I'm in the process of building a full tube chassis for my vert and eliminating everything unibody. Basically all I'm re-using is the body skin itself. It will remain a street car, thus on 17" wheels, full-power accessories, a/c, etc. The engine will be set-back about 3-4" (4th gen dash has room), the fuel tank will hang out back, the rear seat is history - new location for my stereo system. I will be retaining the front strut suspension and the sliding tq arm system, but will be running coil-overs all around.

I believe firmly in the abilities of the sliding tq arm system, as my car has gone 1.66(consistent 1.69-1.66) 60fts on 17" wheels, at it's current 4001lbs. I have a fairly good grasp of how different length tq arms work/react, and my current set-up has an adjustable front mount height which I will be duplicating for the new chassis. I also understand how the lca angle works/reacts. I will included 2-3 mount holes at the front of the rear lca to further tune with, as well as 3 at the diff that I currently have. The thing I'm not sure of is the lca's length effect on the car.

- would you change the length of the lca, if so why?

As for the front suspension, I intend on retaining the strut system because I see no benefit in changing for street/strip/"pro-touring" use. I was wondering about the angle of the control arm though. The angle of the mounts(imaginary "V" drawn through bolts on either side), and the angle of the arm itself(from the ground). Would changing it make for better handling and/or a better ride quality?

- would you change it, if so why?

So, if your angles were vertually infinite, how would you set it up? All experiences, thoughts, and opinions greatly appreciated.

thank you,
Justin Shawgo

 

I don't see any reason to change the rear LCA length. It is just used for fore/aft forces and length won't make a difference for that. I think it is smart that you are putting adjustment in the front. I have some theories about the rear relocation brackets that I need to sit down and do some math and figure out if they are really helping with antisquat or not. I think moving the front up is better than moving the back down.

As far as the front geometry... A corvette double wishbone willl allow you to put on wider tires. The struts are going to limit you to about 9.5" wide. The other thing that I don't like about the strut suspension is the large scrub radius. It makes the car kind of "drive itself" when you get on roads with ruts. I'm sure that you have felt this before. I've considered keeping the lower a-arm and just putting in an upper control arm mounted to the frame/strut tower. Maybe not really considered but more of a pipe dream.

As far as the lower a-arm mounting locations... Something else I plan on looking into in the near future. I'm going to try to calculate the roll center, and then see what that really means to me (us). I have some other pipe dreams about moving the mounting location up and in. Moving it up will allow the control arm to remain parrallel to the ground with the car sitting low. Moving the mounts in will allow more room under the fender for bigger tires/wheels (I think 18x10.5's will will fit pretty easy).

 

Your going to build a full tube chassis and keep the torque arm suspension? Why not just put a 4-link in?

Here's what you need
Chassis Engineering - Drag Racing Chassis, Ladder Bars & Suspensions

You should also read these books
Drag Chassis Tuning Package: Door Slammers Chassis Book
Amazon.com: Chassis Engineering: Automotive: Herb Adams

 

What you need to be concerned with is the intersection point (aka instant center or IC) as this will have the greatest effect on pitch rotation. As the IC gets higher, the chassis will hit the tire harder, and vice-versa. Obviously a change in the length of the LCAs will correspond to a change the angle which will change the IC. Just remember this rule: Low torque, high RPM motors want more pitch rotation to hook, a high torque low RPM motor will need less pitch rotation to hook.

 

BIG_MODS - I'm not changing wheels, thus the front only needs to clear a 17x8. I have never pushed it hard enough in corners to need a wider front, therefore see no gain, especially since it would just create more drag(road friction). The struts with a coil-over would be lighter, so that seemed the best route for me. I do understand what you're saying about the scrub radius, and that was my sole reason for thinking of switching, but slightly better tire wear/less road pull aren't enough IMO to justify the weight.

Stephen 87 IROC - I do understand why you say this, but I'm a firm believer in the tq arm system. It gives me a lot of leverage to hook my 17's. I could get this from a race style 4-link, but a traction oriented setting would induce rear steer while on the brakes around a corner. I don't push it hard, but I do push it. - I believe in it enough that the 10.5 outlaw car I'm working on will also have it. I've been around the 4-links in 3 other outlaw cars and I'm just not impressed. I realize that much of our problems stem from the small tires with 2000+hp, but I think there's more to be had. - Thanks for the links to the books, I'll have to look into them.

Time2Fly - This I've read and to some extent understand. I've never really measured and calculated all the angles and such involved with the system, but I have a pretty firm grasp on how each component reacts and how to set it to achieve what I want. - That part about rpm power vs bottom end torque makes sense, although I had never thought of it.

I don't see a reason to change the lca length, just wondered what others thought. I didn't think longer would gain anything, and shorter would change angle quicker through suspension cycle. - My current tq arm is about 4-6" shorter than stock and has worked the best with about 6 degrees of down pinion. - A shorter arm would allow me to get back to a better(lesser) pinion angle and still have enough hit to plant the tires. I'm gonna calculate that after I see where the weight ends up. - The floors will be steel up front, but the rest will be aluminum tin. I am also going to hook my sway bar up with heim joints, thus zero "drag" for full drop on drag launches, but still there for cornering. I intend on getting the car down to around 3000lbs with full power access and a/c. This will be hard to find without some sacrifice.

- I'm building it as a very fun "toy". It will be daily driveable and solid performing.

Thanks for the responses, keep them coming!

 

Anti-squat and rollsteer do not remain constant over the range of ride height. Longer LCAs slow down the rate(s) of change in those things as rear ride height changes.


Basically, you want the control arm to be close to horizontal as seen in front view. A case could be made for running them slightly 'uphill' toward the chassis if handling is a priority. Running the chassis end lower produces greater amounts of roll and adversely affects the dynamic camber situation for the outside front tire while cornering (translation: less front lateral grip, more mid-corner and corner exit understeer).


Norm

 

what about the angle of the arms, in relation to the frame rail. - factory the front is inward from the rear, should I change this? If so, more or less offset? I'm not sure what difference it would make.
this I understand, which is why I said I could see no reason to go shorter. - I guess my question is for a street car that sees straightline track use and pushes corners around the back roads, should I lengthen them? If so, how much would you go?

 

other coments or anyone else?

 

Don't ignore your front roll center. It is easy to get it WAY wrong. Programs are cheap. Get one!

Lest you ignore the advice, let me tell you about my friend Hank's Open Wheel Modified. He just put it together in a way that seemed to make sense. The R/C was 1.5" high and 20" to the right. We checked our options. One had it 20" to the left. Another, 34" right, going to 111" right when it rolled. This was with moving the upper frame pivots between two places, 1" apart. Eventually, we moved the left upper frame pivot 1" and the right upper ball joint up a 1/2". The result was 2.5" left that goes to 4.4" right under roll. 2.5" high.

As long as you keep dimensenions the same right and left, you will keep your roll center centered. HOWEVER, you want to make sure your roll center is not 5 feet below the pavement, or 10 feet up in the trees. ALSO, you want to try to avoid having a roll center that moves drastically when the car rolls. Since you are starting with a clean sheet of paper, spend the $75- and know what you are putting together. Stock locations owe a lot to mass production requirements. Small dimensional variations can make BIG geometry changes.

Good Luck.

 

thanks!
- keep the info coming please. I've never done any chassis work other than drag race and off-road(4-link) stuff, so I'm a bit lost.......

Flip 2 - what program(s) would you reccomend?

anyone - books/computer programs on suspension geometry?

 

You need to pick up Carrol Smith's "XXX to win" series of books, "Tune to Win" is probably where you need to start, but don't skimp on the rest of his books they are worth every penny.

 

Performance Trends. You should find them online. If not post. I moved a flyer from one garage pile to another, just this morning.
I have seen programs where you have to re-enter data every time you change wheel width or offset. PT's is not like that. It is very easy to use. It also gives you an easy view of the dynamic workings. You won't need the three-d version. Just the basic works fine.
Carroll Smith is good reading, but a slog for all but the most dyed in the wool racers. On the other hand, doing a whole system, it might be worth all the head scratching.

 

thanks again!

anything and/or anyone else?