Unequal a-arm

[kozak]

Ok on most frames the a-arm mounts are not in the same vertical plain the a-arms attach to the frame at different distances from the centerline of the car. what is the agvantage of this again i forgot, and also what is a good difference in the step size i see some teams running like .5 in and some teams are running like 5 inches different.

[kozak]

Ok on most frames the a-arm mounts are not in the same vertical plain the a-arms attach to the frame at different distances from the centerline of the car. what is the agvantage of this again i forgot, and also what is a good difference in the step size i see some teams running like .5 in and some teams are running like 5 inches different.

[Jonathan D]

Read "Tune to Win" by Carrol Smith.

[fade]

its all about aero advantage. having your upper a arm 4-6 inches longer than your lower will shave at least 2 seconds off your lap time. If i were you though i would read Tune to Win to make sure http://fsae.com/groupee_common/emoticons/icon_smile.gif

[kozak]

Oh you tricky bastard nice try!

[kozak]

ok thanks but what does it do, is it anti dive?

[UTA racer rikki]

kozak,

What I would suggest is getting ahold of some suspension software, like Mitchell's wingeo or something similar and playing around with the points. For one, you'll learn exactly the answer to any question you may have. Secondly, someone telling you the answer doesn't mean you will remember it when it comes time to explain it to someone else or even a design judge.

If I understand what you stated at the beginning of this thread, then anti dive and anti squat is another beast in and of itself. It occurs when your inboard points on each a-arm are at different vertical heights. To clarify, your front upper a-arm's foreward joint is higher than the rearward joint.

At any rate, I think playing alone in a quiet room in front of a computer screen with some suspension software would do you a lot of good and answer a lot of questions for you.

Have you had Kinematics and Dynamics yet???

[kozak]

yeah suspension software would be awesome but i don't have $400 to spend on anything right now. And if you mean statics and dynamics yes i have.

[BStoney]

Kozak,

Erick means Kinematics & Design of Machines from what I understand, (correct me if I'm wrong Erick)...as in 4 bar linkages, and other types...that is the basis for any suspension kinematic design understanding....

[kozak]

ok

[Erik Whoa]

Such great help...

Equal length arms would give no camber change in suspension deflection.

Longer upper, decreased camber in bump. Shorter upper, increased camber.

[Denny Trimble]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Erik Whoa:
Such great help...

Equal length arms would give no camber change in suspension deflection.

Longer upper, decreased camber in bump. Shorter upper, increased camber. </div></BLOCKQUOTE>

Not necessarily; Parallel equal length arms would give no camber change in bump, but nonparallel equal length arms will have camber change.

Unequal length, nonparallel arms give a changing front view swingarm length (FVSA) with bump and roll, i.e. the rate of camber change increases with bump / roll.

[RickyRacer]

If you can get a copy of Race Car Vehicle Dynamics by Milliken. I will just quote him. "The length of the upper control arm in relation to the lower arm adjusts the shape of the camber curve. If they are the same length the camber versus wheel travel curve will be a striaght line. If the upper is longer than the lower, the curve will be convex with its curvature towards positive camber. If the upper is shorter than the lower, the curve will be concave towards negative camber. As the upper arm is made progressivly shorter, the curvature increases."

Ricky
Long Beach,CA

[kozak]

Actually i jus got Racecar vehicle... from our president. so i understand that you want the upper a-arm to be shorter to pull the wheel towards 0 camber or even negative during body roll to keep max contact patch. any ideas for maping that to get a decently good link length i don't have any computer programs so don;t even mention that.

[Marshall Grice]

It's all in the book. Draw it by hand if you don't have a cad program to do it for you. There are some equations in the book that help also. just read it.

[Erik Whoa]

You can go through a bunch of iterations in any CAD package... but since you don't have that, you could make a smaller scale mock up using string as your arms, nails as your inner mount points, and something rigid to mimic your upright. Then you could move the setup through 360 deg. of bump and droop if you so desire.

[kozak]

yeah cad would work i totally forgot about that. i'm just scared that i'm going to make something that will be utter crap.

[Jeff The Pyro]

honestly, we're not trying to be jerks by telling you to read a book... the question you asked is just much, much more complicated than you think. we could give you a simple one sentence answer, but if you just accepted that as "the answer" it would probably just get you into a whole lot of trouble.

[kozak]

i'm just looking for guidance from people who have already made suspensions before. and i will read the book or read certain parts to understand what i need to.

[Cement Legs]

When I first started designing our first suspension system I read all of the chapters from Miliken on Tires, Suspension, Steering, and Steady State Cornering; then I asked some questions. Then I went back and read most of Caroll Smith's Racing Chasis and Suspension Design. Now when I ask question, which are still many, the boys out there with experience dont feel like they are wasting there time teaching me how to do something they spent weeks laboring over. Its not that your 3rd year thermodynamics prefessor minds teaching you what 's' is, but he expects you to know how it works with other variables so when he explains it to you, he wont have to explain all of the underlying theory as well......

[Erik Whoa]

Well... I think most people have no idea what entropy is. http://fsae.com/groupee_common/emoticons/icon_smile.gif