Stuff two cool not to share II PDS Neadles

Jeremy Wilkey

Owner, MX-Tech
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Jan 28, 2000
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Thanks guys! I've really been missing my forum stuff.. I've been really busy this summer with KTM and all the other devlopments, but I've got a little more time these days and wanted to get back to some of the cool topics that come up talking about my favorite bikes..

Ok needle stuff..

The needle controls the distribution between the first and second pistons.. First we need to identify a couple of important points about the needle design. The needle does not seal off the passage perfectly, it creates a virtual seal, but if you where to move the shock slowly enough then it would effectively do nothing to block fluid through the passage and the secondary piston would do nothing.. The importance of this fact is only in explaining a basic principle.

Couple of important valving concepts.. Say we have a valve of certain configuration that produces a certain damping coefficient at a certain speed and subsequent flow rate. (Speed of the fluid is really only changing the volume that has to travel through the valve and hence its damping rate.)

So if reduce the the amount of oil flow to a valve the same valve produces less damping.. If we increase the flow to the same valve then in produces more damping and a higher damping coefficient.

Some more history that is relevant, KTM used the linkage less system as a way to save weight, money, and create a notoriety for doing something outside the box. Japanese Manufactures have long wanted to use such as system. If you consider the cost of say 4-6 lbs in materials, the manufacturing cost of the extra castings, welding etc, the cost in performance KTM has a real leg up in this regard. They can use cheaper materials on the whole bike yet still save lbs's.. Honda and Yamaha are in a battle right now, they are using exotic metals shaving everything to the last collective ounce, at a huge expense to try to capitalize on a weight superiority and performance now imagine what they would do for 4-6 lbs weight savings for less money..

Anyway before I digress to much father, back to the PDS needle.. The job of the needle is to create a change in damping rates as the shock moves through the stroke, by changing the oil flow through the system. In doing this we increase or decrease the damping coefficient without accelerating the shock..

The needle length determines where the change in distribution begins. The older 02-03 current WP shocks used the Needle more as a bottoming control rather than a way to change the damping into the stroke for say stadium whoops. The new shock needle begins to distribute a small portion of the oil flow though the secondary Piston about 3/5 of the way through the stroke.

The Original PREPRODUCTION needle was interesting in that it had only one taper from 8.3 to 9 something top to bottom. So the Shocks secondary damping came in quickly and completely linearly but again, it could be brought in much softer overall. (Remember the concept of average damping coefficient) It (Secondary comp) did less work at any given point in the travel over a longer travel thereby creating the same bottoming resistance but more compliance, and a rise in rates sufficiently soon enough to help the bike in stadium whoops. The only flaw with the pre-pro needle was simply the final diameter was not big enough to limit bypass sufficiently as the total bottoming resistance was a little low. You could increases the damping rate by stiffening shims, however that made the initial transfer to the needle to pronounced at higher shaft speeds. (Slightly too high overall damping coefficient).

I received a another needle in August and was told that was the new needle To be used in 04 Production. It was still long however it had a small tip and multiple steps.. The design feature I liked over the first needle was it attained a full 10.3 mm OD in the final step and thereby would increase the fluid flow to the secondary circuit and generate more compression in the final part of the stroke. What I found was this design had good bottoming control but did not produce enough compression in its early segments to do much for whoops, and worse again if you stiffened the valving to help whoops then the shock was too harsh deep in the stroke when hitting bumps.

The needle I designed is a the original preproduction needle only with a slightly steeper taper and a wider 10.3mm base, 12 mm from the bottom. This allows the secondary valving to be very light, yet effective for whoops, and relatively substantial in bottoming resistance, as the secondary has maximum fluid flow in the last 1/5 of the stroke. Another intresting note, I've only talked to Pete of Novation one time, but when we where talking he told me he had diferent needle, I'm curious to see what his angle is...

I think when arguing straight verse progressive springs the needle design is immaterial. 1st-4th generation needle is pointless... It seems pretty clear if you think about it the straight rate is a marketing/ must do something idea. If the straights worked they would have worked the first time out, the advantage would have been noticed and refined , but it never has been, secondly they redesigned every other aspect of the system to make straights work, (which they still don't BTW IMO) Would it not make more since to tune the spring related issues with spring and the damping rates with things associated with damping. My Good Friend Ross Maeda and I debate about PDS system all the time, and he thinks we try to mix too many things as it is, yet its still just a rising rate damping, and rising rate force curve if you use a progressive, but if you use a linear spring then you have the equivalent of a progressive linkage system and a falling rate shock spring.. Makes a lot sense doesn't it.....

The PDS system continues to evolve, several years ago I would have argued the straight rate issue, not from a shock performance issue but from a handling stanpoint, today I argue from accross the tracks, I hope only one thing.. The PDS system is the best in the world for offroad bikes, and I sincerly belive it.. I hope we can continue to push the devlopment, it would be a shame if we lost the system to some blocks of AL.. So I hope this string cause more apperciation, rather than arguing over who knows the best set-up... If you think your company is best great, I'm just going to keep working as hard as I can to devlop an intracte and amazing shock system..

BR,
Jer