Improve Handling with Stock Spindles

[gchandler]

If I was to change the lower ball joint mounting position and use a taller ball joint would I see am improvement in camber gain because I am effectivly making the spindle taller? How much of a change would I need to see an improvement.

This is on a 64 chevelle, but a camaro would be similar.

[Mean 69]

Things aren't that easy. If you change both the upper and lower BJ locations, all bets are off. For certain, the FVSA will be shorter, roll center height will most likely change, and it goes on.

Camber gain is only one aspect of the overall task of the front suspension, and it is a pain, but when you try to "optimize" it, other things will suffer as a result.

Rather than trying to alter camber gain (or anything else), first ask yourself what differences you want the car to make. I see so often that folks want to change something, but don't really know why, or what. I'd be so happy to see someone first state what the behavior of the car is, and what they want to improve. That is actually a harder thing to determine though....

Thoughts?
Mark

[David Pozzi]

Probably a little, but way less than a taller upper balljoint would do. The upper arm would still be fairly level and that wouldn't provide much neg camber gain. Most lowered cars have the lower balljoint a bit higher then the inner pivot and a taller lower bj would fix that, but the upper bj really needs it more.

[Marcus SC&C]

Gchandler,you`ve got a good head on your shoulders. YES, it WILL make a difference. In fact it`ll make more than one difference in this case. The A chassis suffers from a much too low RC height and reversed (from optimum) camber curves (much like the 1st Gen Camaro). It also has rather impressive (in a bad way) bumpsteer. The tie rod end of the steering arms are too low but about 5/8" for best bumpsteer. There`s a swap involving a taller spindle (slightly over and inch taller) which dramatically improves the RC height and camber curves but the steering arm is in a much worse location still and is longer,messing up the bumpsteer (even more) ackerman angle and steering ratio all at once. Not good. A taller LBJ,can both simulate a taller spindle AND raise the steering arm improving bumpsteer. A tall UBJ can be used in concert with it to further raise the RC and improve the camber curves. Using both and lowering the car slightly puts the RC height and camber curves in the same ball park as modern performance cars. How do I know all this? We`ve did all the computer models, R&D and on road testing already! I just described our Street Comp Stg.2 package for A body. Since there are no compatible taller stud factory ball joints we worked closely with Howe Racing to introduce a line of their excellent modular ball joints (originally designed for circle track and Nextel Cup cars) for classic muscle cars. At this time we`re the only place ANYWHERE you can get the tall stud UBJs for 1st gen Camaro and A body. We use the tall upper and lower modular ball joints and top them off with adj. tubular upper control arms. Depending on ride height,tire height,alignment specs etc. the RC height is raised about 4" and the camber curves reversed from +.3*/in to -.6*/in. on average. RC lateral migration is much less than stock also. I`ve installed a number of these packages and driven the cars before and after. To say the difference is a dramatic improvement is a gross understatement! There`s a huge decrease in understeer (plowing) and body roll. Where the tires used to howl in protest the car simply grips and turns. Turn in is much improved also. The car simply feels much more eager and predictable in the corners. We`ve gotten nothing but great feedback from our customers on this one. Ad a set of Baer 12" or 13"/PBR brakes and some good shocks (we really like adj. QA1 shocks) and you`ve really got a great steet performance package even with stock F-41 style springs and sway bars. Performance springs,larger bars and good large dia. wheels and rubber just make it that much better. If you`d like to take a look at the system and tall BJs you can see them at www.SCandC.com Marcus

[gchandler]

That is exactly the sort of information that I was looking for. I have a system planned out to use the howe ball joints and actually have a couple on the bench. I just wanted to see if anyone had put some actual road time on a setup like this. My 66 chevelle is set up with the HTH tall spindle front kit and I am very pleased with the results, but that required more extensive modifications such as a faster box and different outer tie rods. My desire is to reverse the camber gain (at least make it neutral) and reduce the amount of plow through the turns. Looks like I will be able to achieve both of these with some careful planning. Personally I have been driving A-bodies since I got my drivers license (10 years) and love the way they handle when modified. The cars are both equiped with HTH truckarm suspension in the rear and the front of the 66 chevelle is a negative camber tall spindle kit and the 64 is bone stock in front.

[Marcus SC&C]

The Howe BJs are great pieces. I have about 25K hard miles so far on the set in one of our test cars. With a lower than stock ride height you should be able to get neutral camber change within the most used range of travel and raise the RC height to near 0. Not great but better than stock,especially with the improvement in bumpsteer. Watch for UBJ bind if you`re using the stock UCAs with that combo and lowered ride height though. If you decide to go for the tall UBJs give us a call. Marcus SC&C

[Mean 69]

the RC height is raised about 4"

From what, to what? I am having a really hard time trying to figure out why you'd want to "raise" the FRCH. My guess is that the reason the car rolls less is due to a dramatically reduced roll moment (assuming you used the same roll bar). It would also seem that moving both ball joints away from the stock pivots would create a pretty dramatic change in the FVSA, making it far shorter and thereby potentially introducing a lot of roll center migration in bump, roll, etc? What about weight jacking?

Sounds like your customers are happy, which is terrific, just seems to me that some pretty important sacrifices were made in order to improve camber gain?

Mark

[David Pozzi]

Mean69,
If the camber curve is as bad or worse than a first gen Camaro, the roll center is most likely at or below ground level! The FVSA is probably at infinity with a RCH like that. Changing the geometry will have to reduce the FVSA but not to a critical point if the change isn't severe. I wouldn't think you'd want to go crazy with extending balljoint shanks and weakening them, I'd think a half inch change from stock or so would be as much as you'd want to venture.

Marcus, PLEASE throw some paragraphs in your posts, my eyes are hurting!

[Mean 69]

the roll center is most likely at or below ground level

That in and of itself is not necessarily a bad thing, in fact, the roll center height and migration is the "most" important aspect of the suspension design, within reason, of course (everything is a compromise).

I'd really like to hear Marcus' theory of why the modifications he suggests work, and why raising the roll center height in particular is the preferred method. I am always eager to learn new things.

Mark

[Marcus SC&C]

Mark the factory RC height is well below the ground about -2"! The camber curves are the reverse of what we want in a performance car,they have quite a bit + gain (+.15/in. or so average) in jounce. The low RC makes the front end want to roll and plow into corners. Raising it (to about +2.5",coincidentally the same as a C5) makes corner entry much flatter,smoother and improves turn in. Reversing the camber curves to achieve notable - gain (around -.6/in.) provides all the usual improvements. It should also be noted that the rear RC is around 18"-19" above the ground giving the car a grossly angled RC axis inclination. All of these #s depend on ride height, tire height etc. so there`s no way for me to give them to you precisely unless we`re talking about a specific car.

The factory RC migration isn`t too hot. In 1" dive and 2* roll the RC migrates laterally 19". Yep,that`s a lot. With the Stg.2 package it moves 6.5". It could still be better but that`s quite an improvement.

This is the same principal used on Camaros with the G mod, or Penske`s special TA tall spindles. The proof is in the pudding,driving the same car with no other changes before and after installing the Stg.2 package makes it immediately obvious,the geometry changes work and work very well. Between the improvements in bumpsteer and RC migration the car becomes much more predictable and much easier to drive near the edge as well as more pleasant to drive everyday.

David,you`re right about the BJ studs +.500" is max and that`s with components that are much more durable than factory parts. Better with paragraphs? ;) Marcus

[David Pozzi]

Thanks!

[Mean 69]

Hey, thanks Marcus! That was a very nice explanation, with numbers. I like that, it means a lot more to folks like myself than the usual "it works really well," which too often is the case. Specifics are always nice.

With regard to the front roll center height of the stock configuration, yes, it is low, but in and of itself is not really too much cause for alarm. 2.5" above ground is fine too, too much more than that is not really good though, jacking begins to take a large effect, and that is not a good thing at all. I am still confident that the reason that the car enters flatter is due to the decreased roll moment, i.e. making the stabilzer bar "more effective," or conversly needing less stabilizer bar to impart the same roll resistance.

What is really interesting here is that by making the FVSA shorter, that the roll center migration is less. Is this possibly because the orgininal configuration was in a lowered setup, possibly with the LCA inclination (front view) being inclined toward the center of the vehicle? If so, then the addition of the increased height LBJ would obviously help this issue. Good lesson here, you don't need to move the pivot points around very much at all to have a dramatic effect, which further suggests that if you don't have things mapped out, probably not too good an idea to just "try things out." Might get a LOT more than you bargained for.

Thanks again, nice explanation.
Mark

[Salt Racer]

Mark,
More than likely, the reduction of lateral RC migration is a result of taller effective height of spindles. From what I've seen, RC migration is relatively insensitive to FVSA length. The change in spindle height and UCA/LCA length have greater effects.

For a given LCA length, taller the knuckle, the shorter UCA you'll need for good RC migration curve.

You're absolutely right that it doesn't take much to make drastic changes on SLA IFS. It's really fun to mess with!

[EDIT] RC also moves around quite a bit when static RC height is very close to the ground (near parallel VSAs [force lines])

[galopin]

This is a great discussion.

Marcus, Mark, Katz, and DP: Thanks for taking the time to share your theories, observations, and results. I can always depend on you to inspire me to open up my Herb Adams and Fred Puhn books.

[Marcus SC&C]

Mark,you hit on one of the little perks of this type of setup. It requires less front swaybar and spring rate while still cornering very flat and handling very well. In areas that have less than perfect roadways (like here in Pa. the pothole capital of the universe ;) ) running less total individual wheel rate (springs + swaybar) improves the ride quality and makes the car less nervous on rough/uneven surfaces vs. a typical big bar/stiff spring combo.
Yeah you can run them if you like and the system will respond with even higher limits,you`ll just pay the normal price in ride quality. Our `87 Cutlass with our C5 based front suspension (G-5),prototype 3 link/PHB rear and LS1/6 speed combo is set up very firm (705lb/in 250lb/in) with big bars (36mm Fr./ prototype rear) and although the ride is a little rough it`s limits are extremely high. It`s easy to run out of nerve before you run out of car with that one.
Galopin,I just wish we could all get together and discuss this stuff over a couple cold micro brews! Marcus SC&C

[Salt Racer]

Mmmmm, microbrew...

I hate living in northwest, but one consolation is there are many good dark winter brews!