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Suspension .... boingg! |
Raise the forks through the
yokes to drop the front end
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Now suspension consists of those long bouncy things
at the front which hold the wheel on and the little springy thing
squeezed between the the engine and the swingarm which gets covered
in crap from the back tyre.
On any half decent sports bike you've got 8 forms
of adjustment in total - ride height, spring pre-load, rebound damping
and compression damping front and rear. 'Course, that's 12 if you
count both forks. So twiddling with any of this stuff is a trip
into mystery and adventure ..
Use a suitable spacer to
increase rear ride height
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Ride height does what it says, changes the height
the bike rides at ... which is kind of self evident but we have
to make the point just to keep you awake. The most common mod is
to speed up the steering by raising the front forks through the
yokes, so lowering the front end, and jacking up the back end either
by using a spacer between the shock top and mount or, if you've
got a really posh bike, winding up the inbuilt ride-height adjuster.
Normally the most you can reasonably go to is 10mm each end. Raising
the rear will also help ground clearance. It won't turn an old R1
into a K5 but it will help the steering turn-in a little bit better.

Alloy collar above spring screws down to increase preload
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Spring pre-load determines the amount of static
sag and the shock will either have a screw collar for adjustment
or a posh remote hydraulic twiddler. An easy way to check this is
to park the bike on its sidestand, then simply rock the bike and
watch what happens to the suspension. If it compresses noticeably
as it comes upright then time for a proper check.
Get someone to hold the bike upright and measure
the distance from the axles to a mark somewhere above on the chassis.
Then lift each end in turn and measure between the same points.
Now sit on the bike and do it again. If you're a quick rider you
want only minimal sag, perhaps 10 mm at the rear and no more than
25 mm at the front. Too much and the bike will get very unsettled
over uneven roads at high speeds.
The little screw does the rebound and
the silver nut does spring preload
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Rebound damping, adjusted by the little screws
at the top of the forks and the screw or knob on the bottom of the
rear shock. Start by backing all the screws out and then do a static
test, bouncing the bike up and down and increasing rebound until
you can feel some resistance as the springs unload. Now go for a
ride. If the front bobbles as you come off the brakes or weaves
about as you bounce out of small dips you need to increase rebound
at the front until this goes. If the back end weaves about as you
power through bends then increase rear rebound. Keep fiddling until
the bikes feels stable. Go too far and the tyres will have to help
the suspension too much as it fails to recover quickly enough from
the last bump and pumps down - then you'll start to lose grip.
Knurled knob at top adjusts
compression on rear shock
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Compression damping - probably the hardest one
to get a feel for. Adjustment is by the little screws at the bottom
of each fork leg and either a screw on the shock top or the knob
on the remote gas reservoir. Too much fork dive under braking and
a loose feel when suddenly tipping into a corner indicates insufficient
from compression damping. A slappy front end when accelerating hard
means the rear shock is compressing too much, so unloading the front
- increase rear compression. A loose feeling from the back when
powering though bends also indicates insufficient rear compression
damping. The end result is a very personal thing, as it's a compromise
between bone-jarring accuracy of line and luxomatic plushness with
'orrible vague handling.
Projecting screw on the bottom of the fork
leg adjusts compression
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Don't be afraid to experiment hugely with the suspension
settings. If you're a scaredy-cat note down your original settings
on a piece of paper and stick it on your fridge. If you've never
fiddled properly with all those little screws and spring collars
you'll be amazed how much you can change the feel of your bike.
And you can create some proper set-ups for track use - rather than
wallowing about in the slow group you will be Mr. Getoutamyway in
the fast lot! At the end of the day you can simply return your suspension
to pot-holed crap British roads settings and wallow homeward in
perfect comfort, but this time with nicely re-profiled footpegs
and end can and thoughts of rearsets for more ground clearance ....
Tie wraps on both the fork legs and
the rear shock (or O rings if you can be bothered to fit
them) show you how much suspension travel you are using.
On a given road or track outing, if the units bottom out
the suspension effectively stops working - if you're only
using 50% of the available travel the units are probably
set up too stiffly for general road and trackday use. Reader
John Higham suggests fitting adjusters to the top nuts so
you can turn them easily and tighten up or slack off till
you've got 80% / 90% travel. When you've got that far it's
time to fiddle with damping. He sees loads of guys adjusting
damping at the track when they've got the springs set up
too stiffly and they end up over-compensating.
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Regular twiddling will also keep your bike handling
as best it can. All of us are guilty of getting good settings and
then forgetting them for ages. Then we ride a new bike and think
"Blimey, this is sharp". So immediately we start adjusting
our own bike and bingo ... mega sharp handling again, as we compensate
for wear and tear on springs, damping oil, etc. If your bike's a
few years old it's worth changing the fork oil and seals. If the
rear shock is showing its age it's probably best replacing with
Ohlins, WP, Penske or whatever takes your fancy rather than going
for a rebuild - many factory shocks aren't rebuildable anyway. Trouble
is, the front end will then be letting you down as standard production
forks are often built way down to a price, and valving can be suspect.
You don't necessarily need to buy new forks, but replacing the internals
with K-Tech kit can improve control and the cost of the bits you
need should not be much more than £200 plus fitting.
A word on high and low speed damping. Bang though a bloody great
pothole in the road and wham!, the suspension has to blow oil fast
to allow a sudden large amount of spring movement to absorb the
shock. Basically the shim stacks lift and allow the oil to flow
through bypass holes - this is high speed damping, which often happens
when you're travelling slowly.... Now you're belting along a good
road with some cracking dips and rises, compressing the suspension
by fine degrees, the oil flow controlled by the shims. This is low
speed damping in action, even though you're going quickly the suspension
is moving relatively slowly to absorb the rise and fall of the bike
as the loading changes.
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Rear shocks |
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Bouncy back end? Handling all gone to bollocks? You need a new
rear shock ...
Original manufacturers' shocks on all but the most expensive bikes
are necessarily built down to a price. After a few years and thousands
of miles they lose damping and most are not rebuildable. Many do
not offer enough compression damping, causing the bike to sit down
when exiting corners. This makes the front feel light and twitchy
on bumpy roads. So a good quality replacement shock can offer real
advantages to the bike's handling, particularly if your present
OE shock is shot!
The aftermarket shock range is dominated by Ohlins, White Power
(WP nowadays), Maxton and, increasingly, Penske. Prices range from
£450 or so for the more basic typres to £800 plus for
the full house multi adjustable stuff with ride height adjustment
and hydraulic preload.
Any shock you fit should be sprung for your body weight, and the
basic adjustment needed is compression, rebound and spring preload.
This is enough to enable you to set up the shock for your riding.
More expensive models offer variable rate adjustment where the high
speed and low speed compression damping can be adjusted separately.
High speed damping is controlled by the bypass valve or blow-off
rate of the shims, and low speed damping by the shim stacks.
Spend more money and you get variable length, so you can adjust
the ride height, and hydraulic preload. Ride height adjustment is
useful, but hydraulic preload is unnecessary - although it does
look trick! Some argue that it's useful if you regularly carry a
pillion, but as the spring rate is then all wrong it's not really
a viable argument.

WP do two basic configurations, a road shock and a more
adjustable race shock.
3612 / 4681 SA shock
Rebound damping adjustable in 11 positions
Compression damping adjustable in 7 positions.
Spring pre-load continuously adjustable (hydraulic adjuster optional)
Shock absorber body contains an oil/nitrogen mixture - nitrogen
reservoir to separate oil from the nitrogen
WP 4618 high performance shock
Available for supersports bikes such as the R1, Blade etc., this
shock has both high and low speed compression damping and ride height
adjustment.
Rebound damping adjustment in 35 positions
Compression damping low speed in 24 positions, high speed continuously
adjustable
Spring pre-load continuously adjustable (hydraulic adjuster optional)
Axial spring bearing
Standard with adjustable length.
Ohlins
offer a wide range of shocks depending on the type of bike and the
intended use. The types offered are:
Type E:
An emulsion shock absorber where oil and gas are mixed in the main
body. Used on small, light bikes and where space is too limited
for a type P. Performance degrades rapidly with heat.
Type D:
A De Carbon based shock with internal reservoir and dividing piston
built into the main body. The damping oil is placed under pressure
by gas and separated from the gas by a floating piston. Improved
cooling gives more consistant damping and longer damper life.
Type P:
De carbon with external piggyback reservoir and dividing piston.
The reservoir is an extension of the shock absorber. More oil and
larger cooling areas improve performance and durability.
Type H:
De Carbon shock with hose mounted reservoir and dividing piston.
The remote reservoir stays much cooler to give improved performance
and durability under more extreme conditions.
Features, depending on model (and price!) include:
Adjustable compression damping - adjuster wheel on reservoir
Adjustable rebound damping - on piston shaft above end eye
Hose mounted hydraulic spring preload adjuster
Integrated hydraulic spring preload adjuster on shock body
Adjustable length
Separate adjusters for high and low speed compression damping.
Penske 8900 Series
The 8900 series shock is completely owner rebuildable and revalvable
if required. Integral reservoir contains increased nitrogen volume
for more consistent damping over a long duration.
Fully CNC machined 7076 - T6 aluminium, no castings.
Hard anodised finish, making the unit both lightweight and strong.
Completely hand built and dyno tested.
Heavy duty 5/8" diamter chrome plated stainless steel shaft.
The best spring available matched to your weight.
Adjustable spring preload.
Low friction/stiction shaft bearing and high quality seals and wiper.
Adjustable length eyelet, tune for the set up you need.
25 click rebound adjuster for extra fine rebound settings.
Three Choices For Compression Adjustment
8981 - 6 click compression range. Proven performance.
8986 - 10 click compression range. Step-up to a smoother ride.
8987 - Independent high and low speed compression damping.

Maxton
Maxton have been building road and race shocks for donkeys' years.
They are based on Koni units but modded to suit customers' requirements.
Their units are fully adjustable via a shim stack system and has
a spring to suit rider weight. They basically do two types. Both
are full adjustable for compression, rebound and preload but the
more expensive (£560) type has a second compression damping
adjuster to give variable high and low speed damping.
A big advantage buying Maxton is the fact that they are built locally
in the UK, so any rebuilds or modifications should be easy to obtain.
Having said that, there are many good suppliers who undertake full
servicing and setting up of their supplied shocks so it should never
be a real problem.
All
shocks should come with a spring suited to your weight and with
basic settings. After that you can tweak away to your own requirements.
Life is easier if the adjusters have decent knobs rather than fiddly
screws.
This
WP unit has concentric knobs, one each for high and low speed compression
damping. At the base is a chunky adjuster for rebound - easy for
quick adjustment on the road without having to rummage about in
the toolkit for a screwdriver.
Which one to buy? It's your choice. Talk to the suppliers and check
with anyone you know who already runs a replacement shock. Remember,
set-up advice is important so choose a supplier who can offer you
good backup and knows what he's talking about. If you go to club
races talk to racers in the paddock - they can give invaluable advice.
I
treated my old 2000 R1 to a new shock - the old OEM one has done
nearly 30,000 miles and has lost any semblance of meaningful damping.
On the advice of Darren Wnukoski of Motorcycle Technics I bought
a WP 4618 - he reckons this is tops for the R1. The main benefit
from my viewpoint was no dangly bits to find a home for, the reservoir
being mounted on the shock body, and adjustable high speed compression
damping - useful on bumpy back roads.
The WP has made a huge difference to the stability of the bike.
It no longer bucks and weaves its way out of bends but tracks like
a thing that tracks very well. The WP unit is good at soaking up
the bumps as well as transforming the bike's handling. If in doubt,
listen to Darren - he knows what he's talking about.
Tet had a quick go on the R1 and was so impressed he has fitted
a WP to his Blade ...
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Fork oil level |
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Upside down forks are very sensitive to
variations in oil level. The level does not have much affect in
the early stage of fork travel but increases as the forks compress.
When the oil level is lowered the 'air spring' in the latter half
of travel is lessened, thus the forks are softer. Manufacturers
normally quote their recommended air gap, the distance between the
top of the fork stanchion and the oil surface. Usually this is in
the range 80mm to 110mm with the spring removed and the fork fully
compressed, although Ohlins forks are measured with the spring in
place.
The above diagram shows the relationship between
the fork offset, trail and castor, the latter two often quoted in
bike road tests in magazines. These determine the level of resistance
to turning the forks from the straight ahead position and the stability
of the steering in its steady state. With telescopic forks, everything
changes when you hit the brakes, as the steering head dives down,
shortening the forks and reducing the castor and trail and also
the wheelbase of the bike. This effectively quickens up the steering,
helping the bike to turn, but unsettling the front when the suspension
unloads on release of the brakes. For fast road and track riding,
fork dive is minimised by stronger springs and increased compression
damping, while increased rebound damping helps control the change
in attitude when the brakes are released.
If you really get into suspension tweaking you
will meet such fascinating mysteries as air gaps, linear versus
progressive springs, oil viscosity, shim stacks, etc. etc. Learn
enough about all this stuff and you can phone up Ron Williams and
tell him why he set your forks up all wrong! Yup, you too can fine
tune your compression damping by decreasing your air gap by 2mm
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If your bike looks like this then sell
it and get something with adjustable suspension!
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Front frok re-valve |
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It's becoming increasingly popular to re-valve and respring standard
production forks. In view of the slight vagueness of the Yamaha
R1 forks we thought we'd try modding them to see what the effect
was.
First stage it to buy the Ohlins kit - valves, springs and oil.
Then get your hands on a spring compressor and holding plate, otherwise
you'll damage the forks trying to get them apart and you'll never
get 'em together again.

The basic fork components
- damper cartridge is still in the stanchion.
Strange tools at the top are the spring compressor and holding plate.
Before you take the forks off the bike, back off the spring preload
and loosen the cap nuts - they can be bloody tight and the yokes
are a safer way of gripping than having to trap the fork tube in
the jaws of a vice.
Holding plate doing its thing
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Undo the fork cap and drain the oil. Using a strongish friend and
the spring compressor mounted on the spacer tube, compress the spring
to reveal the locknut and then slide the holding plate under the
nut. Now you can remove the fork cap, spacer and spring.
Pull the main fork tube off the stanchion, taking care not to damage
the dust and oil seals. It's worthwhile replacing the fork seals
while the forks are stripped.
Now a slightly tricky bit. At the base of the fork leg is a recessed
allen bolt which secures the cartridge. This is often a bugger to
remove as the cartridge turns around with the bolt - use a hammer
air drill to spin it off.
Once
the bolt is off, gently withdraw the damper, covering yourself with
a generous amount of fork oil in the process. Be a bit careful here,
'coz what you've now got in your hands is a very expensive bicycle
pump full of oil, so start waving it about and pumping the tube
in and out and you'll cover your bike, garage and helpful friend
with jets of 'orrible fork oil. So point it into a drip tray and
pump the oil out in a more considerate fashion.
Prize off the spring seat ring to expose the castellations so you
can use a C spanner to unscrew the damper tube, holding the outer
tube with the compressor gizmo, as shown in the photo on the right.
Be careful to support the tube and don't bend it! There's a lot
of fairly feeble light alloy here, so it's easy to damage things.
With the gizmo still in place, unscrew the compression
damping assembly from the bottom of the cartridge tube.
Withdraw
the cartridge tube and you should have something which looks like
the photo on the left. The rebound damping control assembly is screwed
onto the end of the tube. Use the fork cap and locking nut at the
other end, lock 'em up tight and then hold them while you unscrew
the rebound assembly. Once it's off, the needle and spring are inserted
into the tube and the new valve assembly screwed on.
On the R1 we found that the damper rod was now too long, as the
needle projects much further into the tube than the original setup,
so we had to trim 20mm off the rod. If you do have to shorten the
rod make sure you are completely sober and measure everything at
least six times before cutting.
Unscrew
the retaining nut from the compression damper assembly and remove
the shims and valve. Our new stuff came on a tie wrap - the components
are in order and it's important to keep them in the same sequence
as supplied, so make sure you don't cut the tie and then drop 'em
all over the floor! Put the various shims and the valve on in the
required order and secure them with the supplied locknut.
Now put everything back together and fill up with oil. We used
a 110mm air gap with the spring out, but you'll have to check the
best setting for your bike. Springs are 9½ pounders, but
may need varying if you're a fat bugger.
Initial impressions? Damping is more progressive and the range
goes right from super-plush to hard as nails, with good control
of the front even on the softer settings. A blast over to Nurburg
via the Ardennes and a couple of dozen laps of the 'Ring showed
that the forks work well. Mind you, Scott Ingram on a bog stock
'99 R1 was still quicker ... so fancy forks can't make up for crap
riding!
The rebound valve on left comes assembled - the
needle sits in the
cartridge tube and regulates the rebound damping. The compression
bits are in order on the tie wrap - don't get the shims out of order!
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Some common front end problems |
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Front wheel chatters entering a corner, the
problem disappearing as soon as you let the brakes off or when
power is applied.
The fork is working too low in its travel.
Solution:
Apply more preload
Change to a harder spring
Reduce oil level if a tie wrap on the fork tube indicates a lot
of stroke is unused
Check fork friction (stiction)
Rear ride height is too high - possibly too much spring preload.
Reduce ride height.
Front wheel skips during heavy braking
Forks are bottoming out
Solution:
Increase spring stiffness
Lower oil level if a lot of stroke remains
Front end feels vague mid corner
Poor damping control
Solution:
Insufficient rebound damping - increase
If suspension feels harsh it may be too much rebound or compression
damping - reduce
Front end loses grip exiting corners
Insufficent spring compliance or damping control
Solution:
Increase front rebound damping
Reduce front spring preload
Increase rear compression damping or spring rate
Unfortunately the rear shock set-up affects the
behaviour of the front end in some circumstances, so there is
often no easy answer to a particular handling problem. The most
important thing to remember is never change more than one thing
at a time .... Always test the bike after any change in the
setup to see what affect it has. And make sure you note down your
original settings, so if it all goes haywire you can start again
from scratch.
Preload:
Preload controls ride height. It does not make the suspension
harder or softer. What it does do though is alter the angle of
the steering, which affects turning speed, and it also changes
the weight distribution, which can affect front/rear grip.
Front Preload:
Increase it to put more weight on rear to get better rear traction,
or stop the bike diving on the brakes. Too much will cause slow
turning and possible front lock ups on braking.
Decrease it to get more feel from front tyre in corner. Puts more
weight on front which increases front traction. Too little will
cause dive bombing.
Rear Preload:
Increase it to quicken the steering. Too much will cause loss
of traction as bike skips over dips in road, and can make the
bike generally unstable.
Decrease it to improve stability. Too little and the bike will
be slower turning and it will squat when you accelerate, leading
to tank slappers.
Compression damping:
This affects the speed at which the shock can compress, under
accelerating (rear) or braking (front), and also when riding over
bumps. High speed damping usually operated by blowing the shim
stack, allowing quick release of oil to compensate for a sudden
shock like a pot-hole. Low speed damping controlled by the shims,
allowing very subtle oil flow according to suspension loads.
Front Compression:
Increasing will remove some of the dive under heavy braking. Also
it will increase the feedback and soak up small bumps better.
Too much will cause instability, a rough ride, and it will reduce
the grip available at the front.
Decreasing will smooth the ride. Too little will cause excessive
front tyre loading and can have the bike standing up on the brakes
mid corner.
Rear Compression:
Increase to make the bike run true and hold a line around a corner.
Too much and the bike could launch you into space after a bump,
and the rear tyre will lose traction on undulations.
Decrease compression to smoothen the ride. Too little will allow
the bike to squat under power and run wide in corners.
Rebound damping:
This affects the speed at which a shock rebounds, which allows
the wheel to return to the ground after hitting a bump.
Front Rebound:
Increase the damping to help the bike hold a line, and help front
stability. Too much will gradually jack the front down as each
bump compresses the front further and further. Also it will cause
loss of feel and a tendency for the front to wash-out.
Decrease to help the front react to bumps, and to keep it in contact
with the tarmac. Too little will decrease front stability.
Rear Rebound:
Increasing will help to stop the rear bouncing around, and the
front "pushing" in corners. To much will cause front
end shake and overwork the rear tyre.
Decreasing will smoothen the ride on a bumpy road, and decrease
the rears tendency to step out on a bumpy corner. Too little rebound
will cause running wide on corners.
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