Cheap tricks for the YZ shock


23 replies to this topic
  • grayracer513

Posted May 06, 2016 - 09:18 PM

#21

The '07 shock was almost certainly valved differently than the '06, but only a shim or two here and there.  It's not uncommon to see two bikes made the same year with slightly different valving.  The bolded shims are shims that were changed from the stock size.  Occasionally there is one added. 

 

I weigh 170, so it's not so different.  The symptoms in your rebound as you describe them are classic YZ/KYB complaints.  This shock setup originated with Dave Johnson of SMART Performance in almost this exact form.  I've only made minor changes.  I was getting rear end kick to the extent that the bike of the bike was moving around a lot, and the tail high attitude on hitting the next successive whoop was causing the front to be unsettled and squirrely at speed.  This shock addressed that completely.  The HSC modification came later to make the rear more compliant among big rocks in 1st and 2nd  gear. 

 

Originally, I could sit the bike on the ground, bounce the seat with my hand, and it would rebound a bit beyond its static height and then settle back.  The fender used to wiggle up and down freely while it rode down the freeway in the truck.  No more.  Now it takes a full second or so to rise from the same seat bounce, and doesn't float over at all.

 

I found it really hard to believe, just on the surface, that that much stiffening of the face stack would not cause packing, but the thing is that with the stock setup, any time you get the rebound just about right, most of your damping is being done by the adjuster needle, which is a fixed orifice once you set it.  With a stiffer valve stack, the bleed through the adjuster is greater, and more of the damping control lies with the stack, which does the job much better.  If I hit a series of whoops, the bike does actually squat just a little bit, but it stays down, and stays behind me, and the front doesn't twist into the next one, it just tracks straight.  Running through a string of whoops in the desert, I never feel like the rear end "packs", that is, the compression never suffers from the slower rebound or the "squat". 

 

Since you are 20 pounds lighter, you might try using 0.30 shims in only the first 6 positions off the piston instead of the first 7. 



  • heart_of_darkness

Posted May 08, 2016 - 01:00 PM

#22

Note also that the concept of applying spring pressure to the back of the face shim does not apply to this setup, as the spring pressure is borne by the two 11's, the effective "clamp", and not the face or other larger shims.

highspeedUnitLS-HS-1_zpsd225380f.jpg

Grey, thanks for the detailed explanation.

At the beginning of this thread is a picture of a modified spring seat which applies the spring pressure to the face shims. Do you think that modification is useful for increasing the range of adjustability of the HSC? Or, if there's not a greatly independent flexing of the face shims and 11mm shims, would it not make too much difference?

Edited by heart_of_darkness, May 08, 2016 - 01:03 PM.


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  • GHILL28

Posted May 08, 2016 - 10:41 PM

#23

There are some differing opinions on that rebound setup.  While most would agree that the stock YZ/YZF shocks could use some stronger rebound damping especially from deep in the stroke, many have found the use of a large stack of .3mm shims to produce an excessive effect that can cause packing and can sacrifice ride qualities elsewhere for stability in individual deep-travel events.

 

I've thought for a while that my '14 YZF could use some significantly stronger rebound in the back for stability in whoops, but I'm very hesitant to try the stack of .3mm shims again since I had poor results with it on my YZ250 a couple years ago, and I found the stock setup to be more predictable (not faultless, just more predictable).  Again, the bike behaves VERY well everywhere else, and I don't want to sacrifice that but I think at some point I'll 

 

The thread in the suspension forum by Clicked started touching on rebound acceleration curves I think.  I'd like to learn more about that aspect of it to optimize the rebound behavior a bit better.  I do agree with GR observing that the free-rebound stroke will allow the rear end to come up above ride height and oscillate a bit to settle.



  • grayracer513

Posted May 09, 2016 - 06:41 AM

#24

At the beginning of this thread is a picture of a modified spring seat which applies the spring pressure to the face shims. Do you think that modification is useful for increasing the range of adjustability of the HSC? Or, if there's not a greatly independent flexing of the face shims and 11mm shims, would it not make too much difference?

 

I'm not sure.  Also not really sure why the spring seat needed to be modified.  I haven't messed with that approach.  With the reshimming I did, it seems likely that there would be less overall tendency to flex the 11mm shims against the spring seat, and it might have the effect of reducing the range of adjustability.  I've thought about playing with changing the 11's out for 12's or 13's to see the effect that would have.







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