Some stuff too good not to share...

Jeremy Wilkey

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#1
Gentlemen,
The Straight rate question is looming over many minds, and its a topic I know very well. Starting with the first Question.

I don't know what KTM was thinking, and one of the Engineers responsible for the development of the Shock offered little in way of an explanation. His explanation was simply we have a new needle and because of that we can run a straight. This unfortunately is circular logic. Well talk about the needle in a few paragraphs, but the other interesting part about the spring that to me really shows a major confusion is this little know detail..

When I was in Europe in the lat summer of 02 having a meeting about 03 no one mentioned straight rate spring springs. In Fact they proudly showed us the prototype Ti PDS spring.. They said that all the SXS shocks would come with this ultra light weight wonder. The TI springs where due in a few weeks at the time of the meeting however they continued to delay and delay the resale of the springs.. In the mean time Renton Coil spring (Manufactures of the high quality and popular Ti springs every tuner in the country is now selling) decided to change its marketing from a few distributors to manufacturer direct. In this I talked to the the sales Engineers about there product line and naturally KTM came up.. They laughed at the efforts KTM was going to to make a cheap Ti PDS spring. They flatly told me that KTM would fail making a PDS out of TI, because they where using a cheep alloy, and the delays where a function of development problems. Interesting...

Well finally 6-8 months late the Ti spring shows up with a note, explaining that the Part number we ordered was superseded by a new part number for a straight rate.. Interestingly enough the rate was almost an average of he PDS numbers it replaced.. So in other words they where going to use a 8. something for a PDS 6 Yikes!!! And a 9 something for a PDS 7...

About this time Ryan and Burt (Engineer for WP), where in the US doing development for 04 and they where talking up the new needle and the Straight rate springs!! The rates they where using where huge! Which they have to be if you want to get bottoming resistance. It was at this time that we found out about the new needle etc.. And it was also at this time when the path of logic was not demonstrated.. Over time however they hired Chris Wheeler to do development and he was lowering the numbers of the straight more in line with what will work initially rather than what will work later in the stroke..

Anyone familiar with KTM's know that the bikes really struggle with Stadium Whoops.. The lack of rise to the motion of the system is partially to blame for this. Japanese Bikes accelerate the shock about half way into the stroke to induce a compression pack that allows the bike to skim whoops.. With a longer needle the overlap of the 2 pistons begins sooner thereby making the shock slow its movement sooner as it travels into the stroke. Also when the valving is brought in sooner it can actually be made to be softer overall.. Which is great think about it like this.. Say your 3/5 in the stroke and you hit some nasty square edges, with the new needle your going to have to deal with both compressions, so by making the secondary much softer overall the shock is still sufficiently plush, yet still has more bottoming resistance than the older shorter needle. The alternative, say you have the old needle and your 4/5 through the stroke and you hit some big nasties the valving is so stiff to control bottoming that ytou can't bare it in this situation.. This is put in simplest terms the difference between a softer longer total average coincident and a stiffer shorter total average coefficient. In my own opinion the original preproduction needle was better than the production version, and I've actually made a conglomerate of the preproduction and the production needle.. The details can be discussed later if any of you find the needle concept interesting..

So what about the Race-Tech spring.. Paul Thede wrote a cool piece on Progressives, years ago and recently republished a chart that showed how the springs store energy over deflection, and showed how the KTM had a soft rear end when you compare force to bottom.. (Think of force to bottom as stacking weights on the back of the bike till it bottoms. NOT MEASURING DAMPING CHARACTERISTICS) It was during that time that I started to see the error of my own ways (I had recommended straights for some time.) What was even more glaring when you compared this force to bottom with a straight.. Thede took it a steep farther with his idea to make the spring softer initially and then stiffer than a PDS so to create a CR250 like spring force curve.. It was a interesting idea, and it may work well, I've got colleagues who swear by it.. I don't value the CR linkage as the greatest ever, and the amount of wire and shear weight of the RT spring discourage me from its use. As for the RT springs and sag , with the softer initial rates than the PDS series unless RT makes a really big one a 245 rider won't come close to getting the sag they need.

My friend Chuck of Fab-Tech and I have had lots of discussions about the straight rates.. Chuck went out in Ernst and attempted to make the straights work, only to find that they don't, even for his main line customer woods riders.. In our discussions the only person we mutually feel they work well for is someone who rides almost trials like conditions where bottoming control is not wanted, and initial rates are chosen only for there ability to produce a desired sage..

I could go on but simply the math and logic don't add up when using straights on PDS shocks..

Anyway I hope some of the history behind this stuff helps identify the problems of straights, I really hope KTM corrects this problem.. And next year when the bladder comes out I'm saying right now they are doing it only for economic reasons

BR,
Jer
 
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#2
Jeremy
Your comments about the progressive and straight rate springs are completely valid. But whats the solution? Paul Thede has certainly taken up the challenge with his latest offering for the KTMs and his springs appear to work better than the others. However they still fall short of the ideal in my opinion. The RaceTech springs emulate the performance of a straight rate until appr. 70mm of compression where a dramatic transition occurs and the rate increases significantly. I would prefer to see the rate inrease a little earlier and more gradually. Your work with the PDS needles sounds interesting but rather convaluted. Why not try a two stage stack on the secondary piston? The crossover point is completely tunable as is the degree of damping. You may achieve the effect you desire with a lot less effort. The bottom out bumper on the KTMs is too soft to offer any serious halting of momentum and could also be addressed. The bump rubber that Showa produce for the XR 650 does a much better job. It has a much higher duro rating and is a little longer. When trying to find a solution for the PDS we can't blame just one area. It's the sum of all the parts. Position sensitive damping was never going to be easy. I'm coming to the States in just over a week to release a new suspension development. I'll be hooking up with Larry Rosseller and trying a few things with his KTMs as soon as he gets back from Baja. We will also be testing a variety of springs which we have in prototype form. I'll keep you posted.
 

Jeremy Wilkey

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#3
Originally posted by terry hay
Your work with the PDS needles sounds interesting but rather convoluted. Why not try a two stage stack on the secondary piston? The crossover point is completely tunable as is the degree of damping. You may achieve the effect you desire with a lot less effort.
Terry,
Good to hear for you in Race-Tech land AU. I see only one posible exsplantion for your statment, and frankly I doubt it completly.. I'd be intrested in hearing how you see multiple stages being able to accomplish the goal of both postion and speed control practicaly, without being a strange twist of theory or ungodly convoluted as you say..

Controlling the size and length of the needle determines what the damping rate is at any point as a function of speed and postion..(So damping rate changes with both position, and also seed). A transition while somewhat tunable offers nothing of the such as an option. It simply changes damping rate as a function of speed, and not also position.


BR,
Jer
 
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#4
Jeremy
My whole point is that position sensitive damping has brought about a new wave of problems that have confused the masses entirely. Mainly because damping simply doesn't work that way. KTM has offered us many sizes and shapes of needles since 98 and it would appear the smaller the needle (less influence) the greater the improvement we have seen. This years example of the PDS shock sees KTM employ less spring force to achieve its progression and a more abrupt needle. A step forward? I doubt it. You can play around with the needles until the cows come home and granted, you may make improvements. What I am try to say is that we may be able to achieve greater results easier in other areas. Even if you hit upon the "Perfect Needle" the secondary piston will still have to be tuned to suit. The valving here will obviously be easier to tune for effect if we use a two stage or even a multi stage stack. If you are trying to achieve position sensitivity, why not use the spring? After all, it is "position sensitive". As I mentioned, a longer stiffer bump rubber gives you an effective "position sensitive" change. This too can be modified for different results. Your quest for the ultimate needle will be a long one and the results will be subject to personal opinion. A rider going across a set of stadium whoops doesn't care about a dyno graph. As tuners we are constanly trying to further development for the "ultimate ride" but what we (as tuners) believe is right will always take a back seat to what the rider prefers. So once again, its the sum of all the parts that makes the difference.
 

Jeremy Wilkey

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#5
Originally posted by terry hay
Jeremy
My whole point is that position sensitive damping has brought about a new wave of problems that have confused the masses entirely. Mainly because damping simply doesn't work that way.
Terry you are obviously the one confused here... Or you simply don't have the time with the system to understand what the system is trying to accomplish..


Originally posted by terry hay

KTM has offered us many sizes and shapes of needles since 98 and it would appear the smaller the needle (less influence) the greater the improvement we have seen. This years example of the PDS shock sees KTM employ less spring force to achieve its progression and a more abrupt needle. A step forward? I doubt it.
You doubt it? How's that Terry? Not wanting to be too difficult I gave you the benefit of the doubt and keep it simple assuming you come back with a hint of knowledge... Instead you do what every techno slacker does when they are asked to defend something and they are over there point of understanding and you make general statements that wish-wash the scientific nature of the question into useless drivel.. Sorry Terry, Clearly you don't understand the system. How does your suggested use of Transitions have any relation to the overlap of the PDS shock?

Originally posted by terry hay

You can play around with the needles until the cows come home and granted, you may make improvements. What I am try to say is that we may be able to achieve greater results easier in other areas. Even if you hit upon the "Perfect Needle" the secondary piston will still have to be tuned to suit. The valving here will obviously be easier to tune for effect if we use a two stage or even a multi stage stack. If you are trying to achieve position sensitivity, why not use the spring? After all, it is "position sensitive". As I mentioned, a longer stiffer bump rubber gives you an effective "position sensitive" change. This too can be modified for different results.
Once again not understanding the variables Terry.. Bumper, and Spring are different versions of the same thing an they don't directly relate to damping.. We want to raise the damping rate as a function of speed and position just like a linkage..(Or posibly better) We do this by using a needle that controls distribution of oil, and hence damping rate for a given speed.. Perhaps if you did some exasperations or math you might find that the blunt needle actually is about at the bleed threshold of practical use, in other words if we made the needle any smaller it would offer so much bypass it would not do anything at an average shock speed.. So its blunt yes but fairly progressive in nature, and quite a bit longer than the last few years..

Originally posted by terry hay

Your quest for the ultimate needle will be a long one and the results will be subject to personal opinion. A rider going across a set of stadium whoops doesn't care about a dyno graph. As tuners we are constanly trying to further development for the "ultimate ride" but what we (as tuners) believe is right will always take a back seat to what the rider prefers. So once again, its the sum of all the parts that makes the difference.
No Terry I first understand the system and how the variables relate, and then make experiments while observing the results.. Its pretty straightforward and wish-wash theory art arguments don't hold water...

This is not a RT style debate about making things simple.. We don't remove midvalves and CV's and other varibales and then overcompensate with other aspects, blaming valve restriction.. I don't appolgize for making things complex and dealing with all the issues in the most specific way, if you intnend to make the WP shock work better than or equal to a Linkage equiped bike, your going to have to do the same..

BR,
Jer
 
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#6
Jeremy
Obviously I have offended you in some way. I'll see your diatribe and raise you one! Seriously though, as you point out with your comment on the economic reasons for the straight rate spring, don't you see what has occurred with the PDS shock. It put KTM on the map for christ's sake. Once just another struggling Euro, KTM have now become an important player in the Offroad industry. It was one of the most successfull marketing ploys ever. It's up to guys like us now to make it work. My whole point to you in the first place was to exhaust the possibilities within the parameters that KTM shocks offer before you commence the arduous task of reinventing the wheel. Put your ego in your back pocket for a minute. The unfortunate thing about the written word is that you don't hear the tone that goes with it. I'm certainly not questioning your intelligence and I would thank you to offer me the same courtesy. There is obviously an element of tension between yourself and RT. I'll leave you to deal with that. You must have your reasons.
 

Jeremy Wilkey

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#8
Originally posted by terry hay
Jeremy
Obviously I have offended you in some way. I'll see your diatribe and raise you one! It's up to guys like us now to make it work. My whole point to you in the first place was to exhaust the possibilities within the parameters that KTM shocks offer before you commence the arduous task of reinventing the wheel. I'm certainly not questioning your intelligence and I would thank you to offer me the same courtesy.
Terry,
Thanks for trying to make nice on this one but seriously..Your not off the hook yet. The problem I have is this.. Your supposed to be an expert a professional shock builder, but you don't understand the difference between speed and position and how it relates to valving in a PDS shock.. Yet you have the audacity to critique what those who do understand what they are doing.. So yeah I'm more than a little fired up.. I don't suffer so called experts for a minute. I do understand your a knowledgeable guy, but I think you need to investigate PDS suspension more thoroughly. As for the RT thing I just think this argument typifies what Rt does, remove the technology and make it simple.. (even though this is off topic, I see a relation)
I've put my foot in my mouth more than once, have the courage to own up to your short comings when its your turn, and I'll be over with this.. Then we can actually use our typing time to discus other things where both our expertise's can be put to good use..

BR,
Jer
 
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#9
Jeremy
I'm fine with position sensitivty. Obviously your not convinced. How are you with objectivity and conjecture? Sometimes we get so wrapped up in looking to the stars, we can't see the problems that lay at our feet. I'll leave you to extrapolate to zygydy and I'll fix the obvious. Where is your shop? This whole thing can be worked out with a couple of beers, a whiteboard and some boxing gloves.
Terry
 
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#10
Originally posted by terry hay
Jeremy
Sometimes we get so wrapped up in looking to the stars, we can't see the problems that lay at our feet.
Terry
I agree with that all out 100% and I've been guilty of this very thing in the past myself.
 

bclapham

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#11
Originally posted by Shocknut


I agree with that all out 100% and I've been guilty of this very thing in the past myself.
yes, but what lies at your feet sometimes isnt all that good from a marketing standpoint! ;) I heard a story once about a major pharmaceutical company that spend hundreds of millions of dollars on a new drug- got it all the way past the trials and onto the market- a few weeks later, some dudes published a paper and it turns out tylenol had the same effect as their new blockbuster, dont think they sold much after that!
 

Jeremy Wilkey

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#12
Guys not to be a jerk, but your still not getting this.. Terry came on here missed the whole point of whats going on, made gross mistakes and then when I've called him out on it, makes small talk, and excuses.. My point, I'm over it, but Terry can't hang on this topic and he's going to use his new found practicality as a way out. Prety lame....

Missing the forest through the tress is not the case here, so I'm not going to let it go there.. If you guys want it over fair enough, but Terry is dispatching no wisdom in this case, just cop-outs..

Jer
 

marcusgunby

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#13
Jer i see you want answers, but you come on a bit aggressive in your post.Maybe a more subtle approach would tease terry into discussing it more.
 

MXTex

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#14
My Dad always told me, "You can't argue over facts". Jer's definitely got the facts here; and Terry, well we're glad to have you anyway. Your indoctrination is now complete.
 

bclapham

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#15
Originally posted by Jeremy Wilkey
Guys not to be a jerk, but your still not getting this.. Terry came on here missed the whole point of whats going on, made gross mistakes and then when I've called him out on it, makes small talk, and excuses.. My point, I'm over it, but Terry can't hang on this topic and he's going to use his new found practicality as a way out. Prety lame....

Missing the forest through the tress is not the case here, so I'm not going to let it go there.. If you guys want it over fair enough, but Terry is dispatching no wisdom in this case, just cop-outs..

Jer
Jeremy, we've seen this happen before, and despite your arguments, none of them warrant a personal attack, which is very much how it appeared.

sincerely, BC.