MOTORCYCLE SUSPENSION

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al
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MOTORCYCLE SUSPENSION

Post by al » Thu May 14, 2015 4:17 pm

MOTORCYCLE SUSPENSION

The main purpose of suspension is to keep the wheels in contact with the ground it should allow the wheels to move up and down absorbing bumps and smoothing out dips and let the tyres get on with the job of
providing grip. The rest of the motorcycle should remain undisturbed by the vibration and impacts caused by the road surface staying level and comfortable.

Suspension Adjustments

PRELOAD
This compresses the suspension springs so lighter springs can be used any changes alter 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 it's self. Too little compression damping allows the wheel travel too much over bumps and dive too much under braking.


Suspension Setup

Before you start to make adjustments to a motorcyles suspension make sure all of the basics are right first.

TYRE PRESSURES
Check the tyre pressures with a good quality gauge and adjust them to the manufacturers recommended figures incorrect tyre pressures can cause numerous different handling problems.

WHEEL ALIGNMENT
This is simple for bikes with single sided swinging arms as wheel alignment is assured as long as all of the bearings are in good condition and the bike hasn’t been bent in an accident it’s probably still a good idea to check the alignment though. Ignore the adjustment stampings on the rear swingarm or adjusters as they are always inaccurate instead use two long straight edges which are longer than the wheelbase of the bike and clamp them either side of the rear wheel then with the bike upright adjust the rear wheel until the spaces between the front wheel and the straight edges are equal both sides. Wheels that are out of alignment can cause wobbles and steering problems.

STEERING HEAD BEARINGS
Steering head bearings are crucial to good handling as all the steering and braking forces act through them. There should be very little resistance and definitely no notchiness. New bikes tend to come with the bearings
set too tight from the factory so they are always worth checking. Lift the bike so the front wheel is off the floor and turn the bars left and right and feel for any knocking (too loose), resistance (too tight) or notchiness (worn out). If they need adjustment loosen the lock nut and use a c spanner to adjust then until they run smoothly. If the bearings are worn out they need replacing have them replaced with taper rollers by a competent motorcycle mechanic as they can require some specialised pullers and drifts.

CHAIN ADJUSTMENT
A tight chain will stop the rear suspension from working. The Suzuki TL1000 rear suspension is especialy prone to locking if the chain is too tight.

WHEEL BEARINGS
Worn wheel can cause the bike to wobble and weave as the wheels can move independantly

LADEN AND UNLADEN SAG
The laden and unladen sag are set to ensure the suspension works in its most effective range and has enough travel to let the front wheel follow both the bumps and hollows in the road. Laden sag should be set to 25% of the wheel travel both front and rear. Unladen sag should then be checked it should be 15% of the wheel travel at the front and between 5 -15mm at the rear the lighter the bike the less sag required. If the
unladen sag is to small then the springs are too soft and the suspension will top out when the suspension is unloaded. If the unladen sag is to large then the springs are too stiff.

REBOUND DAMPING
The rebound damping controls the way the suspension returns to its original length. Front suspension can be set by applying the front brake and pushing down on the bars the rebound damping should control the return so that the suspension extends and then settles to its original length without bouncing. Rear suspension is a little more difficult to feel and it is set by holding the rear tail unit and pressing down hard the supension should compress and then return slightly slower with no bouncing. Check the rebound balance by pressing down just behind the fuel cap to compress front and rear together and make sure that the rear returns slightly slower than the front.

COMPRESSION DAMPING
The compression damping is down to personal taste so start small and work up. Increasing compression damping improves feel and reduces dive but too much makes the suspension to hard over bumps.

EXPERIMENT
If in doubt don’t adjust anything. The easiest way to feel what difference each type of damping makes is to note the current settings and then adjust rebound damping to half way between hard and soft chnage compression damping to minimum and ride he bike over a familiar section of road. Adjust one setting at a time and work through the whole range of adjustment on the front and rear separately this will give you a good idea of what affect each of the adjustments have. Once you have finished return the suspension to the standard settings and you should then be able to adjust out any problems based on your experience.


COMMON PROBLEMS

BIKE DECKS OUT EVERY WHERE
The suspension is too soft. Increase the preload or change to stiffer springs. adjust the ride height if possible.

BIKE SKIPS OVER BUMPS
Reduce rear comression damping and/or preload

BIKE WALLOWS AROUND CORNERS
Increase rear rebound damping

FRONT END SHAKES IN CORNERS
Increase fork rebound damping

FRONT END SHAKES OUT OF CORNERS AND OVER BUMPS
Reduce fork preload or compression damping

FORKS JUDDER UNDER BRAKING
Reduce compression damping or preload

FORKS SHOOT UP AFTER BRAKING
Increase front rebound damping

FORKS DIVE TOO FAST
Increase compression damping

FORKS BOTTOM OUT
Fit stiffer springs, decrease air gap, apply more preload

REAR SHOOTS UP WHEN BRAKING
Increase rebound damping

REAR SQUATS ON BUMPY ROADS
reduce rebound damping

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dimdunc
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Re: MOTORCYCLE SUSPENSION

Post by dimdunc » Thu May 14, 2015 11:19 pm

Easy way out, go to someone who knows what they are doing :P
Always found suspension a fooked to set up right

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RK6
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Re: MOTORCYCLE SUSPENSION

Post by RK6 » Fri May 15, 2015 12:14 pm

Great post Big Kneed Al (master of the emergency stop & "stand up" comedian)! :worthy

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Coully
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Re: MOTORCYCLE SUSPENSION

Post by Coully » Mon May 18, 2015 10:14 am

like the explanations , most helpul, might have to take note of how the vfr behaves next time i'm out

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Zathos
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Re: MOTORCYCLE SUSPENSION

Post by Zathos » Mon May 18, 2015 12:00 pm

Good advice. Never used it myself as I am just a scrub who jumps on and rides.

The only bikes I have ever thought were 'not right' for handling were those which had some ham fisted adjustments made to the set up.

By the same token I remember riding Zax YZFR6 and thinking it was a fantastic handling bike.

So, good adjustments can make things better, but bad ones will ruin the ride.
It is up to the individual to decide if they have the skill.

As a hint, if you don't know which way brake pads fit, don't touch the bike ;)

willian
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Re: MOTORCYCLE SUSPENSION

Post by willian » Mon May 18, 2015 12:12 pm

Beware of the tinkerer ......Always the risk when buying a second hand anything and possibly even the reason why something's being sold on :roll

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