Ideal Geometry

[ccracin]

Originally Posted by novanutcase

BTW thanks for your advice on the fire suppresion system. I don't think I ever really thanked you for your advice!

No problem John. Just happy to help. It's not often you can give personal experience with something like a fire system. I hope my experiences in that are are done and I hope all you ever have to do is wax the bottle!

[ccracin]

Originally Posted by fasterpatrick

Very good thread guys, but all I have to add is been there done that. If you what to find a geometry nirvana give up. I spent six months studying countless chassis design books and geometry articles for every type of car imaginable. My head hurt for weeks afterword. What I came up with is a untested compromise of every thing I absorbed. Sorry there are no numbers to give out did not use them. If you want to design a suspension system start at the corners and work inward at ride height, thats the best way I found.
I'll be watching,
Patrick

Patrick,

Awesome build.. The Cobra has been on my "Want To Build" list for a long time. I'll be subscribed to your thread.

I know exactly where you are coming from. I have read and researched for a long time. The Holy Grail is obviously not out there or everyone would have the same setup already. I was hoping to extract some information to help the folks that are caught up in the marketing wars and really don't even know where to start looking to develop the headache we have all had. But after a couple asprin and some time, this suspension thing is alot of fun. It is very satisfying to have conceived and built a chassis that meets or exceeds your personal goals for it.

Later,

[chevyIIpost]

Bump Bump

[ccracin]

Sorry Ted, I am a bit under the weather. I am hoping to keep this going. I hope Matt, JP and others are working on some ideas. I am going to take a stab as well, but frankly until I kick this bug I'm just not up to it. Hopefully some others will jump in.

Later,

[ironworks]

Not that I have any more info then the next guy these are some things that I take into account when setting up some of these suspension numbers.

1. Overall tire height
2. Widest Track width possible with given tire height and ride height of
vehicle, The fender over hang, or how much the tire tucks affects this.
3. Desired Suspension design to be used Mustang II or corvette, ETC
4. Physical contraints of the car, size of car, spindle vs desired rim size.
5. Avaliblity of rack and pinion for proposed narrowed suspension geometry
or will you have to do a custom width rack.
6. If your building you suspenion to an already avalible rack width then more then likely you will have to adjust your suspension track width to optimise. We do this in Solidworks. You must also take into consideration the steering arm height of the spindles and how that rack location will affect engine mounting and Engine dampener clearance.
7. After you have figure out all these different issues, you must decide what specs can and would like to have in your suspension. Do you want a high roll center or a low? What kind of camber gain are you looking for? The length of the upper control arm determines this along with the static angle it is mounted at.
Roll center, upper control arm to lower control arm ratio, instant center, anti-dive, scrub radius, and an million other things that all affect each other. If your using alot of stock parts things like ackerman and King pin inclination and overall spindle height are already determined.




Then once you think you have it all figured out, you find out the suspension will not droop enough to get the back tires out so back to the drawing board so you don't have to drop the rear trans axle to get a tire off.


Interesting thread but my head hurts.

[Beach Cruiser]

I'll Chime in with my .02, I went through this whole exercise a year or so ago, reading everything I could read and asking everyone I could ask. There is no Ideal, just a mixed bag of trade off's. 1st trade off is that you got to get the motor in between there somewhere, second the wheels and tires can't stick outside the fenders (in our version of the sport anyway)

I started with the wheel's and tires I wanted to run, 17x9.5 Z06 wheels. Second was the overal width of the track so I won't rub the fenders. I knew I wanted to run stock Corvette (C5) parts, so the spindles and control arm dimensions were fixed. But to get this config under the front of my camaro it ended up being about 5" narrower than the stock vette geometry. So I had to go back to the drawing board and refigure all the geometry with the new track. I ended up with the roll center about 1.5" above ground. From there I tried to optimize camber gain and minimize bump steer. The Rack location is the hardest part, With some help from Matt at AME we came up with a solution to lower the mounting points on the control arms and get the rack low enough to clear the engine. I also set my engine back about 1.5 inches so that the rack sits in the "sweet" spot behind the balencer and in front of the pan. Every 1/4" helps.

Everything on my suspension is adjustable, lower control arms, upper control arms, tie rod mounts ect... I havn't driven the car yet so I can't give you any real world feedback, But I will say that My Daily Driver Trans AM that I auto x with is a handful on the street in full auto X trim. There are to many inperfections in the road, it wants to dart off in any number of directions and rides like a brick. After every event I dial back down the shocks to a softer setting to make it bearable.

My Two cents, hope it helps.

[Silver69Camaro]

Originally Posted by ironworks

6. If your building you suspenion to an already avalible rack width then more then likely you will have to adjust your suspension track width to optimise. We do this in Solidworks.

Just curious, why not use a program like WinGEO? Solidworks can be very cumbersome for assemblies like that.

[ccracin]

Originally Posted by Silver69Camaro

Just curious, why not use a program like WinGEO? Solidworks can be very cumbersome for assemblies like that.

Roger,

I use and love Solidworks as well, but I agree with Matt. I use specific software that just crunches the geometry numbers. Much quicker to do "What Ifs" IMO. What's your motivation on this one? I'd like to hear you wrote some cool Macro that you are willing to share to automate this process in Solidworks.

[ccracin]

Originally Posted by ironworks

7. After you have figure out all these different issues, you must decide what specs can and would like to have in your suspension. Do you want a high roll center or a low? What kind of camber gain are you looking for? The length of the upper control arm determines this along with the static angle it is mounted at.
Roll center, upper control arm to lower control arm ratio, instant center, anti-dive, scrub radius, and an million other things that all affect each other. If your using alot of stock parts things like ackerman and King pin inclination and overall spindle height are already determined.

Interesting thread but my head hurts.

The initial base for this thread was to try and answer some of these questions or at least give folks some legitimate targets. Alot of guys can choose alot of parts and put them together, but have no idea what the end target should look like. I think we are turning on some light bulbs with regard to this stuff.

Your complete post just gave alot of information that I guarantee guys that spent thousands of dollars on parts never even considered.

My head hurts too, literally I'm still sick! Crap.

Thanks for jumping in Roger, your thoughts are well respected around here.

[ccracin]

Originally Posted by Beach Cruiser

I'll Chime in with my .02, I went through this whole exercise a year or so ago, reading everything I could read and asking everyone I could ask. There is no Ideal, just a mixed bag of trade off's. 1st trade off is that you got to get the motor in between there somewhere, second the wheels and tires can't stick outside the fenders (in our version of the sport anyway)

I started with the wheel's and tires I wanted to run, 17x9.5 Z06 wheels. Second was the overal width of the track so I won't rub the fenders. I knew I wanted to run stock Corvette (C5) parts, so the spindles and control arm dimensions were fixed. But to get this config under the front of my camaro it ended up being about 5" narrower than the stock vette geometry. So I had to go back to the drawing board and refigure all the geometry with the new track. I ended up with the roll center about 1.5" above ground. From there I tried to optimize camber gain and minimize bump steer. The Rack location is the hardest part, With some help from Matt at AME we came up with a solution to lower the mounting points on the control arms and get the rack low enough to clear the engine. I also set my engine back about 1.5 inches so that the rack sits in the "sweet" spot behind the balencer and in front of the pan. Every 1/4" helps.

Everything on my suspension is adjustable, lower control arms, upper control arms, tie rod mounts ect... I havn't driven the car yet so I can't give you any real world feedback, But I will say that My Daily Driver Trans AM that I auto x with is a handful on the street in full auto X trim. There are to many inperfections in the road, it wants to dart off in any number of directions and rides like a brick. After every event I dial back down the shocks to a softer setting to make it bearable.

My Two cents, hope it helps.

Thanks for jumping in. You just solidified some points made earlier. Most people get wide eyed at all these trick race parts and just have to have them. What they don't realize is they may be building the most untamed, kidney busting street car they ever saw. It is no fun. Where I live in South Western PA, the roads are terrible. We are the pothole capital of the country! I have a friend with a tire shop, he just told me last month he replaced 3 factory wheels on SUVs because the owners hit a pothole and bent or broke the wheel. Imagine driving your race car into one of those!

Anyway thanks for the input, this just adds more credibility to what is being said in this thread.

Later,