that, but it is something to avoid.

As for the amount of camber change, (assuming 60" tire center-to-center - not sure what it really is) I figure 2 inches of compression means roughly 2 degrees of body roll assuming there is no lifting on the inside (which clearly is not the case) I would think that 2 or more degrees of camber change would help keep the tire flat. If you figure the inside lifts 2" when the outside compresses 2", then more like 4 degrees. The angle and length of the upper strut rod will determine that. I would start from the assumption that the lower strut rod is level at static ride height.

Shortening the upper strut rod means that the camber change will happen faster and there will be more of it. I'd be interested to know why the other posters are so adamant about limiting in-out movement of the yoke.

Chris

 

because stub movement will wear it down and will create slop and probably an oil leak over time.

 

I was not concerned with wear because the yoke slides in and out of the rearend. Normal driveshafts do this all the time in the back of the transmission.

As for seal replacement if this starts to leak it is simple since the rearend doesn't need to come out. Pull the 1/2 shaft , the yoke and it is ready to change. They are also readily available from any bearing supply hose. Not a specialized seal and cheap.
My biggest fear was the yoke hitting the pin and binding the suspension.

I always set up my ride height by leveling the 1/2 shafts. As for rolling/tilting in a corner the car seems to sit perfectly flat on a hard corner and with no camper change hopefully the tires remain planted.

 

I agree about the binding being the primary point of concern. If binding was taken in consideration, Mark could design the upper struts to be as long as possible, no?

No disrespect, but you are dreaming here Norval. I have taken a lot of photos at autocross events and historic road races, and they ALL roll, even the full-on race cars. Cars are actually designed to roll some, it gives the driver an indication of the limit of the car. If there was no roll, there would be no warning the car was about to break loose, it would just happen.

Chris

 

guys, if you do it like I said w/ the IC all the adjustment you make is outward and it can never bind that way, why make something difficult if it can be done easy, why choose for stub movement if you can eliminate it easily with some geometry???

 

Mark, I agree that what you are doing is very nice but, if I were you, I would establish the position of the normal ride height BEFORE I started making CAD geometry. I agree with all who have responded to your original question. Your halfshafts should be parallel to the ground for a reasonable ride height.

I am not critisizing your work. I just know how much it would suck to start over.

 

BBshark,

What I have done here is create a 3D working model of my suspension in the computer. Setting ride height is a matter of changing one number that controls the rotor in relation to the differential and then reset the length of the rods to suit my initial camber setting.
With my model I can move the assembly up and down with the mouse to see how things move with the changes in suspension.




TT,

With my system I have decided to retain the stock strut rod bracket and aim for a camber curve that gives me similar values to that you would get with smart struts. I can do this with a total of .08" of yoke travel thru the 4" of suspension travel that I have been using in this thread. The total yoke travel thru total suspension travel is .130" I am confident that I will be able to set this system up too miss the center pin.

 

does anyone have the measurements for the smart strut bracket?? I'm really interested in how much the hole is relocated
Also, do you know how long your lower strut rods are??? something like 13" right?

 

I think the smart strut is the same as the mod described in Vette power where they lower the center whole bracket 1/2" with a spacer.

I doubt Vette brakes did any serious suspension analysis

 

Mark,
you said...With my system I have decided to retain the stock strut rod bracket and aim for a camber curve that gives me similar values to that you would get with smart struts. I can do this with a total of .08" of yoke travel thru the 4" of suspension travel that I have been using in this thread. The total yoke travel thru total suspension travel is .130" I am confident that I will be able to set this system up too miss the center pin.

As long as the bottom strut starts out level you should be alright. What they did in the old days was stick a spacer plate between the strut bracket and the pumpkin - not very adjustable, but cheap. If that bottom strut is not level, as the suspension compresses it pushes the bottom of the TA out until the strut is level, as it moves into an upward angle it starts to pull the bottom of the TA in changing the camber change dramatically. And since you will be removing the C clip that holds the yoke in you can grind the stub down to ensure there is no binding. The stubs wear down normally anyways.

 

Mark, I understand how CAD model analysis works. However, you have started with your axles down at the outer ends 1.07 inches. Then you look at extremes of travel (up and down 2 inches). If your axles are REALLY going to be horizontal as many have suggested, it means that you are analyzing a system with .97 travel up and 3.03 down. Again, not to be critical but if I were you, I would analyze a system that started with good information.

 

[
No disrespect, but you are dreaming here Norval. I have taken a lot of photos at autocross events and historic road races, and they ALL roll, even the full-on race cars. Cars are actually designed to roll some, it gives the driver an indication of the limit of the car. If there was no roll, there would be no warning the car was about to break loose, it would just happen.

Chris[/QUOTE]

That's ok Chris. Since I installed the longer spindles the car seems to sit really flat in the hard corners. Raise the roll center high enough and the car completely stops rolling over but then the tires take to much of a beating.
Sure it rolls over but it seems my carbs are the limiting factor in how hard I can corner. Fuel slosh seems to temporaily flood them if pushed too hard,

 

Guys,

The reason to set the ride height (at rest) with the outer U-joint 1" lower than the inner is to compensate for the toe-in changes that occur through suspension travel with the stock trailing arm setup. As the rear suspension approaches the point where the axle shaft is parallel it will achieve maximum toe-in. Moving away from parallel (in either bump or rebound) the tire will toe out. By setting ride height with outer u-joint 1" down on the outside; when the suspension loads up through a corner and outer (loaded) tire goes into bump it will toe in slightly as it goes through 1" of bump (axle shaft now parallel) and then return to the "at rest" toe setting as it gets to 2" of bump. Setting ride height at "parallel axle" (or lower) will cause your outside tire to toe out under load and induce oversteer (oops, was that my rear bumper I just saw go by?).

 

Red73Vert

That was my initial thoughts as well. I have not had a chance to take a close look at the toe change relationship to initial ride height yet. I am planing on doing it tonight. I will post what I see.

Mark.

 

That is all well and fine (and correct) it still places the rear of the car FAR too high in the air. Any advantage gained by controlling toe would be lost to the center of gravity being raised and to aesthetics. Everything is a trade off, but jacking the rear is not for me, thanks. The only way to achieve what you describe without raising the rear end so high is to raise the center section, and there just isn't that much room and it is a lot more work.

Chris

 

Looks pretty good. Good solidworks work too. That program caused me many stressfull nights last semester.

 

Ok I spent some more time tonight look at the 6 link system starting with a ride height that has the half shafts parallel to the ground. BBshark you were right, it changes a lot. I went back and looked at the origional corvette setup again. I now have a gain of almost 2 deg over 2 inches of suspension compression. With smart struts (assuming 1-1/2" drop in hole position) I now have a gain of .41 deg. A big difference from stock.

Here is the system that I am going to build unless someone can talk me out of it. I am trying to copy the smart strut geometry for camber gain, and per Twin Turbo's advice, also minimize yoke travel.

At ride height



At 2" of compression



AT 2" of rebound



Any thoughts?

 

Mark,
It looks like you are dropping the strut rod bracket 1.25in? Before I would do that, I would make a new strut bracket with pivots as close to centerline as possible (see below). You could do this in about .50in more space than the original bracket. This is a quick attempt at a long lower strut rod with a short upper arm. You will see that a long lower arm has a number of functional as well as packaging advantages. It has zero yoke travel distance, 0 degree initial camber, 1 degree at 2" compression and .2 degree at 2" rebound (and could certainly be optimized).
Black layer is ride height with axles horizontal.

 

Mark,
I am missing something here. I only see .52 degrees of change on compression, not 2 degrees. Also, the arms look parallel now. How about putting a vertical slot on the inner mounting point to make it adjustable or make the outer point vertically adjustable? and does the smart strut really move the inner point of the lower strut down 1.5"? I know my lower strut is horizontal but am not sure how much it moved to get there.

I know I am late to the party, but I am very excited about your work and since I just bought a TIG welder I am itching to get working on some cool new projects and have been looking at the rear end as long as everyone here.

BBShark, I think a longer lower strut is a good idea, but we need to clear the exhaust! Mine is tight to the bracket and it still occasionally scrapes.