Ideal Geometry

[ccracin]

Well as I have been ready on this site over the past years it seems a large portion of the debate has to do with front end packages. Sub-frames, control arms, spindles, etc. etc. Alot of companies have great marketing practices but never really provide actual data. Others do. So here is my question. What would everyone consider the ideal suspension geometry to be? This is assuming we aren't worried about track width (with in reason) or frame rail width (again we still have to have an engine up front for this exercise). The ride height would have to be reasonable. I guess ideal is also different for different needs. So lets say we break it down to 3 separate areas. Street, Open Track, Auto Cross. I'm really hoping to see some of the heavy hitter chassis guys respond. I love looking at the dynamics of all this. I have read all the standard fair as well as magazine articles. They all tell you how to measure bump steer, ackerman, roll center, etc. But very very few of them actually recommend specs. Some things I would like to see:

Roll center location and migration specs. in dive and roll
Roll center to center of gravity relationship
Caster
Camber
Camber gain per inch of travel
Caster gain per inch of travel
Ackerman for a given steering input
Bump steer ( amount of toe in or out per unit travel)
King Pin angle
Scrub radius
Anti-dive
Ideal amount of body roll to design for at max lateral-g

Have I missed anything or am I full of SH...... on one of the items I listed?

Don't disappoint me folks!

[ccracin]

What's up, no opinions?

[chevyIIpost]

Bump.............. Would love to hear some opinions and debates. This thread/topic is wide open...................

[novanutcase]

I think the reason no one has really responded is:

a) This is such a wide open question that any answer would be both wrong and right.

b) A lot of these guys would be giving away their hard earned secrets. That would be like asking Smokey Yunick how he got his motors to work so well!

John

[ccracin]

Originally Posted by novanutcase

I think the reason no one has really responded is

a) This is such a wide open question that any answer would be both wrong and right.

b) A lot of these guys would be giving away their hard earned secrets. That would be like asking Smokey Yunick how he got his motors to work so well!


John

Hey John,

Thanks for the reply. I agree about it being wide open. That basically is the point. Folks can say why they believe what they are posting is IDEAL! I don' t agree with the secret part. I'm asking for the final readings. In my mind it is like asking Smokey for his opinion on the ideal torque & hp curve for a road course. I'm not asking how to get the curves. Does that make any sense?

Later,

[pro-tour79]

your questions can't realy be answered because those values are different for different vehicles, there is no "one best" and most importantly is the driver's confidance in the seat is what makes a car handle well.

[ccracin]

Originally Posted by pro-tour79

your questions can't realy be answered because those values are different for different vehicles, there is no "one best" and most importantly is the driver's confidance in the seat is what makes a car handle well.

Good suspension geometry is not different for different vehicles per say. My question was for what folks would call ideal without the confines of a particular body style. This comes down to physics and dynamics. The way a suspension system works has nothing to do with what sheet metal is wrapped around it. (Except for how that sheet metal affects weight and balance) So to clear this up a bit more. Lets just say we are all able to build a tube chassis ACME Hot Rod (Think Old Road Runner Cartoons Here!) What would the ideal front geometry be for the 3 areas I listed in the first post? Oh and to some degree I agree with driver skill and confidence, but a confident driver does not make say...........an old Willys Jeep handle "WELL" at Road Atlanta or on an autocross course. But I get your point.

[ccracin]

Maybe I should get this started. These are all guesses on my part to get this going. I am by no means an expert, obviously based on me asking the question. At least these numbers may garner a B... Sh.. or Yeah that will work. Lets see if we can keep this going.

Street
Roll Center location Static +4"
Roll Center Migration In Roll <1" / Degree of Roll
Roll Center Height in Dive and Lift <= The Amount of Dive or Lift
Roll Center to Center of Gravity relationship Short as Possible ** This one is somewhat dependent on the vehicle.
Caster +4 Deg.
Camber -1 Deg
Camber gain per inch of travel 1/2 Deg More Neg. / Inch of Travel
Caster gain per inch of travel 1/4 Deg More Pos. / Inch of Travel
Toe 1/16" In
Ackerman for a given steering input 2 Deg. Per 20 Deg. Of Steering
Bump steer ( amount of toe in or out per unit travel) .015 / Inch Of Travel
King Pin angle 8 Deg.
Scrub radius 1" - 3"
Anti-dive 3 Deg.
Ideal amount of body roll to design for at max lateral-g 3 Deg.

Track
Roll Center location Static +3"
Roll Center Migration In Roll <.75" / Degree of Roll
Roll Center Height in Dive and Lift <= The Amount of Dive or Lift
Roll Center to Center of Gravity relationship Short as Possible ** This one is somewhat dependent on the vehicle.
Caster +5 Deg.
Camber -2.5 Deg
Camber gain per inch of travel 3/4 Deg More Neg. / Inch of Travel
Caster gain per inch of travel 1/4 Deg More Pos. / Inch of Travel
Toe 1/16" In
Ackerman for a given steering input 1 Deg. Per 20 Deg. Of Steering
Bump steer ( amount of toe in or out per unit travel) .015 / Inch Of Travel
King Pin angle 8 Deg.
Scrub radius 0"-1"
Anti-dive 4.5 Deg.
Ideal amount of body roll to design for at max lateral-g 2 Deg.

Auto - X
Roll Center location Static +3"
Roll Center Migration In Roll <.75" / Degree of Roll
Roll Center Height in Dive and Lift <= The Amount of Dive or Lift
Roll Center to Center of Gravity relationship Short as Possible ** This one is somewhat dependent on the vehicle.
Caster +2 Deg.
Camber -3 Deg
Camber gain per inch of travel 1/2 Deg More Neg. / Inch of Travel
Caster gain per inch of travel 1/4 Deg More Pos. / Inch of Travel
Toe 1/16" In
Ackerman for a given steering input 2 Deg. Per 20 Deg. Of Steering
Bump steer ( amount of toe in or out per unit travel) .015 / Inch Of Travel
King Pin angle 8 Deg.
Scrub radius 0"-1"
Anti-dive 4.5 Deg.
Ideal amount of body roll to design for at max lateral-g <2 Deg.

[chevyIIpost]

I would venture to say that anyone on this site understands that there is not going to be One correct answer to each item listed. But there has to be a narrow range of good and a much wider range of bad to the list of items mentioned that started this thread.

Roll center location and migration specs. in dive and roll
Roll center to center of gravity relationship
Caster
Camber
Camber gain per inch of travel
Caster gain per inch of travel
Ackerman for a given steering input
Bump steer ( amount of toe in or out per unit travel)
King Pin angle
Scrub radius
Anti-dive
Ideal amount of body roll to design for at max lateral-g

And even if that range is wide than the discusson and opinions that will follow will be interesting and may educate and enlighten. This is a black magic area to most beginners and as you learn more about suspension design and function you will realise that it is less black magic but requires a whole lot of knowlege and understanding of a very dynamic system. So I hope some of you more educated suspension guys will lift the magic spell and throw out your opinions and points of veiw for the rest of us to learn form.

That Acme Road Atlanta Car could go from having a 1969 camaro front clip and be upgraded to a C6 set up and we discuss what changed and/or improved as a result.

[ccracin]

Thanks for helping with this Ted. You are definitely catching what I am pitching. This thread is meant to educate us all as the discussion builds. Hopefully we will get some takers.