The composition of a knave (polyanarch) wrote in sport_tour,
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Setting up suspension

I posted this on motorcycles about a month ago but I figured it wouldn't hurt to put it here for reference. The Hoi Polloi and n00bs in the big cycle community probably didn't really appreciate it. I lost it and had to surf back through 74 "OMG, I just got my new VINO scooter and have already put 40 miles on it already!" posts to find it because I am going to help a friend set up his BMW K1200 better. I noticed his rear end is set up WAY too stiff the other weekend and it was really pounding him on every expansion joint.

Suspension 101

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/Rear Shock - Race sag 25-30 mm, 1 - 1 3/16 inch
: Forks/Rear Shock - Street sag 30-35 mm, 1 3/16 - 1 3/8 inch
: Check chain alignment. If not correct, sprocket wear is increased.
: Proper tire balance and pressure. If out of balance, there will be
vibration in either wheel
: Steering head bearings and torque specifications, If too loose, head will
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

Forks: Adjustment Locations

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

Forks: Lack of Rebound


: Forks are plush, but increasing speed causes loss of control and traction.
: The motorcycle wallows 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.
* Insufficient rebound. Increase rebound "gradually" until control and
traction are optimized and chatter is gone.

Forks: Too Much Rebound

: 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.
: With acceleration, the front end will tank slap or shake violently due to
lack of front wheel tire contact.
* Too much rebound. Decrease rebound "gradually" until control and traction
are optimized.

Forks: Lack of Compression

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

Forks: Too Much Compression

: Front end rides high through the corners, causing the bike to steer wide.
It should ride in the middle of suspension travel.

* Too much compression. Decrease compression "gradually" until bike neither
bottoms or rides high.
: Front end chatters or shakes entering turns. This is due to incorrect oil
height and/or too much low speed compression damping

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

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

* Decrease compression "gradually" until control is regained.
: Ride is generally hard, and gets even harder when braking or entering
Solution:* Decrease compression "gradually" until control is regained.

Shocks: Adjustment Locations

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

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

Shock: Too Much Rebound

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

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

Shock: Too Much Compression

: 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.
* Too much compression. Decrease compression until harshness is gone.
Decrease compression until sliding stops and traction is regained.

Stock Tuning Limitations:

New motorcycles purchased from the dealership are generally set-up on the
soft side, for a rider in the weight range of 140-165 lbs. If you are not in
this range, you must retune the suspension for your weight within the
internals of forks and shocks, the manufacturer puts valves with small
venturis. This, along with shims, creates a damping curve. This works okay
at slower speeds, but at higher speeds, when the suspension must react more
quickly, the method cannot low enough oil, and you experience hydraulic
lock. With hydraulic lock, there is no damping. The fork and/or shock cannot
dampen correctly and handling suffers. The solution is to re-valve the
active components for the proper damping curve. It does not matter what
components you have, (Ohlins, Fox, KYB, Showa). If you can achieve the
damping curve that is needed, it does not matter what brand name is on the
component. Sometimes with stock components, when you turn the adjusters full
in or out, you do not notice a difference. This is due to the fact that the
manufacturer has put the damping curve in an area outside of your ideal
range. After re-valving, the adjusters will be brought into play, and when
you make an adjustment, you will be able to notice that they affect the way
the way the fork or shock perform.

One of the problems with stock springs is, in most cases, it is of a
progressive rate. This is to say, a spring at sag may be .85 kg per mm, and
at 2.5 inches of travel, it may be 1.05 kg per mm, getting progressively
stiffer. The ideal solution is to install a sprig with a straight rate,
specific for your weight, and the weight of your motorcycle. In some cases,
the factory installs a straight rate spring, but often the incorrect rate
for your weight.

Dave W. Hodges
Circuit One Suspension
Tags: wrenching
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