Spring rate how progressive?

[Double D]

I have a bussa powered buggy and I'm having problems bottoming out when hitting the bottom of bowls going fast.  The car goes through the whoops pretty good and it rides good the rest of the time; so I think I'm close on valving. (2" fox coil overs)  If I use a 2" longer spring on the bottom and a 2" shorter on top with the same rate as is on there now how much difference will it make?  Maybe go up 50# on the bottom spring  And of course adjust the stop for the spring.

[Punkur67]

Where are your secondary stops at? You would be shocked at how much change it makes moving the secondary nut up.

[BDKW1]

What are your current springs and how much preload do you have on them?

[fabr]

? We need a bit more info to help out any.

[Double D]

I have played with the stops; I started out with setting them just before coil bind on the top spring and have moved them down from there, rear is 14" 150 over 200 front is 10" 200 over 250. I'm pretty close to 60 40 travel on both ends with me in the car with a 150 lb person it goes to around 50 50 but it is just me most of the time.  The front shock is about four inches in from the spindle but the shock lays over allot at the top.  So it's very progressive; the back is pretty good and is 90% at full bump to the trailing arm.  Just looking for a little input if someone has done this before I spend $400 on springs how much difference it makes

[Double D]

forgot.  As far as preload it is not very much If you run the collars down on a fully extended shock and maybe an inch or less of pre load it gives you ride height

[Yummi]

Double D - Welcome to the site. 

Some pictures of the rear end will help with the input.  Post em up. 

[fastcorvairs]

DD

Are you bottoming out on the rear or the front?  Either way if you feel that the valving is right then you should look at upping the spring rate on the bottom springs.  Leave the top one be if it is gong through the whoops OK but stiffen up the bottom ones.  Your top spring will take care of the little stuff but let the bottom ones take up the hard impact stuff.  If the car is not pogoing then the valving is right if it is then the valving mite be off some.  From what you are saying you just need to up the lower springs 50 to 100#. 

[Punkur67]

Your title is asking about progressive rates. You can set your shock angle to be progressive or regressive. It all depends on the shock angle in the travel.

[Double D]

 When you fly the car it lands really smooth; but that lets it go to full droop;I have had it about four feet up in the air and it still lands real smooth.  The problem is in the bottom of a bowl the car is at 50%of it's travel all ready; so it's the last 8 or 9" of travel where I need to slow it down.  @punkur67.  The rear shock is at 90% to the trailing arm at full bump, and it only has 18" of travel; so it's not very regressive through it's travel maybe just the first four inches but this is what I think makes it ride nice.  The last Half of it's travel is close to 90% so that's about as progressive as it gets. @ V.I.P. just asking if going to a longer spring on the bottom will help as it will increase spring weight as it compresses without going up in spring weight on the top of the spring cycle, I get to keep my ride and I don't think it will effect valving to much (hopefully).  But how much difference will 2"  make? Has anyone done this?  I have a car that I use in the desert that is set up this way. I think my shock guy set it up this way to help with bottoming out; but we never talked about why he did it that way and it's the only reason I can think of.  But it weighs four times what this car dos and has Bypasses on it. so no way to compare it.  And it's way easy er to tune.  Lost my shock guy last year so just looking for a little help.

[BDKW1]

Light cars are kind of hard to tune. Generally, what I have found to work better than the dual rate set-up is a long bottom spring with a 5" tender spring on top. Run around a 150 main spring. The tender will be collapsed at ride height. You set ride height with preload. This will really help with bottoming and keeps the car from leaning in corners as much.
With your current set-up, when you move the secondary stops down enough to keep it from bottoming under a constant load, you will develop a rebound in the rear. Progressive spring rate is only good if you have the damping to match. Right now in the rear your going from a 86# initial rate to a 200# rate. Thats a huge jump and really hard to control. Front doesn't matter as much as it just gets hard to steer, your not going to nose wheelie over..........

[Double D]

I have some 90# 4" tenders from another project If I do this I would need a 24" bottom spring To keep from coil binding or am I missing what you are telling me.  I haven't done the math on a 24" spring but that will go up allot on bottom will that not change valving?