Here are some of my findings with the VBP set up. I have experienced the ride harshness, bouncy feeling, and vaulting off the back side of bumps that others have reported.
After driving over the same bumps many times in my TA and several factory Fords, I noticed that going into dips that the front end drops going into the dip on my TA, but the front stays fairly flat over the same dip on the other two cars. Hitting the back side of the dip was down right painful and the car seemed to vault out the back of the dip.
I tried going super soft on compression to try to soften the jolt with no effect. I tried going super stiff on rebound to control the bounce with no effect. By this time I was getting frustrated as I had spent around 1k on a new suspension and high end shocks.
I went back to the basics of a fiberglass spring and remembered that they are generally bad for drag racing on the front as they don't store energy. This keeps the front end from rising on heavy acceleration. This got me thinking that maybe the fiberglass spring doesn't rebound with as much energy as a coil spring and actually needs less rebound control. I felt that I may be on the right path as the suspension did not feel like it was dropping fast enough into dips.
Believing this hypothesis, I surmised that the suspension was bottoming out on the back side of the dip and was hitting hard as the weight of the front end was all doing down into the dip. To test the theory I backed the rebound down to 8 from 10, leaving the compression still at 8 and the ride got better. This seemed to work but it seemed like I was getting bounced all over on rough roads.
I backed it down to 6 R leaving compression alone and the ride got amazing. The nose stays nearly level over dips now. You can actually feel one wheel drop now to accomodate the road. I figured if some was good, more was better, and dropped to 5 R. The ride is amazing. I can visualize all four wheels now dropping to accomodate the road. Impact harshness is as good as my 05 Taurus and Crown Vic. The bouncy feeling is gone. It feels as good as a new car. Bumps are soaked up so much better that most of the rattles are gone (I still have a problem with my windows occassionally, but that is an issue with them).
I think the problem with off the shelf shocks is that they are valved backwards. They are soft on compression and let bumps input way too much into the suspension. The shocks can't keep up the car bounces. People expect some ride harshness from a stiffer spring and figure the problem is on the rebound side and try to go firmer. It doesn't work and the system gets a bad rap.
From my experience and research, I think that a composite spring, at least in the VBP system, is stiffer on compression than rebound and needs a shock to match. Most of the shelf shocks for coil springs are soft on compression and stiff on rebound. This lets to much input in on bumps and doesn't allow enough drop on dips causing a rough ride on almost all occassions.
I'll post more as I keep tuning, but the where I am at now I am stoked. The system is giving me what I hoped for. It is a smooth, highly adjustable, quick responding suspension. Once I get the ride dialed in I can start pushing the handling capabilities.
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