I posted this in tech but I figured you guys might know--I'm just curious as to how spring/damper rates are chosen for a car. i.e. how the spring rate relates to the corner weight of the car, and how the damper rate (how is that measured?) relates to the springs. Anyone know of any good sites that explain this? Thanks

 

Anyone?

 

You find a car like yours and copy their suspension and tune from there.
Seriously though, I'm not sure there's a given formula. If there was, I'm sure Scott would know.

Oh Scott.......?

 

There are no pat answers. There are some basic rules for individual configurations (FF, FR, RR, etc). Honda's run a rear roll stiffness bias, Porsches often appear to run a front roll stiffness bias. Look at which end lifts.

Spring rate selection is entirely dependent on intended use, and for track use you typically keep stiffening the car untill you don't go any faster (about there you find the car unmanageable as well).

Search for some of my posts about suspension and you'll find some directly relevant data for the G3 chassis.

Selection of damping curves is not simple or formulaic. If you were to hire an expert to help you with this they would likely design a testing program after having borrowed or guessed a starting point based on the collection of experimental data. Even if you buy a set of Moton's you would be reduced to this process assuming you were capable of tuning for optimal speed. If you are not, then something off the shelf will likely be good enough for you (it's been good enough for me to this point). That being the case you might choose something that has demonstrated satisfactory performance in observable competition. I chose Mugen on that basis.

You will discover if you dig deep enough that every vendor sells the superiority of their product. You can beleive each one untill you talk to the next one, and in the end buy the product on the personality of the person selling it. I think that that is dumb. You will not find a simple technical method to make your own evaluation - unless you have a specialized ME and massive current field experience in racing dampers. It's really easy to go to a few high level races and look at what the fast and successful teams are running.

Sorry it's not any easier than that.

Scott, who suggests that you that you can still go pretty fast on vanilla equipment....it's the last few tenths and hundredths that cost so much money and time....which is of course the difference between ho-hum and DAMN!......

 

Well...I'm actually working on a project on a much smaller scale, say ~40 lbs at each wheel, so percentages or formulas would be nice... It stinks because it's too big to use R/C car suspension, but too small to use Kart suspension oh well...

 

Thanks for the great response Scott, I do realise that it isn't a cut-and-dry thing, I just get confused seeing people talking about 300-400lb/in springs when I know the corner weight of the car is way more than that. I guess it will end up being trial and error.

 

In most cases wheel rate is less than spring rate. You can think in terms of static deflection - I'm at 2-3 inches front and less than 1 rear. My front wheel rate is 1/2 to 1/3 corner weight, my rear wheel rate very close to corner weight. We can't get much comfort out of 1 inch of travel out in the real world. We typically can't get the response rate we want out of a car with 5-6 inches of travel out on the track. The relation of corner to wheel rates is one subject to many erroneous ideas. With ever changing tires and dampers many old rules are an impediment to understanding and speed. I understand you're working on a micro car of some sort, but the basics are the same. One aspect of the beauty of competition is that it forces reality on you, and you ahead with it if you're paying attention. Good luck.

Scott, who would have had a hard time picking between VIR and BW this last weekend.....wish I could have done either....



[Modified by RR98ITR, 1:05 PM 12/10/2001]