Testing
Your
Forks
There are
a few simple tests you can do to determine whether your forks
are in good condition.
By pulling
the front brake lever and depressing the forks as far as they
go and then, whilst holding the brake lever in, release
your weight from the forks you can determine their state of play.
Forks that are well maintained and in good order will return
evenly to their upright position without yo-yoing. They should
also not spring up too quickly or slowly.
General
Front Suspension Issues
Use the following to trouble shoot general fork performance
issues.
Problem: Front
forks sluggish/nearly immobile, handlebars “jump” in
your hand when accelerating and crossing ruts, front wheel
bounces / chatters on poor road
surfaces.
Cause: Spring
pre-load too high, spring too hard,
air chamber too small.
Modification: Reduce
spring pre-load, fit softer springs or progressive springs
with a lighter initial
strength,
increase air chamber (reduce oil level in front fork).
Problem: Motorcycle
sags too deeply on the springs,
too much negative suspension travel,
suspension occasionally bottoms out,
front forks shake when braking and travelling downhill.
Cause: Spring
pre-load too low,
springs too soft,
air chamber too large.
Modification:
Increase spring pre-load,
fit stiffer springs or progressive front fork springs with a
heavier initial strength,
reduce air chamber (increase oil level in front fork).
Problem: Front
forks sluggish/nearly immobile,
shocks in the steering when accelerating,
front wheel chatters when braking hard.
Cause: Ingoing
(compression) damping too hard.
Modification: Reduce
the ingoing (compression) damping,
possibly use lower viscosity fork oil.
Problem: Front
forks shock when braking and on uneven road surfaces,
dips rapidly when braking.
Cause: Ingoing
(compression) damping too soft.
Modification: Increase
the ingoing (compression) damping
possibly use higher viscosity fork oil.
Problem: Front
forks spring back slowly,
front wheel unable to cope with uneven surfaces,
indirect steering behaviour.
Cause: Outgoing
(rebound) damping too hard.
Modification: Reduce
the outgoing (rebound) damping,
possibly use a lower viscosity fork oil.
Problem: Front
end is lively,
bouncing and shocking on uneven surfaces,
front forks spring back too quickly.
Cause: Outgoing
(rebound) damping too soft.
Modification: Increase
the outgoing (rebound) damping,
possibly use a higher viscosity fork oil.
Problem: Front
forks shock,
front wheel shudders,
not enough progressive hardening of the spring towards the end
of travel.
Cause: Air
chamber too large.
Modification: Increase
the oil level in small steps of 5 to 10mm.
Problem: Forks
hard,
steering shock,
front wheel bounces when braking due to hydraulic stop blocking.
Cause: Air
chamber too small.
Modification: Decrease
the oil level in small steps of 5 to 10mm.
Key
Terms:
Pre-load: This
compresses the suspension springs and alters the amount of
sag front and rear allowing the suspension to work in it's
most
effective range
the middle two thirds of suspension travel. Too little preload
causes the spring to work in the soft part of its range and
so needs more damping. Too much preload causes the shock to
top out over bumps and reduces the working range of the suspension.
Rebound
Damping: Controls the speed that suspension springs return to their
full length after being compressed. Without rebound damping
suspension
would bounce up and down uncontrollably. Too much rebound damping
slows down rebound and causes the front of the bike to pump
down over bumps. Too little rebound allows the front to bounce
back
too quickly reducing control.
Compression
Damping: Controls the speed the suspension is compressed.
The amount
of feel and feedback from the front tyre vary with the amount
of
compression damping. Too much compression damping causes
the wheel to be deflected by bumps and the tyre has to work
harder
absorbing the bumps itself. Too little compression damping
allows the wheel travel too much over bumps and dive too
much under braking.
|
