Ideal Geometry

[parsonsj]

Originally Posted by Matt

If it is a true street car, even with some moderate autocross or lapping, don't get overboard with caster and camber gain; and choosing a suspension frequency "race car" high will make it terrible to drive on real roads. Be realistic.

Amen. Double Amen. Sing it to the heavens, my brotha!!!

Race car suspensions aren't really that enjoyable on the street. No doubt it's cool to take freeway off-ramps at triple their rated speed, but the rest of the time a twitchy, tire-wearing, bone-rattling, NVH on steriods ride will just annoy and tire you out.

Make your shocks adjustable, keep your caster and camber at reasonable levels, don't go for too-quick steering, and use bushings with some compliance.

jp

[parsonsj]

Originally Posted by Matt

For some reason, people always want to build a car around an existing set of wheels

You're right: it's all about making sure the suspension will fit inside the car body. Reasonable choices here make the rest go much better.

jp

ps. And Matt, it was your boss who taught me to choose the wheels and tires first. Art wouldn't make me a chassis until I spec'ed the wheels.

[ccracin]

Guys,

This is exactly what I was hoping for. I have seen the need for this type of info, but didn't know how to go about extracting it. I feel like a lawyer here, asking all these leading questions. I figured if I could get some recognized people in the industry to speak up it would have more credibility than some nobody spouting off.

Matt,

When I said I picked wheels and tires first, I meant for diameter. Then i choose my ride height. It looks like we all tend to agree on this point.

I also agree with issues dealing with driving a race car on the street. When people get it, most don't like it. I guess that is why they call them "Race" cars and "Street" cars. I guarantee I would not want to drive a car that rode like my circle track cars on the street for very long.

Later,

[Silver69Camaro]

Originally Posted by parsonsj

ps. And Matt, it was your boss who taught me to choose the wheels and tires first. Art wouldn't make me a chassis until I spec'ed the wheels.

Yeah, wheels and tires need to be picked when doing our chassis or else we don't know how wide to set the rear clip or what hub track width to use. But when designing a suspension from scratch, only a range of wheel sizes and backspacing is needed...instead of designing the suspension around an existing set, which only puts limitations on the design and will more likely be less than optimum.

Heh, who does Art think he is, anyway? (just kidding!)

[novanutcase]

I'm going to tiptoe through here and make a suggestion.

Why not try and separate both types of suspension? Street and Race. I think this will help focus a lot of questions that everyone would like to hear the answers to within that specific genre. Maybe pick a model of car for street that is typical and run through the process of setting it up. A camaro maybe? Same for a race car although in that case you're not really limited by packaging constraints other than whatever the rulebooks limit you too.

John

[ccracin]

Originally Posted by novanutcase

I'm going to tiptoe through here and make a suggestion.

Why not try and separate both types of suspension? Street and Race. I think this will help focus a lot of questions that everyone would like to hear the answers to within that specific genre. Maybe pick a model of car for street that is typical and run through the process of setting it up. A camaro maybe? Same for a race car although in that case you're not really limited by packaging constraints other than whatever the rulebooks limit you too.

John

Sweet! I'm game. John, that's why you get the big bucks. You're an idea man!

We don't even have to say "Camaro". We could just give a jump off point.

I'll throw this out to what you guys think.

Front Tire diameter: 25.5"
Rear Tire diameter: 26"

Front Track Width: 60"
Rear Track Width: 61"

Wheel Base: 108"

Start here and indicate whether you are setting up a street car or a race car. If this doesn't work, where should we start?

[parsonsj]

Sure ... this could be fun.

But we need more contraints: wheel diameter? what kind of spindle? base chassis? engine placement?

jp

[ccracin]

Originally Posted by parsonsj

Sure ... this could be fun.

But we need more contraints: wheel diameter? what kind of spindle? base chassis? engine placement?

jp

Constraints...we don't need no stinking constraints! Sorry I couldn't resist.

I would say for the race car, you choose with regard to all of those.

For a street car, how about:

18" Wheels

You choose the spindle. That is part of the magic, right? Anyway this seems to be an area of great debate lately.

Custom Chassis with the track width and wheel base i mentioned above. With these dimensions it should be close to alot of cars guys on this site are working on. Right or wrong I don't think in most cases it is cost effective to modify a stock chassis to the extent that some do. JMO

Front Engine. Hmmmmmm how to explain placement. For the street it would have to fit in an engine bay with in reason.

These are just suggestions on my part to keep this going. I am open to any suggestions.

[novanutcase]

Originally Posted by ccracin

Constraints...we don't need no stinking constraints! Sorry I couldn't resist.

I would say for the race car, you choose with regard to all of those.

For a street car, how about:

18" Wheels

You choose the spindle. That is part of the magic, right? Anyway this seems to be an area of great debate lately.

Custom Chassis with the track width and wheel base i mentioned above. With these dimensions it should be close to alot of cars guys on this site are working on. Right or wrong I don't think in most cases it is cost effective to modify a stock chassis to the extent that some do. JMO

Front Engine. Hmmmmmm how to explain placement. For the street it would have to fit in an engine bay with in reason.

These are just suggestions on my part to keep this going. I am open to any suggestions.

There ya go!

I'm sure a lot of guys that don't really understand what a street type suspension is made of will get some great info from this thread. I see a lot of guys setting up race suspensions that will, more than likely, never see the track. This thread can help them differentiate what is considered best for street and what is considered best for race or any mix thereof!

I would think that setting up a race suspension would be easier since most of the components and setups are pretty tried and true for the most part but seeing all these great race parts a lot of times many people get mesmerized by the allure of the part not realizing that for their application it would be better to use something more geared for the street.

I know I'll be reading posts from Matt, John and whoever else chimes in(Norm Peterson, Where are you?!?) VERY CAREFULLY and absorbing as much as I can.

John

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

[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