Linkage or PDS.

[svi]

I've said here before that I know very little about the PDS system, so aside from marketing reasons I'm looking for somebody to convince me why it is necessary and why some class it as the future for suspension.
The case for linkages:
short shocks can be used making them lighter.
the shock can be positioned close to the bikes centre of gravity.
they can have infinately variable motion ratio's with respect to wheel travel.
a linkage changes the rate of velocity as well as spring force.
the shock compresses in a straight line with very little rocking motion.
Is a complex link and simple shock the way forward or a complex shock and no link?

 

[marcusgunby]

No point in asking as the PDS will be dropped in 05, the linkage KTM has been seen testing.

 

[svi]

Is that it then consigned to history, or are Husaberg going to continue development?

 

[dthoms]

Quote:
No point in asking as the PDS will be dropped in 05, the linkage KTM has been seen testing.

Marcus,
I'm surprised at your reply, you may or may not be correct about KTM going back to linkage, but the question still raises a valid point.
I for one think the non-linkage system has got a bad rap. I have ridden/owned (many) bikes with and with out linkage. I have a 02 KTM and will admit it tooks some tuning to get it right, I am very satisfied with the rear suspension. If I had any complaints about the suspension on my KTM it would be that the forks are to flexible.
I also had a chance to ride one of the late model Cannondales and I would have to say it had the best suspension of any bike I have ridden, it also sports a non-linkage rear suspension with a Ohlins shock.
What areas do think the non-linkage suspension are weak in?
I will admit that I'm no motocrosser, so there might be some valid points of the non-linkage vs. linkage that I wouldn't consider.
Happy Holidays,
Dave Thoms

 

[terry hay]

As i've said before the PDS system was one of the greatest marketing exercises we've seen in the motorcycle industry. It has advanced KTM into the mainstream of motorcycle manufacturing. I'm not surprised to hear that KTM are now leaving the linkless system behind for more conventional methods. They have achieved a level of credibility akin to that of the Japanese manufacturers and can now set about beating them at their own game. Last time I spoke on the subject of position sensitve damping I managed to raise the ire of one Jeremy Wilkey and my knowledge of the subject was severely questioned. Well, I would just like to say that position sensitive damping does not exsist within the confines of this design, and at best, we can only experience a positional influence from the PDS system. And given the design of the linkage assisted shocks we also experience a positional influence, only over the full travel, and with a nice progressive nature. The PDS system has seen both manufacturers and aftermarket tuners struggling to compensate for the lack of a linkage, falling short all the while. The truly sad thing is that they are getting closer all the time. The simplicity of the linkage system is spectacular when you consider the comlexity of trying to do without it. Now that things are calm Jeremy I'll happily answer any question you have for me regarding my views on the PDS shocks.
Regards
Terry Hay -- MERRY CHRISTMAS!!!

 

[svi]

What I'm really trying to nail is why was it conceived, I can't believe it was conceived with no technical merit, what were the perceived advantages over a link, you could never argue it was less complex.
You remove one maintenance task in that there is no linkage to clean and grease but apart from that I can only see disadvantages.
Can a progressive spring be wound to give an accurate rate of progression?
What were the thoughts on damping requirements that led to a twin piston design?

 

[marcusgunby]

dave yes my reply was lacking to be honest , as usually i love to talk for hours about all suspension stuff.Sorry about that svi , i was just trying to put out some info and did it badly.

Well IMO the linkage-less design has merits and shortcomings, in theory its lighter(but a CR weighs less than a KTM) and has less stiction(well if it wasnt for the 2 piston rings and big 18mm shaft it might have less)is easier to service (hmm not IMO due to the complex pds internal design)and the bottom bearing requires no maintenance(well it would if it lasted 2 seasons LOL)
So what are we left with?, well it is easy to remove and replace.

I believe the pds can work for woods stuff, but mx and sx is its downfall IMO.Now saying that the later ones are actually not too bad and feel IMO more like a normal bike.

So back to a linkage bike-its more tunable and easier to tune IMO.Its got a harder to service linkage and its more costly to service.However it crosses over the different terrians better IMO.I think a good chassis dyno could have got the PDS working alot better than i does.

Overall i will take a linkage bike just because i believe they are ultimatly better.

 

[380EXCman]

No point in asking as the PDS will be dropped in 05, the linkage KTM has been seen testing.

Yamaha has been testing a aluminum chassis now for quite a few years but its still unclear when or if they will put it into production.

Some PDS positives.

Shock can be offset allowing for a more direct intake track = more hp.
Lack of linkage = less weight.
Lack of linkage = less maintinance.

I think that the PDS represnts the cutting edge in suspension technology. They have come along ways since 98. I think what they have now "04" is as good as the Japanese equipment. Maybe the PDS just needs more time to develop. But to scrap the whole deal at this point would be just going backwards. They currently sell every bike they make, so its not as if the PDS is holding the bike back so much that no one is riding them. Also look at how successful they are in competition, The PDS does not seem to hold them back to much there either......

 

[marcusgunby]

svi as far as i know one big shortcoming was the progressive springs were all testing too much away from specified-so you need to get maybe 3, to actually find one that is as you expect.

 

[380EXCman]

I believe the pds can work for woods stuff, but mx and sx is its downfall IMO.

Im not so sure of that. The vairiables incountered in off road is much greater than on a MX or SX track. In the desert where I do most my riding you can go from hard pack to sandwashes to whoops so big a volkswagon will sit upside down in, to rocky sections and all at speeds ranging from 5 mph to 85 mph.....

As i've said before the PDS system was one of the greatest marketing exercises we've seen in the motorcycle industry. It has advanced KTM into the mainstream of motorcycle manufacturing.

I think what has made KTM so successful is their vision and their commitmnet to dirt bikes (not drums, keyboards, lawn mowers, cars, etc, etc). The quality of componets, like the hydro clutch, plated pipe, chromoly frame, qualtiy bars and chain, no tools air filter access. I think this is what has made KTM what they are today. Not to mention offering a competitive alternative to the japanese MFG's...

 

[svi]

Originally posted by 380EXCman

I think that the PDS represnts the cutting edge in suspension technology. They have come along ways since 98. I think what they have now "04" is as good as the Japanese equipment. Maybe the PDS just needs more time to develop. But to scrap the whole deal at this point would be just going backwards.

But why is it cutting edge what technologies does it contain that has not been seen before? Is being different cutting edge?

Marcus,
I thought the fact that they are scrapping it was a valid point, have you heard any reasons why?

 

[marcusgunby]

No KTM has ever came much of the bottom in a shootout of the suspension.Also i know of many riders that were lulled into going to KTM after watching how good the factory bikes went(little did they know some of those top riders will ride a plank, if its a fast plank)after a season or two they are dissalusioned why there bikes dont work for as many tracks as there previous bikes, thats the weird part of a PDS, one week on one track it feels great and you think you have cracked the problem, next week on a different track and it feels like it wants you off the bike.

As for cutting edge-i used to think the same, until my wheel bearings went in less than a season, the shock broke at the clevis, the parts used to routinely fall off even when i went over every bolt each ride.The footpegs drooped.The slave cylinder on the hydro clutch wasnt too reliable either.Sorry but i maintain all my bikes the same and the ktm wasnt a reliable bike.

 

[380EXCman]

Is being different cutting edge?

I think to a certain degree it is. I think the hydro clutch is similar type of deal. I would consider it cutting edge. Sure its not new technology, but it is not widely used by the other MFG's. Its possible that they could be changing but I find it hard to see where the pay off is... What are they working towards?

 

[380EXCman]

Marcus, Now I dont want to turn this into a one bike is better than the other type deal. But For all the problems you had there are people who have had none. It happens. I have had 3 KTM's and 1 Husaberg. All were very reliable and gave me zero problems (knock on wood) :worship: ...

As for the shootouts, the 04 stuff seems to be doing pretty well. Both have there advantages and disadvantages. I think the WP stuff now is very competitive. Competitive enough to continue on with the PDS. Sure I have been a guinnea pig the last 5 years (and thats a downside) but I have seen a steady progression. Im almost affraid that if they do go back to the linkage that there will be a learning curve so to speak..

 

[marcusgunby]

380 i am mentally scarred from my owning a KTM so ignore my ramblings.The one thing it did, was to bring me into the suspension forum, and i have been hooked on looking at bendy washers ever since.

marcus.

 

[380EXCman]

The one thing it did, was to bring me into the suspension forum, and i have been hooked on looking at bendy washers ever since.

And thats a good thing..... :thumb:

 

[Jeff Howe]

This is OT, but I looked at that Performax website and noticed the fuel fragrance. Are people really buying that stuff?? I cannot beleive somebody would want their bike to smell like a piece of fruit.

 

[terry hay]

SVI
We can only guess as to what was the real reason behind the introduction of the PDS shock. It was obviously not superior performance that persuaded KTM to employ the product in their bikes. Simple side by side testing would have shown that it wasn't as good as a linkage setup. There were other performance benefits that were made possible by having an offset shock that perhaps swayed their decision. Power gains that created truly impressive rewards for 125 pilots. Smoother power delivery for the 250, 300, 380 riders.
Without doubt KTM now makes the japs look pretty ordinary when it comes to 2stroke motors. I guess when you look at the big picture the PDS decision was not just one of suspension performance. Another viewpoint; Perhaps the concept was adopted with an ongoing commitment from WP for product development. I mean, to be fair to WP we have seen upgrades every year since its inception. As for the future of the PDS shock. BMW are now using the shock on some of their latest bikes so perhaps WP are not ready to throw the towel in just yet. Given the lower rates of change in the leverage ratios of road bikes maybe the PDS will find a new home.
Regards
Terry

 

[svi]

Terry,
Do you know what the percentage change in leverage ratio is?

 

[bclapham]

i am not sure about the straigter intake tract is the big bonus of the linlkess system- look at a rm125 manifold its real straight!!! i think half of the jap bikes have been held back on power since they have been using outdated engine designs, eg cylinders and reed blocks- from what i have gathered speaking to marcus of late, the 04 kx and rms are making ktm power- this year the kx straightened out the manifold and made big power and the rm has a ktm copy engine and makes good power.

the ktm 250 makes the bet power but looking at what happened with Dobb, Crockard and McGrath, i would hardly call it a smooth motor!

 

[terry hay]

Bruce
The fact that KTM have the japs concerned is proof enough that they are doing their job(motorwise). Wether McGrath or others can do the job is perhaps a question that needs to be asked on a personal level. Here in Australia KTM is a force to be reckoned with. When a stock bike is produced it has completely different characteristics from a factory bike. When you are looking for maximum horse power from smaller engines it is usually the one with the narrowest powerband that produces the highest peak horsepower. Sadly this is also one of the most difficult to ride. Who knows how the factory bikes are set up? The more I have to do with so called factory mechanics the more contempt I develop for them. They have such an easy job dealing with one rider, one bike and a tonne of support that you couldn't comprehend. Its their job to turn out the best machines, yet sometimes they miss the mark so badly. You talk about Suzuki - look at Albertyns bike. The guy deserved a medal for just staying on that piece of crap. It was one of the worst handling bikes I've ever seen. And I don't think old Mc was too thrilled with the performance either. So maybe the PDS deserves more credit to the overall performance than simply its suspension performance alone. At least for us mere mortals who are destined to ride store bought machines.
SVI
Your average road bike has a change of around 11%. So far we have seen a variation in the PDS (Due to lean angle) of around 12-15%. All of a sudden the future may not look so bleak!
Terry

 

[svi]

12-15% is that common for an offroad bike?
Like you say most street bikes are around 11-12% so I would have expected linkage equipped off road bikes to be more progressive.
I like to use around 6% for road race bikes, anything more linear which is becoming more popular with the Japanese never seems to work on our tracks, you loose a lot of compliance on our bumpy circuits, their tracks must be like billiard tables.

 

[terry hay]

SVI
We have seen the YZs get up to 36% which is a little too progressive. Personally I would like to see them around 30%. also If you make them too linear they tend to either bounce off the face of the bumps or blow through the stroke. Depending on how they're set up of course. If you're setting the road bikes up with only 6% change I presume you must be using heavier springs with less preload or you stiffen up the high speed on your comp.adjuster.
Regards
Terry

 

[svi]

So a standard link system with a 30% rising rate would also have a 30% increase in velocity which would create a large rise in damping force preventing the shock falling through the stroke and bottoming harshly.
It would also allow a light spring to be used for initial compliance as the progression will allow for big hits.
A PDS system will not have the increase in velocity so relies on the 2nd piston for the increase in damping force and relies on the rate of progression on the spring to allow it to be compliant initial and take the bigger hits.
How could they ever think that a straight rate spring would work?

 

[svi]

Terry,
Wtih regard to the changes in the rate of progression on the road race links, I make the spring harder or softer dependant upon the changes to the initial start point leverage, and revalve internally if necessary to allow for the changes in velocity.