rodgling
|
 posted on 12/12/11 at 03:12 PM |
|
|
dual rate / progressive springs
As a way of improving the ride & handling, I'm considering dual rate springs at the moment. The intention would be to have them so that I
get a small amount of travel at the combined rate (maybe 10mm?) before the softer bit of the spring goes coil bound and I get the rate of the stiffer
spring. Hopefully, this would give me a soft ride over small bumps but good body control in roll.
I'm getting good comfort from 350 lb springs at the front (yes, my car is a little lardy at around 670 kg unsprung with driver), so I was
thinking that a dual rate of about 350/550 (i.e. combined rate of 220 lb/in) will feel very forgiving over bumps but will control roll very well after
the initial soft travel. The downside might be that it won't respond well to mid-corner bumps since the soft bit will be coil bound already, but
we'll see.
Anyway, has anyone tried this and got any advice? I'm particularly interested in the amount of travel I should allow at the combined rate.
|
|
|
|
|
MikeRJ
|
| posted on 12/12/11 at 03:30 PM |
|
|
Dual rate or progressive rate springs are a compromise e.g. which spring rate are you going to valve the damper for?
How much travel will you allow for the lower rate, since if only a small amount then bumps aren't going to be absorbed well, but if a larger
amount the roll will be unaffected.
Have you considered an anti-roll bar to improve body control?
|
|
|
rodgling
|
| posted on 12/12/11 at 03:43 PM |
|
|
Well, if I assume the wheels are about 130 cm apart, then 1 cm of "soft" travel would mean that the first 0.44 degrees of roll would be
soft, and after that it will be firm - so I think that would probably be pretty acceptable for both absorbing small bumps without overly compromising
roll. 25 mm would correspond to 1 degree of "soft" roll, again not too bad. So I think this isn't a big problem.
It's true about the damper valving being a compromise, short of getting dampers with separate fast and slow bump adjust. Sadly I don't
think my wallet is up to the job so it would have to be a compromise.
An anti-roll bar is probably the more traditional way of getting a second spring rate involved, and obviously it has the advantage of only doing
anything in roll. It's certainly an option but I guess I'm just interested in exploring the dual spring rate option. Certainly Caterham
use this on some of their cars so it clearly has something to offer.
|
|
|
ffrgtm
|
| posted on 12/12/11 at 09:04 PM |
|
|
You're better off getting 3-way dampers. It isn't really the springs that cause a rough ride... it's damping of the springs. Springs
don't do anything but hold the friggen car off the ground (and the split between f/r contributes to the roll stiffness gradient... understeer or
oversteer steady state).
Get some nice dampers that have low speed (realize we are talking about damper piston speed, not vehicle speed) valving (you want this stiff to
control body roll) and high speed valving (this is where you control bumps... so slightly softer).
Progressive springs seriously blow.... they belong on honda civics with aluminum wings.
|
|
|
daniel mason
|
| posted on 12/12/11 at 09:38 PM |
|
|
A quick visit to matt at procomp would probably sort out all your issues. And I'd imagine you'd save yourself the cost of new dampers or
springs. Everyone highly recommends him and I'll be going there In The spring to get mine sorted
[Edited on 12/12/11 by daniel mason]
|
|
|
rodgling
|
| posted on 12/12/11 at 09:42 PM |
|
|
Thanks all for the input. The dual-rate springs I had (an opportunistic ebay find) don't have the soft bit quite long enough for my car, so it
would be coil bound after about 1mm, leaving the car much too stiff. Old ones back for now then, I'll have a think about where to go next with
it.
|
|
|
loggyboy
|
| posted on 12/12/11 at 10:04 PM |
|
|
Try softer springs but use adjustable dampers. I found my single adjustables on my tintop could make a massive difference with the odd tweek for road
and track/comp use.
|
|
|
britishtrident
|
| posted on 13/12/11 at 07:08 AM |
|
|
On the best course on the front would be get the damper settings looked at + softer but longer springs (more pre-load to retain existing ride height)
) and fit a front anti-roll bar to restore the front roll stiffness. Generally the rule of thumb is don't go overboard on anti-roll bar
stiffness any anti-roll bat should be soft enough not to interfere with the working of the springs.
At the rear initially at least I would only advise changing the damper setting as rear anti-roll bars can reduce traction on all but perfect
surfaces, if a rear bar is fitted it should (normally) contribute much less roll stiffness than a front anti-roll bar.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
|
|
|
