PDS..straight rate or progressive ?
- Thread starter Garyb
- Start date
Jeremy Wilkey
Owner, MX-Tech
- Jan 28, 2000
- 1,453
- 0
Garyb,
I belive that straight rate springs best suit the average rider. If i had control of the winding and could change the crossover points between rates then a progressive spring would make more sence. In it's current form I feel that the progressive springs contribute understeer and packing.
Regards,
Jer
I belive that straight rate springs best suit the average rider. If i had control of the winding and could change the crossover points between rates then a progressive spring would make more sence. In it's current form I feel that the progressive springs contribute understeer and packing.
Regards,
Jer
- Thread starter
- #7
Well - tried a 9.0 straight rate yesterday and found that it definitely does not hookup as good as the PDS. It also gives the feeling of "going over the bars" compared to the PDS and feels generally squirelly. This is with the same clicker settings as the PDS. I also felt cautious about hitting waterbars etc hard...I felt like it would blow through the travel and launch me. Harder clicker settings just made it more squirelly....
Any ideas ?
Gary
Any ideas ?
Gary
Strick
LIFETIME SPONSOR
- Nov 8, 1999
- 1,782
- 2
I am sticking my nose in a forum that I seldom approach, because I have no advice to give 99.8% of the time. AND Jeremy is a very active participant.
I do want to give my personal experience on this matter. I had a '99 380exc. It came stock with a PDS-2. I put on a straight rate spring (8.4). I was told by a racetech tuner that my weight (195), and riding desert that this spring would be 'the bomb'. I was able to set the static and race sag to spec. The bike was was too sprung in the initial part of the stroke. It also (as per GaryB) did not hook up as well, I think because of it. The guy I sold my biike to had the same comments on the rear suspension.
Jeremy, I know you have spent quite a bit of time now on PDS set-ups, based on what I have heard/read. He is my total novice outlook, and it must be stated in question form: If the entire suspension was engineered (German) for a progressive rate spring, how can you be effective in performance with a straight rate?
I do want to give my personal experience on this matter. I had a '99 380exc. It came stock with a PDS-2. I put on a straight rate spring (8.4). I was told by a racetech tuner that my weight (195), and riding desert that this spring would be 'the bomb'. I was able to set the static and race sag to spec. The bike was was too sprung in the initial part of the stroke. It also (as per GaryB) did not hook up as well, I think because of it. The guy I sold my biike to had the same comments on the rear suspension.
Jeremy, I know you have spent quite a bit of time now on PDS set-ups, based on what I have heard/read. He is my total novice outlook, and it must be stated in question form: If the entire suspension was engineered (German) for a progressive rate spring, how can you be effective in performance with a straight rate?
Last edited:
Jeremy Wilkey
Owner, MX-Tech
- Jan 28, 2000
- 1,453
- 0
Strick,
You should come here more often! Honestly a very fair question.
My thought just like you is based on my opion, which is based on my biasis and practical exspereince. Iwould argue that this is a function of many things.
1.) I spend very little time working with stock bikes or set-ups. I make assements of valving and spring issues based on my science, which you might want to consider a function. After I have made those assementsI decide what needs to be changed to produce the feel that I beilve my rider base will prefer.
2.) Honestly changing springs only is a crap shot at best.. Consider the range of shocks and valving that these springs will go on. Most current PDS shocks used a preloaded rebound shim stack. They do this to make the low speed as stiff as posible yet keep the bike jumping flat. It's a cool concept, but then they have to use this huge bleed port.. thats bazare, and I know that they are hoping to overlap with clicker and deflection but it is a strange concept in a slow moving shock.
Whats my point? I give advice that is often stated as well this is what I think you need , but what are your long term goals/plans.. If you want the right spring IMO I'll tell you but often I preface my advice with do you want the right spring or do you want a revalve in a bottle? In other words longterm or short term fix.
3.) PDS shocks are frankly diferent across the baord.. I chcuckle to myself when we worry about say the diference from 9.0- to say 9.2.. Theses shocks require larger changes to make the same diference as it would on a linkage system..
4.) The verdict is never in... Suspension is constantly changing topic. Just like evolution of species, sometimes we do something ultimately for it to become vesideual, only to use it agian later..
Still all things considered I beilve that a progressive spring causes understeer as it places less dynamic weight on the front wheel, and causes packing becasue the spring does not offer enough up force at near exstended postions. Lighten up rebound and you end up with a kick on medium sized bumps as now the spring returns with more energy..
Regards,
JEr
You should come here more often! Honestly a very fair question.
My thought just like you is based on my opion, which is based on my biasis and practical exspereince. Iwould argue that this is a function of many things.
1.) I spend very little time working with stock bikes or set-ups. I make assements of valving and spring issues based on my science, which you might want to consider a function. After I have made those assementsI decide what needs to be changed to produce the feel that I beilve my rider base will prefer.
2.) Honestly changing springs only is a crap shot at best.. Consider the range of shocks and valving that these springs will go on. Most current PDS shocks used a preloaded rebound shim stack. They do this to make the low speed as stiff as posible yet keep the bike jumping flat. It's a cool concept, but then they have to use this huge bleed port.. thats bazare, and I know that they are hoping to overlap with clicker and deflection but it is a strange concept in a slow moving shock.
Whats my point? I give advice that is often stated as well this is what I think you need , but what are your long term goals/plans.. If you want the right spring IMO I'll tell you but often I preface my advice with do you want the right spring or do you want a revalve in a bottle? In other words longterm or short term fix.
3.) PDS shocks are frankly diferent across the baord.. I chcuckle to myself when we worry about say the diference from 9.0- to say 9.2.. Theses shocks require larger changes to make the same diference as it would on a linkage system..
4.) The verdict is never in... Suspension is constantly changing topic. Just like evolution of species, sometimes we do something ultimately for it to become vesideual, only to use it agian later..
Still all things considered I beilve that a progressive spring causes understeer as it places less dynamic weight on the front wheel, and causes packing becasue the spring does not offer enough up force at near exstended postions. Lighten up rebound and you end up with a kick on medium sized bumps as now the spring returns with more energy..
Regards,
JEr
Jer
I see Stricks point and my lard butt feels the Progressive is better but then again my shock was revalved with the progessive in mind.
We spoke a few times about progressive rates, crossovers etc. Would you pursue the use of progressive springs and create valving changes if it was possible to control the progressive springs properly? Or do you feel valving with straight rate' can achieve results that most of us can be happy with, thus making the progressive theories stay in the closet.
Mike
I see Stricks point and my lard butt feels the Progressive is better but then again my shock was revalved with the progessive in mind.
We spoke a few times about progressive rates, crossovers etc. Would you pursue the use of progressive springs and create valving changes if it was possible to control the progressive springs properly? Or do you feel valving with straight rate' can achieve results that most of us can be happy with, thus making the progressive theories stay in the closet.
Mike
The reasoning behind the progressive spring is the lack of rising rate with the KTM linkless rear end. Dirt Bike rag (Nov. '01) has a very good diagram that shows the relationship between force required and travel of all the '02 125's overlaid on one another. Even with the progressive spring the KTM has the least progression toward the end of the stroke . Using a straight rate spring will only worsen this. What the KTM actually needs is a progressive spring with more radical progression if it wants to mimick the action of the jap bikes with the best rear suspension. IMHO
marcusgunby
LIFETIME SPONSOR
- Jan 9, 2000
- 6,450
- 2
I would love to see the graph
If anyone could scan and e mail it to me i would really appreciate it-i struggle to get almost any mags here now days-even uk ones.:(
If anyone could scan and e mail it to me i would really appreciate it-i struggle to get almost any mags here now days-even uk ones.:(
Jeremy Wilkey
Owner, MX-Tech
- Jan 28, 2000
- 1,453
- 0
WOW!! This was the last string I relpied to about a week ago but my responce is gone.. Werid.. I wonder if Okie edited it for my speed induced typing babile...
Any Couple of things CP380SX your right and wrong.. The linkage induced progression does not occur on the PDS system.. This is very good for outdoor condtions as the the shock does not have to deal with aincrease in damping due to a increase in shock speed (Due to linkage) Most Jap systmes actualy place the chnage in the bottom half to promote a pack that allows the suspension to slighlty pack in stadium whoops.
A PDS system does not do this which allows the shock to respound better when say under severe weight load.. Translation much better action.. unless your Ricky Carhmical doing stadium whoops..
The Dirt Bike article does not take into consideration damping only spring, so in the final few inches of wheel travel a KTM massively increases compression due to speed.. I think for the average rider it is way better..
When I first saw the graph I was like what? Then after investigfating it is only a force to bottom measuremnet and while cool is not really showing the linear advantage of the PDS system.. One other thing the Graph was scalled in minimizing units..
Regards,
Jer
Any Couple of things CP380SX your right and wrong.. The linkage induced progression does not occur on the PDS system.. This is very good for outdoor condtions as the the shock does not have to deal with aincrease in damping due to a increase in shock speed (Due to linkage) Most Jap systmes actualy place the chnage in the bottom half to promote a pack that allows the suspension to slighlty pack in stadium whoops.
A PDS system does not do this which allows the shock to respound better when say under severe weight load.. Translation much better action.. unless your Ricky Carhmical doing stadium whoops..
The Dirt Bike article does not take into consideration damping only spring, so in the final few inches of wheel travel a KTM massively increases compression due to speed.. I think for the average rider it is way better..
When I first saw the graph I was like what? Then after investigfating it is only a force to bottom measuremnet and while cool is not really showing the linear advantage of the PDS system.. One other thing the Graph was scalled in minimizing units..
Regards,
Jer
- Thread starter
- #14
I think that the reason a progressive spring feels better is that you steer a motorcycle with the rear wheel......I can understand why a motorcross rider would want more weight on the front wheel, but for offroad the progressive spring is more confidence inspiring. Consider Shane Watt's riding style..he sits towards the rear of the bike and he only stands when absolutely necessary..he steers with the rear wheel and by moving his weight around. I believe that the progressive spring allows you to relax a little more in offroad conditions and this pays off during a long race.Of course I may be all wet and somebody will probably tell me so, but its an interesting topic.
Another thing...if the rear shock is the most important part of the suspension, wouldn't you want to have more emphasis on the shock than on the fork ? (I mean the progressive spring seems to put more weight on the rear of the bike, or shift the balance to the rear.)
I have both and the progressive seems to feel more "natural" or puts me at ease on the bike. I do agree on uphills the shock does pack with the progressive on but it also hooks up much better everywhere else. The straight rate severely impairs hook-up on cornering and gives that "stinkbug" feeling on downhills.
Ah well its probably my weird riding style
:)
Happy new year
Gary
Another thing...if the rear shock is the most important part of the suspension, wouldn't you want to have more emphasis on the shock than on the fork ? (I mean the progressive spring seems to put more weight on the rear of the bike, or shift the balance to the rear.)
I have both and the progressive seems to feel more "natural" or puts me at ease on the bike. I do agree on uphills the shock does pack with the progressive on but it also hooks up much better everywhere else. The straight rate severely impairs hook-up on cornering and gives that "stinkbug" feeling on downhills.
Ah well its probably my weird riding style
:)
Happy new year
Gary
Well I hope we dont get into another heated debate about pds but I would like to share my results trying the progressive verses straight rate.
On my 02 520 we revalved the shock to absorb sqaure edged bumps
under full throttle speed. ( more high speed comp)
this also took away the packing felt when braking into a bump laden corner
from high speed from a long straight.
I felt the stock pds 7 spring was too soft the first 2 inches of its travel and then was way too firm from there on.The shock was in the stiff part of its stroke too early on those high speed bumps.
Checking the spring on a spring rate tester pretty much confirmed what I was feeling. I could flat land the bike and the bottom out resistance was great but
all those little bumps seemed to be much more noticable on the 02 than my 01 520. We ran anywhere from 20mm of unladen sag to as much as 40mm
just to get a feel for its action .
On went the 8.4 straght rate. The same small bumps were absorbed
and the bike was very plush on all high speed sections.
On flat landings it worked as well as the progressive.( needle engagement)
On steep jump faces I felt the shock had a tendancey to compress more and not give me the lift to clear doubles like the progressive spring did.
I had to use more throttle and be on the gas a little longer concentrating on giving the bike more preload and pulling my feet up sooner and more to get the bike to rise off the jump faces.
Going into banked corners the bike would want to climb the bearm and not turn as easy but I felt comming out of the turn on the gas the bike would sqaut and hook up like crazy.
We tried to balance the bike out front to rear and add and subtract preload
but myself and one local pro came away thinking the same thing.
The overall action was better with the progressive spring even though some areas of the track the bike worked better with the 8.4.
WE ALSO TRIED AN 8.8 AND A 9.2 WITH PRETTY MUCH THE SAME RESULTS.
I actually put on a pds 6-265 from my 01 520 and slowed the low speed comp and ended up with what I felt was best for me. Even though this spring shouldnt it actually held the back of the bike up a liitle better and was more plush in the mid stroke. On paper the pds 7 should do a better job of holding up the bike but in reality it did not.I am 195 with gear and ride
vet 25and 30 A on mostly high speed outdoor tracks . Red Bud very often.
The straight rate works pretty good and I feel the right valving would make it work better.
I think it depends on what you are looking for and each rider is different.
The 98 shocks had straight rate springs on them but got the extra resistance
from using a longer shaft needle that engaged sooner in the shock compression travel.
We are actually machining some progressive and longer needles for the 02 shock to test with.It is a shot in the dark but we are trying to combine the
longer needle and the straight rate combination without resulting in the harsh action the 98 shock had before drilling free bleed holes.
So I think as I said before, try some different springs if you can get you hands on them cheap as we did here.
The problem with all the progressive springs we have tested is they are way
off on there advertised rate more so from mid stroke to full compression.
The straight rates are usually very close and consistant.
Take it for what its worth but so far the progressive seems the best for a wide range of terrain. White bros insists on using a straight rate spring but
Factory connection uses a progressive on Dowds bike and they have done allot of testing with him using the two spring types.
He runs a pds 3 which was stock on the 99 sx 380.
On my 02 520 we revalved the shock to absorb sqaure edged bumps
under full throttle speed. ( more high speed comp)
this also took away the packing felt when braking into a bump laden corner
from high speed from a long straight.
I felt the stock pds 7 spring was too soft the first 2 inches of its travel and then was way too firm from there on.The shock was in the stiff part of its stroke too early on those high speed bumps.
Checking the spring on a spring rate tester pretty much confirmed what I was feeling. I could flat land the bike and the bottom out resistance was great but
all those little bumps seemed to be much more noticable on the 02 than my 01 520. We ran anywhere from 20mm of unladen sag to as much as 40mm
just to get a feel for its action .
On went the 8.4 straght rate. The same small bumps were absorbed
and the bike was very plush on all high speed sections.
On flat landings it worked as well as the progressive.( needle engagement)
On steep jump faces I felt the shock had a tendancey to compress more and not give me the lift to clear doubles like the progressive spring did.
I had to use more throttle and be on the gas a little longer concentrating on giving the bike more preload and pulling my feet up sooner and more to get the bike to rise off the jump faces.
Going into banked corners the bike would want to climb the bearm and not turn as easy but I felt comming out of the turn on the gas the bike would sqaut and hook up like crazy.
We tried to balance the bike out front to rear and add and subtract preload
but myself and one local pro came away thinking the same thing.
The overall action was better with the progressive spring even though some areas of the track the bike worked better with the 8.4.
WE ALSO TRIED AN 8.8 AND A 9.2 WITH PRETTY MUCH THE SAME RESULTS.
I actually put on a pds 6-265 from my 01 520 and slowed the low speed comp and ended up with what I felt was best for me. Even though this spring shouldnt it actually held the back of the bike up a liitle better and was more plush in the mid stroke. On paper the pds 7 should do a better job of holding up the bike but in reality it did not.I am 195 with gear and ride
vet 25and 30 A on mostly high speed outdoor tracks . Red Bud very often.
The straight rate works pretty good and I feel the right valving would make it work better.
I think it depends on what you are looking for and each rider is different.
The 98 shocks had straight rate springs on them but got the extra resistance
from using a longer shaft needle that engaged sooner in the shock compression travel.
We are actually machining some progressive and longer needles for the 02 shock to test with.It is a shot in the dark but we are trying to combine the
longer needle and the straight rate combination without resulting in the harsh action the 98 shock had before drilling free bleed holes.
So I think as I said before, try some different springs if you can get you hands on them cheap as we did here.
The problem with all the progressive springs we have tested is they are way
off on there advertised rate more so from mid stroke to full compression.
The straight rates are usually very close and consistant.
Take it for what its worth but so far the progressive seems the best for a wide range of terrain. White bros insists on using a straight rate spring but
Factory connection uses a progressive on Dowds bike and they have done allot of testing with him using the two spring types.
He runs a pds 3 which was stock on the 99 sx 380.
Last edited:
Similar Topics
