Vulcan Grey· Registered
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.
But how? Rebound is from 0 to 24 and for example low compression speed is from 0 to 6 clicks.
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.Jrz guy said i have to start with correct platform, which is springs rates as start point...
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 :
there is mark on the shocks +or -
Have you checked that pressure yourself? Or is that from the email?The gas pressure in the dampers is 18 bar.
The working range is 12 bar up to 24 bar.
Ok , now I think I see why you have been reluctant to lower the rebound damping...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.
The large piston (and shaft) are part of the JRZ philosophy, according to the book written by the founder Jan Zuijdijk.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?).
more hereThe 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.
• Make components interchangeable between different applications.
• Put emphasis on bright color and industrial design
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.
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.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...
As good of a place as any to start.so I will try this Sunday:
HS 6 (14)
LS 3 ( 6)
RB 6 (24)
HS 8 (14)
LS 4 (6)
RB 8 (24)
so I will try this Sunday:
HS 6 (14)
LS 3 ( 6)
RB 6 (24)
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.
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.
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.
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.
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.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).
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.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).
Phil,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...
There needs to be a "like" button for your post Simon.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.
What settings did you try?Gents, I'm still nowhere and no time left...
btw after 20 laps my rear and front tires were 40C max ambient was 19C