I've been waiting for this day! I'm ready to bring a long standing debate to the front of the line..

It is intresting to me the amount of misinformation going around about PDS systems in general. So having had the opertunity to run some simple exspereiments, exchange information with crediable sources I thought it would be finnaly a good time to bring this up. We can presnt the facts over time as you have jsutified your own reasoning.. But for those who love suspension we have plenty to talk about.. I'm going to the WP factory here in a week. We are surely going to talk about many of these things so I can bring back some perspectives form the enginers who have created this wonder of function.

So Issues we need to adress,

Nose pressure: What is the role in a PDS?

Piston? Does frinction count?

Bladder? Whats the purpose?

Nitrogen? Does volume have something to do with it?

Let the debate beging.. I'll be checking in and reporting.



Regards,
Jer


PS vote on first instict, then lets talk amoungest the group.

I voted for the shock piston.

Well Jer, here goes.

I think that before I, or anyone gives their theory on anything to do with suspension, we need to issue a disclaimer. I guess it should go something like this.

As we go on through the years building and tuning on these things we begin to understand one very important thing. We really do not know as much as we think ! The best thing about being a suspension geek is that almost every day I learn something that I did not know the day before.
It is still a black art that even the best engineers in the world still strugle with.
What works for one person, the next one hates.

Take for instance the debate over gas piston vs bladder. I installed a bladder in Two customers KTM SX 250's this year, one liked it, the other wanted to hit me over the head with it. The big differance was riding ability.

The guy who liked it was a better rider. I like the piston better, I can control oil volume more prisicely with the piston, I also feel that I can run lower gas pressure with out the fear of dumping & cavitation. I think that it creates a higher nose pressure, sure there is more friction, but with all that area of a bladder, do you think it would create more heat?

The fact is that they both work. I am going to do some testing in the near future on some cup cars by running a bladder against a gas piston damper. The car will have a PI system on it, so I should be able to get some very good info for you.
Hope that I did not ramble on to much.

What I feel about piston is that if lack of maintenance, there will be sticktion caused and it wouldn't have a smooth movement.

I have once strip down a 98 KTM PDS shock and are shock to see that the piston are stuck! It seem to be lack of of grease, low on nitrogen pressure, and less amount of oil left.

After replacing the piston ring with grease and some polishing on the internal wall of the canister, I can hear some piston "movement" sound inside when I compress the shock on the bike. It did goes away after some riding.

I feel that a bladder would be more sensitive to smaller bumps.:D

I'm surprised if there is a noticable difference, but fundamentally I prefer the bladder because the piston has more inertia which means it will resist changes in velocity more than the bladder.

I think the bladder is a bit easier to assemble as well. My experience with the piston is very limited though (only once - my shock deflowering....).

Of course if I were designing the shock and there was little if any difference in performance, I would choose the bladder. The piston is much more expensive to produce.

I fitted a bladder to make serving easier on a 00 PDS and i could not tell any differance what so ever.Im a 170lb exp mx rider.

It boils down to whatever you like better and what your conditions are and what your setup is. Drew Smith of WER who is a w/p distributor and ISDE multi time medalist did mine and used a wer bladder. Drew is from North NJ as am I and knows the terrain I ride on. The shock works very well although I would like a wider range of adjustability as in more clicks on compression. That is not Drew but WP's design. It also depends on if you race MX, Enduro or just trail ride.

Ok.. Good points here are some thoughts.. We need to spend some time giving reasons..!!


Ok.. Here are some intresting facts..

Bladder designs.. ALl the avlaible systems use a KYB 46mm x 103 bladder.. This is important to recognize. It has no difrence in function in terms of mechaincal area. The shape does not matter.
The Cap made by WER, and UltraMAX have significantly less nitrogen volume!

What does that do in relation to nose pressure? Increases the rate at which it rises signifactly. So the nose pressure is nearly twice that of the standard shcok at the end of the travel.



Factory connection runs a longer tube, that I beilve adds oil capacity not nitrogen volume. This may help temperature issues.


PC, and Factory R and D make a kit with a bladder and nitrogen volume exstension tank.. These actually result in a nitrogen volume that is still 25% less the standard.. Which you guesses it results in a much higher nose pressure still.

So the advanatage can't be a reducing of pressure or area.. Simply the facts don't add up. Ok which leads us to service ablity... The Bladder does make it easier to work with, for the average guy.

Friction... I think we should talk about this detail.. What is the ratio between the piston and the wheel? I've figured it out, and I want you guys to think about this point, and how it may impact shock performance.

Heat: This may be the best argument I've heard yet..How does the bladder impact the distrobution of heat, and the specific heat capacity of the shock.


Cool Keep it up! Talk with you in a few weeks...


JW

A few weeks im really starting to think about this topic which i havnt in the past-the hole nose pressure thing -does it end up just bieng a spring which we have to take into account when lloking at the shocks intended use?im really surprised about the bladders all bieng the same.And im surprised N2 volume is reduced-this in an age where most are quoting increased N2 volumes,i will leave the friction part to others as ive read a post of your before that goes into the maths and it convinced me.

When do we get more info on this? I'm about to get my shock revalved [98 exc 300] and the shop doing the work recomends the WER bladder kit. I like the idea because it will be easier for me to change the oil, but not if it's a performance or functional disadvantage.