I am considering updating my suspension on a 69 and I was wondering if I could get some feedback. For an autocross car, with some occasional drag racing would a 4-link or ladder bar system be a worthwhile investment. I am not sure how these types of setups work under hard cornering. I know they work well for launches, but I am not sure about anything else. Who else here autocrosses their camaro. What kind of setup are you using. Thanks in advance for any feedback.

That much of a modifcation to the rear suspension would put you into a modified class. Not a class you would want to run.

Forget lift bars, they will bind in the corners. A four link with parallel links would work, probably better than leaf springs, can't say how much better.

Four link with non-parallel links would run into cornering bind problems, can't say at what point it would happen though, the more angle the sooner you'd have problems.
David

I am not really concerned about running nationally, only locally so being in the modified class isn't a big deal. I think with the modifications I have now I think I would already be in modified anyway. I believe if you have modified spring perches it bumps you out of prepared; however I could be wrong. Do you know any good places to look for what people are doing for their rear suspensions. I can find some decent info on front end, but not much on rear end.

Lots of late model Mustangs are converting to a torque-arm.
There has been a lot of discussion on http://pro-touring.com about rear suspensions, also the truck arm rear suspension.

The Global West cat 5 rear spring uses spherical bearings to free up binding in the leafs. I talked to Doug about it at SEMA two years ago and he wasn't preferring it to his standard springs for autocross. He felt the binding of leaf springs may help gain some corner exit oversteer but was wanting to try the cat5's on an autocross Camaro to see if there was any benefit.
A lot depends on how much body roll the car has.

A three link is supposed to be the best but the upper link intrudes into the rear seat area.
David

http://www.miracerros.com/mustang/t_suspension.htm MUSTANG SUSP AND TORQUE ARM INFO.

http://www.grmotorsports.com/techmain.html HANDLING TECH INFO - AUTOCROSS

http://www.asedan.com/

http://cp.carlc.com/cars.html

[ 01-30-2004, 09:50 PM: Message edited by: davidpozzi ]

neverending, it also depends on how much cash you want to spend. I am putting a fourbar in my 67 and can help with what I know and what direction to look for more info. The main advantage of the fourbar is the adjustablitiy. David knows much more than I can imagine about first gens. I second the www.pro-touring.com, (http://www.pro-touring.com,) they gear more towards what I think you are after. email me if you like at bzinvegas@msn.com.
Brian

The battle between straight line and corners regarding rear suspension is an interesting one. Because the overwhelming majority of muscle car owners are straight line types, there are alot of offerings for this application. Not so in regard to the corners, but things are starting to change a bit.

I am not really certain about the four bar systems that are out there in terms of being adjustable for cornering emphasis, but I bet you could do a fair job at sorting them out. One thing is for CERTAIN though, the systems I have seen NEED to be supplemented with a lateral locating device, the leafs do a really good job at resisting side to side motion, but a four bar can't do it on its own. Don't be fooled by the "track bar" that they offer, which is a ~45 degree bar that is supposed to help out with this, it will NEVER stand up to the cornering forces that today's street tires can enable. You'd need a Panhard Rod, or a Watt's linkage to locate the rear laterally. Period. And it needs to be strong, really strong. The three link that David mentioned is essentially a four bar system where the two upper bars are coincident, eliminating the potential bind that would be present with two upper bars. A really good way to go, tough to package.

I'd recommend buying a good suspension book to read up on the subject before jumping in with both feet. As was mentioned, a lot has to do with the amount of money, self-fabrication skills, and how far you want to go to hack up the car. David mentioned the torque arm setup, highly popular with the Mustang crowd, it is a pretty darned good system in practice. I have fabricated one for my 65 Mustang, its a prototype, but the packaging is nailed, so once the car gets paint and body, etc, it will be turning as well as any car available on the market. I did a lot of studying, invested in a good tubing bender and other fabrication tools, and worked quite a while on it. Still, when all is said and done, even with the investment in the tools and my time, I will be way ahead in terms of dollars spent (the two offerings for the early Mustang rear suspension systems, both Torque arm ap's, start at ~$3k), better components (for instance, Bilstein mono-tube shocks), and in my opinion, a better design approach. If you are going to cut the car to install a four link, you probably have the skills to make your own setup, with the help from a mechanical engineer to make sure the approach is safe (ME's LOVE this stuff, I get help for free most of the time!).

Just remember, it is ALOT easier to make a really good cornering car be acceptable at the drag strip than it is to make a strip-emphasis car even acceptable at the corners.

At present, this is my favorite subject in the world, if you want to continue the tech discussion, let me know. It is really cool, and not too many people out there really understand what the rear system needs to do, and how it really does it.

Mark

What books do you guys suggest on suspension design. I've started reading the posts on pro-touring.com and I'm starting to get a better handle on the subject. However, it seems like people favor the corvette irs and front end for a no compromises handling car. Thanks for the input guys. You answered my questions regarding how much bind you would have with a 4-link and ways to solve it. I think I am actually starting to lean toward a corvette suspension conversion. We have a national autocross champion corvette driver here locally and I think it would be fun to have a suspension that is equal to his C4 but with over twice the horsepower.

I think a good book to start with is Herb Adams, Chassis Engineering. It is a good overview book that starts with a basic explanation of what a suspension system is trying to do (which is to keep the darned tires perpendicular to the road, to manage roll and forward/rear weight distribution, etc). This is the first one that I read. Carroll Smith has a good selection of books that starts with Prepare to Win, then goes on to Tune to Win, and Engineer to Win. I have the latter two, Tune to win is another great resource but not too much on sedans, Carroll's stance is that if is not a purpose built open wheel machine, it's not really a race car. The last one in the series I am reading now, it goes into the theory behind materials, and is a great source for metallurgy, etc. I am only about half way through that one. I also started reading Stanniforth's (sp?) latest book, can't recall the title off of the top of my head, and so far I like it alot. He has a great writing style (he's a Brit, so a tire is a "tyre.."), but so far I am only through the first couple chapters.

If you are really core, and want to be reminded of your graduate level mechanical engineering courses, then Race Car Vehicle Dynamics from Milliken is for you. Written by two brothers, who came primarily from the aerospace industry, there is alot on aerodynamics info included. It is pretty heavy duty, lots of serious equations, etc. Not a book you read, but it is a great reference. Not cheap either, I think it is over $100.

Start with Herb's, you can buy it from Amazon for around $20. Great start.

Mark

By the way, I don't have any experience with IRS, it can be a great way to solve some of the problems associated with rigid axles, especially on bumpy roads. Keep in mind though, it has been shown that a well tuned solid axle car will perform as well as an IRS car on smooth roads. If the race track is kind of nasty, the IRS has an advantage in that it can keep the rear wheels on the ground better, IF it is tuned to do so. Seems to be a really popular conversion though, you'd probably get lots of support from people who have done it.