PDA

View Full Version : Suspension


kozak
02-20-2005, 03:30 PM
Hey whats up i'm new to the forum and this year my team is designing and making a car for 2006 season. My first question is what kinds of rocker ratios do you guys use on your inboard suspension setups.
kozak
02-20-2005, 03:30 PM
Hey whats up i'm new to the forum and this year my team is designing and making a car for 2006 season. My first question is what kinds of rocker ratios do you guys use on your inboard suspension setups.
Lyn Labahn UW-Madison
02-20-2005, 03:38 PM
Your ratio is going to be highly dependent on your shock, and spring rate. We use larger shocks and have a 1 to 1 ratio. You are going to have to pick your shock long before you start asking what ratio to run.
Cement Legs
02-20-2005, 04:48 PM
Our ratios are 3:2 (pushrod:shock). With our spring rate still to be determined once we have accurately quantified the total unsprung mass. We are aiming for about 3" of total travel at the wheel with around 1.5 inches of travel through our shock. Here is some more info that may help...

(from a previous post, cant remember where but it was put up by Denny Tremble)


Definitions:
Motion Ratio (MR) = Wheel Travel / Spring Travel (Carroll Smith)

Installation Ratio (IR) = Spring Travel / Wheel Travel (Milliken)

Ks = spring rate (coil itself)
Kw = effective rate at wheel
Kt = tire spring rate (vertical)
Kr = ride rate (Kw + Kt in series)

Kw = IR^2 * Ks = Ks / (MR^2)

Don't forget the squared term...

1/Kr = 1/Kt + 1/Kw

Natural Frequencies should be around 3Hz (+/- 3 )

Natural Frequency (Hz)= (1/2pi) sqrt((Kw or Kr)/M)

M = quarter car sprung mass

Units need to be consistent; K in newtons per meter or pounds per foot; M in units of kg
or slugs.

What I've found is that if you fill in all of the above blanks your rocker points will be a function of geometry.

I hope that helps... If I screwed something up, let me know.
Frank
02-20-2005, 10:40 PM
http://www.uq.edu.au/fsae/statics.xls
kozak
02-24-2005, 10:39 PM
i'm sure i'll have several more questions after this but MR and IR do you guess thoes?
Denny Trimble
02-24-2005, 10:58 PM
Yup, the answer is 47.
kozak
02-24-2005, 11:15 PM
ha...ha...ha
Denny Trimble
02-25-2005, 02:24 AM
Well, I don't see how it could be simpler. If you know your shock stroke and desired wheel travel, you take one number and divide it by the other.

Can you state your question more clearly? What exactly are you wondering?

Tune to Win by Carroll Smith was a revelation for me when I read it on the flight back from my first competition. Dig in!
Jarrod
02-25-2005, 05:03 AM
it will also be dependent on how adjustable your shocks are, and the range of damping you want at your wheel.