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The Stig
Some say, that I only know two facts about ducks, (both being wrong); and that if I could be bothered, I could solve the "da Vinci Code" in 47 seconds...
All I know is that I'm called "The Stig".
GTM #0081
My car will be out of the paint booth in a week or so. Not long after that I plan on taking it to the alignment shop. In trying to find out what I should tell the guy running the machine I have read so much conflicting info that I don't really no what I should say. I found this in the other forum, is this still close to what you would shoot for in castor and camber adjustments?
That said, I think I would start at these static #s
Front toe 1/8 toe in. No more though.
Front camber -.5 to -.9 degrees. If you put in too much you will get bad tire wear depending upon driving conditions.
Front caster AS MUCH AS YOU CAN GET! Normal car would be 3-5 degrees, but the Vette goes extreme at 10 degrees!! No way you can, or should, get that on a GTM.
Rear toe 1/16 to 1/8 toe in. 1/8 in the rear is alot and if you go too far with toe in or have ANY toe out in the rear the car will want to rear steer all over the place.
Rear camber -.5 to -.9 degrees again depending on tire wear from given driving conditions.
Rear caster is really not an issue because the rear upright should not be going through the travel that caster effects much if at all, so as long as both sides are straight up to a little positive caster, that should be fine, and both sides should match.
Take this into the alignment shop for referrence. If you are having issues with bump steer changes, I believe that FFR sells rack lengthing kits to help with this.
On reading this thread from front to back Ls man says 1/16 front toe out and 1/8-3/32 toe in rear.
While Spytech had his best luck at 3/16 front toe in and 1/16 rear toe in.
Just looking for something that I can print off and hand to the guy and say here.....get it as close to this as possialbe. I don't mind doing the leg work but when info starts to conflit I figured that I should ask instead of guess.
I believe I am the one that wrote that quote in the other forum.
Let me explain what front toe does from my experiences.
If you have a slight bit of toe in you will have a car that tracks straight, but doesn't want to "dive" into the corners. If you put a bit of toe out into the car, which is actually what we do on the race cars, then the turn in to corners is improved. It doesn't make it terribly unstable on the straights, but at the same time, it's no Sunday cruiser either. In other words, both setups are correct depending upon what you are trying to achieve.
Personally, I wouldn't have toe out in my daily driver, hence my recommendations for initial settings, but a slight bit won't "kill you" either. As I have said before, don't be afraid to just try this stuff out. Just be aware that what seems like small changes can have big effects upon how the car handles. Toe can be done by ANY GTM builder with just a couple strings and 4 jack stands, or a simple toe bar that is used for measuring toe in about 60 seconds. This "toe bar" can be made for ZERO $$ from scrap pieces of metal from around the shop. Toe plates, such as you see in Ted's video can also be used, and again are pretty cheap to make.
Now, again, as I have said previously, messing with static numbers is fine, but the proof is in the pudding, and since our suspensions are not a static system, it is also important to consider what the wheels are doing throughout their length of suspension travel.
The two ways to do this are computer modeling or actually measuring at different points in the suspensions travel. At this point, I don't think either has been done with the GTM setup. Joel, aka JCHracer may have though, or possibly David Borden?
Last edited by crash; 06-22-2011 at 05:00 PM.
Thank you Crash for taking the time for a well thought out answer. As you mentioned I will more then likely have to make make minor changes to get the car to handle just like I like it. That I don't mind trying as long as I can get it close from the alignment shop. I have found a guy that I hope will let me put my car on his scales so that I can do the hole weight bias thing like they have done in this wonderful thread. Also I have the bump steer kit installed.
This car will never see the track.
Thanks again and I will post my updates with how these settings work for me. Kris
Last edited by GTMKris; 06-22-2011 at 05:35 PM.
I have computer modeled the GTM/Vette suspension geometry but only as a baseline for the race suspension I am designing. With the stock Vette bushings, the computer model is of very little use....when the tires are loaded up under cornering, braking and acceleration, the tires are not going to point in the same direction as on the alignment rack.
I'm with Crash on this one. For a "well behaved" and stable street car, start with the recommendations of this thread and then experiment until you get the feel you are looking for.
Ciao,
Joel
Working ever so slowly on GTM #269, Twin Turbo SBC, Ricardo, Kit arrived April 5, 2009
http://photobucket.com/JCHRacer_GTM_Build
Joel,
What type of bushings are you and Crash thinking of the keeps the tires/wheels pointed where they should be?
Since the Control arm assemblies are the only Donor parts left on my car, (and the steering column), I may as well consider "re-building" them as well at some point...
BUT... I don't want it to ride like a tank!!!
The Stig
Some say, that I only know two facts about ducks, (both being wrong); and that if I could be bothered, I could solve the "da Vinci Code" in 47 seconds...
All I know is that I'm called "The Stig".
GTM #0081
I don't think you can describe it as "should be", just a compromise. I am going with solid, teflon lined, spherical rod ends or needle/roller bearings at all inboard suspension pick-up points.....I am making all my control arms from scratch. Very little deflection under load but the "ride quality" suffers. Not something I would suggest for a daily driver. My car is intended for track days with occational street use so I can live with the harshness. As a compromise some people replace the soft rubber bushings with a harder plastic (usually urathane) but I dont like that option because they tent to stick if you dont grease them often. Pfadt (sp?), the Corvette racing guy has a spherical replacement kit I believe for the stock Corvette control arms. For a daily driver, I would stay with the Stock Corvette bushings and play with the alignment untill I got something comfortable.
Ciao,
Joel
Working ever so slowly on GTM #269, Twin Turbo SBC, Ricardo, Kit arrived April 5, 2009
http://photobucket.com/JCHRacer_GTM_Build
Ciao,
Joel
Working ever so slowly on GTM #269, Twin Turbo SBC, Ricardo, Kit arrived April 5, 2009
http://photobucket.com/JCHRacer_GTM_Build
Thanks Joel. That's what I've been thinking as well. I don't plan to have this car on the track very often at all. But I definitely want to do whatever I need to make sure that it is stable and handles well (and safely). There are lots of bumps in the roads around Charlotte, and I don't want to end up in someone's flower bed.
For my purposes, I agree that the softer (stock) bushings should be fine. If I find later that I need to, I'll look into replacing them.
The Stig
Some say, that I only know two facts about ducks, (both being wrong); and that if I could be bothered, I could solve the "da Vinci Code" in 47 seconds...
All I know is that I'm called "The Stig".
GTM #0081
No. I think that the donor route is still very valid. Especially where budget & keeping costs down are concerned. In my build, I just found myself making decisions to change one thing and then another, until I got to the point that there wasn't really much left to change.
I absolutely think that it makes sense to use donor cars with these builds though.
The Stig
Some say, that I only know two facts about ducks, (both being wrong); and that if I could be bothered, I could solve the "da Vinci Code" in 47 seconds...
All I know is that I'm called "The Stig".
GTM #0081
I have had good luck with setting the rear bump steer to produce loaded tire toe-in when the car rolls under cornering loads. This combined with static toe-in produces a very "stable" feeling car. The opposite is also true….if the rear loaded tire is experiencing toe-out under cornering loads (either from bushing deflection or bump steer) the car will feel “wickedly unstable”. Maybe someone with a completed car can check it out.
Ciao,
Joel
Working ever so slowly on GTM #269, Twin Turbo SBC, Ricardo, Kit arrived April 5, 2009
http://photobucket.com/JCHRacer_GTM_Build
Ron-
Random question - did you have to compress your springs or anything to get the ride height up to 5" in the rear? I'm at 4.25" right now and I could get maybe one more turn out of the collars on my koni coilovers on the driver's side, and I can't get any more turns on the pass side. If the sleeves didnt spin freely it probably wouldn't be an issue, but as a result I have to figure out a way to compress the springs a bit so I can get those remaining turns.
Spy
Ron may be using a different type of Koni (from the PDG racecar) with different external threads on the body.
Would a spring compressor tool help you preload your spring to get a higher ride height?
Here is a tool from Eastwood.
http://www.eastwood.com/external-coi...ompressor.html
Just an old man with a great hobby
Roger-
Thanks for the feedback. That should work perfect. I just wasn't sure if compressing the spring/preloading it more, is the optimal way of adjusting ride height with the FFR black konis. Other coilovers I have used in the past had 2 collars - one for adjusting the spring perch, and one for lowering/raising the actual sleeve that the perch spins on. Obviously the Konis only have the perch and the sleeve just floats, but wasn't sure if I had overlooked something.
If this comes up as a duplicate, I apologize. I posted this response before and it disappeared.
Roger-
Thanks for the reply. That compressor should be perfect
With the black FFR konis, is adjusting the spring perch collar to preload the springs more the optimal way/actual way of adjusting ride height? On other coils I've had there were 2 collars - one for the perch to preload the spring, and another for the sleeve itself to raise/lower it on the shock body, which raised/lowered the ride height. The koni sleeve just spins freely, so wasn't sure if I was missing something.
Spy
There are 2 grooves and 2 snap rings per shock. My black Koni's are using the upper snap ring as a seat for the threaded sleeve. Do your sleeves go down to the lower groove and is that why you can't get a 5 inch ride height?
Just an old man with a great hobby
The sleeves sit on the 2nd groove of the shock, so there is plenty of thread left on the sleeve (right now the perch is maybe halfway up it?). I just cant turn the perch/collar anymore without turning the sleeve at the same time, since the spring is now constantly pushing down on the collar that I'm trying to turn.
I am not a spring/shock expert, but I know a couple people who are and they all have told me that too much preload on a spring is NOT a good thing. You should up the spring rate when excessive preload is required to get the car where it needs to be.
Perhaps drill a 1/4" hole in the sleeve near the bottom and use a spanner wrench like this one.
http://cgi.ebay.com/ebaymotors/SPI-S...item2c5af5b591
Just an old man with a great hobby
No, I have the same problem as spytech. The car is in the air and wheels at droop and there is still preload on the spring. The front springs are loose when the wheels are at full droop.
GTM #26
Stock LS-6. PHII G50-50, Shane's Louvers, Nordskog Dash, Shaved Door Handles,
David Borden's Aluminum Dash Cover for Nordskog Dash,
Roll Bar Covers -- http://quickracingproducts.com/html/interior.html
Are you guys saying it is difficult to adjust to proper ride height when trying to turn the spring collars by hand, or with a spanner wrench?
GTM #26
Stock LS-6. PHII G50-50, Shane's Louvers, Nordskog Dash, Shaved Door Handles,
David Borden's Aluminum Dash Cover for Nordskog Dash,
Roll Bar Covers -- http://quickracingproducts.com/html/interior.html
I'm glad I'm not the only one with this problem.
I am trying to adjust with the wheels in the air, suspension 'unloaded'. This just seems like a half-assed coilover design, lol.
Last edited by spytech; 06-27-2011 at 11:06 PM.
I had the wheels off tonight to do the FFR shock mount 'safety recall' fix and messed with the shocks a bit, or tried to rather. The driver side has a few more turns left - I could get it to 5" ride height if I wanted to. I turned it up once more so now it sits at 4 5/8" or so. The pass side is immovable, at a hair under 4.5". I just don't get why that side is so much different.
GTM #26
Stock LS-6. PHII G50-50, Shane's Louvers, Nordskog Dash, Shaved Door Handles,
David Borden's Aluminum Dash Cover for Nordskog Dash,
Roll Bar Covers -- http://quickracingproducts.com/html/interior.html
Hey Spytech, the reason you can't tighten the rear springs anymore is that the rear shocks don't have enough rear droop - the shock is topped out. You are pushing against the shock, & without compressing the spring you can't tighten the spring adjuster anymore. These cars need a slightly longer shock in the rear.
The ride height problem in the rear may be an adjustment problem in the front. Try raising the RF 1 or 2 turns, & lowering the LF the same, & see if that doesn't even out the rear.
Ciao,
Joel
Working ever so slowly on GTM #269, Twin Turbo SBC, Ricardo, Kit arrived April 5, 2009
http://photobucket.com/JCHRacer_GTM_Build
Joel- He's saying that he can no longer turn the collars to get the needed height out of the spring. From what I understand, this is while using a spanner wrench. IMHO, this is definitely too much preload. When you have to use spring compressors to get the collars where they need to be, there is too much preload.
If you need to compress the spring 1/4 inch in addtion to using the spanner wrench.....yeh, I agree...too much preload.
Shorter spring but the same rate won't help....you will still need to a compressor. Higher rate spring will solve the preload problem, but change the handling characteristics.
Taller tires?
Ciao,
Joel
Working ever so slowly on GTM #269, Twin Turbo SBC, Ricardo, Kit arrived April 5, 2009
http://photobucket.com/JCHRacer_GTM_Build