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If your rebound is clicks from softest, then you have too much rebound damping. I know we talked about this before. Rebound damping should be much less than compression damping.

 

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But how? Rebound is from 0 to 24 and for example low compression speed is from 0 to 6 clicks.

Jrz guy said i have to start with correct platform, which is springs rates as start point...

JRZ's adjust backwards from every other shock. Which is why I specifically ask about your settings on your JRZ. I received no instructions on mine, so I emailed JRZ, and only received a 1 page sheet. So then I read a book written by the founder of JRZ.

The rebound adjustment is on top of the shock shaft and is counter-clockwise (viewed from the top) for + rebound damping, and clock-wise for - rebound damping. Too much rebound damping will not let the tire follow the road, and will cause the suspension to jack up with every compression.

Your google+ photo link doesn't work now, but I saw a photo of your car in a corner that showed the inside rear tire nearly off the ground. That with the fact that JRZ shocks adjust backwards, and your lack of grip leads me to believe you probably have too much rebound damping.

The JRZ compression damping is on the remote reservoir knobs, and is also counter-clockwise (viewed from the top) for increasing compression damping, and clock-wise for decreasing compression damping.

You can use compression damping to help increase traction, up to a point, since the higher compression damping will help suspension force the tire into the ground. Too much though will also cause the tire to overheat and slide.

The platform that the JRZ guy mentioned is part spring, part nitrogen spring (pressure in the remote reservoir), and part compression damping. You need springs that hold the car up and resist the aerodynamic down force, and resist large weight transfers with braking/accelerating and roll. But too stiff of a spring will cause the tires to slide too easily, increasing tire temperature too much. A softer spring that can resist most of the weight transfer and aerodynamic forces is better, and then the nitrogen pressure in the remote reservoirs of the shocks is what adds to the "platform". The Nitrogen pressure (up to 350psi) acts on a large piston that works through the compression valving system. So you add nitrogen pressure to adjust the "spring rate" to adjust how the car rolls and pitches with weight transfer. Generally a higher slow compression damping setting helps keep the car from rolling and transferring too much weight, and fast compression rebound lets the tire follow the road and generate grip.

So how much nitrogen pressure do you have in your JRZ remote reservoirs?

and what are your settings for;

1)Rebound damping clicks from fully clockwise?
2)High speed compression damping clicks from fully clockwise?
3)Low speed compression damping clicks from fully clockwise?

 

[Vulcan Grey]

Looking at your old thread.

Looks like you went backwards with your JRZ adjustments.
http://www.lotustalk.com/forums/f3/trying-find-more-grip-much-more-118880/index5.html


Based on what you said starting on page 5 and after. You had also adjusted the compression lower, and then got more roll in corners.

I would suggest you try a very low rebound setting like 3 or 5 clicks from soft (3 or 5 clicks from full clock-wise)

Since these are your adjustment ranges.
- Rebound 0-24
- High speed bump 0-14
- Low speed bump 0-6


I would try your low speed compression nearer the max at 4 or 5 clicks from full soft (4 or 5 clicks from fully clock-wise)

I would try your high speed compression near the max at 11 to 13 clicks from full soft (11 or 13 clicks from fully clock-wise).

Then make small adjustments from there. Increase slow speed damping to decrease weight transfers, make sure to slightly adjust the high speed compression damping lower a click if you increase the low speed damping a few clicks since they are cross related.
Suspension Technical Article - Issue #1

And I would pressurize your remote reservoirs to around 200psi to start. Go up if you have too much roll in corners. Or go lower if your tires are sliding.

 

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This is the photo that I was talking about.

Lifting the inside front here

 

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cant find the mail with the pressure set info but he mentioned its same as usual, but will check again.


here are the last sunday setings :

F 650LBS
HS 8
LS 4
RB18

R 750LBS
HS7
LS3
R16

there is mark on the shocks +or -

The gas pressure in the dampers is 18 bar.

The working range is 12 bar up to 24 bar.

Have you checked that pressure yourself? Or is that from the email?

Your rebound above is still very high, if those are clicks towards+?

 

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I decide to run this time high rebound becouse my rear dampers are too long, so I lift up the car to have better damper movement.
No, this is what jrz replayed.
Yes, clicks are+

Tomorrow will have new dampers, im thinking about spring rates.
650/750 or 600/650?
If i should reduce rebound than I should keep stiffer springs combination i think.
I will also reduce ground clirance to 100 and 110.

Ok , now I think I see why you have been reluctant to lower the rebound damping...

The problem is that people think that higher suspension damping makes the suspension stiffer and less likely to allow the body to roll. Most people also think that less body roll is better, and it is usually perceived as being more comfortable and predictable for the driver if the body doesn't roll.

The problem is that while greater rebound damping does make the suspension stiffer in a way, but not in the way that people think. Rebound damping slows the shock piston from returning after a bump. This means that the tire will not return to the ground after a weight transfer, the tire will want to remain at a fixed position due to both compression and rebound damping settings trying to slow the piston movement in both directions.

So with high rebound damping, once the weight transfers, the rear suspension doesn't extend the tire back towards the ground, so you get a loss of traction in the rear. Then after the weight transfer if the front shocks have high rebound damping, then the front shocks tires won't push back against the ground to help the weight transfer back to the rear for acceleration out of the corner.


A good, easy to understand (I think) example is to look at mountain bike suspension. If you increase rebound damping, then after you push down the front fork of the bike, the suspension will very slowly return to normal height. If you decrease rebound damping, then the suspension will quickly return to normal height after you push it down. When riding a bike, with a high amount of front rebound damping, when you hit a bump and the front suspension compresses, your weight goes forward! Since the front fork is slow to return, and doesn't push your weight back, you end up flipping over the handle bars. With low rebound damping, the front fork pops back up faster, and keeps your weight from continuing over the bars.

Back to the car.
If you try very little rebound damping, then your tires will be able to maintain grip with the ground after a bump or a weight change.

If you want to control the "stiffness" of the suspension, then increase low speed compression damping to prevent large weight transfers that cause the body to roll. Use higher high speed compression to increase grip and reduce it a bit if the ride becomes to harsh or the wheels are being popped of the ground by bumps.

After setting high speed and low speed compression damping, then adjust the rebound upwards to prevent oscillations in the tires and wheels and lower the wheel rate (lower resonant frequency of the system), but always use as little rebound damping as possible.

Then if you need more control of the body roll due to weight transfer, increase the nitrogen pressure in the remote reservoirs. If that is not enough then increase the spring rate.

JRZ usually ships their shocks with rebound and compression set somewhere near the middle, same for everyone. Do not trust what they say for nitrogen pressure, it may change or leak or whatever, you should check it! And buy a pump or pressure gauge like I recommended in your old thread. You can use air for testing, but nitrogen is best for less change with temperature.

 

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also, those dampers have a very think shaft? must make rebound damping interesting?

soften up the damping (although without knowing the characteristics of those JRZ's no idea if you can get there?).

The large piston (and shaft) are part of the JRZ philosophy, according to the book written by the founder Jan Zuijdijk.

The parameters for the new damper design would incorporate:
• Instead of putting the emphasis on damping of the sprung mass, focus on damping the un-sprung mass of the suspension.

• Use an inert gas as additional spring and damping medium in combination with the largest possible working area’s of piston andpiston rod compression damping.

• Produce lift through the use of gas pressure working on the piston rod area.

• Use an external reservoir to accommodate the largest possible gas oil/gas volume.

• Select the largest possible piston rod diameter for optimal fluid displacement and lifting force.

• Make the damping forces adjustable in both rebound and compression.

• Make the damping forces as effective as possible at piston velocities from 0 to 5 cm or 2 inch per second where it counts.
Page 2

• Make components interchangeable between different applications.

• Put emphasis on bright color and industrial design

more here
Vehicle Dynamics and Damping: First Revised Edition - Jan Zuijdijk - Google Books


I'm not sure what JRZ does for the valving of different applications, but I believe they don't revalve for each car... I think they just offer a wide variety of adjustments within each shock... I may be wrong... Seems to me that they are quite different than the Penskes, in that Penske sells you a ton of different valve orifices and shims and you can revalve them yourself. JRZ would rather you have them rebuild the shock and they will consult with you for help with the setup...

JRZ 12 31

An easy to use system, the JRZ 12 31 enables the chassis tuner to achieve the desired mass control and handling with precision. Digressive high speed compression blow off adjustment allows for a stiff compression valving while maintaining smooth response and without losing traction.

The low speed adjustment is a powerful tool that enables the chassis tuner to maximize grip and optimize vehicle balance. The result is a damper that provides ultimate chassis and ride height control with maximum mechanical traction. The JRZ standard large 22 mm piston rod works in concert with the high speed valving to maximize blow off valve response, achieving solid chassis control without using a high spring rate.

To customize track to track setups and tailor the chassis to the driver; the JRZ 12 31 has an adjustment range able to provide damping to spring configurations ranging from 1.5-6Hz on vehicles with moderate to large aerodynamic loads. Even with a large range, each adjustment is designed to be small, even steps giving precision and confidence when making changes. The JRZ 12 31 is here to take you to the next level. Dedicated racing cars with experienced drivers deserve the professional technology JRZ delivers.

With valving designed and innovated by JRZ Suspension Engineering, the JRZ 12 31 is shipped as a custom configuration always tailored to the customer’s needs, and always comes with our world renowned personal service.

 

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The stiction would probably be the smallest effect in terms of the damper characteristics. not really worth worrying about. The shock manufacturers all talk about using DLC (diamond like coatings that are vapor deposited) on the surfaces to reduce friction and heating these days. A larger piston should give a larger bearing surface, and can actually reduce pressure loading of the piston into the journal, making it run more true, while keeping a better oil film.

The internal gas pressure is normal for keeping the fluid from experiencing cavitation. They aren't using the normal gas charge in the mono tube as an "air spring". The Nitrogen pressure in the remote reservoir (up to 300psi) is also what they call a zero rate (or helper) spring. The gas cannot offer any real increase in spring rate since it is compressible. They do use it as a lifting force, part of what they call "platform", where the ~300psi gas pressure is acting on a 46mm diameter piston, and the movement of the piston is restricted by the compression damping (LS & HS) valving. The spring rate remains the same as the coil springs. I'm going from memory here, because a friend borrowed the book.

 

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of course pressurized gas in a piston will be a spring, but the ratio of the metal coil spring to gas "spring" will be large. The gas spring is basically similar to a helper spring under the coil spring. Not a significant fraction of the coil spring. The word I left out would have been "too" compressible.

 

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I guess it depends on whether you think ~5% is significant or not?

 

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no worries.

 

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disagree...

the higher the gas pressure, the more load on the seals, the more friction and stiction.

this is very evident and measurable on dampers, even at (relatively) low gas pressures.

Also, the force resulting from the gas charge is the gas acting on the displaced fluid from the shaft diameter, the size of the piston is irrelevant to this, and with a huge thick shaft like that, 300Psi is going to be significant, as well as I assume that the 300Psi is at damper max extension, with the (small) canisters, what's the pressure at full compression?

my view of charge pressures is that they should be as low as practical so as to resist cavitation of the oil - which in practice means it has to exceed the max pressure of the oil in bump (at max speed), this will obviously be different depending on the fast bump valveing and the size of the piston (bigger piston, lower pressure)

having spent some considerable time playing with this stuff, I can tell you that stiction is a big problem, and as you say, top damper companies all offer low-friction kits, coatings, etc to combat this, others just ignore the problem (due to the costs of talking it) or just build the best they can (ie, the low-friction stuff is standard not an option).

biggest issue on the Elise that shows this up is lack of low-speed mechanical grip, ie, pulling out of low speed corners in a low gear and it being all too easy to spin up the unloaded rear tyre (at which point everybody cries for an LSD).

the actual problem is that with reduced load on the tyre, and corresponding lighter spring load, the dampers stiction/friction become more dominant, preventing the wheel moving to follow the road, no matter how much you back off the damping adjusters.

Now, on a heavier car, this is much less problematic as the spring loads will be proportionaly much higher but the stiction/friction is the same.

a good damper dyno will measure stiction and friction, and having done this to a few different dampers, the difference is staggering, the other thing that stood out was with some dampers this gets' far worse as the damper wears with use, I dyno'ed one that had done a couple of years racing, and it's friction had gone up by more than 3 times (on pulling it apart, the cause would appear to be bore/piston wear leaving a poor surface in the tube that was no longer 'parallel'.

this is one of the reasons externally valved dampers are used, as the gas charge in them only has to deal with cavitation, not any of the damper forces, so the pressures used are trivial (relatively).

I am somewhat surprised they you suggest the valving in the JRZ's is all the same too, unless it's a 4+ way damper, that's going to mean it's probably never going to be right for a car it was not valved for in the first place?

be interesting to get one on a dyno rig and graph it out...

I agree that it would be good to get a JRZ on the shock dyno! I'm about to remove mine to replace all my bushings in my suspension. I only have the double adjustable JRZ Race with remote reservoirs. I might be able to have the local race shop that races the McLaren GT3 cars do a dyno for me...:shrug: worth asking.

I'm not saying I know for sure, and I don't have my book in front of me for reference, but I believe I remember Jan saying that his philosophy is to use a minimum gas charge in the monotube, just enough to stop cavitation. The pressure in the remote reservoir is a different story (the JRZ remotes are of fairly large diameter and capacity). Due to the surface area difference between the front face of the piston and the back face (with the large diameter rod taking up a large fraction of the effective area, the force ratios are different than another similar shock with a smaller piston. As I said, that large diameter piston and rod also have a larger bearing surface making pressure loading smaller than a comparable shock. The friction/stiction should go down, surface wear should go down. The oil film, having more surface area to hold on to, and less pressure loading, should be more evenly spread on the surfaces. Viscosity effects might go up due to the higher surface area, but stiction should be less. IMO

I'm not sure if JRZ customizes the valving and shims for each car/weight/application or not... But their literature suggests that they offer adjustments to suit a wide variety of frequencies... Which brings up one more point about JRZ's philosophy, which is that they are tuning the resonant frequency of the unsprung weight... not the sprung weight! So if that is true, then there isn't that much variance between cars in unsprung weight/wheel rate...

 

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so I will try this Sunday:

F 650LBS
HS 6 (14)
LS 3 ( 6)
RB 6 (24)


R 750LBS

HS 8 (14)
LS 4 (6)
RB 8 (24)

As good of a place as any to start.
If you want more grip or less body roll, adjust HS and LS compression before RB. Then adjust pressure in remote if possible (use a $30 mountain bike pump 300PSI if needed) Amazon.com: RockShox High-Pressure Shock Pump (300 psi max): Sports & Outdoors

Then adjust RB a small amount to damp the wheel vibration, to lower its resonant frequency.

 

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so I will try this Sunday:

F 650LBS
HS 6 (14)
LS 3 ( 6)
RB 6 (24)


R 750LBS

HS 8 (14)
LS 4 (6)
RB 8 (24)

As good of a place as any to start.
If you want more grip or less body roll, adjust HS and LS compression before RB. Then adjust pressure in remote if possible (use a $30 mountain bike pump 300PSI if needed) Amazon.com: RockShox High-Pressure Shock Pump (300 psi max): Sports & Outdoors

Then adjust RB a small amount to damp the wheel vibration, to lower its resonant frequency.

Actually let me rephrase what I said. Those settings are probably better than what you had, but I would start with minimum rebound (though some say not to drive on full soft with JRZ) so lets say start with RB=1.

Here's a good explanation
http://www.penskeshocks.co.uk/downloads/AdjustableTechManual.pdf

Basic Start-up Procedure

The following setup procedures are basic recommendations for reaching an initial starting point using double adjustable Penske Racing Shocks. This procedure is ideal for use on an open test schedule. A race weekend
may not allow enough time. Start by making the compression adjustments as described below, until it feels right, then move to the rebound adjustments.

COMPRESSION
The idea is to set the compression damping forces to suit the bumps in critical areas, such as corners, corner exits and braking zones.
Increasing or lowering cannister pressure (range 150 to 300 psi) can have an influence on support under brak- ing, acceleration, and tire loading on turn in, and on mid-corner grip.
Step 1 - Set the rebound adjuster at full soft. (1 in the case of JRZ)
Step 2 - Starting with the compression setting at full soft, drive a lap then return to increase the bump settings. Continue this process of adding bump control to minimize the upsets until the car becomes harsh, loses tire compliance and traction. At this point you know that you
have gone too far on the compression settings; back off one click.

REBOUND
The idea is to tighten up the car, stabilize the platform and eliminate the floating "Cadillac feeling". This will also reduce the rate of body roll.
Step 1 - With the rebound setting at full soft (1 for JRZ), add clicks of rebound adjustment, then return to continue the process until the car becomes "skittish" or the rear wheels hop under braking. At this point you know you have gone too far on the rebound settings, back off
one flat at a time for final balance.

Once again, this is a basic procedure for finding your initial setup for a given track.

Rebound adjustments are usually indicated by the driver asking for more stability. By increasing low speed damping, stability will be enhanced; decreasing damping will allow more movement in the car, but will result in a
little better tire wear. Also, the amount of rebound can have a great influence on weight transfer. Less front rebound allows weight transfer to the rear under acceleration. Less rebound in the rear allows for a greater amount of weight transfer to the front under braking and turn in.
When a car is over damped in rebound it can pack down in a series of bumps and a driver will recognize this as too stiff and usually will think it is compression damping. Too much rebound can cause lack of grip on cornering. When making a large spring change keep in mind where the rebound adjuster is and do you have enough range to compensate. Sometimes a spring change will bring a better balance to the damping values after the spring change. If the spring/shock combination was balanced, the rule of thumb is a stiffer spring requires lower compression and higher rebound. A softer spring requires higher compression and lower rebound.

 

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Spoke with race shop that runs McLaren GT3 cars... they want $100/hr for 4+ hours to dyno my JRZ's.... To much for curiosity's sake for me

 

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No disagreement there. You are basically saying the exact same thing as JRZ.

For me the stiction is a non issue, just because you can't get a way from it. All hydraulic shocks will have the same issues. A large piston and rod make more sense to me.

The remote reservoir with the nitrogen spring also make sense to me. Having the piston operating through the compression valving rather than an inline air spring like most monotubes, or even worse the twin tube with the air spring infusing into the hydraulic fluid.

When I highlighted the JRZ philosophy of "reduced spring rate" I'm not commenting on your comment about EVO11 needing more spring. There are always varying levels of lesser and more. If JRZ says less spring, they may just mean less than 1500lbf/in...??? My only comment on EVO11's setup has to do with the JRZ adjustments. They were in my opinion, set up wrong and clearly causing his particular issue. Once he changes those, I'm sure he will see improvement! Then he can read what everybody else said about camber, toe, sway bars, wings, and springs...

I actually last adjusted my JRZ while I was on track, and haven't re-adjusted them for the street... I know what you are saying about there shouldn't be a need to adjust them all the time, and most adjustables are a waste for street driving. Many lower adjustables adjust compression and rebound together, or just rebound, which makes the car "stiffer" when you push on it in the lot, but doesn't allow the suspension to work. It just add to the drivers feel of stability by reducing body roll.

Some of the benefit is driver "comfort", not the Cadillac kind of comfort, but the confidence to be able to predict what the chassis and tires are going to be doing at all times. JRZ's thing isn't to totally cater to a drivers desire for minimum body roll, but to control the response of the tires to the ground first, and then to offer some control of body motions to give the driver precise feel and confidence without stiffening the car to the point that it skitters over the ground like a go kart.

 

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err... OK..

let's start with stiction, trust me, it's a big issue, the difference between a good and bad shock is actually huge, not only in terms of dyno measurements, but in actual car performance, to ignore it's effects is really missing a trick (or three).

Yes, we aren't talking about Tokico or Koni.. Mostly talking about Penske (small shaft) or JRZ (large shaft)... Both are excellent shocks. Since all systems will have stiction to some degree, unless you plan to go Maglev... You aren't going to make a big improvement. Both Penske and JRZ use the same remote Nitrogen charge... no variable there.

I also disagree with the JRZ philosophy as you have stated it, dampers are not there to make up for springs, and a remote canister is only there because they failed to package everything into a monotube, having a remote canister on the end of a flexible hose is a massive compromise, which get's even worse when they then put the bump adjusters on the canister, as you are now trying to control the damper on the displaced oil flow, not the main piston (kind of defeats the point of a BIG piston if you then use the shaft displaced fluid flow to control it).

There are other advantages to a remote, like increasing fluid volume, reducing temperatures... better, more precise valving becomes easier to package. JRZ lists many advantages to using the gas spring through valving. Not making up for springs, but supplementing them with another layer of adjust-ability. He's not saying run 200lbf/in springs. He's saying run a spring that is suitable to deal with the aero and dynamic loads, but not so stiff to control all the body motions, that it overloads the tires and increases tire wear and loss of grip.

 

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VG and SS et al,

So let's just assume that you've got a customer running your favorite shocks and you're confident in the hardware geometry, because you set it up. The valving curve is your own, front and rear droop are where you like them, and there's adequate bump travel, etc-- again, hardware you're happy with/designed/etc...

Your driver comes in and says car feels good, but having some understeer in mid corner in addition to some inside rear tire spin in the slow sweeper. Beyond telling the driver to use more diligent throttle application and take a different line through the corner, what do you tweak? You're obviously sure you're not lifting the rear tire since it's your setup and the setup isn't that far off... you're just tweaking at this point to perfect the platform.

What adjustments might you tweak if you have fully adjustable shocks (ie, your hardware) and a front bar. No rear bar...

-Phil

Phil,

you are alluding to essentially a steady state cornering condition where both front and rear lack grip. So, since it's steady state, our high speed damping doesn't have an effect (assuming it's in a suitable range for quick turn in and the more dynamic moments, not totally at some ludicrous setting). So we'd probably want to look at reducing some of the low speed damping front and rear.

 

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total horlicks...
rear bump is not going to affect mid-corner understeer.

and having the toelink mounted off the wishbone does not eliminate bumpsteer.

for an engineer, you seem to have no basic comprehension of kinematics.

There needs to be a "like" button for your post Simon.

 

[Vulcan Grey]

Gents, I'm still nowhere and no time left...

btw after 20 laps my rear and front tires were 40C max ambient was 19C

https://www.youtube.com/watch?v=MNtowOXiuZs

What settings did you try?

That video looks like the car was much more controlled than your previous videos... How did it feel?