General theory question

[Zefhix]

I've tossed this around a bit and I think I'm right but have no math or experience to prove it. So, there's alot of talk about how to improve rear suspensions and stuff, especially on Abodys. Often 3 links and truck arm suspensions are recommended to help improve the car's overall handling and traction. So this is my thought. At the time, were these rear susp. setups designed to accomodate the limitations of the front suspensions (even with a few bolt on mods?) or is their function primarily not related to how well the front susp. works? I guess what I'm asking (and making very little sense, I'm sure) is if I had a space-aged, kick ass ideal front suspension for my car wouldn't that mean that rear wouldn't have to work as hard? That, concievably, I wouldn't have to have a truck arm setup to achieve the same results?



So is my thinking kindof off it's keester or are the front and rear susp. setups pretty independent of each other?

[wally8]

I think where you might be going with that thought process is that rear suspensions (with a stick axle) are inherently more simple than an independent from suspension (link wise). However, you still need something that is stable and consistent.

Take for example a 3 link with a PHB. It's a pretty simple layout but you still have to consider locations and geometry or it won't work well. The rear end still has to work to make the other two tires do their job. It will always come down to that: 4 tire contact patches that have to work as well together as possible. Roll center, SVSA, and a lot of other parameters still apply, so I wouldn't write it off as that simple.


Wally

[baz67]

Keith

If you upgraded just your front, you will see better handling, of coarse. However, and I know you know this, but the car does not use only the front. The whole thing should stay in balance.

I guess what I'm asking (and making very little sense, I'm sure) is if I had a space-aged, kick ass ideal front suspension for my car wouldn't that mean that rear wouldn't have to work as hard? That, concievably, I wouldn't have to have a truck arm setup to achieve the same results?

So is my thinking kindof off it's keester or are the front and rear susp. setups pretty independent of each other?

Lets turn that around. If you put a truck arm on the rear and did nothing to the front, how much would cornering power increase? My guess with the added control with the rear and no improvements to the front you would be understeering like crazy and would not be able to utilize the upgraded rear to its fullest. It goes back to the overall balance of your chassis. I hope that made sence.

Brian

[Zefhix]

Okay. Let's say my goal was 1g. I have stock UCAs with the b-body spindle and tall BJ mod up front. I then install a real trick truck arm setup and the car meets my goal (hypothetically, of course). Lets take the very same car and do a full custom fab front suspension that corrects every single major front suspension weakness their ever was (still hypothectical, of course). Now, can I downgrade to maybe just tubular upper and lowers with poly bushings in the back and still reach my 1g? In otherwords, bacause I made the front so kick-ass does that mean the rear has to work less hard? I would say we could flip that around but the front affects more chraracteristics of the cars handling, right? Yes, I'm talking stick axle not IRS.

I know that the front and rear suspensions have to work closely together but I guess I was wondering how close or how independant are they of each other aside from the obvious. I know these are probably super broad questions with no simple explanations I just hope you catch my drift. (get it? drift... )

[wally8]

Since you're talking about an A-body's rear suspension. I would say yes you may reach that goal but how will it actually handle on some actual series of corners. You can make it pull 1g but it's when you start trying to turn serveral corners in a row from left to right that the stock design will show it's deficiencies even with good pieces installed.

The main problem is that the roll center is too high and moves around too much. That will always come back to bite you. You can't just add a PHB because you'll get into too much bind with converging roll centers.

It sounds like these are all things you know and you're just trying to synthesize some new ideas for a plan, right? I'm actually a big fan of putting together something that is relatively close but not necessarily textbook theory perfect. However, I don't see a way to do that with an A-body 4 link. I've had the chance to compare them apples to apples to a 3 link or torque arm in a dirt environment and there is absolutely no comparison in regards to corner speed or forward bite. You'll get your ass handed to you every time.


Wally

[Zefhix]

Since you're talking about an A-body's rear suspension. I would say yes you may reach that goal but how will it actually handle on some actual series of corners. You can make it pull 1g but it's when you start trying to turn serveral corners in a row from left to right that the stock design will show it's deficiencies even with good pieces installed.

The main problem is that the roll center is too high and moves around too much. That will always come back to bite you. You can't just add a PHB because you'll get into too much bind with converging roll centers.

It sounds like these are all things you know and you're just trying to synthesize some new ideas for a plan, right? I'm actually a big fan of putting together something that is relatively close but not necessarily textbook theory perfect. However, I don't see a way to do that with an A-body 4 link. I've had the chance to compare them apples to apples to a 3 link or torque arm in a dirt environment and there is absolutely no comparison in regards to corner speed or forward bite. You'll get your ass handed to you every time.


Wally

haha..that was more or less my question. I not brewing anything up top secret I just was very curious as to cause and effect.

[David Pozzi]

In general, improving the front suspension does the most for handling, it affects the heaviest end of the car, and affects corner entry speed and middle corner the most, the rear can more or less be balanced to the front with spring rate or antiroll bars to get the car balanced enough to get out of the corner but what I have heard of how poor the Chevelle rear suspension is, and if you have much horsepower, your speed out of the corner and down the next straight will be compromised. This would really hurt lap times because the corner exit affects you down the whole straight.

I'd do the front first, then do the rear to match it and balance the handling. You might get 1g with very little in the way of mods, but it isn't going to feel good, or work well if you don't do a lot more.

[pav8427]

very interesting thread. i'll have to digest that a few more times.

is not any one of these rear set-ups we all use some form of really
just half of a front set-up?

different RC's and swing arm lenths,they should both be able to
be tuned in a similar fashion.

doug.

[dennis68]

Tuning rear stock suspension, especially the OE converging link is almost impossible at best. I think that is where this thread is going...what is involved in replacing the OE parts with something that works and can be tuned.

The converging link was the most cost effective way for GM to put a system in place that would handle OK, control anti-squat OK, and ride nicely. It was never designed to be a road course set-up nor a drag race set-up. Guys on both sides try to "fix it" but it is just throwing fuel on the fire.

The only way to really make an "A" body work is to start moving pick-up points or redesign the whole darn thing. I would not try to fix the rear before the front, that could lead to a very dangerous oversteer condition, I'm not one to say a little oversteer is bad (fun if nothing else), but if you really tighten up the back and make it work well I would guess it would send the back all the over the place with stock front components.

I don't think being able to pull "X G's" has any value other than bragging rights. I would rather pull a very smooth and comfortable .9 than a rough and hard to control 1G.

[RaceMan]

All I can say from a true racecar background is the better one end works the harder you have to work on the other. if the front sticks too good the back will be all over the place this might not be the same on the street but i'm pretty sure its the same . they have to match each other somewhat or they work against eachother. You can gain preformance with better parts anywhere on your car but when they work together its the best thing by far. Just my 2cents

[Zefhix]

You understand that these questions aren't really related to the car I'm building, just curiousity questions.
I'm slowly trying to learn more about various susp. setups so I might have more redundant questions later on. Sorry...sorta.

[Norm Peterson]

. . . So, there's alot of talk about how to improve rear suspensions and stuff, especially on Abodys. Often 3 links and truck arm suspensions are recommended to help improve the car's overall handling and traction. So this is my thought. At the time, were these rear susp. setups designed to accomodate the limitations of the front suspensions (even with a few bolt on mods?) or is their function primarily not related to how well the front susp. works?
. . . if I had a space-aged, kick ass ideal front suspension for my car wouldn't that mean that rear wouldn't have to work as hard? That, concievably, I wouldn't have to have a truck arm setup to achieve the same results?

David has already identified GM's design philosophy for the converging 4-link. OK at all the tasks the average lowest common denominator car buyer requires (this includes the guy whose purchase credentials consist of having a pulse greater than zero and apparent proof of sufficient financial means). But really good at none of them. Didn't have to be, with the then-available tires. Remember that the A-body design process dates back to the early 60's, when customer appreciation of things like handling and hard cornering was all but non-existent. If it went straight down the road and wasn't a bear to parallel-park, that was fine with most folks. So it was designed to be "good enough" for the then-current front suspension and tires, without being better than necessary. Actually, it was sort of a step backward from some of the early 60's cars, which came OE with a 3-link/PHB.

I think you need to separate spring/bar/shock tuning from the geometry and compliance effects. It's the geometry and the necessary compliance compromises of the converging 4-link that you want to fix. And I'd argue that this piece of the puzzle can be addressed even before doing wholesale mods up front, as you can deal with the rear axle compliance issues at the same time. Making the rear axle behave properly in a geometric sense makes it more predictable, which is a good thing pretty much regardless of what you do or don't do up front. Swapping springs/shocks/bars is for the most part final tuning. If you really anticipate making big changes in the front roll center height at a later date, you can always plan for some roll center height and roll steer adjustability with a 3-link or truck arm rear. That's a tuning tool not readily available with a C4L.

I'd also argue that the better the front suspension gets, the better the rear suspension had better get. Something about the end that you don't steer losing its grip first in a hard corner (or otherwise wandering off the path you're expecting it to take) being a less-than-pleasant surprise . . .

Norm