Originally Posted by lakesmod
I am cutting a lief spring in half to make a 1/4 elliptical spring.
The lief spring is rated @ 1000 lbs. Buy cutting it in half will the 1/4 spring be rated @ 2000 lbs since it is shorter therefor stronger?
The original rate of the spring was 500lb/in. The new rate for each spring half is 250lb/in. When you use two halves as you've shown above, the combined rate will be 500lb/in (as if you hadn't cut the spring at all). All you are effectively doing by cutting the spring is rearranging it. Also important to note is that your suspension geometry produces a motion ratio of 1 since the tire moves with the end of the spring (as opposed to on a control arm where the spring moves less than the tire).
For your 2,400lb vehicle, this is a fairly high spring rate. What I'm about to type up is based on handling theory (specifically ride frequencies) and some rules of thumb. For more info read these articles: http://www.rqriley.com/suspensn.htm
Let's assume the vehicle weighs 2,400lb and has near perfect weight distribution, so 600lb on each wheel. With a 500lb/in rate, your ride frequency is around 172CPM or 2.8hz. That is pretty dang stiff.
Here are some typical ranges I have read in literature:
Passenger cars: 30-90CPM (0.5-1.5hz)
Performance/racing: 90-120CPM (1.5-2.0hz)
I don't know if you're racing or cruising or both, but I'll suggest you are building a performance-minded vehicle and have some tolerance for a rough/stiff ride and want to target around 120CPM or 2hz. Again assuming 600lb on each wheel, to get 120CPM you would need a spring rate of a mere 250lb/in.
. You can obtain this by cutting a 250lb/in leaf spring in half and using both halves.
Furthermore, you may want to design your suspension for a "flat ride" response. The idea of this is to make the rear suspension stiffer so that after your front hits a bump, the rear can bounce faster when it hits the bump so it can catch up with the front and the vehicle pitches less. A decent rule of thumb that I've heard is around a 10% different in front to rear, so in your case you could do 225F/250R or 250F/275R.