KTM setup questions.

[mxbundy]

Hi guys I have a new 400SX and have Pro-Action do the suspension. And I have a couple of questions.
Race sag? Do you take this measurement into account when setting up a KTM? My guy said to go with 35mm static sag and not to worry about the race sag, is this correct? They put on a 8.8 spring and I feel it is to soft. the bike feels like it sags to far down in the back. So whe checked it and I have 120mm racesag, is this too much? He said that was as stiff as a spring as he could get. But doesnt mx-tech list a whole range of springs for this bike, up to about 11.0 or something? according to there spring chart I should be running a 9.4 or something. But after having done a search on the subject, I see guys who are lighter than me running springs heavier than mine and guys heavier running lighter springs. So what gives? Could they as an Pro-Action guy buy springs from mx-tech? Is there a vendor other than mx-tech that has these springs. I think pro-action uses eibach. What about progressive springs? My main complaint is that it may be affecting the steering of the bike. it feels like there is no weight on the front end, so it pushes and slides the front wheel around, could this be from the race sag being to low? And it bottoms really easy on big whoops and G-outs.
This problem didnt surface until I went out to my favorite riding spot which is all whooped out and rougher than hell.
When we did the intial set up they where out at Glen helen and the bike worked pretty good there after some intial clicker turning, but glen helen has no massive whoops or G-outs.

thanks
bundy


For the record I weigh 265# and I am an expert level offroad rider.

 

[Unit74]

Shoulda had Dicks do your Bundy!! J/K

Why don't you try a PDS? My PDS 6 ends up being a 9.7 and starts at 7.5

 

[lawman]

yep, too much sag. that's exactly how mine felt, the dreaded "chopper effect". now i'm running an 8.8, on a 200 (heavy guy with a lot of heavy enduro gear & water, etc.). i run about 20mm of free sag, about 90-95mm of race sag. bike handles WAAAAAY better (thx, jeremy!)

 

[WhiPit]

I can't wait for Jeremy's response............ :p

 

[John Curea]

IMHO, setting the race sag is ideal, this way we know the geometry of the bike WITH the rider on. 120mm is too much race sag, it will hinder the bikes ability to turn. Get the proper spring for your weight, dont try to address bottoming with stiffer than recommended springs, the bike will be a dread every where else on the track.

As long it is C.U.F. (cash up front), PA could buy springs from whomever ...

my apologies Sir Whipit, I couldn't resist.....

Take Care, John

 

[KTM-Lew]

I'm curious what Jeremy rec now since he has gone back to the progressive spring. I bought an 8.0 at their rec, but didn't like it. Back rode too high and wasn't plush on the little junk. :whiner: :confused:

 

[Jeremy Wilkey]

Bundy,
First thing first... Go to Pro-Action ask them for there assistance. YOu've spent your money and are therefore obligated to help you out. Ask these same and important questions.. This will be vital for you case...

When they give you some less than satisfactory answer you can decide to go somewhere else next time.

The fact is Straights or ProGrsesives where very hard to come by this spring at one point I had over 30 8.4's on back order.. And often made a compromise here or there (IE 8.6 /8.2) to get work out the door and people riding.. Maybe PA had a simlair problem considering they had less supply options.

(If you get a chance, ask em if they want any.. I got a fire sale on them right now... But as JC said.. CUF)

Back to the real questions. Free sag or Rider sag I belive that Rider sag is more important. The goal is to establish a basic Gemoerty that will be influenced by rider weight more than it won't, and with all the older than 03 suspension top-out less shocks the basic gemoetry is fixed. Now thats not to say that free sag is uniportant. Free sag will directly impact how the bike works when the riders weight is not being applied to the bike and this is critcal in some situations.

If your bike has a 02 SXS shock in it.. Free sag becomes more critical.. The Free sag indicates the level of preload on the spring, Since the shock has a top-out spring the higher the preload the longer the shock! Now Free sag numbers become more ctritcal. Fortunalty the good folks at WP did the math and made the spring stiff, so in reality the effective lenght varies only slitghly, and the advangatge seems to out way the disadvantages by a significant margin.

Progressives... As its been pointed out we orginally changed the Progressives, for straights after struggling to make the KTM handle.. We found that the system was fiarly insesetive to spring rate. We could go up what would be a rather large incoment in a linkage equiped bike and it would make a minimal impact on the KTM.. This is predictable however based on the rate of progression with the linkage less sytem, and the basic motion ratio.

So what do I recomend? Clearly the progressives for the average sized dude.. However you are likely off that range. I may still run a straight, but you could try a PDS #3 if you wanted. Well talk a little more about progressives but let me give you a little history behind the why I came to where I'm at now..

We at one point ran single pistons in the KTM shocks... With the Single piston set-up you you could valve the thing and not worry about overlap, and when you ran the straight albeit very large spring we got the bikes to work well.. (Well I'd hate to ride one now.. but back then it was good compared to stock..) Heck I made a quick return to racing for a few mounths on a single pistoned bike.. My Main shop guy even ran a supercross and national on one... We thought we had the world by the tail, I was convinced that the WP engineers where of there keel, and I knew what was up... Well I comited to making a sinlge piston production and called my CNC source and next thing you know I've got 100+ of these exspensive buetuys and much lighter wallet..

One night out a Joliet, I'm watching John go around and he's just getting cloberd by this one werid sized bump.. And Like a ton of bricks falling out of the Sky it hit me... It all made sence.. Wether I could make it work for 85% of the track flawlessly it did not matter beacuse that one bump was always there...And if we got it working there the house of cards completly collasped.. I was flat wrong.... (Well I'd still recomend the Single piston for a 98 but thats a whole other deal..)

(just to help me feel better I was talking With Ross Maeda a while back and he was strongly under the impression that the factory KTM of Lanagston was a single piston unit..)

I was wrong.. And I knew it..So what did I do... Well I stoped in my tracks and changed directions... Before long I realy begun to see the beuty of the PDS..... Its a work of art.. The timing of the overlap, the transtion, the awesome advanatage of being able to increase compression signficanlty at some point in the late stroke is just such a cool thing..

I started over and made quick progress, I'm convinced as a function going down the wrong path it gave me insight into the real direction..

So now We've got two pistons, why straight rate? Well still we had the handling concearns and the straights gave us what we needed, also controling the rebound was easier with the straight. We could better control the KTM tendency to kick or pack.. In simplest terms we hade less variables to consider and the PDS system had plenty to throw at us.

Over time we continued to devlop our ablity to improve and deal with more and more of the variables.. Eventully our rates went down... We where able to reduce spring rate, beacuse we did not have as much of a need to control botoming.. So we went from say a 10.0kg/mm to a 9.4 for the same rider..

In the end a spring shortage brought me back to thre Progressives. We where at a track in Texas, and needed a rate we did'nt have.. Shane and I made some valving consideration changes and away we went.. It worked.. Quickly I came back did more testing and made the offical change.

A while Back Paul Thede did a thing about bottoming load and had this Chart with a force to bottom calculation..

With a linakge bike the ratio of movent between the wheel and the changes in a way to make the shock move faster. (Transalation harsh) And it also serves to effectevly increase the rate of the spring.

With the PDS the damping will not increase signifcantly, until you hit the last portion of the travel. The progressive spring effectlvy adds rate.. You end up with way more bottoming resitstance, and way less valving induced harsheness even thought your force bottom graph claims you way off... Well Mr. you can't double the valving on your YZ 4/5 of the way through the stroke...But with your PDS you can.. ;)

So whats the deal with the Numbers?

Well its simple:
Rate 1@20mm of deflection Rate 2 @100mm deflection
PDS0-250 6.5 8.3
PDS1-250 7 9
PDS2-250 7.5 9.7
PDS3-250 8 10.3
PDS4-250 8.5 11
PDS5-265 6.6 8.6
PDS6-265 7.15 9.05
PDS7-265 7.6 9.5
PDS8-265 8.1 9.95


Why the difrent lengths for simlair springs.. Well the shorter springs cross over to the stiffer rate faster, so you can chose a intial rate and ending rate crossover that best fits your aplication.. Rather ingenius..

Philospohically I have no problems talking about my stupid mistakes, or mis understandings.. I'm sure a few months years from I'll find some humor in what I thought I knew now... The point is I have spent my life in a persuit that does have right and wrong answers but worse at times huge grey area. I make my living by recomeding what I think is best for my customers at any given moment. And subsequently judged by the results. When things change and inprove its a sing of progrees, and I'll never applogize for that, If I did I would limit my forward progress and the progress of my customers..

Best Regards,
JEr

 

[mxbundy]

Thanks Jeremy,

So you think a PDS 3 will work? One thing that I think is affecting the attitude of the bike is my height. I am 6'4" and when I move to the back for the big whoops I think that is a massive weight transfer. In fact in the garage when checking the sag, when i lean back the bike goes down another inch or so.
My PA guy has already said that he is working on getting another spring, well see.

Now this kinda off topic, but doesnt Husaberg use the same type of suspension system? I rode 380EXC mans bike up at the Reno ride and it worked pretty good. Only thing that I noticed was it had a slight kick to it on small abroupt hits and especially on a trailing throttle.

What about Cannondales, have you had the opportunity to get inside one of these yet. Do they use a system that is close to KTM? I know they have an OHLINS shock, but would it not have to be based on the same principle as a PDS shock?
You see I have a friend who is a Cann. sponsered rider and he loves it so far. Of course when you are ridding someone elses bike for free, I could see how you would have a rosy outlook on things. But he is coming of a 01 426 with a Race Tech setup. And he says it works great. He is down in Fla. racing cross country races, land of giant sand whoops and tree roots.
And finally, which discipline of racing do you feel it is harder to set a bike up for, MX or Off-road?
Thanks for letting me pick your brain.

bundy

 

[Jeremy Wilkey]

Bundy,
I've seen a few Bergs, They have a slighlty longer stroke, so ths shoke moves faster.. I think they are fundemnetally harder to tune..

The Ohlins is a diferent design.. The shock uses a recessed clinder, the shocks primary piston has a larger, od, and when it reaches said point it creates a seal with the the top cup. And now you have two working pistons..

It is cleaner in someways buy less tuneable, and actuallly limted in overall tuneablity as a function of length. However a PDS would have difucuties if you made them move much faster as weel. I feel the biggest problem facing the Ohlins PDS is insuficent body/shaft size. The limted area causes heat induced fading far worse than the KTM..

As for set-ups, well they all have there challanges... I would say presently the most challanging group of riders to tune for are Offroad guys in soft condtions. They need lots if lowspeed to keep the bike stable, hgowever they can't be fatigued by too stiff of a feel for long rides..

We've made huge step forward with all these aspects, regarles of bike.. With the home team we have assembled we can get lots of feedback fast..

Best Regards,
Jer

 

[WhiPit]

Jer,

That was really cool. Thanks for taking the time to explain all of that as well as you did.

:D

 

[DEGBERT]

A couple of weeks back I had my shocks revalved and resprung by TC suspension (2000 300 EXC for the woods with 8.0 spring and 2001 520SX for MX with 8.8 spring). A couple days after the revalve I read your post on now using progressive springs and two pistons. Should I send them back for rework or wait till they need to be serviced and have the changes done then.