Some thoughts for PDS Shocks

[MXTex]

I love this type of data. You can't argue over facts.

Jer, I just posted this over at KTM talk. Hope you don't mind.

Thanks for pulling this together. I would like to see the hand bleed vs pump bleed comparison.

Jim

 

[Jeremy Wilkey]

Jim,
Your welcome, I did not want to get to argumentative in the con call, I already ruffled a few feathers. I senced a certain amount of contemp over the dyno... :)

Jer

 

[elf]

Intreresting stuff Jer. That explains why some riders feel like the shock is softer with the bladder. I am glad to see your so involved with the pds shock, there are so many theory's out there on how to make it work you just don't know who to believe.

 

[Jeremy Wilkey]

Elf,
Thanks! The PDS is still my favorite topic. Given time I'll write and post some of my other exsperimnets with hard data..

BR,
Jer

 

[marcusgunby]

Jer we tested the bladder vs piston back in 2001, and the rider did say the bladder was the harder of the two shocks, i put this down to smaller N2 vol at the time.Its good to finally see proof of what we thought, so many people were saying the bladder made it softer, i thought i had done something really wrong.

 

[Jeremy Wilkey]

i put this down to smaller N2 vol at the time.Its good to finally see proof of what we thought, so many people were saying the bladder made it softer, i thought i had done something really wrong.

You know how we KTM guys like to argue... I never thought anyone was not telling the truth becuase I've felt the same thing as you but there have allways been those that insist on how much better it makes the shocks.. I'm looking forward to seing what number we get when we run this as a hand bleed. I'm not sure if you had a pump or not, but you must have taken your time bleeding it if you did not..

More later!

Jer

 

[steve125]

Very interesting info Jer, thanks for posting it. In another thread over on TT that John C put up was very suprising to me. It showed how high the N2 pressure goes up from the cold fill of 155 PSI on a heated/worked shock. I would think that(high pressure) would pass on to the rider much more than the differences between the bladder or piston design? I always assumed the N2 was in control of this heated pressure rise. :bang: I have since lowered my fill PSI from 160 to 140, maybe I need to go a bit lower?

 

[marcusgunby]

Jer i used my own design special bleed lol, basically i bleed into a big tank like KTM used to show in the manual, then once no more air was coming out -i pulled a huge vacuum for about 5 minutes-the amount of extra air that came out of the oil was unreal.It wasnt a pump system but it was as good as i could get.

 

[Wile_E_Coyote]

Thanks Jeremy for your insight into the piston / bladder debate. I am glad to see that there are others out there that take these issues seriously enough to do the testing and find the truth. If you had been driven by greed there would be no reason to ask the questions and find the answers. In today’s world most would just do what was cheaper and made the most profit. Obviously you are driven by the desire to provide the best quality and performance. That is refreshing.

What formula or "rule of thumb" do you use to determine the proper piston location in the reservoir? This measurement is critical in setting the correct N volume. I re-check the piston depth through the N fill hole after the shock is completely bled, just before filling with N. I have found some specs, but there are conflicting figures. Is there a good source of information on the WP shocks that you can share?

I may be wrong but have you noticed that the 2005 PDS shock has less free bleed through the rebound adjuster orifice than the 2004? If so how does this affect performance?

Is there a link to see a detailed photo of the WP bleed pump? I have heard about it, but I have never seen it. I use a manual bleeding procedure that works just fine but can be rather time consuming. I would like to find out more about the WP pump.

Thanks, and keep up the good work.

 

[WhiPit]

Hey Jer! I'm baaaack!

:nener:

 

[fuzz]

sorry if this conflicts with hard facts already posted (I didn't read all the posts). From what I have seen, dealers and shock experts sell the bladder idea so they will not have to purchase the expensive jig needed to charge the standard WP shock. It is a simple decision to make "should I spend $200+ on special shock tools or, should I sell more parts?"

 

[Masterphil]

It is a simple decision to make "should I spend $200+ on special shock tools or, should I sell more parts?"

I think that it is more of a decision between, Am I willing to compromise in order to save myself some more $$$ or do I want to provide the best possible suspension service to my customers.

 

[Jeremy Wilkey]

I think that it is more of a decision between, Am I willing to compromise in order to save myself some more $$$ or do I want to provide the best possible suspension service to my customers.

Amen...or another way.. I take my profession seriously enough to invest in my business, before I expect my customer invest in my business.

 

[Roost1]

Jeremy, this is a great thread thanks for sharing the info with us. I have a shock clock data gathering devise and have had readings up at 150in/sec. Since the dyno info shows the travel at 14in/sec. can we assume that the dyno info would be linear out at the much greater velocity? I know that there are constraints with a dyno and that it is only diagnostic a tool. I'm just trying to better understand the graph. I also understand that the point of the graphs were to compare the piston vs the bladder but can we be sure that they won't act differently at the velocity the shock actually sees on the motorcycle?

Thanks Again

 

[Jeremy Wilkey]

Jeremy, this is a great thread thanks for sharing the info with us. I have a shock clock data gathering devise and have had readings up at 150in/sec. Since the dyno info shows the travel at 14in/sec. can we assume that the dyno info would be linear out at the much greater velocity?

Pete Payne and I have one and I can concur with your findings. In regards to the assumption of continued linearity, maybe, depending on valve design and shim configuration. We can say that speeds that high generally are on sharp curb type hits? They may not produce a sustained stroke. Where it can get complex is a curb during a bottoming load so we must consider a broad context.

I've mentioned this many times, but in an effort to test piston designs at higher shaft speeds than the dyno I have would run we have changed the volume side of the equation. In other words active piston X operates in a column of fluid 28mm wide and the dyno only test to 21in/s then what would rate we effectively test at with a column of fluid 50mm in diameter? The results where surprisingly liner, but with a crank we can not judge the instant velocity increase only an acceleration. Bottom line an EMA works best for these types of tests.

I know that there are constraints with a dyno and that it is only diagnostic a tool. I'm just trying to better understand the graph. I also understand that the point of the graphs were to compare the piston vs. the bladder but can we be sure that they won't act differently at the velocity the shock actually sees on the motorcycle?

The piston velocity is pretty low even at 150in/s wheel rate. I figure conservatively about 1/30th the speed of the wheel 3:1 wheel to shock 10:1 shaft to piston, so even at 150in/s we have only 5 at the piston. That’s such a huge mechanical advantage it’s just not meaningful IMO.

Thanks Again

Jeremy P. Wilkey

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