Sag/Geometry Question

Discussion in 'Tech' started by Atahan Koymen, Jun 9, 2020.

  1. Atahan Koymen

    Atahan Koymen Active Member

    If a bike is set up (2015 kawasaki 636) with 2 different set up in terms of sag which one of these set ups is most likely to have lazy turn in, have harder time to go from straight up to lean position, and also have tendency to head shake under heavy acceleration(full throttle) coming out of corners when the bike is still leaned not completely straight up. Turns I am referring to if it makes difference is final turn at pittrace (2nd gear) and top of the hill before turn 7(3rd gear)

    All measurements taken slacker zeroed when tire fully off the floor and measurement taken with rider on the bike with no gear)

    Set up 1

    front sag 27mm
    rear sag 24mm

    Set up 2

    front sag 30mm
    rear sag 34mm
     
  2. rob linders

    rob linders Well-Known Member

    I would encourage you to work with a suspension guy at the track. BAck when we raced, at trackdays they usually charge $40 for the day and are very helpful. Having said that, my suspension tuner never measured sag when my son was racing.

    I think @metricdevilmoto works at tracks in your area and he is well respected.
     
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  3. RM Racing

    RM Racing Tool user

    Sag isn't enough information. The youtube videos that tell you sag is so very important - don't watch them.
     
  4. Atahan Koymen

    Atahan Koymen Active Member

    I understand. I am in a dilemma. The bike was stock last year suspension wise with set up#1. Over the winter installed racetech gold valve with rebound separators. Also changed fork and shock springs to a stiffer spring as racetech recommended for my weight.

    Current sag numbers set up2 and bike gets terrible headshake and wants to lift the front end up coming out of corners under heavy acceleration. It never did that with stock set up. Also what puzzles me is with the racetech gold valve set up forks got longer and now they sit almost flush with caps(7mm on one side and 7.8mm on the other legsticking out to be exact) I was thinking my geometry is tail down now and causing all this problems. Both set ups had identical Q4 tires by the way if that makes any difference

    Can u even tell from just these numbers in which set up front end sits higher than the rear??

    Thanks

    Sent from my SM-N950U using Tapatalk
     
  5. Bruce

    Bruce Tuck & Roll

    There is no way for anyone to really know by a verbal description without the bike in front of them and having more info. Like current spring rates, fork and shock length, etc. I'm just going to give you a stab in the dark. Setting sag is a tool, not an end all be all. That being said without knowing more, and being a novice at suspension setup, I would guess you're squatting too much in the rear.
     
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  6. stangmx13

    stangmx13 Well-Known Member

    A few things:
    - Theres no point in comparing to your original sag numbers because you've changed so many other things since. Forget about them.
    - The forks probably didnt get longer with a valving change. Someone mounted them in the triple clamps in a different location. This changes the ride-height, which is a useful tool for setting up a bike. If the forks did get longer AND they are mounted more-flush, you have even more effective ride-height.
    - Concept like "tail down" or "nose down" arent going to help you here. The terms dont describe an actual setup, nor is one way necessary for the bike to get around the track well. The terms are somewhat meaningless anyway because you arent comparing to a known good setup.

    Heres a good way to approach setup issues:
    1. Change one thing at a time. When you have issue X, adjust A. If A improves X, you know that X was caused by A (or a lack of A). Theres no way to know what caused X if you adjust A, B, & C at the same time.
    2. When you adjust A and notice improvement, change it more to look for further improvement. If adjustment A made it worse, try adjusting it the other way to look for improvement.
    3. Take care to notice if adjustment A actually caused a change that you can feel. You mind may trick you into feeling something that doesnt exist. If you are a new track rider, you likely cant feel a 2mm change in fork sag. Id guess you will definitely feel the results of a 5mm change.
    4. To start, adjust the forks for corner entry issues & change the shock for corner exit issues. Once your setup gets good, this may not apply. But you are probably way out-of-range right now.

    Frankly, id never run any of those sag numbers. I think you have BPF forks and I think they have a long top out spring. If so, I think that works better with a bunch of fork sag, say 35-40mm. For me, 24mm shock sag is too little and 34mm is too much. I generally stay with 28-32mm range. This assumes your new spring rates are within range.
     
    Last edited: Jun 10, 2020
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  7. beathiswon

    beathiswon Well-Known Member

    Atahan, get yourself the "Race Tech Suspension Bible". A great source of suspension theories and explanations that will teach you the basics of how to setup your suspension. Not a replacement for a good suspension pro but you'll have a much better understanding of what does what.
     
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  8. Atahan Koymen

    Atahan Koymen Active Member

    Forks got clearly longer because when the tuner got done with one leg and compared to the original leg there was clearly a difference. And on top of that now these longer forks are sitting out 7mm. They used to stick out lot more when it was stock. Guessing may be 14mm or so. And yes I have Bpf and he changed the top out springs too. Stock shock was 515lbs and we put 600lbs rear springs. I weigh 160 no gear.

    I was thinking to bring the bike to set up#1 sag and fork height numbers and give it a go next month at the same track but as u stated that's probably changing too many things in once And those numbers are irrelevant because of too many changes.

    I will start with the rear of the bike since the headshake is an exit issue. One change at a time.

    Sent from my SM-N950U using Tapatalk
     
  9. D-Zum

    D-Zum Alex’s Crew Chief

    Take Mr. Linder's advise and work with @metricdevilmoto at your next event....ask him if he will give you a little info on what he's doing to your suspension...write it down. Go out and ride...if there's something you don't like, come in and advise him what the bike is doing...let him suggest changes. See how those affect the bike's handling.
    Lather, Rinse, Repeat.
     
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  10. stangmx13

    stangmx13 Well-Known Member

    Changing the top out spring will often change the fork length, especially if you compare without fully compressing top out spring. Longer forks can be a good thing. Id say that most forks on race grids are extended at least 10mm. This impacts everything about the bike including the optimal setup and optimal riding style.

    You should ask the tuner that installed those parts for his recommended setup. A good tuner that already knows your equipment including spring rates and valving should be able to give you a quality base setup. You at least need fork height, fork preload, fork damping, shock length, shock preload, shock damping, & chain length for your sprockets. If said tuner cant provide that, find someone else and pay them.

    You will save a lot of time and headache by paying to work with a professional. You are paying for their setup, their knowledge, and their previous experience. Its absolutely worth it.
     
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  11. pscook

    pscook Well-Known Member

    If you had a tuner build your suspension, you should have this on your fork and shock:
    upload_2020-6-10_13-8-4.jpeg

    This shows that the tuner is paying attention to the build and provides you with a starting point.

    And regarding the tuner handing you forks with different lengths? That, to me, shows a lack of experience and knowledge. I would immediately question what is inside of the forks and why I paid that person one thin dime.
     
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  12. RM Racing

    RM Racing Tool user

    So you paid someone to revalve your forks and he’s not answering the questions you’re asking here? Not money well spent.

    One simple answer- front is way too stiff in both cases, even is weight is biased to the rear.

    Pay a suspension tuner, a real one, to get you in the right ballpark, and don’t poll the paddock or this place. Stick with that technician until you get comfortable.
     
  13. rob linders

    rob linders Well-Known Member

    A good suspension tuner, we used Lenny Albin now with Ktec, can tune from your feedback over the phone. That was always amazing to me.

    I don’t understand suspension like @RM Racing or @stangmx13 but understand basic concepts. Even after reading the Racetec book mentioned above I still needed the help of a competent professional.

    I often would conclude the right direction in preload changes or spring changes, but was always amazed when I would think to do one thing and Lenny would come back and say move the front fork tubes 3mm in the clamps.

    Then the kid would pickup 1/2 second or a second just off such a minor change.

    Down the road if you continue to race, get springs and tools. I don’t know BPF, but with Ohlins cartridges on a R6, and the proper tools to changes springs, it is very easy to swap and can really help Dialing in your setup. Many times you only need to change one spring because they work as a unit you don’t have to put the same spring in each side.
     
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  14. Atahan Koymen

    Atahan Koymen Active Member

    I talked to my tuner and he talked to racetech about my complaints of headshake and not turning in like it used to. Racetech suggested to install the 2mm rear shock shim we pulled out doing the install to bring the swing arm angle back to normal. We initially thought the spacer was a aftermarket from the previous owner but actually it's an oem piece.

    And also need to bring the fork tubes stick up 5mm from where it is To get more weight on the front tire and get the trail numbers where it needs to be. And if it gets better may be try another 2-3 mm more to see if I am going to feel any more difference. I will give this a try. As a rider that's what I felt too front not loading enough through out entry and exit. What they said kind of confirmed my feelings.

    I appreciate everyone's input and completely agree the importance of a ontrack suspension guru to sort things out rather quickly and safely which I will do soon.

    Sent from my SM-N950U using Tapatalk
     
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  15. stangmx13

    stangmx13 Well-Known Member

    @Atahan Koymen

    did you ask the tuner for all the other setup parameters? did he communicate all that setup info to RaceTech as well? playing a game of telephone with setup kinda sucks if everyone isnt on the same page. all the setup parameters affect the other ones, so everyone needs all setup parameters for most advice to be complete and meaningful.

    for example: u are running 34mm shock sag, which is near "a lot", making the rear end "low". the 2mm shim will raise it, but it still won't be as high as when you were running 24mm sag (the heavier spring is only good for a few mm, not 8mm). on top of that, trail is affected by shock position. so "get the trail numbers where it needs to be" won't work with the rear too low.
     
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  16. Atahan Koymen

    Atahan Koymen Active Member

    Well I sent a comprehensive email about my previous set up and current set up. My complaints. So my tuner forwarded my email to his racetech contact in California. And as per racetech contact conversation he said my rear sag number is right on. I know I hear you I feel the same. I think its sagging too much but that's what the contact said. And told him to install back the 2mm shim in the rear first. Then pull the fork tubes up (drop the front end down)

    the biggest mistake here I believe was not installing the 2mm rear shim and more importantly installing the forks almost flush with the green fork caps to the triple clamp(the 7mm gap from green fork cap to the triple tree plate. The tech said there needs to be gap of 7 mm from fork tube to the triple tree. I am nowhere even close to that. I cant even see my black fork tube right now. Its buried under green fork cap.



    Sent from my SM-N950U using Tapatalk
     
  17. stangmx13

    stangmx13 Well-Known Member

    Good stuff. Sounds like you took the correct approach and know how to address issues later.
     
  18. Suzuka_joe

    Suzuka_joe Well-Known Member

    just wanted to say that after a few years at the track i just started messing with suspension setup this year and this is great advice. speaking with my suspension guy who is usually only at race events and not track days adding a click here and there to see where the bike improves has been huge. one thing to add- always keep a notebook and write down the date/track/temp/tires used/pressure's and any change of settings with the suspension.
     
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  19. KneeDragger_c69

    KneeDragger_c69 Well-Known Member

    Sounds like your rear is too low and your front high... surely reason why you are lifting the front wheel so much and the rear squating under acceleration.
     
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  20. JCW

    JCW Well-Known Member


    I tend to think of sag and shims as about doing the same thing dynamically. They are used to adjust your swingarm angle where it matters most, exiting a corner. The difference is sag changes the working range you are on your shock while the shim changes the swingarm angle independent of shock working range.

    At the track, a quick sag change can be made to see if the bike tracks better, and then later, shims added or removed and the shock returned to previous sag.

    In this guy's case, I would really like to know how far off bottom his shock gets on corner exit. How much the shock is compressing, provided he has correct spring rate.
     

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