640 Suspension question

Discussion in 'Thumpers' started by lpcassie, May 4, 2005.

  1. lpcassie

    lpcassie Sieg

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    Noob question- I picked up a '05 640 about a month ago and I got it in me today to set the rear sag. I'm kind of a light weight(bout 150lbs in my b-day suit) and have a limited inseam(31"), so I figured that softening up the spring might give me a little more purchase at stoplights. I think the stock spring is set up for someone around 175lbs. To make a long story short when I adjusted it to the recommended total sag (90mm +/- 15mm) I found that the rear ride height sag now exceeded the recommended limit. (recommended 15-20mm) I was at about double that. So what I did was kind of compromise, I decreased the total sag to about 80mm which left my rear ride height sag at around 30mm. I was wondering if all these settings are just guidelines or if I should concentrate on keeping one or the other within the suggested limits? I didn't get to test ride it after I changed the sag today because it was raining(lame excuse). Hopefully tommorow!
    #1
  2. ram1000

    ram1000 Long timer

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    Not only are they just guidelines, but they are guidelines for the optimal suspension effect on a motocross track. The ideal set up is that you would bottom your suspension on the hardest jump or bump you have hte ability to take. The lighter you are the less chance of bottoming, but the harder you ride the more cahnce of bottoming. If the rear of the bike sets lower you can compensate for this by lifting the fork tubes into the tripple clamps till the adjuster touches the handlebars. I am 6'1" and have my tubes slide up lowering the bike about 5/8 of an inch. This makes it steer faster, although if the rear is lowered it will not be much different that the stock steering geometry.
    #2
  3. Renazco

    Renazco Formerly AKA Boejangles

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    Even at your weight you need to consider front end dive into corners and such as well as a faster rebound . I'm no expert by no means but the suspension feels spongy enough as it is for a 175# person. WP in harmony with KTM set parameters for adjusting the suspension and warn against over stiffening.

    I would say, play around with the front or rear first so you can actually feel the changes being made. Go from one extreeme to the other to see what the suspension is doing and this will pretty much give you a guide.
    #3
  4. lpcassie

    lpcassie Sieg

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    Thanks for the input. If it ever stops raining in California this spring I might get a chance to test out the advice.
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  5. meat popsicle

    meat popsicle Ignostic

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    i am going to disagree with ram1000 on this. i don't think they are just "guidelines".

    the shock manual is pretty clear on this point. I don't have it in front of me right now but it doesnt sound like they are inferring its a range for optimal effects, MX or otherwise. To me it sounds like they are laying down the min/maximums.

    It states fairly clearly that the operator is to change the spring if the sag doesnt fall within the stated parameters. I think that if you don't stay inside the guidelines you are likely unduly taxing the shock and decreasing its lifespan. At some point I bet the adjustment and operation would reach the possibility of catastrophic failure.

    If in doubt contact a suspension tuning shop; don't trust a bunch of blow hards on the net. :lol3 replacements are EXPENSIVE!
    #5
  6. clintnz

    clintnz Trans-Global Chook Chaser

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    My '03 640 was, according to the manual, set up for a 70kg (155 lb) rider, I am 71 kg & it certainly felt about right. There have been no suspension changes to the '05 (AFAIK) so your bike most likely came out of the factory already set up for your weight.

    Cheers
    Clint
    #6
  7. lpcassie

    lpcassie Sieg

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    Thanks Mr Popscicle, I took your advice and called Aftershocks in Palo Alto and spoke with the owner. (probably what I should have done in the first place) He said for that model shock the static sag is the most important measurement, He sets it a 22mm.
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  8. meat popsicle

    meat popsicle Ignostic

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    Glad to be of service cassie (?). Wish I could afford to pay those people to upgrade my suspension - I am 200 +gear... rides kinda like a 72 cadillac. :lol3

    BTW, you don't have to be so formal around here; call me meat. :D
    #8
  9. Velocibiker

    Velocibiker Adventure Antagonist

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    I'm with bo and meat mixed together :D .

    The best thing you can do is play with your suspension settings to find out what's BEST FOR YOU. I say start at the recommended/factory settings. Adjust your static & race sag. Take note of those settings and then go ride your favorite trail & street.

    Start making changes to the settings and see if that helps or hurts how the ride goes. But, like re-jetting, try to make only one change at a time.

    Eventually you'll find the setting(s) you like best.

    Personally, I have mine all set in a compromise. I almost always have side panniers on while on the street, but everything comes off if I'm going to riding in some tight trails. To prevent me from having to readjust the rear shock every time I drop the luggage, I measured sag both loaded and 'naked'. Set it for the middle. I'm happy with the way it works.

    I little psi change in the tires & a few clicks up front and it runs/handles just fine for my desert riding conditions. When the day is over and I'm riding home via the highway, the psi gets returned & the clickers are set back to 'street'.

    No hassle. :D
    #9
  10. lpcassie

    lpcassie Sieg

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    Thanks for the input. Ive been dicking around with it for the past 3 hours and I think Im where I want to be for now. Im a little over the 22mm recommended static sag but I dropped my triple clamps down about 5/8 in. on my forks. This combination lowered my seat height a little bit so Ive got a little better purchase at a standstill. The front end is a little more responsive and the rear isnt so jarring in the rough stuff. I might buzz it down to Hollister tomorrow morning to give it a workout. Thanks again, great website!!:D
    #10
  11. meat popsicle

    meat popsicle Ignostic

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    If you are going to hollister, you are just a wee bit shy of "clear creek", and from what i hear its a fantastic place (long as its not dusty). search for it on the web, it is supposedly just past Pinnacles on the 25 (though I didnt see a sign last time thru...).

    Hello from San Jose :wave check out the regional west forum for local rides and such. don't forget to sign in and show us a pic of the bike in the KTM threads; it's kinda like dogs sniffin eachother... :arg
    #11
  12. makazica

    makazica Been here awhile

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    First of all, I admit that I am maybe a bit dumb and unaducated about the topic, but I'm having a little trouble understanding the pic below.

    On the pic there are two lines on the upper part of the shock absorber, and the distance between them is called A. A = 27mm.

    I'm having trouble understanding what A is. The difference between the fully extended spring and, in this case, the basic setting for preload??

    [​IMG]
    #12
  13. stephano

    stephano Long timer

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    I'm also a shorter light weight but for whatever reason I have some long sticks.:huh So I can tippy toe my bike. All geared up, I'm fine. But when I first got my bike I loosened the rear a bit and called it good. I tend to ride hard enough that I dont want a spongy ride anyways. Although the front is almost to soft sometimes but I attribute that to the freaking huge fuel tank holding 4+ gallons of fuel.
    #13
  14. Luke

    Luke GPoET&P

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    A is the amount the spring is compressed when the shock absorber is fully extended. To set it, remove the spring from the shock and measure the length. It should be about 260mm. Then install the spring on the shock and adjust the preload collars so the spring is 27mm shorter- or about 233mm.

    Edit: note that the conversion is wrong. 27mm is 1.1 inches, not 0.9
    #14
  15. makazica

    makazica Been here awhile

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    Thanks Luke....that's the answer I was looking for. Now it makes sense.
    Do I really have to remove the spring to measure its length or is it good enough to go with the specifications listed for my spring.....?

    Thanks again!
    M.
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  16. Luke

    Luke GPoET&P

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    My stock spring was within one of mm of the spec. The 27mm number should be regarded as a starting point for tuning, anyway, so getting it exactly right isn't so important.

    For tuning it's much easier to measure the distance from the shock upper casting to the top preload collar, and use that number in your notes.
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  17. makazica

    makazica Been here awhile

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    Luke,

    would you be a mate and tell me how much do you weight and what is the distance between the upper starting point of the threads and the upper locking collar on your bike...

    As you can see from my posts, I'm deep into tuning my suspension while not being the most educated suspension guy around.

    I weight around 95 kg (200 pounds??), my bike is a '01 Adv and on my spring it says 66-260.

    Ideally, I'm looking for somebody round same weight who is going to tell me the distance mentioned above to make my life easier....

    Thanks!
    M.
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  18. meat popsicle

    meat popsicle Ignostic

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    makazica,

    I don't think you should use other folks' numbers because things differ between everyone's bikes that influence static and dynamic sag. You should adjust your shock's preload to conform to KTM's sag guidelines, or the guildelines of a good suspension tuner.

    My own work on this is chronicled HERE.
    #18
  19. Luke

    Luke GPoET&P

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    My shock is not stock at all- I changed the extended length and the spring.

    On both the '02 and '97 shocks with stock everything the number should be about 25mm. However, KTM changed the internal and external spacers from year to year, so there's no guarantee that it's right for the '01. The fact that the '97 and '02 are about the same is coincidence. The total length of the shocks differ by 10mm.
    #19
  20. makazica

    makazica Been here awhile

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    Yeah, I expected somebody is going to say what you sad, but actually I'm not looking for other people's sag numbers ( as some members did before ).

    What happened is, I started messing with preload a couple months back and now I can't find the paper I wrote the measurements on....:baldy

    I was hoping for somebody around the same weight to give me, for example, the number of visible threads above the upper locking collar to start setting preload from scratch. I'll go with what Luke's mentioned.... 25 mm.

    My intention is to get four settings (me on the bike for the roads; me and my gf on the roads; me, my GF loaded with luggage on the roads and me on the bike for trail riding)...yup, I know....it would be easier to buy a BMW gsa, a Ducati 1098, a BMW r1200r and keep the ktoom for the trails.....:evil....not happening....

    Also, the trick with turning the spring with your hands is a great one....the stupid KTM tool is useless....i'm not going to post a pic of my locking collars:D, BTW. what is the price for a new set of collars...? A friend messed them up......

    Cheers!
    m.
    #20