FRPP Dynamic Suspension with K-Springs Question?

Norm Peterson

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The adjustment only affects rebound, not bump, so changing the adjustment for street use has no discernable affect on ride quality. At least, that was my experience.
Actually, it can. There is some "cross-talk" between bump and rebound, which I think can be seen in a shock plot (where the bump and rebound traces do not return exactly to zero).

I've found there to be considerable difference in ride quality just between any two of the three general settings I've used so far. Track (firmest), and driving with the wife aboard for more than a short hop (softest but not completely full-soft), and DD for just me (roughly midway between those two). When I swapped to the stiffer springs, ride quality seemed to get more sensitive to damper settings rather than less so.

At least one of the roads between my home track and the hotel that we stay at is rough even at settings 'for her'. Truly miserable at 'Track'.


Norm
 

bujeezus

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The Bilsteins that Vorslag sells will make the car sit 1/2" higher.
Where did you get that info? When I contacted Vorshlag about those, Jason told me their Bilstein's would maintain the same drop with H&R Super Sports as the OEM struts.
 

stevbd

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There is a lot of anecdotal evidence Bilsteins raise the car slightly. On my car with the Vorshlag P spring, Bilsteins, and camber plate combo the car is level and wheel gap is even around the entire circumference of the fender. It sits a little high for my taste and makes my 275/40/18 wheels/tires look a little puny. I think with 19's it would sit and look perfect. But I like the 18's for the track and handling.

Concerning the ride with Bilsteins, I'm no expert but it was explained to me in terms of the speed of the shock movement. Normally the faster the shock has to travel the stiffer it becomes because the oil inside the shock can't get through the internal valve opening fast enough. With Bilsteins (and maybe other shocks?) the internal valve is spring loaded so it "blows off" to a more open position when the pressure of a fast shock movement reaches a certain level. Once the valve opening blows open, the oil can flow through faster and the shock damping doesn't stiffen as dramatically as it otherwise would. Bilstein markets this as "digressive valving." The net effect of all this is the shock feels stiff on low speed suspension movements such as when the car leans in a corner or squats or dives on acceleration or braking. But when the shock has to move really quickly, like over a pothole or expansion joint, it blows off and the impact isn't as harsh.

All this said, I feel like the rear axle is still a little underdamped on high speed impacts. The impact harshness is not bad, but you sometimes still get two suspension cycles instead of just one nice up and down movement. It's WAY better than stock but it's still there a little bit on the really fast sharp bumps. This may be a trade-off for the reduced high speed shock damping.
 

Sky Render

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Actually, it can. There is some "cross-talk" between bump and rebound, which I think can be seen in a shock plot (where the bump and rebound traces do not return exactly to zero).

I've found there to be considerable difference in ride quality just between any two of the three general settings I've used so far. Track (firmest), and driving with the wife aboard for more than a short hop (softest but not completely full-soft), and DD for just me (roughly midway between those two). When I swapped to the stiffer springs, ride quality seemed to get more sensitive to damper settings rather than less so.

At least one of the roads between my home track and the hotel that we stay at is rough even at settings 'for her'. Truly miserable at 'Track'.


Norm

Every Koni Yellow shock plot that I've seen shows that bump is hardly affected at all by the adjustment. A quick Google image search shows this:

koni_yellow_rear.jpg


Very little cross talk.

I originally thought the adjustment screw on the Koni Yellow tightened the entire shock (bound and rebound), but someone showed me this plot a while ago to set me straight. The adjustment only applies to the rebound, with very little effect on the bound.
 
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kcbrown

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The Bilsteins are a popular choice for handling and comfort.

I'm still running Koni Yellows. They handle pretty damn good, but I would not call the ride comfortable.

Interestingly, the ride is quite a lot better than stock. I'm on Boss 302 springs (but switched to the Konis long before I changed the springs). The ride no longer has a harsh quality over bumps. Bilsteins might be better in this regard. Can't say.

The rebound damping setting may play a major role here. I adjusted mine on the basis of the spring rates versus the rebound damping curve from a dyno run of my dampers.
 
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Sky Render

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Those charts still don't show nearly as much movement on the bound as the rebound. But it does show a bit more crosstalk than the ones that I've seen previously. Did you get those plots using a chassis dyno? I'm curious if the real world measurements show more crosstalk than what Koni claims.

Koni's website at least claims that the rebound is adjustable while the bound stays relatively consistent:
http://www.koni-na.com/en-US/NorthAmerica/Products/CARS/Sport-(Yellow)/

KONI_Graph_Sport.aspx
 

kcbrown

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The plots I got should still be around here somewhere. I uploaded them directly to the forum, rather than use an external image site that would have expired them.


Sent from my iPhone using Tapatalk
 

Vorshlag-Fair

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DSC_6115-L.jpg


The Ks, the Ps, the rest of the "alphabet soup" of lowering spring options are all fairly similar: they are all shorter, and still BARELY stiffer relative to the stock springs. They are made to lower the car, which addmitedly looks better than the stock OFFROAD look. ;) That's about it.

DSC_6175a-ride-heights-L.jpg


The main issue with "ride quality" comes from the fact that people couple these with stock length springs. These cars have a finite amount of suspension travel dictate by the strut and shock lengths. From ride height you have "droop" travel down and "bump" travel up. The shock and strut length is the same (95% of all aftermarket struts/shocks are made to the same OEM length) but the spring now let's the car sit 1.0-1.5" lower at ride height. Guess where all of that length came from? IT ALL COMES FROM BUMP.

DSC_8191-L.jpg


One of the main things we look at when lowering cars properly is how much do we shorten the shock or strut housing compared to stock. AST ran into a little problem in 2010 when they made a coilover that was too long - and had too little stroke. We found this out because when we lowered the car the 2" we normally shoot for with coilovers the rear shock would bottom. It RAN OUT OF BUMP TRAVEL. When you do that the spring rate goes INFINTE and the suspension crashes down on the bump stops. BAM! Ride quality suffers - this is what people on lowering springs usually complain about.

DSCN1414-L.jpg


The image above is what we want to see... the S550 OEM rear shock at bottom is shown next to a 2" shorter MCS RR2 remote double. It has much shorter than stock to gain some of that bump travel back when the ride height is lowered. The total shock travel usually goes down a bit, but the relative amounts of bump to rebound remain the same. When we design a shock/strut length we shoot for 3/5ths travel in bump and 2/5ths travel in rebound... because running out of bump is a LOT more painful and detrimental than "topping out" a shock when you run out of rebound.

IMG_0515-L.jpg


How do we fix this? Well for the most part - avoid lowering springs with OEM length struts and shocks. We found one S197 Bilstein that was 1.5" shorter than stock, so we made our "Street Pro" suspension kit use these. They've been out of stock for 6 months, maybe 3 more to go... but "that's Bilstein". Otherwise look for a quality coilover kit. :)

Cheers,

The
 

Vorshlag-Fair

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Great information. Is there a way to get notified when the shorter bilsteins arrive? I'll check out your website.

Yea, as soon as we "turn them back on" we will blast it out there. Its a lot of Bilstein entries, and they are ALL out of stock. :(
 

Senna1

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Those plots might actually be kc's.

The plots I got should still be around here somewhere.
Those look like yours, I distinctly remember being interested to see the OE TP dampers next to the Konis, and grateful you got them done (so, thanks again). The hysteresis in the Konis surprised me too...

Do you happen to remember if the place you had dyno them did just the 10 in/sec CvP, or did they give you a full PvP sweep?
 

kcbrown

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Those look like yours, I distinctly remember being interested to see the OE TP dampers next to the Konis, and grateful you got them done (so, thanks again). The hysteresis in the Konis surprised me too...

Do you happen to remember if the place you had dyno them did just the 10 in/sec CvP, or did they give you a full PvP sweep?

It’s been long enough that I don’t remember those details at all. I recall that I uploaded the raw files I got from them as well, so if you can find the messages in question, you might be able to determine the answer directly.
 

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