Most liked posts in thread: Thank you Onasled Racing and TSW...

I heart this thread.

 

Throwing in a weight number:

2593 lb with 1/3 tank of gas, driver's seat replaced, harness bar and harnesses in place, rear seat in place. 2003 MCS, no sunroof.

 

Made a table of all the weights.

 

To confirm Mike's numbers:

2597 lbs - rear seats and hardware removed along with tool bag.

2003 MCS without sunroof. Half a tank of gas.

Alan

 

here's a quick easy write-up on motion ratio i did on an mitsu evo board:
Choosing coilover spring rates for your EVO - evolutionm.net

tried to make it easy to understand.

the good part:

The numbers and motion ratios are obviously a little different for the Mini, but the idea is the same. It can help to have a little more rear rate than usual in a FWD car, especially for auto-x. But not everyone likes a hairy oversteering car.

I haven't had time to take too close of a look at the 2005 MCS i just got a month or so ago, so i can't comment on specific rates. It certainly looks like the TSW guys know whats up, and I do like KW.


Oh and hi. I'm Andrew.

 

So if I understand this correctly, the effective spring ratio is affected by its placement in the suspension geometry as related to the length of the control arm? Sort of like the old lever analogy?

 

Does the angle of inclination have an affect as well?

 

In that case it is certainly feasible for higher rate springs in the back even on a car so heavily weight biased towards the front.

Is this the angle of the dangle question?

 

Yup.

- Andrew

 

I am late to this party, but came to the same conclusion this spring. I wish I had found this tread before I got my stuff. TSW sells stuff that actually works and they have excellent support. I installed KW V-3s on my 06 JCW. I haven’t had it on the track yet, but have autocrossed a few times. Going up Hell bender was a blast. The Dragon had two to many cops. Nathan is very good at prompting discussion. A simple way to think about motion ratio is to think about how much the spring/shock compresses for every inch of wheel travel. The two do not compress or travel the same amount. The lever arm analogy used earlier is a good one. Nathan introduced the concept of angle of inclination. I think he is talking about the mounting angle of the spring from vertical. I want to introduce the idea of wheel rate. Ultimately that is what we really want to know. If you know the wheel rate you can compare the handling characteristics of cars with the same suspension. To compare different vehicles you need to go a step further and look at suspension frequency. The single biggest contributor to wheel rate is the motion ratio that is expressed as the distance or length from where the spring/shock attaches to the control arm to the inner pivot point divided by the length of the control arm from the inner pivot to the center of the ball joint. There are two other factors; the affects are real, but a lot less significant. Every type of suspension is made up of more than one link in the vertical plane. A strut is about as simple as it gets. There is an attachment at the top of the strut, and at the inner control arm pivot. Because there is more than one attachment the ark the wheel travels is not the ark created by the length of the control arm. The actual ark or swing arm length is determined in the case of a strut suspension by drawing a line perpendicular to the top of the strut and the center of the inner and outer pivots on the lower control arm. Where the two lines intersect is the instant center. The suspension pivots around an ark determined by the instant center at one end and the center of the tire contact patch at the other. The line connecting the instant center and the center of the tire contact patch is called the swing arm. The swing arm motion ratio is the distance from where the spring attaches to the lower control arm to the instant center divided by the swing arm length. Because on any car I can think of the swing arm length is over 100 inches and the lower control arm is normally 10 to 14 inches there isn’t a big affect. The mounting angle of the shock/spring can have a big affect, but most of the time it is small as well. The angle is defined as the angle the shock/spring is from vertical. The higher the angle the less affect the spring has (for each inch of wheel movement the spring moves less than an inch). This affect is also progressive. (The more the wheel moves up the less affect the spring has because the spring is moving a smaller amount relative to the wheel.) The angle changes as the wheel moves up. If the spring/shock was mounted at 90 degrees to the wheel it would not compress at all. The motion ratio of the spring angle is the Cosine of the angle from vertical. At the angle shock/springs are in any car I can think of except the front of a Lotus super seven, there is little affect. Finally we are on to wheel rate. The wheel rate is defined as the motion ratio of the control arm squared multiplied by the motion rate of the swing arm squared multiplied by the motion ratio of the mounting angle of the spring/shock multiplied by the spring rate. If someone wants to figure all this out there are some very good computer programs that do it for you. You only have to spend hours and hours under the car making a three dimensional (we have only been talking in one dimension, but if you really want to do this there are a bunch of other affects) map of all the suspension and steering pivot points. Then you can spend hours and hours more trying different setups in the computer.