solid rear lower link question

[AutoMods]

i haven't really done much research on the geometry or physics of my solid rear setup. i hear increasing this lower link angle helps anti-squat and tries to lift the body during accel.

i just moved my chassis connection up to a higher hole. so what happens if you have too much angle? this isn't my car but its another fc rx7 with the same rear setup i have

http://i152.photobucket.com/albums/s167/rotary1307cc/2012-09-15_16-08-10_61.jpg

[sparkles]

I thought it was supposed to be parallel with the ground at ride height.

[FiFdYnUtZ]

Are you talking about relocating your lower control arm? Hard to see on my phone

[APPLES355]

I would say it depends on the suspension as a system. Triangulated 4-link is a bit different from a torque arm for example. In the case of a triangulated 4-like it has to do with the angle of the lower arms/upper arms and where the converging line is in relation to the cg and neutral line as to how you car will react off the line. The point where everything converges is you instant center. A torque arm is different as the pivot on the front of the torque arm dictates the instant center.

for handling it a bit different as you are looking for more from your suspension. Leveling your lower control arms will help the car be more neutral from side to side. Try to picture what your rearend might do when truning hard right with the way ryan's control arms sit now. The left rear will compress and pushing the rear back while the right will extend pulling the rear forward producing quite a bit of oversteer going into a corner. By leveling you gain in turning but loose in forward bite.

To really get what ryan is looking for you need to identify you cg and take some measurements to see where your instant center sits and play around until you get it right.

sorry for any mistyping as my phone sucks to type with.

[APPLES355]

There is more to consider around weight, spring rates, etc... as well.

[Scott]

i haven't really done much research on the geometry or physics of my solid rear setup. i hear increasing this lower link angle helps anti-squat and tries to lift the body during accel.

i just moved my chassis connection up to a higher hole. so what happens if you have too much angle? this isn't my car but its another fc rx7 with the same rear setup i have

http://i152.photobucket.com/albums/s167/rotary1307cc/2012-09-15_16-08-10_61.jpg

What Josh said is correct, to add to that, increasing that angle "higher in the front" will give you more anti squat and theoretically more forward bite, it will push the tire down into the ground seperating the tire and chassis when torque is applied.. talking drag racing this should help with initial grip right when you let the clutch out, the trade off is sometimes the car can start bouncing or porpousing down the track as the tire will initially grip then slip then grip again. You will never know if the car likes it or not untill you try it, it helps if you have adjustable shocks to fine tune the movement, you can calm down the bouncing by stiffening the compression so once the chassis seperates it tends to stay that way. Aim your go pro where you can see the tire/chassis/ground all at once and look at that.

making corners this change effects alot more, when your brakes it applies a torque to axle tube, it will try to pull the tire away from the ground making it feel loose, and as the body rolls thru a corner it will actually add rear steer making it feel loose the more body roll you have, and when you start to tip into the throttle it will actually have the same effect as stiffening the spring rate making it loose sidebite on corner exit but this is a all dependant on so many variables none of this may hold true when actually tested.. lol

If you set it parrallel like sparkles said it will feel neutral and throttle input will have the least effect on handling characteristics, if your trying to go fast dont set it like that, but it would be best for beating around on the street.

[Scott]

After looking at the picture if your trying to turn corners you need to revisit the panhard bar all together "assuming that swedged tube with rod ends is actually your panhard bar", its pretty short and at a slight angle at ride height and the center of the bar is not centered in the chassis so I woud assume you will always have a weird handling car untill that is fixed or changed to a different style locating device. Roll center is all messed up

[AutoMods]

thanks guys. i'm just trying to set it up for this weekend so straight line traction is all that matters for now. i brought the car to NL Auto for an alignment and Terry miller said I should move the front of the links up a notch to get more angle. so i did that.

then i talked to another rx7 guy online who made a bracket for even more adjustment holes to lower the bar on the axle/shock side but then he said it ended up giving him too much anti-squat. so i was wondering how do you know how much is too much and what the side effects were. but i know your can read entire books devoted to suspension setup and the answer may not be cut and dry

that bar is not a panhard its part of the watts link, here is a picture

http://members.tripod.com/~grannys/1TASA3500w.jpg


below is my rear setup without the watts link installed
http://members.tripod.com/~grannys/TASA8500w.jpg

[derek072887]

ryan answered first

[APPLES355]

To me that looks close to a torque arm setup with a defined mounting point on the front of the arm. Apparently in those systems the lower control arms do play a role in where the Instant center is located. From what i understand if your instant center is below the neutral line your car will squat and you will have a softer hit on the rear tires. If the IC is above the neutral line you will hit the rear tires harder. As with everything you will just have to play with the setup until the car is happy.

Here is a link to a picture that kind of shows how the IC is found with a torque arm setup. http://www.jonaadland.com/Ta.jpg (http://www.jonaadland.com/Ta.jpg)

The neutral line is measured used both front and rear tire centerlines/contact patches. The front tire you draw a vertical line up until is crosses the perpendicular line Drawn through the CG. Next you draw a line from the centerline/contact patch of the rear tire to the intersection of the CG line and vertical line drawn on the front. This line is the neutral line for your car.

With your car having such a small wheelbase i can see you needing more angle to get the IC where you need it, but without measuring it is just quessing until you find what the car works best with.

I hope this helps.

[AutoMods]

To me that looks close to a torque arm setup with a defined mounting point on the front of the arm.

actually the above picture was missing a couple bars under the torque arm that I think swivel. i always thought your car left the line good for its power level

http://members.tripod.com/~grannys/TASA9500w.jpg

[AutoMods]

recorded some tire movement today. roads were not allowing any sort of a hard launch though

kinda looks like i'm gaining camber but i don't think thats possible, must be tire distortion


http://www.youtube.com/watch?v=EY-E5sB1aek
http://www.youtube.com/watch?v=EY-E5sB1aek

[derek072887]

recorded some tire movement today. roads were not allowing any sort of a hard launch though

kinda looks like i'm gaining camber but i don't think thats possible, must be tire distortion


http://www.youtube.com/watch?v=EY-E5sB1aek
http://www.youtube.com/watch?v=EY-E5sB1aek

do you know how much nitrous you would have used doing that!!!!

[Scott]

Cant tell much from that video with no traction, but it appears to be fairly neutral or even a little bit of seperation, try it and see

[Scott]

do you know how much nitrous you would have used doing that!!!!

None! nitrous makes too power to use on the street, I've tried it, never again.. but then again with a LS he might need it