GSXR 1K fork swap: anyone have any experience with the GSXR valves/shimstacks?

[MonsterHPD]

Well, FrankenDuc, this got steam coming out of my ears, I'll re-read when my head cools down again 

I suppose the next "necessary" purchase will be some proper suspension data-logging equipment. With the guesswork taken out of the shimstack layout, and from the suspension movement caracteristics, surely suspension heaven will result ...      

[FrankenDuc]

been keeping an eye out for years for an excuse to pick up some nifty little MEMS inertial units:
https://www.sparkfun.com/categories/160
I think this might be the perfect application! I just have yet to pick out the appropriate acquisition/storage device - the Arduino's I think not quite fast enough for suspension characterization...

I've still got a few more miles of "human" testing to go through though - End of day, as long as the suspension gives me more confidence, let's me push harder and wears me out less, even if it slides a bit more, it's better!

[koko64]

Very impressive guys.
Learning a great deal from this. Will have to read and reread though.
Thanks heaps.

[FrankenDuc]

Digging around the web over the past week or so, I stumbled across a set of whitepapers from Optimum G Vehicle Dynamics Solutions that might be useful to anyone venturing down this path:
http://www.optimumg.com/technical/technical-papers/
Look for the set of 5 whitepapers under the "Springs and Dampers" section of the page.  It's aimed at the four wheeled race variants, but I'd venture to guess most of it applies to our two wheeled steeds.  100% applicable or not, this is a great set of papers to read through, a lot of really good information in them!

As I'd mentioned in an earlier post, the single greatest struggle I've had has been determining a starting point for setting my damping curves - "what the heck sort of damping do I want out of my suspension and how the heck do I put what I want into mathematical terms???"...

If I look at the work I've done on my forks and compare it to what Optimum G recommends, mine actually pretty closely matches their recommended curve for a damping factor of ~0.7 (a little rough on city streets, but I have to admit the setup seems to be working very well, nice and smooth, as I push hard and fast).

Based off of Optimum G's papers, if I've done the math right, my 210lbs of sprung mass on the front end with two 0.85kg/mm springs gives:
- natural frequency ~2.0Hz
- base damping of ~14.8lbf-s/in at a factor of 1, multiply by damping factor to get target base damping coefficient.

At 0.715 damping factor, damping base is 10 lbf-s/in:
- recommended 2/3 low speed slope on compression is 6.67 lbf-s/in
- recommended 1/3 high speed slope on compression is 3.33 lbf-s/in
My low speed compression is ~6.67 lbf-s/in, and though my mid-high speed compression is a bit lower than 3.33 lbf-s/in (in the 100-500 in/s range), but at the "bump at highway speed" range >500in/s I'm ballpark ~3.33 lbf-s/in (it's a bit progressive in this region, so give or take...).
Here's the curve again for reference:
https://docs.google.com/open?id=0B1DE0ZygiWDyYkw5RDZyYVdXWmc

On the rebound side, it's probably useful if I provide the damping coefficient graph (as opposed to the damping force graphs I posted earlier):
https://docs.google.com/open?id=0B1DE0ZygiWDybnptUDF0RHVFVFE
Note, this is at 0clks.  I started test riding with rebound at 4clks out, and I've been turning it in one clk at a time, and I'm currently road testing at 1clk out on rebound. It seems like I'm gaining stability as I close off the valve, and I can't notice any loss of traction (although perhaps I'm not pushing it hard enough...). I'm testing on the road, not the track, so maybe my results would be different if I had a wide open space with no cages, safety runoffs, and everyone going the same direction as me to really push it on  Maybe next season
- recommended 3/2 low speed slope on rebound is 15 lbf-s/in, which I roughly match (14.3 at ~5in/s)
- recommended 3/4 high speed slope on rebound is 7.5 lbf-s/in, which I roughly match at ~50in/s suspension velocity
Note, as I've mentioned, rebound velocities are bounded and much lower than compression velocities.  Compression can exceed 1000in/s on large highway speed bumps, but rebound from fully compressed, depending on clicker setting, is somewhere around 100in/s, I consider low speed to be 0-10in/s on rebound, and anything over 20in/s squarely in the high speed realm.

So oddly enough, I think I've stumbled my own way on exactly what these papers outline as the recommended damping starting point of a 0.7 damping coefficient, 2/3 low speed and 1/3 high speed on compression, 3/2 low speed and 3/4 high speed on rebound.  Pretty cool!!!

If you do go down this path though, don't trust my math or results, do your own math and find what's comfortable for you  

Anyways,

[MonsterHPD]

Hello, all.

Lifting this thread again, cause I'm a bit  .... and maybe you can help me

Since I have a couple of different shim stack and piston versions I'd like to try, I've now purchased the pro Shim restackor to help evaluate various layouts.
The restackor in itself is maybe not complicated other than thru all the options where you have to determine what to fill in.
I've also read thru most of FrankenDuc's info, but that will take some time to sink in; unfortunately I can't see the graphs on my PC. Or if it'just me and google not beeing on the same wavelength.....

Anyway, I have one problem and 2 questions with the Restackor:

Problem: When I try to open the facility to define the damper needle geometry, it does'nt open, and does nt seem to be present on the "edit output" screen. Looking up the location "C:\ReStackor\Work_Dir\clkdat.in" on the PC, there is something there, but the file seems to be empty. Any ideas how I could get that to work?

Q1: What sensible value should one pick for Fmax (I'm using the base valve as a training item)?
Q2: What sensible u.wheel should I use?

Any hints would be greatly appreciated.

Kind regards,
Torbjörn.     

[Speeddog]

It's been a while since I messed around with my restackor.....

IIRC, you should first copy the existing clickdat file out into a new folder.
Then open the clikdat file with a text editor.
Modify it and save it with a new name.
Move the original clikdat file out to the folder, then move the new one in.
Then rename the new one.
Something like that....it's quite obnoxious.

As far as the wheel speed and force, I've got some notes at the shop, more later...

[MonsterHPD]

Thanks, Speeddog, I'll try that when I feel bright enough 
However, this causes me to ask a follow-up question: Where do I find the clickdat file? It seems the file on the location given in the manual is empty, and when I check the .txt-file via the "Edit output"button, there is no data indicating any needle geometry at all. The way I understood the manual, there should always be this data, wether default or custom values are used.   

Any reference numbers on the speed and force are most welcome, the restackor thing surely takes some effort before it can be useful.

[Speeddog]

You should find it stored here:

Drive (C or whatever you use) / Restackor / Work_Dir / clickdat.in

The ".in" file extension is crucial when you make your own clickdat file.

This is what I use for the OEM Showa compression valve:

Showa compression valve needle
3.0
Nclk   Dclk[mm]
0      3.0
24     2.52


I've got a seperate folder that I created for putting those files in.
I've got that one saved as a .txt file.
If you open it in NotePad, then do 'save as', enter the name as clickdat.in, *and* Change 'Save as type' to 'All Files' not 'Text Documents', it'll save it as clickdat.in, and the program will use it.

Of course, you have to replace the clickdat file in the above directory with your new one.
And IIRC, you have to have Restackor shut down, then restart after you change the file.

--------------------------------------------------------------

Speed and force, well, I haven't found a great answer.

I was introduced a while back to a Suspension Guru, who had a car background, so I was taking his commentary with a grain of salt.
I asked him about what shock dyno speeds he used.
He said maximum of 5 in/sec usually, but he would sometimes go up to 10 in/sec.
I thought that was *really* slow.
If I'm charitable and use a rear suspension leverage ratio of 3:1, that turns into a wheel speed of 30 in/sec.
Which sounds plausible.

But.

Let's say you're cruising on the freeway.
60 mph is 88 ft/sec, which is 1056 in/sec.

That 30 in/sec wheel speed would be a ramp 1" high and 35.2" long, which is a pretty gentle slope.
Similar to the transitions from the plain freeway to a bridge over a road below grade.

But that's a *way* 'slower' bump than, say, a 1" step between slabs of concrete, or a pothole.`
That's the kind of bump that's the most obnoxious from a comfort and chassis stability standpoint.
That's the wheel speed number I want to know.

I've seen shock dyno curves with 200-400 lbs of force at 10 in/sec.
Taking the 3:1 leverage ratio, and then cutting that in half for one fork leg, you get ~67 lbs at ~30 in/sec.
That's assuming front damping forces approximately the same as rear, which may be a bit off base.
But it gives you a ballpark.

[FrankenDuc]

MonsterHPD,
have you been through their user guide online?  They have a compilation of some suspension velocity data for forks in the user guide:
http://www.shimrestackor.com/Code/User_Manual/Sections/Suspension_Velocity/suspension-velocity.htm

On wheel velocity, tire diameter and deformation play a big role in sharp bumps (potholes, etc).   It's been a while, but IIRC on compression, I assumed 10's of in/s up to 600in/s range for bumps (high speed damping), and the 10in/s ballpark as chassis disturbances (low speed damping - braking/acceleration/centripetal) and road surface variation.  The chassis disturbance and road surface variation range would be of critical interest to somebody tuning for a smooth racetrack.  For rebound, velocities are bounded by the spring force (minus the gravity force from the sprung mass), so I focused on the 0-100in/s range, again with low speed from chassis disturbances and road variation in the ~10in/s range.

(let me check back through my notes though, I frequently get confused...)

the distinction between low speed and high speed was important for me, as I was trying to tune for a high damping coefficient at low suspension velocities and a lower damping coefficient over potholes.

F.max number gets used to determine up to what shim stack force value to run the shim lift calculations - playing around with it will help you see at what point the shims no longer limit oil flow (and damping becomes progressive).  I have to admit, the number is a little IZ_ to me, I'm not sure exactly how to relate it to, say, the wheel velocity at which the damping will start to become progressive, but I would reckon the stack force relates to how much oil must flow through the valve at any given wheel velocity.  You can also look at the damping curves and see where damping becomes progressive (...so, I didn't really pay much attention to the F.max number...)

[MonsterHPD]

Speeddog, Frankenduc, thanks for your input. Any experience you already have is of great value to me; I won't have to find out myself 

The compression needle on the 50/54 forks is not a needle at all, more like a pole, but since only about 15 to 17 of the possible 25 or so clicks, I've been thinking of modifying the needle to make it longer and more tapered. The Restackor might give an indication if I get the needle part to work.

Before I attended the suspension seminar at Reactive Suspension I have not given piston design, or even shimming, much thought, assuming the people at Öhlins, K-tech etc. knows what they are doing. I'm sure they do, but I don't know what their goals are, and I now realize there could be great differences in function depending on design.

I have a set of pistons from italian manufacturer Mupo; they have a total compression port area of some 8.5 mm². The K-tech's have about 9.6 mm², a Gold Valve has about 29 mm², and the stock piston in a DS1000 Showa has about 36 mm². This would probably create big differences at high damping velocities and here also I hope Restackor can give an indication. It's also the reason I'm interested in what damping velocities would be realistic.

I suppose Restackor can save a lot of shop time, but I'm not sure it will save a lot of total time