Comparing tri5 to C4 front suspensions

[Rick_L]

Rocky, negative camber gain is what you want in compression. Think about it. And I don't think Cnut is disagreeing with that part.

Cnut, have you put some numbers to tire scrub? I don't think that's a relative issue, but will admit that I haven't calculated any numbers.

[chevynut]

You said it has postive camber in compression .

No I did not say that. This is what I said:

"So my conclusion is that while a 1" taller balljoint helps correct the huge problem with the positive camber gain of the tri5 suspension,"

I say it has negative base on my cad model and video thats my point. Same thing you stated above that the c4 had and the trifive doesn't I say you are mistaken with my setup as it sits it excerts negative camber gain in compression.

I agree with you, the taller balljoint fixes the inherent problem with the stock tri5 suspension. That's what I said. However, it doesn't give as much camber gain as either vintage C4 suspension. Now the question is how much camber gain is too much? GM says the 90's C4 isn't too much.

I myself have no idea what the perfect roll center would or should be. Your comparing the c4 so what numbers does it have as a roll center in your setup? I do know using C4 allows you to even dial in camber in the rear as well.

I haven't looked into that but I do know that the shorter the instant center lever arm is the higher the roll center (with a level lower a-arm). And I do know that a non-level lower a-arm (pointing up and outboard) lowers the roll center. And the roll center moves upward toward the CG, the roll stiffness increases and I think that's a good thing. As the roll center drops, the car tends to roll more on turns. That's not good for handling.

For this reason I think dropped spindles are a lot better way to go than lowering springs.

[chevynut]

The other thing that a taller balljoint does is decrease the SAI, I believe. That increases scrub radius.

So while the taller balljoint you're using does fix the positive camber gain of the stock suspension, I think it decreases the SAI a bit, which increases scrub radius. Also, you can't use stock length a-arms since they would be too short, correct? I believe your lowering springs cause the lower a-arm to be non-level, which causes tire scrub as the suspension moves, and moves the roll center downward, away from the CG. This hurts handling.

The latter is illustrated in this diagram I posted above:



So If I was going to try to fix the stock supension, I would consider using the taller balljoint, a tubular upper a-arm with increased caster, and of the correct length to allow proper alignment. I'd also use dropped spindles to lower the CG, and a spring that gives a level lower a-arm. I would also add a swaybar. That's about all you can do, and it's still not as good as the C4.

I wonder why nobody has made a spindle and lower a-arm with an inverted balljoint for these cars.

[Rick_L]

I don't know what the formal definition of SAI is, but to me it's the angle between a line drawn through the ball joint and a line perpendicular to the spindle axis. So it's fixed by the spindle's machining dimensions.

I think that some include the camber angle as part of the SAI. But that's a function of alignment and not suspension movement, at least as the starting point.

Perhaps this is all in the twist on words and definitions.

I think I see where you're going but again numbers need to be added to the discussion to understand the relevance.

[chevynut]

I don't know what the formal definition of SAI is, but to me it's the angle between a line drawn through the ball joint and a line perpendicular to the spindle axis. So it's fixed by the spindle's machining dimensions.

I agree. But let's say the holes in the spindle are bored perpendicular to the tapered spindle itself. Then if you increased the length of the balljoints, it would change that angle. Are the holes bored so they line up with each other? If so, the SAI wouldn't change. It's a small mount in any case.

I think I see where you're going but again numbers need to be added to the discussion to understand the relevance.

I'm not really "going" anywhere, just wanted to outline the differences between the various suspensions and analyze what Rocky's changes really did to the geometry. Yes, it improves some things but introduces some other problems, imo.

To me the real questions are how much camber gain is optimal, how much scrub radius is preferred, how much anti-dive is too much, and where should the roll center ideally be. That probably depends on a lot of other stuff.

[Rick_L]

I see your point on the spindle machining. First thought was the holes are in line with a line through the holes, but after thinking about it, maybe not, as I'm pretty sure the flats are parallel to the spindle axis. That would make it logical to machine the holes perpendicular to the flats. I think any difference is slight.

[rockytopper R.I.P 5-13-2017]

The 1/2" taller balljoints and dropped springs put the upper a-arm such that the balljoint end is higher than the inboard end, so you would get camber gain on compression. But the lower a-arm is not level now, and you will get inboard movement of the lower balljoint and spindle as the suspension moves. To me, that means your tire contact patch is scrubbing in and out some as you go down the road. It's definitely not optimal.

I guess you didn't say camber gain here either? The fact is you cannot use drop spindles and fix a trifives handling issues or any other gm car for that matter. Go do some math Cnut. If you drop the CG of the car using drop spindles you have done nothing to correct the trifives positive camber In compression. Adding a taller ball joint to this will reduce positive camber gain but it will still exist. Thats why I've said from the start drop spindles dont cut it throw them in the trash. By using an adjustable upper arm I have effectively shortened it. By using the drop springs I moved the suspension pivots and dynamic travel to produce negative camber in compression. While I have made compromises as you point out I have totally changed the trifives handling characterics. As your diagram shows roll can be controlled by stiffer springs. I'm running 550 plus with sway bars. My cutlass is a proven platform it has the same compromises. Is it optimal compared to a C4? No it isn't but it works and has been proven on a race track many times. Their the good ole boys that figured this trick out. So I'll conclude the trifive suspension will never be made as optimal as the C4 but it darn sure can be optimized to handle pretty darn close to one.

[rockytopper R.I.P 5-13-2017]

Anyone who cares to understand about improving the handling of a classic or muscle car should consult Mark @ SC&C he knows this topic well and is an expert in the topic. If you wish to run C4 he can tell you how to improve it as well. You may also read this link it outlines the issues of the various platforms and how to fix them. As I stated many times the bone stock Abody suspension geometry is worse than a stock trifive. Read it yourself the A-bodys are bad out of the box.
http://www.musclecardiy.com/performa...ance-upgrades/

[chevynut]

I guess you didn't say camber gain here either?

What I said was "The 1/2" taller balljoints and dropped springs put the upper a-arm such that the balljoint end is higher than the inboard end, so you would get camber gain on compression". When people talk about "camber gain" with a taller spindle they are referring to the increase in negative camber. That's what I implied, and it's clear if you read the rest of my comments and analysis that's what I meant. I should have explicitly said "negative camber gain", I guess.

The fact is you cannot use drop spindles and fix a trifives handling issues or any other gm car for that matter. Go do some math Cnut.

I don't need to do any math to see that if you lower the car using shorter springs, you change the angle of the lower a-arm such that it's higher at the outboard end than the inboard end. This lowers the roll center and moves it away from the CG. That's not a good thing, as the car will roll more on turns. Even worse, it amplifies the drop in the roll center as the suspension is compressed from ride height. Not to mention the tire scrub issue. A better solution is to lower the CG with dropped spindles that don't negatively impact the suspension geometry and keeps the roll center higher.

If you drop the CG of the car using drop spindles you have done nothing to correct the trifives positive camber In compression. Adding a taller ball joint to this will reduce positive camber gain but it will still exist.

I agree. I don't think I've ever said otherwise.

Thats why I've said from the start drop spindles dont cut it throw them in the trash.

This is where you're wrong. Dropped spindles lower the CG while maintaining proper lower a-arm geometry. The lower a-arm should be level or possibly even slightly low at the outboard end. This keeps the roll center closer to the CG, which reduces roll and improves handling performance.

By using an adjustable upper arm I have effectively shortened it.

What did you shorten? With a 1" taller upper balljoint your upper a-arm has to get slightly longer to maintain proper alignment. With a 9.75" or 10.25" spindle height the a-arm is theoretically exactly the same length. Any taller spindle and your upper a-arm must get longer to maintain alignment.

By using the drop springs I moved the suspension pivots and dynamic travel to produce negative camber in compression. While I have made compromises as you point out I have totally changed the trifives handling characterics.

I have never disputed that what you have done improves the handling over a stock tri5 suspension. That design is 60 years old and has a lot of deficiencies, one big one being the positive camber gain we've been discussing. It was GM's first unequal length a-arm design and history has shown that all things considered it wasn't too bad of a design. But as I've pointed out, you have lowered the roll center which doesn't have to be done if you use dropped spindles. Your car will want to roll more with the 2" lowering springs than with 2" dropped spindles.

As your diagram shows roll can be controlled by stiffer springs.

Stiffer springs are not always a better thing. They WILL reduce ride quality and they can cause the suspension to not follow road irregularities by limiting suspension articulation. IMO (repeating) a much better solution is to use dropped spindles to lower the CG and maintain correct lower a-arm geometry, which keeps the roll center closer to the CG. Use the lightest spring rate you can to hold the car at ride height and use a reasonably sized swaybar. Too stiff of a swaybar can cause oversteer and understeer issues too. It can also result in reduced ride quality and traction as one tire hits a dip or a bump and the other wants to react.

So I'll conclude the trifive suspension will never be made as optimal as the C4 but it darn sure can be optimized to handle pretty darn close to one.

You once said you could get C4 suspension geometry with bolt-on upgrades. I think this analysis shows that you can't and I'm glad to see you're coming around. It also shows that lowering a car by cutting the springs causes unwanted changes to the roll center. It does lower the CG and make the spring stiffer which could help handling but the negative effect is more roll. It also reduces suspension travel. It's a compromise I personally wouldn't make because you don't have to.

My C4 conversion lowers the front suspension by 3" from a stock tri5. I don't change any of the suspension geometry that GM designed over 3 decades after designing the tri5 suspension. The a-arm angles are left as intended and the anti-dive isn't changed. You can spend a ton of money on new balljoints, new a-arms, a steering box, a swaybar, dropped spindles, disc brakes, and all the other bolt-on stuff and still not duplicate the handling of a C4 front suspension. Lots of my customers have done this and come to the realization that a C4 front clip is the best and most cost-effective way to get what they want. And it's lighter too. An entire C4 front suspension with steering rack, swaybar, and brakes can be had for under $1000.

Thanks for the discussion and debate. I'm not saying that what you've done is necessarily a bad thing, and it will improve the handling of a 60 year old design. I'm just saying there are better ways to do it that don't make the compromises you've made.

Here's a good article on roll center:

http://www.thecartech.com/subjects/a...oll_Center.htm

What is a Roll Center?
A “roll center” (RC) is a theoretical point around which the chassis rolls, and is determined by the design of the suspension. Front and rear suspensions have different roll centers.

A “roll axis” is an imaginary line between the front and rear roll centers.

The amount that a chassis rolls in a corner depends on the position of the roll axis relative to the car’s center-of-gravity (CG). The closer the roll axis is to the center of gravity, the less the chassis will roll in a corner. Chassis rolling at one end of the car or the other gives more grip to that end of the car.

Roll center is one of the most under-utilized adjustments on a car, but one of the most powerful. This is because roll center has an immediate effect on a car’s handling, whereas anti roll bars, shocks and springs require the car to roll before they produce an effect.

For the purpose of this article, I have borrowed explanations from a variety of sources, and I will try to paint a clear picture of how roll center works.

Roll Center Basics
Here are some basic facts about roll center (RC) and center-of-gravity (CG).

* Roll center (RC) is the point around which the car rolls
* Each end of the car (front and rear) has its own roll center
* Center-of-gravity (CG) is where all cornering force is directed
* RC and CG are (ideally) in the middle (left-right middle) of the car
* RC is vertically below the CG in cars
* Rolling produces more grip



Effects of Front Roll Center Adjustment
Front roll center has most effect on on-throttle steering during mid-corner and corner exit.

LOWER front roll center

* More on-throttle steering
* Car is less responsive

* Better on smooth, high grip tracks with long fast corners


HIGHER front roll center
* Less on-throttle steering
* Car is more responsive

* Use in high grip conditions to avoid traction rolling
* Use on tracks with quick direction changes (chicanes)

[chevynut]

I wonder if there's a good bolt-on solution lurking here.

Perhaps one could get a lower a-arm that would accept a "pull-type" modern lower balljoint with the stud pointing up. What if a guy obtained a spindle (steering knuckle) and inverted the taper in the lower hole somehow, or used a different or custom spindle configured that way? When you bolt this together, you have now essentially raised the spindle, thus lowering the car and no longer need dropped spindles. I'm not sure how much it would lower it, but it seems like it would be significant. It would also significantly lengthen the spindle, possibly on the order of 3". This would also fix the positive camber issue with the stock geometry, but wouldn't address SAI or scrub radius at all.

Hmmmmm.