Progressive Springs on my JICs?

[sperry]

Grrr.... that's so far away! I'm already dreading the bumpy ride.

Maybe if I get some progressive springs on the car before then....

[AtomicLabMonkey]

Originally Posted by sperry

Grrr.... that's so far away! I'm already dreading the bumpy ride.

Maybe if I get some progressive springs on the car before then....

I wouldn't get progressive springs if I were you... it'll just make for a non-linear response when you turn the car into a corner. In my opinion, most of the ride quality you feel in a car is dictated by the shock damping, not the spring rates... our race car has pretty stiff linear rate springs on the front and it still has a decent ride down the street.

[sperry]

Originally Posted by AtomicLabMonkey

I wouldn't get progressive springs if I were you... it'll just make for a non-linear response when you turn the car into a corner. In my opinion, most of the ride quality you feel in a car is dictated by the shock damping, not the spring rates... our race car has pretty stiff linear rate springs on the front and it still has a decent ride down the street.

Well, then I need much softer linear springs... because my car's underdamped like a mutha... 'course then I'll be back having a bunch of body roll again...

To be honest, I'm not 100% what's wrong with my suspension. I know that over the small bumps (esp. on the freeway) the car hops around like a biotch. I've tried every which way on the damper adjustment, and the softer I go the more it bounces, so I have to assume it's not overdamped, and I'm actually bouncing on the springs, not the tires. I'd really like a helper spring or a progressive spring that's like 180 to 200lb/in for small bumps that quickly ramps up to 450 on anything but the smallest bumps.

I'll live with the loss of turn-in crispness if it means I can drive the car on the highway for more than an hour without getting so fatigued and sea-sick I need to find a rest-stop. Seriously, I was *spent* after spending 5 hours in the car on Sunday... physically worn out from having to sit in a bumpy car.

I'd even consider some nice soft springs for the off-season if I knew if my dampers went soft enough to work with 'em.

Of course, it could be that my dampers need to be "recharged"... not that I want to spend the money/downtime to send them to JIC to have the gas recharged. I figure, springs are a pretty cheap thing to try out...

[AtomicLabMonkey]

Originally Posted by sperry

To be honest, I'm not 100% what's wrong with my suspension. I know that over the small bumps (esp. on the freeway) the car hops around like a biotch. I've tried every which way on the damper adjustment, and the softer I go the more it bounces, so I have to assume it's not overdamped, and I'm actually bouncing on the springs, not the tires.

What spring rates are you using right now? Did you ever get any shock dyno info on these units?

Does the "bounciness" feel like the entire car is staying level but just moving vertically too much after hitting a bump, or does it feel like the car is pitching - where the back end is still rising as the front is falling?

Is the car noticeably oscillating up & down after hitting the bump (substantially underdamped), does it move & return to ride height within 1 or 2 cycles (somewhere near critical damping), or does it not come back beyond the original ride height point at all after hitting the bump (overdamped)?

Off the top of my head it sounds to me like a shock valving problem. I know we had some problems similar to that in the past with a prototype strut for the Mustangs - too much vertical motion over the regular small bumps in the road, so the car felt like it was jiggling all the time. An adjustment to the low speed damping fixed the problem.

[sperry]

Originally Posted by AtomicLabMonkey

What spring rates are you using right now? Did you ever get any shock dyno info on these units?

Does the "bounciness" feel like the entire car is staying level but just moving vertically too much after hitting a bump, or does it feel like the car is pitching - where the back end is still rising as the front is falling?

Is the car noticeably oscillating up & down after hitting the bump (substantially underdamped), does it move & return to ride height within 1 or 2 cycles (somewhere near critical damping), or does it not come back beyond the original ride height point at all after hitting the bump (overdamped)?

Off the top of my head it sounds to me like a shock valving problem. I know we had some problems similar to that in the past with a prototype strut for the Mustangs - too much vertical motion over the regular small bumps in the road, so the car felt like it was jiggling all the time. An adjustment to the low speed damping fixed the problem.

With the dampers set closer to the soft side of things, the car oscillates on the springs. Small bumps result in the car bouncing a few times, and when those bounces match the ruts in the road at your speed, you quickly run away into rollercoaster land, updownupdownupdownupdownupdownupdown.

Setting the dampers towards the firm side of things, and the car seems to pitch. The front is tossed up by the bump, then as it comes down the rear is tossed up. Match speed with the bumps and it's bucking bronco time! At least in this situation, if the road smooths out a bit, then the car will settle back down. So this is how it's set right now.

What *really* sucks is how the suspension effects steady-state cornering. The car's got great turn in, and very little roll, but I find any little bump in a long corner makes the car oscillate between over- and under-steer. Perhaps that's just the nature of the beast.... I don't really know, since this is my 1st set of coilovers. The fact that the car bounces in steady state cornering does make me think it is valve related, but a new set of dampers from JIC is $260/corner, and I don't see how they'd be different. Springs are like $260 for four, so finding some springs that would better match my driving ability/road conditions to the existing dampers would be more affordable.

Currently the car has 7kg/mm (392lb/in) front springs and 5kg/mm (280lb/in) rears.

If the real solution involves new dampers, then I'm just selling the JICs and getting Nate to build me a custom Koni/Eibach/GC setup.

[AtomicLabMonkey]

Originally Posted by sperry

With the dampers set closer to the soft side of things, the car oscillates on the springs. Small bumps result in the car bouncing a few times, and when those bounces match the ruts in the road at your speed, you quickly run away into rollercoaster land, updownupdownupdownupdownupdownupdown.

Setting the dampers towards the firm side of things, and the car seems to pitch. The front is tossed up by the bump, then as it comes down the rear is tossed up. Match speed with the bumps and it's bucking bronco time! At least in this situation, if the road smooths out a bit, then the car will settle back down. So this is how it's set right now.

What *really* sucks is how the suspension effects steady-state cornering. The car's got great turn in, and very little roll, but I find any little bump in a long corner makes the car oscillate between over- and under-steer. Perhaps that's just the nature of the beast.... I don't really know, since this is my 1st set of coilovers. The fact that the car bounces in steady state cornering does make me think it is valve related, but a new set of dampers from JIC is $260/corner, and I don't see how they'd be different. Springs are like $260 for four, so finding some springs that would better match my driving ability/road conditions to the existing dampers would be more affordable.

I assume you've already tried all the different combinations of damping proportion F/R and it hasn't helped?

Those spring rates sound low enough to get a decent ride out of them. You might try checking how the rates are proportioned front/rear relative to what the OEM rates were, because if they're a different proportion it will change the level ride speed of the car. OEM's tend to design for level ride speeds around what you typically see on the highway. If the rear rate has changed quite a bit relative to the front, it could cause excessive pitching at highway speeds. Just a thought...

It sounds like the low to mid-speed damping could be too stiff, especially in the rear, if it's throwing the car loose even over small bumps in corners. A properly tuned car shouldn't be doing that. Do you know what kind of valving the dampers have - linear, digressive, progressive-digressive, digressive-progressive?

[sperry]

Originally Posted by AtomicLabMonkey

I assume you've already tried all the different combinations of damping proportion F/R and it hasn't helped?

Those spring rates sound low enough to get a decent ride out of them. You might try checking how the rates are proportioned front/rear relative to what the OEM rates were, because if they're a different proportion it will change the level ride speed of the car. OEM's tend to design for level ride speeds around what you typically see on the highway. If the rear rate has changed quite a bit relative to the front, it could cause excessive pitching at highway speeds. Just a thought...

It sounds like the low to mid-speed damping could be too stiff, especially in the rear, if it's throwing the car loose even over small bumps in corners. A properly tuned car shouldn't be doing that. Do you know what kind of valving the dampers have - linear, digressive, progressive-digressive, digressive-progressive?

I've definately screwed around with 'em a lot, but I'm sure I could try is some more. I tried a lot of damping settings early on when my pre-load was wrong on the springs and my ride-height was too low... so there's a chance that something I tried back then might work now that the springs/ride height are better. Plus I still haven't corner-weighted the car properly. I weight it, so I've got the numbers around here somewhere, but I need to get it on the scales, on a level surface, and adjust the corner balance.

As far as specs on the dampers... well, JIC told me they'd have 'em for me before I purchased them, and now they tell me it's "top seceret proprietary data"... So the only way I'll get it is to send 'em off to be dyno'd.

This thread's getting pretty off the original topic.. I'm gonna go split it off.

[AtomicLabMonkey]

Originally Posted by sperry

Plus I still haven't corner-weighted the car properly. I weight it, so I've got the numbers around here somewhere, but I need to get it on the scales, on a level surface, and adjust the corner balance.

As far as specs on the dampers... well, JIC told me they'd have 'em for me before I purchased them, and now they tell me it's "top seceret proprietary data"... So the only way I'll get it is to send 'em off to be dyno'd.

I'd try some different stiffness combos F/R again before ditching the things altogether for another setup.

Corner weight adjustment shouldn't have a noticeable effect on the problems you're talking about, so I wouldn't worry about that as far as this is concerned.

Not surprising that JIC is claiming proprietary... you should dig around and see if there's any data floating around out there from someone else that's dyno'ed the same dampers. You probably won't find anything, but it's still worth a shot...

Is there anyone at JIC worth a shit that you can talk to for some advice/help?

[sperry]

Originally Posted by AtomicLabMonkey

I'd try some different stiffness combos F/R again before ditching the things altogether for another setup.

Corner weight adjustment shouldn't have a noticeable effect on the problems you're talking about, so I wouldn't worry about that as far as this is concerned.

Not surprising that JIC is claiming proprietary... you should dig around and see if there's any data floating around out there from someone else that's dyno'ed the same dampers. You probably won't find anything, but it's still worth a shot...

Is there anyone at JIC worth a shit that you can talk to for some advice/help?

Will do...

The only guys that was at all useful at JIC doesn't work there anymore, but I've picked his brain in the past. Unfortunately he's not running a "stock" JIC setup anymore... IIRC he's up to 10k springs on his car... that guy just likes 'em stiff! :shock:

Nate had some interesting ideas about going stiffer and staying linear. His thinking was that JIC half-assed it when them make the softer US spec coilovers (the JDM versions are much stiffer, esp in the rear). I was under the impression that JIC re-valved the shocks to match the lower spring rates, but there is a chance that they didn't change a thing, so going to the JDM rates would result in a better ride, albiet it with more NVH. 'Course at this point the NVH doesn't bother me... the rodeo bucking does.

[JC]

You are gonna kill the KP? What top mounts do you have?

[sperry]

Originally Posted by JC

You are gonna kill the KP? What top mounts do you have?

I'm trying to come up with a slightly more streetable setup. I've got the JIC pillowball topmounts that come with the coilovers.

[sperry]

Bumpage...

I ordered a used set of 7kg/mm rear springs with 1.6kg/mm tender springs. I figure, since the majority of the bounce is from the rear (as postulated on NASIOC, and backed up by multiple 1st person reports that re-installing stock rear struts all bounce is eliminated), the tenders should cut it down drastically.

Also, many people recommend running equal rates front and rear on the JICs (so now I'll have 7k mains front and rear, which is approx 390lb/in). And if the car is a bit too loose like that, I can always go up to 8k or 9k front springs.

So, basically I'm hoping the rear tenders will eliminate the freeway bounce w/o having to give up linear main rates, or dealing with the turn-in setup delay that occures with progressive front springs.

Either way, the used springs, *with helpers and shipping* were cheaper than getting just a new set of mains from JIC.

If that doesn't work, then it's time to get Nate calculating a matched set of Eibach mains and tenders for me.

BTW: I found this on JIC's japanese website... since I can't read Japanese I don't know what it says. Plus the chart is really tiny. And I don't even know if the US spec dampers match the JDM spec dampers. But, that's the closest I've found to shock dyno data for my FLT-A2s.

[sperry]

One thing to note about the above dyno data... it looks like the "curves" for the bound/rebound are linear with a slope change at 0.1m/s.

Also, it doesn't look like the chart describes how the adjuster changes the curve... is it possible that the adjustment knob only moves the switch-over point between the two slopes (like a brake bias valve)!? If that's the case, then that would explain why the adjustment doesn't seem to have any useful effect on the bouncing from the very small bumps on the freeway...

Someone get Nate or Gary in on this!

[AtomicLabMonkey]

I don't think that linear valving is doing you any favors. The adjusters are probably adjusting the entire curves - but since it's a linear response, shifting the curve up or down isn't going to have much effect on low speed movement by nature. You could change the high speed resistance 500 newtons and only end up with a 50-100 newton change at low to mid speed. A digressive valving would be much more sensitive to adjustment (read: useful) in the low to mid speed range.

I can read the graph, but can't comment much on their damping levels... it's kinda soft compared to what we use on Mustangs, but they're completely different cars... different weights, suspension motion ratios, etc.

[sperry]

Originally Posted by AtomicLabMonkey

I don't think that linear valving is doing you any favors. The adjusters are probably adjusting the entire curves - but since it's a linear response, shifting the curve up or down isn't going to have much effect on low speed movement by nature. You could change the high speed resistance 500 newtons and only end up with a 50-100 newton change at low to mid speed. A digressive valving would be much more sensitive to adjustment (read: useful) in the low to mid speed range.

I can read the graph, but can't comment much on their damping levels... it's kinda soft compared to what we use on Mustangs, but they're completely different cars... different weights, suspension motion ratios, etc.

I was thinking the same thing about the low speed damping. The adjustment definately makes a difference in handling on the autoX course, but no matter what I still hop around on the freeway. I'm hoping that the slow damping is under-damped like I expect, so those soft tender springs in the rear will match the slow bump/rebound better, and stop the hopping around.