Bottoming

Using up the total available travel of the suspension system.

 - Soft Bottom

A term invented by us to define getting close to metal-to-metal but not quite there.  Soft Bottoms are OK but borderline.  We define it as using 90% of the total available travel.

 - Hard Bottom

A DMS term used to define metal-to-metal (or really close to it - we define it as 95% of the total travel).  Hard Bottoms are not OK.  Especially during testing since it generally gets rougher during racing.

Bottoms, Too Soft, Wallows (front)

 - Ask questions:

1. What kind of conditions?  G-outs, landing on jumps, face of jumps, etc. (this is looking for a clue to velocity - high speed or low speed)

2. Does it feel good otherwise? (In this case we would try increasing oil level.)

3. Does it feel too soft everywhere? (In this case we would add compression damping.)

• Oil level low - Raise oil level - affects only the last portion of travel
• Not enough low speed compression damping 
• Not enough high speed compression damping 
• Spring rate too soft
• Not enough preload
• Dirt in valving, broken valve, bent, burr on the piston/shim
• Damping rod bushing worn out - (pre 95 KYB typical problem), street too
• Compression valve o-ring broken
• Damping rod not attached to cap

Bottoms (rear)

• Too much static sag (easy to check)
• Not enough low speed compression damping
• Not enough high speed compression damping
• Spring rate too soft 
• Piston ring o-ring, piston ring or body worn
• Suspension fluid worn out
• Seal blown
• No nitrogen, cavitation

Bounces off the Ground on Jump Landings (front)

• Bottoms severely and recoils
• Not enough low speed rebound damping
• Not enough high speed rebound damping

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Cavitation

Bubbles caused by excessive resistance to flow between hydraulic chambers.  This creates loss of both compression and rebound damping.

Compression

Suspension movement when the wheel hits a bump and compresses.  Also known as the "bump stroke".

Compression Damping

Damping created on the compression stroke as the suspension is collapsing.  Since damping is sensitive to velocity we often use the terms Low Speed and High Speed Compression.

 - Low Speed Compression Damping

Compression damping that occurs when the vertical wheel movements are slow.  Such as when going through a dip or gully or on the forks during braking.

 - High Speed Compression Damping

Compression damping that occurs when the vertical wheel movements are fast.  Such as when hitting anything that has a square edge like pot holes, expansion joints, Botts Dots, some railroad crossings, very high speed braking bumps, etc.

Deflects on Square Edge Bumps (front)

• Too much high speed compression damping 
• Spring rate too stiff 
• Too much preload
• Too much low speed compression damping 
• See "Sticky"

Diving (front)

The phenomenon of the front forks compressing during braking.  The front end should dive quite a bit on braking.  Many linkage type front ends control dive mechanically.  The term usually implies "excessive" diving.

On braking, the total dive is controlled by spring forces (rate, preload and air slightly) only, not damping.

See "Rides Low"

Doesn't Turn (front)

• See “Rides High”
• Rear end rides too low
• Spring rate too stiff
• Too much preload
• Too much tire pressure
• Poor tire type/compound
• Riding Style
• Not weighting the front end
• Elbow down riding style - Dirt
• Sitting too far back - Dirt
• Seat too low
• Bars too high
• See "Sticky"

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Harshness

An uncomfortable jolt that occurs on the compression stroke.  It can be caused by many different reasons such as too much high speed compression damping, too much friction, too much low speed rebound damping (causing packing), too high of a spring rate, too much preload (a lot too much), binding from things like bent fork tubes, excessive friction, poor suspension fluid, poor suspension linkage bearings, etc. as well as severe bottoming.

Headshake

An unnerving phenomenon where the forks oscillate back and forth rapidly and sometimes violently.  Can be caused by many reasons including a frame that is out of alignment (most common - call G.M.D. CompuTrack), too little trail, underdamped rebound, overdamped high speed compression, anything that causes a bind, chassis flex, swingarm flex, etc.

• Steep fork rake or not enough trail
• Chassis not straight
• Chain adjuster off creating misalignment of wheels
• Fork flex, Chassis flex, swingarm flex
• Oil level too high (street)
• Bottom out mechanism too long (street)
• Too much rebound damping
• Not enough low speed rebound damping
• Too much high speed compression damping
• Too high tire pressure 
• Poor tire compound or type
• Tire not mounted properly on rim or cord not straight
• Wheel out of balance
• Brake rotor bent
• Worn out or loose steering bearing
• Anything that makes the front end lower than the rear
• Death grip on the bars
• See "Sticky"

 - Additional solutions

• Steering damper
• Tighten steering bearings so they drag slightly

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Kicking (rear)

Leaky Fork Seals

• Nicks in tube
• Bent tube
• Worn bushings
• Improper installation
• Old seals
• Fork tube too smooth

Loose (front)

• Not enough low speed rebound damping 
• Not enough high speed rebound damping 
• Damping rod bushings worn out - (KYB typical problem)
• Steering bearings loose or worn
• Swing arm pivot or linkage bearings loose or worn
• Tire pressure too low
• Chassis flex
• Worn out rebound piston ring
• Worn out fluid
• Cavitation

Loose (rear)

• Not enough low speed rebound damping
• Not enough high speed rebound damping
• Not enough low speed compression damping

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Packing

When the wheel extends so slowly after being compressed by a bump that it does not return to the proper ride height when the next bump is encountered.  Caused by excessive Low Speed Rebound Damping.  This is more common than you may think.

Pogoing

Uncontrolled rebounding (not enough rebound damping).

Rebound

Suspension movement when the wheel extends.  Also known as "Tension."

Rebound Damping

Damping created on the rebound stroke as the suspension is extending.  Since damping is sensitive to velocity we often use the terms Low Speed and High Speed Rebound.

 - Low Speed Rebound Damping

Rebound damping that occurs when the vertical wheel movements are slow.  Since the force that extends the suspension is primarily due to the spring, Low Speed Rebound occurs when there are small wheel movements.

 - High Speed Rebound Damping

Rebound damping that occurs when the vertical wheel movements are fast.  Since the force that extends the suspension is primarily due to the spring, High Speed Rebound occurs when there are large wheel movements.  High Speed Rebound is often produced when hitting in big dips or gullies at speed.  Of course chain forces and the terrain will affect the rate of extension as well so it is not just the amount of travel used.

Rides Low (Dynamic) - Oversteers (front)

• Spring rate too soft
• Not enough preload
• Not enough low speed compression damping 
• Increase low speed damping adjustment, valving stack or Go to a single stage valving stack
• Low speed rebound too high
• Anything that makes the rear higher than the front

Rides High - Doesn't Turn, Understeers, Pushes (front)

• Too much preload
• Spring rate too high
• Too much low speed compression damping 
• Rear riding too low
• Air pump - replace seals
• Anything that makes the rear lower than the front
• See "Sticky"

Sticky Forks

• Axle clamp not centered - align tubes
• Bad fork brace or fork brace adjustment
• Seals not broken-in or poor design (aftermarket)
• Seals not lubricated
• Poor quality oil
• Bent tubes - bent axle - bent triple clamps
• Dented sliders
• Upside-down fork design with poor bushing design
• Outer tube anodizing worn through
• Air pump - replace seals
• Triple clamp too tight
• Misaligned fork tube height - GMD
• Forks not broken in – (Twin Chamber Showa)
• Bushings damaged from dent or worn out
• Metal imbedded in bushings
• Preload washers not located properly
• Aluminum preload washers
• Steel spring spacer directly on aluminum cap
• Bottom-out system needs chamfering - KYB
• Fork caps "shedding" on installation
• Cartridge rod bushing too tight
• Spring guide rubbing on ID of spring / guide growing from solvent
• Fork spring too large OD

Sticky Shock (rear)

• Linkage not maintained
• Swingarm bearings not maintained
• Shock eyelet bearings not lubed
• Floating brake rod or backing plate not lubed
• Missing or improper bearing spacers
• Bent shock shaft

Stiff - Deflects, Harsh, Nervous, Twitchy (front)

 - Ask question - Everywhere or just on square edges?

• Too much compression damping adjustment – HS & LS
• Too much compression damping internally - HS
• Spring rate too stiff
• Too much low speed rebound damping
• Oil level too high
• See "Sticky"

Swapping (rear)

A disconcerting phenomenon where the bikes rear end is oscillating back and forth with large amplitude.  a.k.a. "pogoing".  It can be caused by many things including non-suspension related causes like a flexible chassis or swingarm, low tire pressure, misaligned chassis or wheels.  Excessive high speed compression or spring rate or extremely underdamped rebound could also be the cause.  Also severe bottoming can cause this.

 - Ask questions:

1) Does it feel harsh / deflect?

2) Does it bottom out easily?

3) One bump or into a series of whoops?

• Too much high speed compression damping
• Not enough low speed rebound damping
• Not enough high speed rebound damping
• Spring rate too stiff 
• Spring rate too soft 
• Bottoming severely
• See "Sticky"

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Topping Out