The Project Pad

thats some cool stuff. If you get the geometry worked out I might have to hop on that bandwagon and make up some stuff myself...

Very cool! Visual aids reallyed helped me grasp things here. I can't wait to see where this is going! :woowoo:

You might want to download a copy of suspension analyzer to try for 30 days...While, from eyeballing there, it doesn't look bad...there's a lot more to suspension than camber curves and it's really pretty important to figure it out . The software helps out a bunch with that, especially if you've already measured everything out.

Sam

PxTx wrote:Very cool! Visual aids reallyed helped me grasp things here. I can't wait to see where this is going! :woowoo:

yeah, me too! i can picture a certain amount of stuff in my head, but this helps bring the concepts together.



and yes sam! i actually downloaded the trial of that program last night. i need to get a bunch more measurements to work with it 8)

here's the vid...

Yeah, the LCA mount needs to go up, and the upper arm needs to be nice and long...otherwise your roll centers get very curious ^_^.

Sam

ok, stock 4kq geometry... with a 4.02" roll center, and camber gain of -.44*



2" lowered 4kq... with a -.35" roll center and camber gain of -.22*



5.5" UCA with all stock location lower control arm, and spindle, just adding the upper control arm... roll center of 9.85", and camber gain of -3.32*



8" UCA, with LCA inner mount point moved up 1". puts the roll center back at 4.61", with a camber gain of -1.86*



i'm going bed, yikes my head hurts. but i do gather that the last scenario is a pretty ok one...

D3R3K-

This will look good on your resume... proficiency in CAD*

*Cardboard Aided Design... 8)

Upper control arm looks better, but is still way too steep in that last one. How does the bumpsteer look with that?

Sam

WAUG0806 wrote:D3R3K-

This will look good on your resume... proficiency in CAD*

*Cardboard Aided Design... 8)

looks like it works nicely

derek, i know this is going to sound kind of silly, but take a look at RC cars. the hobby quality on-road ones. the ones im thinking of are referred to as "touring cars" theyre 4wd on-road sedans. they have a lower H-arm with an adjustable camber link. it seems like they are the closest scale thing to what you're trying to accomplish. check out the Team Associated TC5 or the Team Losi XXX-S. they have very little camber angle when compressed.

i even have some schematics from my old off-road truck i might be able to find.

the CG is nowhere even close to the same though. i believe that if i don't have proper camber gains for my heavy car, the tires will just roll over hard on the sidewalls... if i'm wrong, someone feel free to point it out.

you need to be carefull to have similar camber gain front to rear. If the front gains much more camber then the rear the car will have extreme oversteer that comes on very suddenly. Your actually better off to start with more static camber in the front but have the rear gain more as it travels. This allows a nice crisp turn-in under braking but with a bit of mid-corner and exit understeer that allows you to get on the power and steer with the throttle.
Spring rates and swaybars can mask what the camber curve is doing to a car's handling but only to a point. If you're going to re-engineer it would be very helpful to be able to adjust your pick-up points later on after you have had a chance to explore the car's performance.
Also a higher roll center is not a bad thing, if increases the roll-stiffness by decreasing the roll-couple. Almost all open-wheeled racers do not use swaybars because the roll-center is close to the center of the wheel.

Sorry if this is all review but I've talked with some pretty knowledgeable guys about suspension design.
Cheers,
Grant

hmm, well, with the natural heavy understeering of these chassis, wouldn't it be good to do that and have the rear setup to be able to have just as much camber gain? i want to make the car fairly neutral with a touch of oversteer. i don't want a drift car, i want one that i can come out of corners hard throttle to the floor and let me point it in the right direction haha.

eitherway, this suspension analyzer thing is COOL. i figured out how to animate the system, and my first setup is out the window...lol. 3" of toe change in 2" of suspension compression it's tricky to work with because with the steering rack where it is, there's only so many places to try and stick a steering arm...

i'll keep at it though. one of my ideas has panned out nicely for the upper and lower control arms getting closer in length and not making a huge mess out of the geometry.

The camber change will effect the handling bias of the car in ways which could make it very hard to control, forgiveness often makes for a faster car.
For instance in MkIV Golfs (which is what I know best), going with a set-up that allows lots of camber gain in the front can make them very unpredictable under braking. Especially if you happen to have to brake and change line mid-corner, having a car with more camber in the front with a stiff rear can make the car rotate like mad under braking. Which is fine if your autocrossing, but a bit too unpredictable for track events and street driving where you have to be able to avoid collision.
If your trying to get it to stay in line on the way out of the corner perhaps spending the cash on a high-bias center diff is a better, safer option then re-engineering the suspension.
Also look for camber gain through increased castor. This allows you to run responsible amounts of static camber both front and rear but also lets you dial in more front camber if the front starts slipping by just steering a little more into the turn. Most of the new VW/Audi offerings are going high-castor because it is good for safety, grip and predicability.

With a high-castor set-up it will feel like the front is trying to let-go but as you add more steering lock it grabs even harder. How they do this is with very little steering input the rear has more camber than the front and so the front tires begin to roll over first causing something called "camber steer" which feels like understeer but really isn't because the tires have not lost grip. You feel this as a small pull to the outside of the corner which you correct for with some more steering input, which with the high-castor also gets you more camber, you get more grip in return and you make it nicely around the corner.

So in short, perhaps just adding some more castor will get you all the extra camber you need without wearing the insides of your tires down to belts. The other benefit to reduced static camber is better traction under power.
Cheers,
Grant

ahh, yeah. i forgot to mention that i do know to look for negative camber gains through castor... right now i've got a feasible (read buildable) setup that has

1.2degree negative camber gain at 1" of dive (max -3.6 degrees @2.5" compression on the outside tire, -2.2degrees on the inside tire ),
only .8 degree of toe in gain at 2.5" of compression (which is better than stock mcpherson setup @ .11).
roll center is 3.97" (under 2.5" compression it goes to -.54")
5.7 degrees of static castor (7degrees @2.5")


2.5" is my target compression and i plan to have that my max compression.


do you have any hard #'s of your experience with the MKIV's?

Its pretty hard to roll 285x30x18 race slicks on 9.5" rims

This should give you an idea of how a MK4 is set-up. This of course doesn't take into account camber gain through castor. Here is a diagram of the difference in camber gain vs. steering angle of the MK4 Golf vs. Audi TT steering knuckles. Many people swap these on to the Golf in an effort to get better camber curves:



The thing with this is that because there is more camber gain the tire doesn't loose camber which creates that "camber steer" I was talking about earlier. Which is a mixed bag really. Because the tire has negative camber it's gripping better but because it doesn't roll onto it's side it won't give you much clue as to when it is about to let go. With higher camber comes more grip, but it also means that when the grip is lost it is much more sudden and difficult to recover from. But with high-castor a lots of grip is usually fixed but just cranking in a bit more steering.

Cheers,
Grant

Sounds like you're becoming a suspension guru Derek, but take note that going to a McStrut car for camber gain numbers isn't exactly what you want to go for when you have the ability to make your own SLA setup :woowoo: . Sounds like you're getting some really reasonable numbers now . Are you planning on doing front and rear, or only front?

Sam

McStrut sounds like something you'd get from McDonald's Auto Center.

"yea i'd like a McStrut with cheese and a side of fries..."

As a performance suspension, McPhersons are about as good for a car as eating two #4 extra value meals a day is for your gut.

Sam

once again from my experience with RC, maybe you could mount the lower portion of the coilover on the a-arm and use a parallelogram camber link setup.

i'm not sure how full size performance suspension works.

tricky with the axle in the way, and all

SeStone wrote:Sounds like you're becoming a suspension guru Derek, but take note that going to a McStrut car for camber gain numbers isn't exactly what you want to go for when you have the ability to make your own SLA setup :woowoo: . Sounds like you're getting some really reasonable numbers now . Are you planning on doing front and rear, or only front?

Sam

i dunno about guru, but i'm doing my best to learn what it's gonna take to make this work... 10" rims under the stock sheetmetal or bust! haha. who knows, if it all pans out, there might be room for 11"er's down the road

i have some used 265's on the way for when i go back to CA so i can mount them on the rims and hence go forth to the next step. since i have to take certain steps in order, i think the new front subframe will be in order first, and the 5x130 converted hubs and then i can get into the gritty upper control arm mounts and shocks.

i definitely plan to make stuff adjustable once it's in the car. since i can play with the mounting points on this program, it would give me a good range of where to place those mounting points.


and the rear can be converted without as much hassle as the front since there's not really any steering to speak of. that just really throws a wrench in the simplicity of the whole program

ok, i think i'm getting somewhere!

this last revision is getting me these #'s...

static 11.5* negative castor
dynamic 12.6* negative castor

static camber at 0
1.7* camber under 2.5" straight up and down compression
outside wheel progresses to -7.5* at full lock under 2.5" of suspension compression
inside wheel gains +3.7* at full lock under 2.5" compression

toe changes are .20" toe in under 1" of dive,
or 1.1* of toe in at 2.5" compression
and 2* of toe out at 2.5" above ride height, which as far as i can tell, translates into a littl toe out under hard cornering. in conjuction with the castor and camber settings, the inside tire is getting 2+ degrees of positive camber keeping the tire flatter instead of just dragging the inside edge along the ground and wearing it down to the cords.





i also did a little fiddling around with the rear suspension as it's much simpler

2.5* negative camber under 2.5" travel
-1.3" roll center which should help with understeer (higher roll center in the rear promotes understeer)






if anyone see's any major flaws, i'd really love some input. otherwise i think i'm the right track here and i'll start gathering some parts soon to let the building commence