Shim deflection and piston design

[mog]

you need to be on the payroll ?

[MRW]

Thanks again all. very helpful:ride:

[MRW]

I would guess 0,1-0,3 M/s if the track is relative smooth.

Rob,

Sorry I missed this post "MX'(Rob). This is what I was hoping for:ride:

Thanks

[huskie]

What are the max shock speeds?

What m/s is low speed, mid speed, highspeed for shocks?

Interpreting the abnormall versus normall stack: shim max deflection is approx 0,5mm? I come to this figure since the abnormall stack is not blowing off, deflection is not bigger than the normall stack with crossover and hitting the highspeed stack.

[dbraced]

I believe that using thinner shims on the face gives a plusher feel initially. Then as the thinner shims begin to flex more their combined quantity adds to their overall strength,support thus providing an increase in mid to hsc.

With the thicker face shims initiall resistance away from the face is higher (stiffer)as your trying to bend less but thicker shims. Then once the shims begin to deflect a certain amount they have less overall strength, support thus providing less hsc.

[Jake Z]

Hey Rob, here are two stacks that I've tested back to back on my KX250.

Stock '05-'07 KX250 Shock Compression

12-40.20

28.15

38.25

36.25

34.25

32.25

30.25

28.25

26.25

24.25

22.25

19.30

VS.

Single stage (projected linear characteristics)

40.25

38.25

36.25

34.25

32.25

30.25

28.25

26.25

24.25

22.25

20.30

18.30

Both stacks felt nearly identical in the first 1/3 of the stroke. But the single stage stack shined in cross-grain where the shock needs to "blow off".

The single stage seemed to have a very linear curve and worked well everywhere but in HUGE sand whoops.

With all the stacks I've tested this single stage was the smoothest in tight, technical, and rocky single track.

Have you ever compared these two types of stacks on the dyno before?

[mog]

you have got to be amazed how a single with so few shims can feel similar for even part of the stroke.

[Jake Z]

Believe me, I was surprised the first run out with the single stage. The compression stack was the only parameter changed so the end result was solely from the compression stack. I mean same terrain, shock, spring, rider, sag, etc; all the same.

Single stack is the answer for anyone that's looking for more low and less high speed. I would like to see a dyno comparison.

[mog]

my 2 stage straight stacks are very similar to a single stack, both had 100% of the low speed of a normal 2 stage, but only 75% of the high speed, Kevin stillwell did the dyno runs and posted the numbers a few years back, it was on my 05 rmz shock.

[Jake Z]

I'll have to search for Kevin's thread on the matter.

I've been told by other tuners that I'm crazy for even concidering a single stage stack for desert terrain. Then after riding my bike they try milking me for valving info, and I just smile and tell them I occasionaly use single stage stacks.

I'm finding that bikes with very progressive linkages work well with single stage stacks. If the linkage curve is very progressive, why use a progressive stack with it?

If you guys have any customers complaining about swapping in the whoops but they're not bottoming, try a stack that is less progressive.

[MXSCANDINAVIA]

Here some test regarding shim deflection, just to see how much it moves.

There is two easy stacks like this.

ct02025

40.20 (12)

25.20

4mm stop washer 38mm

ct03025

40.20 (12)

25.30

4mm stop washer

I use jake_normal as reference, dont care about the small dip in the 0-0,1 m/s area, could be a little trapped air. what you see is the ct02025 separate at 0,8 m/s when the shim hit the washer and the restriction take over, and i promisse this is a ass braker, so i think this is how much it lifts up to 0,8 m/s with this clamp dia and rebound needle position .

Huskie wanted to know the speed area low,mid,high. Ther is no standard, i think every tuner make there own preference regarding this matter, this is how i see it, The first partion i called the nose (lowspeed), the finish of the nose zone coincides with the begining of the knee zone (midspeed) where the shimstack begins open and then bleends into the straight line "the slope" with it's slope angle( high speed). Hope this helps

I made some run on Jakes kx 250 (jake001) vs singel stage (jake002) i also blended in Marcus stack as promised (mog001)

dbraced ! what do you mean with thiner face shim ? are you comparing ex 2x0,30 with 2x0,20 or with a shim factor ?

Rob

[mog]

wow jake 002 has almost no damping at all? jake 001 has just as he says a decent amount of hs blow off, like the others but even more pronounced, mine has some serious high speed damping, more than i expected and less low speed as well, but then i really should have expected that with the 0.15mm cross over, for mx mine feels good but for anything else i bet it wouldnt, woods it would have way too much high speed i would think, and sx or whoops it has too little low speed i would guess?

Rob out of the stacks we have seen, which one do you like best(that you have ridden?)

have to say thanks again for doing all this work, its fascinating and i have been looking at the thread twice a day to see updates.

dont really understand the top graphs? 4mm stop washer 38mm?

[MXSCANDINAVIA]

i dont know what you call it ! It's the big thick washer with 12mm id you put on the rod before the shims that stops against the rubber on the seal head, then put 1 020x25 shim and then 12 020x40 and then the piston and then............go for it.

rob

[mog]

so what is the actual difference on the 2 stacks on the top graph?

[MXSCANDINAVIA]

One stack can move 0,20mm the other 0,30 before the whole pack 0ff 40x0,20 hits the washer and stops deflect. the 030 stack shows no sign of hitting the washer but the 020 does so at 0,8m/s and that shows in this case a shimstack don't open no more than 0,2mm at 0,8m/s

[Jake Z]

Rob, your awesome! Thanks again.

Jake002 surprised me a little bit with how much less damping it provided when compared to the others. It just goes to show you how much bleed effects damping.

Jake002 is definitely linear and that would explain why it worked so well in the desert. I mean, that stack never failed to track. No swapping, deflecting, bucking, or anything else that a shock shouldn't do. And believe me, I'm not slow!

Honestly it had fairly descent bottoming resistance; just not the kind you could case the Grand Canyon with.

In the hands of a skilled rider, the single stage stack can work quite well. Given that you ride smooth, smart, and conservative like a good desert racer should.

As for motocross, jake002 doesn't have the bottoming resistance required when over clearing a landing or casing a double. I learned real fast not to make any mistakes on the track with that setup.

Thanks again Rob. Your time is greatly appreciated.

[huskie]

Rob,

i second jake, thx for the data

[mog]

jake i wonder if you used a 16 clamp on the std kx 250 stack, if it would mirror your single stage?

[huskie]

I don't want this topic to be end.

Can you use this dyno for forks aswell?

I wld kill to see the difference in float, piston design, stacks on forks.

If this topic shld end, all great things must....

than what can we conclude out of the given data?

[Jake Z]

Marcus, I think the 16mm clamp would definitely make the the two stacks very similar from low to mid speeds; but I still think the the KX two stage will still have noticeably more high speed due to its progressive nature.