I am currently going through both shock and fork preload, rebound, and compression adjusters determining the best settings for my rider profile. I will post about where they are, how to adjust them, and what effect they have on a motorcycle.
Basic Geometry
- Fork travel/length usually left standard.
- Fork height, the position of the fork in the triple clamps. This can be measured in lines above the top triple clamps. I personally prefer to measure the length of the fork between the bottom of the lower triple clamp and the end of the fork tube. This eliminates the question of do we measure from the front of back of the clamps and gets you used to make small changes, as one line on the clamps will often be 3mm
- Triple clamp offset and rake, again usually left standard.
- Rear shock length, including any raising spacers. A trammel bar is perfect for this. Measure the shock out of the bike with a spring on it to compress the internal top-out spring
- Linkage adjustments (or different length pull rods)
- Swingarm length.
- Tire height if you use different profiles.
Forks:
- Compression (C): For Closed Cartridge forks; Clicker is at the top of the fork. For Open Cartridge forks; the Adjuster is at the bottom of the fork, sometimes covered by a rubber plug.
- Rebound (R): For Closed Cartridge forks; Flat blade screw at the base of the fork. For Open Cartridge forks; the screw is at the top of the fork.
Shocks:
- Low-Speed Compression (LSC): Flat blade screwdriver fitting at the top of the shock.
- High-Speed Compression (HSC): Large hex nut at the top of the shock (it moves independently of the low speed). Some brands have clicks, others you need to count turns
- Rebound (R): Flat blade screwdriver fitting at the bottom of the shock
Sag:
Determine the fully extended height of the suspension. This can only be checked with both front and rear wheels off the ground. If you have access to stands it makes life easier. Use a fixed point at the rear subframe, not the rear ducktail as it can move around. Measure from the rear axle straight up, vertically.
Next, have the rider sit on the machine in his or her riding gear. The first measurement minus this measurement will give us ride height or rider sag. If our first measurement was 500mm and this measurement is 460mm we, therefore, have 40mm of rider sag.
Lastly, measure the amount the machine sags under its own weight with no rider. If you subtract this measurement from the first, you will have a static sag. If this measurement is 490mm, we subtract from our original 500mm we get 10mm of static sag.
- If you have too much rider sag or too little, increase or decrease the amount of spring preload to get it closer.
- Then if static sag is correct, the Rider sag less than minimum – spring is too firm (or if the rider correct & static more than max)
- Static sag correct, rider sag more than max – spring is too soft (or if rider correct & static less than min)
Spring Rates
Front Suspension
Too Firm:
- Hard to turn in
- Good Braking Performance
- Understeer – pushing the front
- Feels harsh in corners
Too Soft:
- Poor braking performance
- Easy turn-in
- The front can tuck under, or feels like it wants to
- Tearing of the front tire
Rear Suspension
Too Firm:
- Rear feels harsh
- Poor traction
- Lack of compliance
- Tire looks polished
Too Soft can cause:
- Good acceleration/traction – sometimes
- Understeer at corner entry – sitting low
- Light front end feeling – Wheelstands out of corners (small increases of spring preload can help this)
- Too much suspension travel – pitching making it difficult to flick the bike from one side to the other
Compression Damping
Front Suspension
Too much Compression:
- Improved braking
- Feels harsh over bumps
- Pattering mid-corner
Too little Compression:
- Strong diving on the front
- Unloads the rear too early causing loss of grip
Rear Suspension
Too much Compression:
- Rear-wheel slides under acceleration
- Harsh ride over bumps, poor ‘hook-up’
Too little Compression:
- Rear-wheel starts to bump sideways under acceleration out of corners
- The bike will squat too much under power and cause the front end to lose grip
Rebound Damping
Front Suspension
Too much Rebound:
- Oversteer
- Poor front tire grip
- Front-wheel feels like it is tucking under
Too little Rebound:
- Understeer
- The front end feels unstable like it is floating
Rear Suspension
Too much Rebound:
- Rear jumps on bumps instead of following the surface
- Holds the rear down, causing understeer
- Overheats shock, causing fade
Too little Rebound:
- The rear tops out too fast under braking causing the rear wheel to lose contact with the ground
- The bike feels unstable as if it is floating
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