4 Link System - Step by Step

[BillyShope]

Setting the suspension links to optimize one instance during the run....

One more time: Optimization is achieved with asymmetry THROUGHOUT the run, As long as the engine is supplying torque...at any level..., the tires are equally loaded.

Preload and/or use of an ARB, however, DOES provide, at best, optimization at a single instant during the run.
http://www.racetec.cc/shope

[bracketracer]

There is a member here that has tried some of Billy's ideas on a very fast car and had some luck with the concept. It's not my place to be sharing what he found however. Maybe he'll comment if he sees this?

All I can say is don't entirely dismiss it, but you'd better think it through..

Are you willing to give it a try when your car is all done John???

[bracketracer]

Question for you Mr. Shope, has anyone you know applied the asymmetrical 4 link approach to a brutish high-horsepower car?



Billy you didn't answer Mike's question.....

[John_Heard]

There is a member here that has tried some of Billy's ideas on a very fast car and had some luck with the concept. It's not my place to be sharing what he found however. Maybe he'll comment if he sees this?

All I can say is don't entirely dismiss it, but you'd better think it through..

Are you willing to give it a try when your car is all done John???

I have a leaf spring stock suspension car, so it's a bit tough to try on mine. If I had a four link car, and IF I was having problems making it work, then sure, I'm open to all ideas to try as long as I think it's safe.

[BillyShope]

I have a leaf spring stock suspension car, so it's a bit tough to try on mine.

John, achieving equal rear tire loading is a problem with both leaf spring cars and ladder bar cars. But, it can be done. The asymmetry has to be at the front of the car, however.

With adjustable coilovers at the front, a higher rate spring can be used at the right front than at the left front. That's a higher RATE. There's not going to be any static preload. The adjustability will be used to bring the car back to equal rear tire loading as it sits. It's going to take more than a few minutes of fiddling with those coilovers before the bumpers are level, the ride heights are where you want them, and the rear tires are equally loaded, but it CAN be done.

With a higher rate spring on the right front, most of the weight transfer will be pulled on the right side. (If you have trouble with that, think of what would happen if the right front were solid. The left front coil wouldn't be changing in length, so all the weight transfer would be coming from the right front.) Since the sum of right front and right rear must always remain a constant (or the car would be rolling over), that means...with the proper left front and right front spring rates...it would be possible to have equal rear tire loading during launch (and, of course, throughout the run).

Since most of you have buddies who are oval racers, you're familiar with some of the crazy spring combinations they use. You might, then, prefer working with this rather than an asymmetric adjustment on your 4link. The results are the same.

There's a spreadsheet for this somewhere on my site. Can't remember the page.
http://www.racetec.cc/shope

[bracketracer]

I can tell you for a fact that unequal spring rates at the front will send you for a ride when hitting the brakes at 100+ at the finish line. And who has not done that bracket racing??? The nose will dip more on one side removing the opposite load on the rear that will send you into a spin....
I have seen this.....Think about it Billy.....You still have not answered that Question so that must be theory and no real track test jus looks good on paper..

[John_Heard]

How do travel limiters factor into what you're thinking about Billy?

[Mike Peters]

I believe this asymmetrical approach discounts the other force vectors being imparted through the suspension links. There are other parameters to be considered with suspension link geometry besides anti-squat percentages. To plot the asymmetrical geometry on paper for cancellation of torque is one thing but, I don't feel this approach takes into account the other properties of the forces acting through the links. One of DragStuff's expert contributors, Patrick Budd, penned one of the best articles I've read on the subject. Here's the link again - http://www.dragstuff.com/techarticles/P ... uning.html

This article encompasses the physics applied through the bars instead of just taking into account the suspension link angles and their relationship to anti-squat percentages. If setting up a 4 link suspension in this asymmetrical fashion is acheived, I feel there's much more to account for than equal side-to-side loading on paper or plugging in figures in a formula. Bar spreads, lower bar attitudes in relation to roll steer, and the force vectors imparted through the upper links as they try to straighten themselves out during the sudden application of horsepower are not being considered. Patrick has real world experience and I think his article is spot on. However, I don't want to detract or ignore Mr. Shope's acheivements through his storied life. I choose not to follow the asymmetrical set-up but, certainly encourage anyone who is or has been willing to try it to please report their findings.

[Mike Peters]

I can tell you for a fact that unequal spring rates at the front will send you for a ride when hitting the brakes at 100+ at the finish line. And who has not done that bracket racing??? The nose will dip more on one side removing the opposite load on the rear that will send you into a spin....
I have seen this.......

[BillyShope]

...instead of just taking into account the suspension link angles and their relationship to anti-squat percentages.

This is certainly not the analysis procedure an engineer would use. A free body diagram must be made and force and moment balance equations established for each suspension component. The result is an equation set with a number of unknowns. If the number of independent equations in the set equals the number of unknowns, an equation can be found which describes each of the unknowns.

This is the procedure I have used, both to affirm Bob Knight's conclusions and to create the spreadsheets at my site for other applications. So, every force is...most definitely...taken into account.

In order for suspension engineers to communicate effectively, agreement has been reached on the meanings of certain terms. It is apparent that Mr. Budd has chosen meanings not used within the automotive industry, which makes it difficult for me to comment fairly on his work.

I would suggest a close read of Page 45.
http://www.racetec.cc/shope

[BillyShope]

How do travel limiters factor into what you're thinking about Billy?

Don't like 'em! While a travel limiter setup might provide equal tire loading at some instant in time, the jerking around can cause too many other problems.

Don't like 'em!
http://www.racetec.cc/shope

[BillyShope]

I have seen this....

Would like more information. Oval racers...often having very different spring rates across the front...apply hard braking thousands of time every Saturday night without the problem you describe. Not doubting you, but I'd like more information.

You still have not answered that Question so that must be theory and no real track test jus looks good on paper..

I answered the question when I said the setup worked for any engine torque level. I learned...many, many years ago...to never supply a "for instance" to justify an analytical solution. The solution must stand by itself. Any example can...and will...be met with a "What if?" response. What if the car was running a converter? What if more tire air pressure had been used? And on and on and on.

John says that he knows of someone who could enter this conversation with an application. That would be interesting, but, if a person is dead set against change unless and until everyone else is doing it, it won't make any difference.
http://www.racetec.cc/shope

[bracketracer]

I have seen this....

Would like more information. Oval racers...



Billy, your on a drag race sight here....We are talking about slaming on the brakes at 150mph on pavement not dirt...

[John_Heard]

Would like more information. Oval racers...often having very different spring rates across the front...apply hard braking thousands of time every Saturday night without the problem you describe.

Those guys are weird, they like to turn left all the time, and run funky brake bias, and slide the tail out too...

If you want to see some weird ass suspension geometry, go take a peak under a dirt late model, or IMCA modified. Billy, you really ought to go to the dirt track races and look, I think your spreadsheets would have a meltdown haha

[BillyShope]

Billy, you really ought to go to the dirt track races....

Wasn't even thinking about dirt track when I posted. Was thinking asphalt. When it comes to dirt, driver skill plays such a large part that it seems car setup can almost be forgotten. That's "almost." I've read the biography of A. J. Foyt. As a kid, his big chance came when the owner of 2 cars offered him a ride in the "clunker," telling him that he knew he'd be slow, but it would give him (the owner) a chance to see how he did in traffic. Well, Foyt went out and set a new track record while qualifying and won the main event.

How are spreadsheets gonna help someone like that? Sure is fun to watch, though.
http://www.racetec.cc/shope