[pro70z28]

I'm building an Art Morrison 4 link (Pic.). This is their large tube 4 link (Weld in tube adapters as apposed to threaded thick wall tubing). I should say some of this is A.M. and some is my own concoction

BTW: I should add the links are set far apart just for mock-up only. If you follow the angles that would put the IC purdy' far forward.


4 bar is sort of the same set up but is not adjustable and still needs a rear housing locater like a panhard bar, diagonal link, wishbone track locater, watts, etc.

A triangulated 4 bar is just that. The top bars are mounted at an angle (triangle shape). This set-up eliminates the need for a locater bar. I.E. early 70's Chevelle and ElCamino type suspension.

[Ayrton]

I have the AM larger 4 link kit and would like some guidance on what length the bars should be before welding in the caps? How much shorter (if at all) should the upper bar be?

Thanks

[BillyShope]

The longer the links...both top and bottom..., the less sensitive the car is to changes in loading and "bumps" in the track surface. And that's good, of course. In other words, if the links are short, the car will be more inclined to act differently depending on whether the gas tank is full or not. So, generally speaking, the longer the better.

In production cars, the upper link is often shorter (as in the 2005 Mustang), but that's usually because of packaging problems. There simply isn't room for a longer link.

And, going back to this matter of sensitivity, another consideration is how far forward the IC is located. Consider a straight line, as viewed from the side, extending forward from the rear tire patch. If the IC is on that line, whether it's 5 feet in front of the rear tire or 5 miles, the car is going to act exactly the same as it launches. But, if the IC is 5 miles forward, the suspension is far less sensitive to travel (jounce/rebound) changes and, again, this is a good thing.

The further forward the IC, however, the more roll oversteer. Roll oversteer has no effect on stability, though, so I wouldn't worry about it. (There's a lot of confusion on this matter, but roll oversteer has absolutely no effect on cornering performance at the limit. In other words, if you have an oval track car that pushes at the limit, you can add roll oversteer until the proverbial cows come home and it will still push at the limit. It's just that, when the car goes into the wall, the driver will be holding the steering wheel at a different angle.)

[pro70z28]

Originally Posted by Ayrton

I have the AM larger 4 link kit and would like some guidance on what length the bars should be before welding in the caps? How much shorter (if at all) should the upper bar be?

Thanks

I have the AM 4 link also, pic. posted above. The top link is approx. 20 1/2" long and the bottom is approx. 19 1/2'' long. I made my own four link brackets for the rear housing so that might vary some from your set-up. Did you get any building guidelines with the 4 link kit? I have the AM chassis, but I bought things like the 4 link separate because I wanted the beefier large tubes. AM (in my situation) called for the centerline of the rear housing to be 27" behind the main cross member. To find the tube length, I set the rear housing in place with the proper angle, etc. then cut the tubes and mocked up the whole suspension without welding. Mine is on a jig, so that was a simple way to find the tube lengths.

[lowROLLERchevy]

Originally Posted by pro70z28

is that an 80's body style camaro / firebird drag car i see taking shape ?? looks good

[pro70z28]

1970 Z-28. Not too much "z-28" stuff left tho. Got more tubes in since that pic.

[Triaged]

Originally Posted by BillyShope

...And, going back to this matter of sensitivity, another consideration is how far forward the IC is located. Consider a straight line, as viewed from the side, extending forward from the rear tire patch. If the IC is on that line, whether it's 5 feet in front of the rear tire or 5 miles, the car is going to act exactly the same as it launches. But, if the IC is 5 miles forward, the suspension is far less sensitive to travel (jounce/rebound) changes and, again, this is a good thing.

It is possible to get the anti-squat value to be fairly consistent (+-5% with +-4" of travel) with short IC lengths. You just have to play with the ratio of upper arm length to lower arm length (length in side view). I had always heard the upper should be 75% of the length of the lower (again in side view) and I found this to be only an OK starting point. My goal with this is to be able to design a suspension that doesn't have to use 100% anti-squat (street truck) yet can still cancel out prop-shaft torque while squatting some on acceleration. I still haven't worked out the torque cancellation but getting the anti-squat consistent is just another step in the process.

I am going to redo my excel spreadsheet to use linear algebra instead of macros to calculate suspension travel and then I could even let the solver work out the length of the upper link (sounds painful but I think I might be able to do it). I wish I had taken a linear algebra class in college...it wasn't required so I didn't

[BillyShope]

Originally Posted by Triaged

It is possible to get the anti-squat value to be fairly consistent (+-5% with +-4" of travel) with short IC lengths.

Yes, I'm sure it is, but why would you ever want to? Are you trying to avoid the roll oversteer?

Originally Posted by Triaged

My goal with this is to be able to design a suspension that doesn't have to use 100% anti-squat (street truck) yet can still cancel out prop-shaft torque while squatting some on acceleration.

Yes, this is possible, but now you leave the realm of simple linkage calculations and enter into a consideration of spring rates and their effects. Besides complicating the calculations, I don't see why you'd want to unload (squat) the rear tires during launch with any application. The cancelation of driveshaft torque doesn't require 100% anti-squat; it just greatly simplifies the calculations. If squat (or rise) occurs, you have to know the "new" link angles in order to determine if driveshaft torque cancelation is still available. And, since the rear end is going to be bouncing up and down, the whole matter becomes a compromise, anyway. (Of course, the rising of the front end...even with 100% anti-squat...changes the link angles a bit, anyway. Now, if you wanted to keep track of that and make the proper corrections, that might be worthwhile. Again, this would require front end geometry and spring rate information so that front wheel rates could be calculated. Very messy, but I have been through the exercise.) You're doing a great job with this software you're developing and you might even be able to make a buck or two to help with your education. But, don't complicate matters with features your customers don't really need. That's my opinion, anyway.

(I'll bet you're taking some aeronautics courses. I say "propshaft" half the time myself for the same reason. When you get into the industry...and I hope you eventually do..., you'll find that even the Greek letters used in your aero courses are the same for corresponding parameters defining automobile performance.)

[Triaged]

Originally Posted by BillyShope

Yes, I'm sure it is, but why would you ever want to? Are you trying to avoid the roll oversteer?

Yes Call me a sucker but I plan on doing all this suspension work in my beat up 87 s10. It will almost never see the track (strip or road course) but I'm sure it will have a go at a lap or 2 of each. I plan on this being my daily driver being capable of driving (if you can call it that) on L.A. roads with 4" deep potholes. My thought is that I would be able to keep the thing on the road a bit easier with no bump/roll steer (less need for steering wheel input). If I was a better driver I might not have to worry about it. I even plan on being able to tow with this thing (not sure what is wrong with me).

Originally Posted by BillyShope

...I don't see why you'd want to unload (squat) the rear tires during launch with any application

I have fears (maybe unfounded?) that driving a truck with 100% anti-squat will get abusive to the driver (me) when hitting speed-bumps/dips/potholes while on the throttle (I guess I'm still too young to lift the throttle when I should). Carroll Smith (R.I.P.) I don't think recommended using over 30% anti-squat and even less anti-dive (in the front). While I'm sure he was a bit (very) conservative in many things I'm sure he had a reason for this. One side of me thinks that if there is no load (other then static) in the springs under acceleration that any extra ground enforced wheel loads will also go right through the links...another side of me knows that reasoning is full of holes and and the truck will ride like a caddy with 100%. I will make this thing very adjustable (which is not to hard to do having so much room under the bed of the truck) and prove to myself which is the case.

Originally Posted by BillyShope

You're doing a great job with this software you're developing and you might even be able to make a buck or two to help with your education. But, don't complicate matters with features your customers don't really need. That's my opinion, anyway.

Thank you for the vote of confidence. My 'customers' right now are asking for driveshaft (their term) angularity calculations (this is mainly desert racing guys who are suspect about the calculations anyways), some graphs of anti-squat vs travel, and having it as a stand-alone program. Right now because I have put all this work into it just to give it away for free I want to do what interests me At the moment that is getting rid of the macro and doing some excel based FEA to figure out the compliance steer effects (displacements angles and loads in the links) of a triangulated 4-link under cornering loads (I like to get in over my head just to see if I can do it).

To me it is just like why climb Everest?...because it is there. I talk to my non-ME friends and their eyes just glaze over...I think it is fun...no wonder engineers get labeled as nerds

Originally Posted by BillyShope

(I'll bet you're taking some aeronautics courses. I say "propshaft" half the time myself for the same reason. When you get into the industry...and I hope you eventually do..., you'll find that even the Greek letters used in your aero courses are the same for corresponding parameters defining automobile performance.)

I think this stems from my older sister always correcting my English as I was younger. Now I try hard to always use the "proper" term for everything. I can't stand it when people call all limited slip diffs "posi", when people talk about motor mounts instead of engine mounts, when someone calls every spherical rod end (with no regard to who made it) a "heim"....I think it is just the inner nerd trying to get out

[BillyShope]

There's a common misconception that 100% anti-squat somehow "locks up" the links. It sounds like Smith had made this mistake. Some voice concern over braking problems, as if the links are no longer free to accept braking loads. There is nothing "magic" about the 100% anti-squat geometry. Yes, the links handle the inertial loads during acceleration and the suspension springs are unaffected, but the ability to handle all other loads is still present and entirely unaffected.