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Suspension Setup 101

Jun 9, 2014
Suspension Setup 101
  • Originally posted by @chubb

    With the amount of suspension set up threads lately, I thought I would post a 101. I'm not an expert and this is from reading lots of internet pages on suspension, watching Dave Moss' videos and help from the local suspension gurus.

    Suspension setup basics
    :
    - Rider Sag: The amount of suspension travel used by the combined weight of the machine and rider, measured from topped out.
    - Static Sag: The amount of suspension travel used by the weight of the bike alone, again, measured from topped out.
    - Damping: Damping is simply the components ability to dampen the oscillating energies that the suspension will be exposed to.
    - Compression: The damping that controls the downward stroke of the suspension. At the bottom of the forks and the top of the shock (typically).
    - Rebound: The damping that controls the upward (return) stroke of the suspension. At the top of the forks and the bottom of the shock absorber (typically).

    REAR SAG SETUP
    Step 1: First find the fully UNLOADED length of your rear suspension. Lift the rear wheel up under the engine so that there is no weight (including the weight of the bike) on the rear axle and wheel. Measure the distance between the rear axle and a fixed point directly above like a bolt or mark. Note this measure measurement. Do not use a rear wheel bike stand as there is still the weight of the bike on the swing arm.

    Step 2: Find the NORMAL length of you rear suspension. This is amount the suspension drops under the weight of the bike alone without the rider. Put the bike on level ground and bounce it up and down to free any stickiness. Measure between the same two points as above.

    Step 3: Find the fully LOADED length of your rear suspension. This is the length of the suspension with the rear wheel on level ground and the rider seated. First bounce up and down on the seat to loosen the suspension then get into your normal riding position with all weight on the bike and both feet on the bike. Measure between the same two points as above.


    RIDER SAG is the difference steps 1 and 3. This is the amount the bike drops when your heavy arse sits on the bike.
    STATIC SAG is the difference between step 1 and step 2. it is how much the bikes weight acts on the rear suspension or how much you can lift the bike rear without the rider on it before it tops out.

    Rear wheel rider sag should be around 30 - 40mm and static should be around 5 - 10mm (Varying with personal taste, bike and manufacturer).
    Less than 30mm = tis a bit hard More than 40mm = tis a bit soft


    Then do the same for the FRONT. Rider sag around 35 - 45mm and static around 25 - 30mm again depending on bike and manufacturer.
    Use a zip tie around the front forks and go out for a ride (no wheelies/stoppies). Find out the amount of travel you have available left to you. For the road you want to aim for around 20mm for unexpected pot holes, rough bumps etc. For the track you probably can aim for around 10mm
    Setting Damping (Rebound & Compression)
    The best setting you can start off with is what is in your owner’s manual. This again will vary for different bikes, rider preference, tyre profiles, air pressures and also when you had your bike’s suspension last refreshed (how old your fork oils are)
    Front Compression
    You want your front to compress under braking and when riding over uneven humps. You want your front suspension to compress slowly and controlled when you brake. As your bike dives under braking, it transfers more weight over the front wheel. This helps slow the bike quicker.
    If the front compresses too quickly, you run the risk of the suspension bottoming out and you will feel that the bike’s nose dives too quickly. If the compression is set too hard, it will skip over bumps and have a very harsh feel to it.
    Another important aspect of front compression is when you brake just before a turn. As you brake before the corner, the bike’s nose dives and it will shorten the wheel base and alter the geometry of the bike making the bike turn quicker into the corner. It is important that your bike compresses predictably and safely in a corner/turn.
    SOFT: If your compression is too soft, your bike will nose dive too quickly, then as you turn into the corner, the bike will fall into it and you end up having to adjust.
    HARD: if you have too much front compression damping, you don’t get enough nose dive and end up fighting the bike to turn in.

    Front Rebound
    Front rebound damping is to control the rate of the bike’s movement back up after the springs have been compressed. If it is too soft, the front end will rebound too quickly. This may cause your bike to feel “bouncy”. If the rebound damping is set too hard, you may have to keep readjusting your line mid corner. You do not generally really want your front end to come back up too quickly after it has been compressed.
    SOFT: If it rebounds too quickly in the corner your bike will sit up very quickly creating a longer wheel base. It gives you the feeling of the front end “washing out” and drift wide.
    HARD: If the rebound is too hard, when you get into the corner, your bike will feel wooden in the corner and turn too quickly. This is due to the compressed shorter wheel base for longer.

    Let’s move on to the rear.

    Rear Compression
    Similar to the front, you want to set up the compression for you to have a comfortable ride and also keeping all your wheel tracks in line. If it is set too hard, then the rear will skip all over the place and you will feel all the bumps. However, if it is too soft, then the bike will squat more than necessary.
    When you accelerate, you want the rear to squat a little, giving tyres the chance to get some traction.

    SOFT: Having too soft rear compression makes the bike squat. You will feel the bike wants to drift out wide.
    HARD: Too hard compression on the rear and you will not get enough “squatting” action and may cause wheel spin.

    Rear Rebound
    At this point you want the rear rebound damping to keep the rear wheel in contact with the road, thereby giving you maximum traction
    SOFT: If it is too soft, the rear will kick up too quickly and unsettle the chassis giving you a bouncy feeling. Or mid corner, you will feel the bike “lurch”
    HARD: Too hard and your bike won’t sit up quick enough, this will be part of the problem of you getting the feeling that the bike is drifting wide. You may also get loss of traction
    Thanks to gostar, Suspension smith and zenodamper for teaching me the basics.

    Suspension Troubleshooting Guide
    Suspension Tuning Troubleshooting Guide

    [HR][/HR]​
    I got the following information from Andrew Trevitt's Sportbike Suspension Tuning. It is a great book and I highly recommend it. Hope you find this useful


    ENTERING A CORNER

    Symptom:
    Steering is heavy and slow
    Likely Cause:
    Excessive trail
    Possible Remedy:
    Reduce trail by raising the rear ride height, adding rear preload, raising the fork tubes in the triple clamps, reducing front preload, or increasing triple-clamp offset

    Symptom:
    Steering is quick and flighty or unstable
    Likely Cause:
    Insufficient trail
    Possible Remedy:
    Add trail by lowering the rear ride height, reducing rear preload, lowering fork tubes in the triple clamps, adding front preload, or decreasing triple clamp offset

    Symptom:
    Steering is slow in side-to-side transitions
    Likely Cause:
    Center of gravity is too low
    Possible Remedy:
    Raise center of gravity by lowering the fork tubes in the triple clamps and raising the rear ride height an equal amount

    Symptom:
    Chassis is unstable in side-to-side transitions
    Likely Cause:
    Insufficient rebound damping is allowing the chassis to unload excessively
    Possible Remedy:
    Add front and rear preload damping

    Symptom:
    Chassis resists leaning while trail braking
    Likely Cause:
    Insufficient rake
    Possible Remedy:
    Increase rake by lowering rear ride height, reducing rear preload, lowering the fork tubes in the triple clamps, or adding front preload

    MID CORNER

    Symptom:
    High-frequency chatter
    Likely Cause:
    Tire is out of balance or out of round
    Possible Remedy:
    Check tire condition

    Symptom:
    Footpegs or chassis parts drag
    Likely Cause:
    Center of gravity is too low
    Possible Remedy:
    Raise center of gravity by lowering the fork tubes in the triple clamps and raising the rear ride height an equal amount, or increase front and rear spring rates

    Symptom:
    Ride is harsh and rough
    Likely Cause:
    Suspension is packing or bottoming
    Possible Remedy:
    Reduce rebound damping, increase spring stiffness, or increase preload

    Symptom:
    Ride is bouncy and loose
    Likely Cause:
    Insufficient rebound damping
    Possible Remedy:
    Add front and rear rebound damping

    Symptom:
    Limited traction over bumps
    Likely Cause:
    Suspension is too stiff
    Possible Remedy:
    Reduce rebound damping, reduce low- or high-speed compression damping, or reduce preload

    EXITING A CORNER

    Symptom:
    Bike runs wide or is unstable over bumps
    Likely Cause:
    Excessive squat is causing the front tire to lose traction
    Possible Remedy:
    Reduce squat by adding rear low-speed compression damping, adding rear preload, adding rear ride height, raising the fork tubes in the triple clamps, adding front rebound damping, or raising the swingarm pivot

    Symptom:
    Sudden loss of rear traction on acceleration
    Likely Cause:
    Insufficient squat
    Possible Remedy:
    Increase squat by reducing rear low-speed compression damping, reducing rear preload, reducing rear ride height, lowering the fork tubes in the triple clamps, reducing front rebound damping, or lowering the swingarm pivot

    Symptom:
    Excessive wheelies
    Likely Cause:
    Center of gravity is too high
    Possible Remedy:
    Raise the fork tubes in the triple clamps and lower the rear ride height an equal amount

    Symptom:
    Excessive chassis pitching
    Likely Cause:
    Excessive weight transfer
    Possible Remedy:
    Add rear low-speed compression damping, add rear high-speed compression damping, reduce front rebound damping, or lower the center of gravity

    STRAIGHT

    Symptom:
    Wallows over rolling bumps
    Likely Cause:
    Insufficient compression damping
    Possible Remedy:
    Add low-speed compression damping

    Symptom:
    Bottoms out in depressions
    Likely Cause:
    Insufficient high-speed compression damping
    Possible Remedy:
    Add high-speed compression damping

    Symptom:
    Harsh over sharp-edged bumps
    Likely Cause:
    Excessive compression damping
    Possible Remedy:
    Decrease high-speed compression damping or low-speed compression damping

    Symptom:
    Wobble (high-frequency headshake) on smooth pavement
    Likely Cause:
    Insufficient trail
    Possible Remedy:
    Add trail by lowering rear ride height, reducing rear preload, lowering the fork tubes in the triple clamps, adding front preload, or decreasing triple-clamp offset

    Symptom:
    Wobble (high-frequency headshake) on rough pavement
    Likely Cause:
    Excessive squat is allowing the front end to unload
    Possible Remedy:
    Reduce squat by adding rear low-speed compression damping, adding rear preload, raising rear ride height, raising the fork tubes in the triple clamps, or raising the swingarm pivot

    Symptom:
    Weave (low-frequency headshake)
    Likely Cause:
    Insufficient rear damping is allowing the rear end to oscillate
    Possible Remedy:
    Add rear rebound or low-speed compression damping

    Symptom:
    Suspension gets progressively harsher over a series of bumps
    Likely Cause:
    Excessive rebound damping is allowing the suspension to pack down
    Possible remedy:
    Reduce rebound damping

    Symptom:
    Chassis feels loose and loses traction or is unstable over rough pavement
    Likely Cause:
    Insufficient rebound damping
    Possible Remedy:
    Add rebound damping

    BRAKING

    Symptom:
    Rear wheel comes off the ground or slides sideways
    Likely Cause:
    Excessive rear rebound damping is allowing the wheel to leave the ground
    Possible Remedy:
    Reduce rear rebound damping

    Symptom:
    Excessive chassis pitch
    Likely Cause:
    Insufficient damping to control brake dive
    Possible Remedy:
    Add front low-speed compression damping or add rear rebound damping

    Symptom:
    Excessive chassis pitch (cont.)
    Likely Cause:
    Center of gravity is too high
    Possible Remedy:
    Lower the center of gravity by raising the fork tubes in the triple clamps and lowering the rear ride height an equal amount

    Symptom:
    Front end feels harsh at maximum braking
    Likely Cause:
    Fork is bottoming
    Possible Remedy:
    Add front low-speed compression damping, add fork oil, add front preload, or increase front spring rate

    Symptom:
    Lack of feel from front end
    Likely Cause:
    Not enough weight is transferring to the front tire
    Possible Remedy:
    Remove fork oil, reduce front low-speed compression damping, or reduce front preload

    Symptom:
    Lack of feel from the front end (cont.)
    Likely Cause:
    Insufficient trail
    Possible Remedy:
    Increase trail by lowering the rear ride height, reducing rear preload, lowering the fork tubes in the triple clamps, adding front preload, or decreasing triple clamp offset

    Symptom:
    Front end bounces when the brakes are released, giving a momentary loss of traction
    Likely Cause:
    Insufficient front rebound damping
    Possible Remedy:
    Add front rebound damping
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