marcusgunby
LIFETIME SPONSOR
- Jan 9, 2000
- 6,450
- 2
Right its been a bit quiet here so im going to give a run down of the pds shock and its history.
In 1997 KTM were making quirky bikes many enduro riders loved-in mx they were less liked and rode by strange people.
Late 1997 KTM released a totally new limited edition 125.It had a new engine and chassis and a link less rear suspension.They called the shock a PDS , progressive damping system i think it stands for-couldnt be less true in reality but we will talk about that later.
The late 1997 KTM 125sx had a ohlins designed shock, for 1998 KTM wanted ohlins to porduce the shock in larger numbers but they declined as they felt it wasnt cost effective for the price KTM wanted to pay.So KTM who owns WP got them to produce it.
Now the original design was British and had a patent on it, ohlins wouldnt let WP build it the same, so WP built a slightly different version. (BTW this is all from memory so it maybe not perfect)
So WP designed a shock which attached straight to the swingarm, it has no linkage but does have progression as its angled and this gives a small amount of progression.
To stop the heavy bottoming that would come form a soft progression WP needed to slow up the shock movement on harder hits-they decided to build a 2 stage damping setup.
This is done internally by having 2 pistons and shim stacks.The first piston is used all the time as in a conventional shock.The 2nd piston moves with the first piston but doesnt create any damping till the last few inches of travel(like a linkage bike has way more damping in the last few inches of travel)how does the second piston not have damping for most of the travel but then suddenly comes into play you ask??? well it has a great big hole in the centre and all the oil just flows through it, UNTIL near the end of the travel, the shock body has a great big needle(at the top of the area where the piston move up and down) that plugs the hole.So when the hole it plugged(last few inched of travel) the oil has to go through 2 pistons and 2 shim stacks.This causes a massive increase in damping.
That is basically the design,
How has it changed over the years??
In 1998 the PDS had a straight rate spring and a very long internal bottoming needle.Another strange design was the bleed for the rebound actually ran all the way down the chrome shock shaft and through the adjuster clevis(big bottom part that attaches to the swingarm)also the compression adjuster worked backwards-in was softer.
In 1999 they made the needle shorter so the second piston only came into play at a later stage.Also a progressive rear spring was used.
In 2000 they made some changes but i think they were only small.Progressive spring used.
In 2001 they changed the rebound bleed to not go down inside the shaft and through the clevis and it was more like a conventional shock.(sorry if this part is confusing but its very hard to explain this part unless you know how a conventional shock works)progressive spring used.
2002 was a step forward, they used basically a semi factory SXS shock in production, this had a totally new adjuster with adjustable high speed.This adjuster works the same sirection as a KYB/Showa , in gives stiffer damping, I havnt seen inside a post 2001 so this is all i know.Still progressive spring.
2003 refined the 2002 shock and used softer progressive spring.Also used a copied idea of a top-out spring-this is a small spring that sits inside the shock seal head and gives a bit of movement when the shock is fully extended like when you nearly high side. I believe this idea comes from road bikes.
2004 they have gone totally full circle and are uising a stright rate spring and a long damping needle so the second piston comes into play ealier in the stroke.
We will talk about design flaws once any questions have been cleared up.
So fire away:)
In 1997 KTM were making quirky bikes many enduro riders loved-in mx they were less liked and rode by strange people.
Late 1997 KTM released a totally new limited edition 125.It had a new engine and chassis and a link less rear suspension.They called the shock a PDS , progressive damping system i think it stands for-couldnt be less true in reality but we will talk about that later.
The late 1997 KTM 125sx had a ohlins designed shock, for 1998 KTM wanted ohlins to porduce the shock in larger numbers but they declined as they felt it wasnt cost effective for the price KTM wanted to pay.So KTM who owns WP got them to produce it.
Now the original design was British and had a patent on it, ohlins wouldnt let WP build it the same, so WP built a slightly different version. (BTW this is all from memory so it maybe not perfect)
So WP designed a shock which attached straight to the swingarm, it has no linkage but does have progression as its angled and this gives a small amount of progression.
To stop the heavy bottoming that would come form a soft progression WP needed to slow up the shock movement on harder hits-they decided to build a 2 stage damping setup.
This is done internally by having 2 pistons and shim stacks.The first piston is used all the time as in a conventional shock.The 2nd piston moves with the first piston but doesnt create any damping till the last few inches of travel(like a linkage bike has way more damping in the last few inches of travel)how does the second piston not have damping for most of the travel but then suddenly comes into play you ask??? well it has a great big hole in the centre and all the oil just flows through it, UNTIL near the end of the travel, the shock body has a great big needle(at the top of the area where the piston move up and down) that plugs the hole.So when the hole it plugged(last few inched of travel) the oil has to go through 2 pistons and 2 shim stacks.This causes a massive increase in damping.
That is basically the design,
How has it changed over the years??
In 1998 the PDS had a straight rate spring and a very long internal bottoming needle.Another strange design was the bleed for the rebound actually ran all the way down the chrome shock shaft and through the adjuster clevis(big bottom part that attaches to the swingarm)also the compression adjuster worked backwards-in was softer.
In 1999 they made the needle shorter so the second piston only came into play at a later stage.Also a progressive rear spring was used.
In 2000 they made some changes but i think they were only small.Progressive spring used.
In 2001 they changed the rebound bleed to not go down inside the shaft and through the clevis and it was more like a conventional shock.(sorry if this part is confusing but its very hard to explain this part unless you know how a conventional shock works)progressive spring used.
2002 was a step forward, they used basically a semi factory SXS shock in production, this had a totally new adjuster with adjustable high speed.This adjuster works the same sirection as a KYB/Showa , in gives stiffer damping, I havnt seen inside a post 2001 so this is all i know.Still progressive spring.
2003 refined the 2002 shock and used softer progressive spring.Also used a copied idea of a top-out spring-this is a small spring that sits inside the shock seal head and gives a bit of movement when the shock is fully extended like when you nearly high side. I believe this idea comes from road bikes.
2004 they have gone totally full circle and are uising a stright rate spring and a long damping needle so the second piston comes into play ealier in the stroke.
We will talk about design flaws once any questions have been cleared up.
So fire away:)
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