Chassis help

Discussion in 'Tech' started by sportracer07, Oct 3, 2019.

  1. sportracer07

    sportracer07 Well-Known Member

    Hey guys I need some chassis/suspension help here. I have an 02 ZX6R that is set up as a track bike. Im running Ntec slicks, the suspension is set up for my weight. The problem I am having is that its really hard to transition from left to right or right to left while im on the gas hard. Especially coming out of the chicane at Road atlanta or other areas or tracks where I need to be on the gas hard. I basically have to let off the gas turn then get back on the gas. The bike just does not want to transition quickly if im on the gas. What can I do to help this? Im not a fast rider, I turn 1;38's at R A and 1;37's at Vir so im not fast, but I think I could do better if I could get the bike to transition faster.
     
  2. WingLeaner

    WingLeaner The Medium Labowski

    My advice won’t be something to modify on your bike but I would suggest reaching out to a trackside suspension guy at your next event. They’re very resourceful and usually want to help. Also, pay the small fee to have them setup baseline and sag on your bike. Cheers!
     
    Dave250 likes this.
  3. lookmtb

    lookmtb Member

    One thing that helped my old gsxr 600 turn easier was raising the suspension. For me, I lengthened my shock by about 8mm and set my forks flush with my triple clamp (again about 8mm). I was directed to set it up this way by traxxion dynamics. The bike feels much more nimble now, like night and day. I have no experience with the zx6r but I think raising the suspension is a fairly common thing to do.
     
  4. SPL170db

    SPL170db Trackday winner

    Yeah I would work with an experienced suspension tech, but generally speaking (at least as it pertained to my GSXR 600 as well) raising it up both ends helped with this problem.
     
  5. drop

    drop Well-Known Member

    What air pressure in front tire?
     
  6. sportracer07

    sportracer07 Well-Known Member

    Drop. I'm running 37psi front and 18 to 20psi on the rear. Thanks guys I may try raising it and see if that helps. Thank u.
     
  7. Pneumatico Delle Vittorie

    Pneumatico Delle Vittorie Retired "Tire" Guy

    OP unless your getting suggestions from another ZX6 guy move right along to a local suspension guy for assistance. The bucks you spend with him will have the most bang for the buck over the long run.
     
    cav115 likes this.
  8. drop

    drop Well-Known Member

    Agree. But if he is running 32psi in the front of a Dunlop, that would be an issue.
     
  9. Pneumatico Delle Vittorie

    Pneumatico Delle Vittorie Retired "Tire" Guy

    Ok but come on tire pressures have been published for a hundred years (here and from the tire companies) so if you aren't on the right pressure then there's no frickin excuse.
     
  10. JCW

    JCW Well-Known Member

    when you try to transition on the gas, it will always require more countersteering input than turning on the brakes or off throttle.

    you can add preload to the rear, increase low speed comp, run a greater swingarm angle with a longer shock or shim or add rebound to the front, (anything to reduce or slow rearward weight tranfer) but the fact that weight is transitioning to the back wheel instead of on the front will always mean get the bike turned on the gas is harder.
     
    Last edited: Oct 4, 2019
    Marid2apterbilt likes this.
  11. stangmx13

    stangmx13 Well-Known Member

    the bike is not setup for your weight. if it was, you wouldn't have issues. plus the faster u get, the less meaningful that phrase actually is. so change something and c if you like it. id also start with adding rear ride-height.
     
  12. Find someone with some old set up notes. No idea what made those things happy geometry wise.
    The bike could be set up for his weight, maybe just not his skill level and / or riding style. I agree with your statement though :)
     
  13. RM Racing

    RM Racing Tool user

    Raise the bike.
     
    nlzmo400r likes this.
  14. nlzmo400r

    nlzmo400r Well-Known Member

    I'll start by saying I mean this post solely to educate, not to say anyone posted previous to this or after is right or wrong.

    1: Understand chassis dynamics and geometry. Motorcycles are so incredibly complicated it's astounding. Here's a great cheat sheet that works regardless of year/make/model. The only caveat is that I'm assuming a 'traditional sportbike setup'. Meaning, no cruisers with front sprockets below the swingarm pivot, no shaft drive that does weird things with antisquat etc. Basically, your ZX6R falls perfectly into what I'm speaking to. Take some measurements before you change anything. It's really great to know the starting point and the behavior of the bike at that starting point. Get these numbers

    2. Rake - can be gotten with a little digital angle gauge easily by sticking it on the fork tube. Fork tube and steering head are almost always parallel which makes this method ok. Bike should be resting on its own weight to make this a usable reference. Expect to see something in the 23-25 degree range.

    3. Trail - Measure the trail number or use an online calculator once you know your rake, triple clamp offset and tire circumference or diameter. Also done with bike resting on it's weight on the tires. Expect somewhere in the 90-105mm range.

    4. Swingarm length - Measure this using a string or straight edge from the swingarm pivot to the rear axle location with bike on its tires. Expect 550-600mm or so. Again, this is just a starting point/reference each chassis will differ a little here.

    5. Swingarm angle - Use a straight edge (or you can draw triangles if you're into trig) and a digital angle gauge to find the angle of the rear axle to the swingarm pivot. This should be done with the bike level, but the suspension fully extended both front and rear. Expect to see somewhere between 8.5-13 degrees.

    6. Take note of your final drive setup (front sprocket tooth count and rear sprocket tooth count. Larger rear or smaller front sprockets create more antisquat effect. The opposite does the opposite.

    Notice I never said anything about ride height. The reason I don't focus too much on ride height is because it varies so much with different measuring tools and points etc. What's important is what ride height affects i.e. Rake, trail, swingarm angle, wheelbase etc.

    Now with these lovely measurements as a reference point, we know what we can adjust back to should we fuck this up to much. The next big step is understanding what each of these measurements does to the behavior of the motorcycle. I'll attack your problem specifically so this doesn't get too lengthy. Your complaint is the bike doesn't capsize quickly on the throttle. (Capsize meaning flopping from left knee down to right knee down. STEERING is from upright to right or left, two different problems. Let's look at capsize. How do you get the bike to capsize more quickly?

    The first way is painfully obvious and requires no changes to the bike. Put more effort into the bars and move your body more quickly. If you feel you're already exerting quite a bit of effort, more leverage may help. Perhaps look into some longer aftermarket clip ons if you're still using stock ones.

    Second way is to adjust the motorcycle. Know that every adjustment comes with a trade off. To get the bike to capsize more quickly, you would want a shorter wheelbase, a higher center of gravity (raising the bike), less rake and trail. Do only one of these at a time.

    If you shorten the wheelbase by moving the rear axle forward, you will shift the weight bias backwards on the motorcycle. This will reduce front end grip under high G cornering and especially on the throttle because more of the motorcycles weight is now over the rear tire.

    If you choose to raise the center of gravity, the bike will capsize faster, but you will also change the rake, trail and swingarm angle as well. The rake will increase as will trail (probably very small amounts) which will make the bike STEER (not capsize) a little slower. The swingarm angle will also increase which will increase antisquat which should also help the bike steer and capsize more quickly on the throttle because it will be slower to transfer weight rearwards. Raising the center of gravity will also make the bike less stable in general, being more likely to wheelie and stoppie under hard braking.

    Now go adjust things and have fun taking notes along the way. The 'expected' numbers I mentioned are just a ballpark. I mean that as in if you raise the bike and like the results, and raise it more and more and more and find that your swingarm angle is 16 degrees and your rake is 25* with 115mm of trail you're out in no-man's land. This is why it's important to take measurements first to know how far off the baseline you've gone.
     
    Last edited: Oct 9, 2019
    90kacoupe likes this.
  15. 90kacoupe

    90kacoupe Novice seeking Help

    This is a problem I am having with my RZ race bike. (R6 front end and FZ600 swing arm) I am having major issues under braking. I do not feel stable at all. I struggle to keep the back wheel down and it is not confidence inspiring at all. I know my ride height is a little high. but this is to help with keeping the chambers off the ground. Would a little bit longer swing arm help this? My only other idea is to go smaller on the master cylinder bore to give me more feel on initial braking, but I think that is just masking the problem.
     
  16. nlzmo400r

    nlzmo400r Well-Known Member

    From a chassis perspective if the rear wheel is coming off the ground quickly under braking, a longer swingarm will help as this would increase the wheelbase. Keep in mind this longer wheelbase will also require more lean angle to maintain a given speed than a shorter one, meaning scraping the pipes and such is more likely.

    An easier method to keeping the rear wheel on the ground would be with suspension adjustments. Make sure the rear shock rebound valve is as open as possible without introducing instability during cornering. This will allow the spring to force the rear tire to the ground with less resistance.

    Lastly a little riding style change could be in order. Briefly pressing the rear brake BEFORE pressing the front brake will squat the rear of the bike effectively lowering the center of gravity, flattening the swingarm and adding stability. By doing this for a split second before applying maximum front brake pressure you reduce the leverage arm the center of mass has to lift the rear tire off the ground.

    Regarding the master cylinder, don't change that unless you specifically want to change brake feel. Like you said, that's a band aid.
     
  17. stangmx13

    stangmx13 Well-Known Member

    have u tried adjusting the front end? its generally easier to fix corner entry problems with the front end. more front ride-height, more fork preload, and more fork compression damping will all help keep the rear tire down.
     
    JCW likes this.
  18. beathiswon

    beathiswon Well-Known Member

    Read Race Tech's "Motorcycle Suspension Bible". I'm just a shadetree suspension guy from when damper rods where state of the art but learned more about my suspension/setup from this book than 40 years of forking around on my own and trying to get top secret advice from those who knew what they were doing. Not a turn-this-screw-3-times type of book but gives an easy to read and understand theory and practical info on how to learn to improve your own setup. (Wow, that reads like an ad but that's how I would describe it) Very helpful. https://www.google.com/search?q=race+tech+motorcycle+suspension+bible&ie=&oe=
     

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