Lowering & Geometry Issues

[DBee]

Just got my FRS a few days ago so I haven't had a chance to peek at the rear suspension yet, but I was curious if anyone who lowered their car is suffering from rear camber gain, especially under compression? Or perhaps even additional scrub (changing the angles of control arms even a little can have a nasty effect on instant centers and roll centers).

There are usually a lot of issues that arise from lowering cars but I haven't heard much about this on the FRS even though many are simply throwing new springs on OEM shocks. However, I did notice that Cusco sells a set of lower control arms which are much shorter than stock. A shorter lower ctrl arm with respect to the upper ctrl arm will reduce the amount of camber gain, so maybe it's related, idk.

Edit: by camber gain, I mean gain in NEGATIVE camber. Coordinate systems for suspension are stupid.

[OrbitalEllipses]

Originally Posted by DBee

Just got my FRS a few days ago so I haven't had a chance to peek at the rear suspension yet, but I was curious if anyone who lowered their car is suffering from rear camber gain, especially under compression? Or perhaps even additional scrub (changing the angles of control arms even a little can have a nasty effect on instant centers and roll centers).

There are usually a lot of issues that arise from lowering cars but I haven't heard much about this on the FRS even though many are simply throwing new springs on OEM shocks. However, I did notice that Cusco sells a set of lower control arms which are much shorter than stock. A shorter control arm will reduce the amount of camber gain, so maybe it's related, idk.

Edit: by camber gain, I mean gain in NEGATIVE camber. Coordinate systems for suspension are stupid.

There's a bunch of literature on this, just search any of the lowering spring threads. From my Plebeian knowledge, I know people are seeing a lot more rear negative camber when they lower.

[VAEsprit]

There are always going to be negative effects to lowering without other modifications. My recommendation, go buy "Tune to win" by Carroll Smith. Excellent book for suspension design. You can take some measurements and assumptions about the car and determine the effects yourself.

[DBee]

Originally Posted by VAEsprit

There are always going to be negative effects to lowering without other modifications. My recommendation, go buy "Tune to win" by Carroll Smith. Excellent book for suspension design. You can take some measurements and assumptions about the car and determine the effects yourself.

Thanks, I use Milliken's Race Car Vehicle Dynamics usually, but will do. I was just curious if anyone had first hand experience thus far. There aren't as many people on this forum tracking their cars as I had expected.

[gmookher]

yes go rad the book or atleast do enough reading to get some basics on what and why and how much

this is a good and Valid noob question: this is normal, whats your question how to dial it out on our cars? Do a search on "whiteline camber" and also search lower control arms.

lower you go more camber you get best to double think of your planning hellaflush stances what the camber specs are. Depending on whether yours is a street or track build u will want to correct to set camber to the ideal range, you may be able to use whitlines or you may need those and LCA depending on your drop and goal. I drive to the track. Till I can afford a trailer..trhen its more camber and R compounds. I am running like 1.6 on one side and 2.3 on the other, would like to see both at 1.1 to 1.3ish,to start, then take tire temps, readjust retake temps, and then settle on what i will be fastest with for track use,.. so for me one side needs more correction, other does not as much. Up front aiming for 2.2 for track use up front, maybe more.

You will want to correct caster, and reset toe, too.Perrins got some inserts that do that for lowered cars. I have the H&R bolts from perrin too, will try those before I bust open the bank for LCAs. havent had the car on a rack since the HR bolt install. If you go LCA, the GT specs are nice neat, but I havent formally gone and done a search looking for reviews. JoeBoxer got the SPC ones, and while they dont look very stout, I understand they work fine, and arent as pricey.

[Supermassive]

With my car sitting on KW V3's, I had to dial out a ton of camber when I dropped it, and I'm still sitting at about 2-3 degrees negative. I had to go with adjustable lower control arms in order to allow me to dial it out. I keep hoping someone will make adjustable upper arms but there has been little to no news whatsoever on that front. Dropping the front on KW's isnt too bad but then again I have Vorshlag camber plates installed so I dialed them in before install and messed around with the mounting bolts on the hub carrier to get everything aligned.

So if you drop the car the rear is gonna be your biggest headache, because there is zero camber adjustment with stock components.

I didn't go super low, but I am running 18 inch wheels:


DSC00097 by Supermassive80, on Flickr

[DBee]

Thanks, Supermassive, that's exactly the information I was looking for.

[Supermassive]

Oh here's another pic, that might help a little when you are choosing. You can see my LCA's are almost horizontal, maybe tipping upwards a tiny bit so yeah there's some geometry changes that occur.

[Racecomp Engineering]

If you're reading (and understanding) RCVD, then you're doing okay.

Yes the rear suspension gains negative camber under compression. We're still running around -2 static with our set-up (KW/RCE coilovers, a lot of bushings/replacement arms, 245 michelin pilot super sports). Did some testing at the track and this was a very good solution.

There are replacement arms and Whiteline has a bushing for the rear upper arm that allows camber adjustment. I prefer the WL bushing because it has other advantages, but it is a pain to install.

- Andrew

[VAEsprit]

Originally Posted by DBee

Thanks, I use Milliken's Race Car Vehicle Dynamics usually, but will do. I was just curious if anyone had first hand experience thus far. There aren't as many people on this forum tracking their cars as I had expected.

I didn't realize you had previous experience with suspension design. That's a very good book for design as well. It's a little more in depth and much recommended for anyone interested in suspension design.

[gmookher]

I will be going with these: some built in correction, if the Whiteline bushes dont cut it these get put on next..

[robispec]

well we started with the front and have front lower control arms that correct/ adjust for
camber
track width
anti-dive
roll center
castor
did we leave anything out?
our car is 3" lower than stock
front camber is -3.7
rear is -2.5
when we "fix" the rear camber with the whiteline bushings for the upper control arm we will be able to reduce the front camber to -3 degrees and run the rear at -2 degrees
8 track days and continuing to fin tune this chassis!
picts
Front view
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yes those are louvers to keep the car cool. the stock hood is lighter than any aftermarket hood sofar.
nose to nose
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and
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rear view
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Robi
http://www.ft86club.com/forums/showthread.php?t=24584

[gmookher]

what camber plate are u on up front robi?

[robispec]

Originally Posted by gmookher

what camber plate are u on up front robi?

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