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Suspension Tuning Guide

Discussion in 'Mechanical & Technical' started by beansbaxter, Sep 10, 2005.

  1. Suspension Tuning Guide
    Street Bike or Road Racing Applications


    With incorrect suspension setup, tire wear is increased and handling suffers,
    resulting in rider fatigue. Lap times can be dramatically slower and overall
    safety for both street and race enthusiasts is another issue. Add the
    frustration factor and it just makes sense to properly setup your suspension.
    The following guide will help you dial in your suspension for faster and safer
    riding both on and off the track.

    Basic Setup: Check the following

    Forks sag 25-40 mm

    Shock sag 25-35 mm

    Check chain alignment. If not correct, bike will crab walk and sprocket wear
    will be increased.

    Proper tire balance and pressure. If out of balance, there will be vibration and
    headshake.

    Steering head bearings and torque specifications, if too loose, there will be
    head shake at high speeds.

    Front-end alignment. Check wheel alignment with triple clamps. If out of
    alignment, fork geometry will be incorrect and steering will suffer.

    Crash damage, check for proper frame geometry.

    Adjustment Locations on Forks

    Rebound adjustment (if applicable) is located near the top of the fork.
    Compression adjustment (if applicable) is located near the bottom of the fork.
    Spring preload adjustment (if applicable) is generally hex style and located at
    the top of the fork.

    FRONT FORKS:

    Forks: Lack of Rebound

    Symptoms:

    Forks are plush, but increasing speed causes loss of control and traction

    The motorcycle wallows and tends to run wide exiting the turn causing fading
    traction and loss of control.

    When taking a corner a speed, you experience front-end chatter, loss of traction
    and control.

    Aggressive input at speed lessons control and chassis attitude suffers.

    Front end fails to recover after aggressive input over bumpy surfaces.

    Solution:

    Insufficient rebound. Increase rebound "gradually" until control and traction
    are optimized and chatter is gone.

    Forks: Too Much Rebound

    Symptoms:

    Front end feels locked up resulting in harsh ride.

    Suspension packs in and fails to return, giving a harsh ride. Typically after
    the first bump, the bike will skip over subsequent bumps and want to tuck the
    front.

    With acceleration, the front end will tank slap or shake violently due to lack
    of front wheel tire contact.

    Solution:

    Too much rebound. Decrease rebound "gradually" until control and traction are
    optimized.

    Forks: Lack of Compression

    Symptoms:

    Front-end dives severely, sometimes bottoming out over heavy bumps or during
    aggressive breaking.

    Front feels soft or vague similar to lack of rebound.

    When bottoming, a clunk is heard. This is due to reaching the bottom of fork
    travel.

    Solution:

    Insufficient compression. Increase "gradually" until control and traction are
    optimized.

    Forks: Too Much Compression

    Symptom:

    Front end rides high through the corners, causing the bike to steer wide. It
    should maintain the pre-determined sag, which will allow the steering geometry
    to remain constant.

    Solution:

    Decrease compression "gradually" until bike neither bottoms or rides high.

    Symptom:

    Front end chatters or shakes entering turns. This is due to incorrect oil height
    and/or too much low speed compression damping.

    Solution:

    First, verify that oil height is correct. If correct, then decrease compression
    "gradually" until chattering and shaking ceases.

    Symptom:

    Bumps and ripples are felt directly in the triple clamps and through the
    chassis. This causes the front wheel to bounce over bumps.

    Solution:

    Decrease compression "gradually" until control is regained.

    Symptom:

    Ride is generally hard, and gets even harder when braking or entering turns.

    Solution:

    Decrease compression "gradually" until control is regained.

    REAR SHOCK:

    Adjustment Locations on Shocks

    Rebound adjustment (if applicable) is located at the bottom of the shock.
    Compression adjustment (if applicable) is located on the reservoir. Spring
    prelude is located at the top of the shock.


    Shock: Lack of Rebound

    Symptoms:

    The ride will feel soft or vague and as speed increases, the rear end will want
    to wallow and/or weave over bumpy surfaces and traction suffers.

    Loss of traction will cause rear end to pogo or chatter due to shock returning
    too fast on exiting a corner.

    Solution:

    Insufficient rebound: Increase rebound until wallowing and weaving disappears
    and control and traction are optimized.

    Shock: Too Much Rebound

    Symptoms:

    Ride is harsh, suspension control is limited and traction is lost.

    Rear end will pack in, forcing the bike wide in corners, due to rear squat. It
    will slow steering because front end is riding high.

    When rear end packs in, tires generally will overheat and will skip over bumps.

    When chopping throttle, rear end will tend to skip or hop on entries.

    Solution:

    Too much rebound. Decrease rebound "gradually" until harsh ride is gone and
    traction is regained. Decrease rebound to keep rear end from packing.

    Shock: Lack of Compression

    Symptoms:

    The bike will not turn in entering a turn.

    With bottoming, control and traction are lost.

    With excessive rear end squat, when accelerating out of corners, the bike will
    tend to steer wide.

    Solution:

    Insufficient compression. Increase compression "gradually until traction and
    control is optimized and/or excessive rear end squat is gone.

    Shock: Too Much Compression

    Symptoms:

    Ride is harsh, but not as bad as too much rebound. As speed increases, so does
    harshness.

    There is very little rear end squat. This will cause loss of traction/sliding.
    Tire will overheat.

    Rear end will want to kick when going over medium to large bumps.

    Solution:

    Decrease compression until harshness is gone. Decrease compression until sliding
    stops and traction is regained.

    Stock Tuning Limitations

    The factories plan on designing a bike that works moderately well for a large
    section of riders and usages. To accomplish this as economically as possible,
    manufacturers install valving with very small venturis. These are then matched
    to a very basic shim stack which creates a damping curve for the given
    suspension component. At slower speeds this design can work moderately well, but
    at higher speeds, when the suspension must react more quickly, the suspension
    will not flow enough oil, and will experience hydraulic lock. With hydraulic
    lock, the fork and/or shock cannot dampen correctly and handling suffers. The
    solution is to re-valve the active components to gain a proper damping curve. It
    does not matter what components you have, (Ohlins, Fox, KYB, Showa), matching
    them to your intended use and weight will vastly improve their action.
    Furthermore, if you can achieve the damping curve that is needed, it does not
    matter what brand name is on the component. Often with stock components, when
    you turn the adjusters full in or out, you do not notice a difference. In part,
    this is due to the fact that the manufacturer has put the damping curve in an
    area outside of your ideal range. Also, because the valves have such small
    venturis, the adjuster change makes very little difference. After re-valving,
    the adjusters will be brought into play, and when you make an adjustment, you
    will be able to notice that it affects the way the way the fork or shock
    performs.

    Another problem with stock suspension is the springs that are used. Often they
    are progressive, increasing the spring rate with increased compression distance.
    This means that the valving is correct for only one part of the spring's travel,
    all other is compromise. If the factory does install a straight-rate spring, it
    is rarely the correct rate for the weight of the rider with gear. The solution
    is to install a straight-rate spring that matches the valving for the combined
    weight of the bike, rider and gear to the type of riding intended.

    Remember

    Always make small adjustments, more is not always better.
    Always keep notes.

    Suspension tuning is an art, be patient. I hope you all find this helpful. Feel
    free to email your questions to us at info@mototechnw.com. We are always happy
    to help inprove your ride. Herb Varin
     
    RSimons and Savage like this.
  2. Jafar

    Jafar Retired Admin

    where did you get this Beans?, Herb Varin is the guy who worked on my 900ss motor. he works for Eastside Ducati.
     

  3. small world, eh.

    I was doing some Yahoo searches for suspension, came across this, thought I'd share it. You know me, trying to reach the end of the Internet and finding motorcycle related stuff along the way.

    Get Herb on the website. Tell him your life produces no more negative due to that 900SS and Amanda being out of your life. Go Team Green!
     
  4. snake

    snake Paralized with excitement

    Nice guide. Thanks.
     
  5. There's also some really good info at http://www.gpsuspension.com -- click on "Services", then "Tuning guide". I just had my racebike forks re-sprung and re-valved by these guys, and got a penske triple in the rear... made a HUGE difference.

    CD
     
  6. Perferd

    Perferd Grade A Champion

    My penske is on and should be doing my forks at GP too...
     
  7. Nice -- you're gonna love it.
     
  8. Perferd

    Perferd Grade A Champion

    I cant wait to even see the bike lol...
     
  9. Moto

    Moto Safety Wire King

    colOn...you twit...you've only ridden that bike in your neighborhood.
    that shock must have less soap on it - that's what you're feeling.
     
  10. Again, always something so interesting to say. What are you saying anyway? I think you should keep your immature comments to yourself from this point on.
     
  11. Moto

    Moto Safety Wire King

    well sorry...
    it's true - you've only ridden the bike 3 times.
    -on you way home with it.
    -to my place to show me crap you bought for it.
    -around your street at 15 - 20mph.
     
  12. So you've been stalking me now? You know how often I ride and which bike? Yeah, right. If you remember, my racebike is street-legal covertible in about 20 minutes... I've ridden it plenty to feel a suspension difference -- I'd better notice for the $$ I paid. How's your suspension by the way? Maybe you need me to come by and adjust it again for you? crackup:
     
  13. Great find...thanks. I'm actually very aware of this now since I bought this latest bike. When I got it I was riding on rocks...so I turned everything out on the front end and started there. I'm about 99% there now after 2 weeks of tinkering but I'm getting more familiar with what adjustment does what.
     
  14. vagrant

    vagrant »-(¯`·.·´¯)-> PNW

    Not kilometers.

    If you get a flathead screwdriver and turn either of your rebound nobs on the top of your forks (or the bottom) you will feel the screw drop into "notches" and may here/feel a "click". Just remember how many and which way you turned so you can turn it back.
     
  15. Great Guide, but think I will just take it to GP, let them do what they do best. :mfclap:
     
  16. is GP the only place in town that adjusts suspensions, or are there others. Bought a used bike and the prior own was abt 100 lbs heavier then I am, so definitely need to get set set for my weight.
     
  17. Lone Rider

    Lone Rider Streetfighter

    I think there are several. Go to the Oregon road racers site and you'll find more I believe.

    Cant go wrong with GP though. Barry here in Seattle will dial your stuff in at a track day. Dont know if the GP guys show up at track days at PIR. I didnt notice them at PSSR track days.
    I strongly recommend PSSR for your 1st track day outfit. Great folks.