UCA mounting points, Ride height vs front uca angle (Gen I)

[Tmzand]

Hey,
Kind of resurrecting my hibernating build... Again.

So, looking at relocating mounting points of the front UCA's.
I know a lot of guys slot the holes in the frame tabs to the back to get more static caster. Only by eye balling, I have very low caster w/stock mounting points. So, obviously that's a good approach.
How much? Relocate backwards much as I can until I hit the frame (and then some) I figure.
I also have Crash's lugs at the LCA's to (one benefit of them) be able to push the LCA upright mounting point forward.

Now, going to static camber and camber gain.

So, looking at camber gain, my gut feeling is that I want my UCA's angled slightly up static (inside to out) for cornering? I mean, as the outer side compresses its camber increases with body roll and as the inner side "lifts", the inside camber decreases and lean into the corner as well. Or is the unequal length control arm geometry enough? Is optimum parallel with ground UCA's at full droop? Maybe I need to get a suspension geometry sw package...

I'm thinking moving the UCA mounting points back and slightly lower would be beneficial?
(Depending on selected front ride height and choice of wheel/tire height of course)

I'm guessing caster gain (or anti dive) by angling the UCA mounting points is not really needed/wanted with the "light" front end?

My racecar theory is lacking, but if I'm cutting up the frame I figure I should get some input.

[Roger Reid]

I moved my Gen I front upper mounts 1" rearward for more caster which turned out well.
I tried moving them down for more camber recovery, big mistake. I experimented both up and down from the stock height. The bump steer went crazy. I went back to stock height.

[beeman]

It is interesting that the C5 UCAs are canted, while the GTM's are horizontal...

[Cattrax]

If the rear of the UCA is lower than the front, it should give some anti-dive. Alternately the rear of the LCA can be higher than the front with the same anti-dive effect. IIRC Carroll Smith covered that in Tune To Win. Herb Adams covers it in Chassis Engineering. As you noted you also get Caster Gain. I suppose that is good for the loaded, outside tire but would be caster loss for the inside tire. Our cars are so low I don't know how much weight transfers unless you are running R compound tires.
Keep us posted.
Ken

[crash]

Just so you are aware, one of the things we tried recently on the FFR PDG GTM race car was to move the rear UCA mount to the bottom of the tab to give the car a little more front anti squat. It seems to have worked nicely.

[Cattrax]

Crash,
Are you messing with us? "front anti squat"
Ken

[crash]

Crash,
Are you messing with us? "front anti squat"
Ken

Sorry, anti dive, if you prefer.

[beeman]

So is there a consensus on the most ideal position of the UCA? No one has ever moved the lower control arm, have they (other than Crash - I believe you widened the front track)?

[Fraser D]

I have a Gen 1 and with the use of Mike's shims and adjustable upper control arms from the other handy Forum Mike, have ample adjustability with the stock upper front control arm locations and the FF5 bump steer kit.
Bump steer is < 1/8" over the length of suspension travel @ 45ft using a laser level.
All wheels with the exception of the drivers side rear are very close to the center of the wheel well, (body symmetry issue).
My settings as they were the last time that I was on the rack were, (before I tweaked them some after driving on the track):

[crash]

So is there a consensus on the most ideal position of the UCA? No one has ever moved the lower control arm, have they (other than Crash - I believe you widened the front track)?

Just for clarity, the front LCAs are all stock positions as from FFR, but we changed the mounting points of the rear LCAs to DECREASE the amount of anti squat that is in the car as from FFR. The front UCA mounts we slotted to get more caster and camber, and then placed the rear mount on the bottom of the tab and the front mount on the top of the tab so the front UCAs would provide increased antidive. The rear UCA mounts are all stock, but I made custom adjustable UCAs for the rear. The car is standard 74" wide and with a 100" wheel base, IIRC the exact stock numbers correctly. We use all stock C5/C6 suspension components. This is for the FFR PDG GTM race car only. The GTMR, which is the car I am building from the ground up uses proprietary suspension that has no common parts with an FFR GTM or a C5, other than using C5/C6 ZR1 hubs. It is 78" X 106" at the wheels.

[Tmzand]

Hi again,
Lot's of good info, thanks guys!
Not being a racer/race engineer for the past 20+ years makes one realize the more you learn about suspension geometry theory (and above all, practice) the less you know :-)
And when you think you're ontop of the left front end, there's always total vehicle dynamics and then we go into airflow/downforce...
It's really an interesting subject though, and I guess the best way to learn is to get into it in real time.
To me that means get it close by listening to awesome input and make things adjustable within reason. Also I might need a reality check since it's not a track sprint car I'm after but a track capable street car which complicates or possibly simplifies things.
So, I need to think afor a bit about front UCA mounting points and adjustability. Moving them back is a clear target, I think rotating the pins to Corvette style allowing for shimming and somehow provide adjustability up/down at each point (anti dive) would be great.

From the little that's been revealed I guess Crash's GTMR build front suspension package is a lot more sexy, like this BMW M1 Sauber look alike build that I came across at a Swedish racing forum: So cool!
63575

[beeman]

Pushrod suspension! I'll be impressed if you pull that off. I've toyed with the idea, but the GTM setup seems awfully good, I'd probably really screw up the car :rolleyes:

[Tmzand]

Yeah, and the high strength sheet metal one off uprights fitting within fractions of an inch into the rims selected. Also housing reluctor wheels for like Bosch M4 motorsport abs. Just laser cut pieces of steel engineered into awsomness. In someones garage. I should stop this and take up knitting.
This is going the extra mile to get not only adjustability of camber and caster but scrub, ackerman and what not to where you want it!
Maybe we all should just cut our front ends off and ask for a kit :-)

Oh forgot again, not a racer. Street and track.

/Thomas

[crash]

You mean something like this...

63599

I am just building the jig plates here so they all come out the same, but those are the sheet metal uprights I think you are talking about. Mine have the option of moving brake cooling air THROUGH them so as to help keep the hub with wheel speed sensor cool. :)

[Tmzand]

Aha!
So there's some progress on the GTMR :) Looking good.

Been a bit distracted lately as I started to look into Hp Tuners and Gen IV ecm Virtual VE tuning. You really need to be a jack of all trades with this project...

Going back to the front UCA's, someone here or on 'the other forum' converted to corvette style UCA mounting (pins rotated 90deg.) using 'slugs' with different offsets for mounting point heights. Can't seem to find that thread. I think that's the way to go...

So. Kickoff soon.

[Roger Reid]

If anyone is interested, Joel on the other forum, did some interesting front upper control arms and mounts. He hasn't posted for several years. Here is a link to his photobucket. http://s926.photobucket.com/user/jchracer/media/GTM_20100812007.jpg.html?sort=6&o=153

[Tmzand]

Exactly, Joels inserts with offset holes would be a wish come true! In the frame bracket it could be incorporated but int the UCA using the stock upper arms and pins, not so much. I'm also adapting my mounts for the AFE/Pfadt sperical bearing "bushings". They look very much adopted to be mounted in the C5 stock orientation (very littlte marerial outside of the bolt through mounting holes) if that makes sense.

So, if I was to cut the tabs off and make new mounts attaching the UCA pins @ 90 deg (Corvette original orientation)...
That gives me roughly 18mm from frame to pin mounting surface to play with. (UCA hits frame)

A base mounting plate welded to the frame and bolted in tabs with offset mouting holes for the UCA pin bolts could maybe work?
I've been skething a bit in Onshape CAD.
64227

Don't know if it shows, but I think it could work OK. Need to go to high strength steel for the gripping theads to be stronger than bolt...

[GTM-S]

Tmzand, nice to see you are back on track.
Would be nice to have a fellow GTM on the streets, I think I would take a trip over to you this summer with the GTM, it needs to be some km´s on my car.

Looks like a good solution on the UCA´s, Let me know if you need some help fabricating your parts.

Regards

Thomas

[beeman]

Is this basically what you did Crash? Move the rear part of the A-arm to the bottom of the mounts? Then add a couple of washers underneath the most forward bolt to take the twist out of the front bushing?
I'm really considering moving the upper mounts back 1" for more caster (7ish degrees), should I build this geometry into the "fix"?
Thanks

http://fs5.directupload.net/images/170312/xcqgpgye.jpg

[beeman]

Actually, it looks like you can only move about 1/2" before hitting the spring... Are people moving the upper shock mounts too? Or running inverted shocks? I don't think I'm supposed to run these inverted (black Koni) ?

http://fs5.directupload.net/images/170312/fvtyaju9.jpg

[beeman]

Or can someone just sell me some adjustable UCAs like I have on my roadster? ;)

[Tmzand]

Thomas, yes back at it. Long way to go. Thanks for the offer, and yes please come by if you're in the neighborhood!

Beeman, there is a "Mike" who put a SPC based adjustable Uca kit together. Looks like a great option. Check out Fraser D's track thread on "the other forum". Near the top. Has a couple of pics.

[crash]

Is this basically what you did Crash?

Yep.