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Suspension Set-Up
 
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"I give up!" resigned a Yamaha RD 350-Rider. The inspired 2-stroke fan could not cure the problem of his beloved machine. This rider does not stand alone here. Many owners of older machines suffer the same problems with ill-fated handling. Owners of brand new motorcycles are annoyed at the machines uncoordinated handling for Australian road conditions - often too soft, doughy, board-hard, over-absorbed or loose. Many manufacturers often equip their machines with basic suspension and minimum tuning components for a variety of reasons.

Often price structuring presses on the quality, occasionally it is the short development time. There are also the requirements of the Australian biker who demands quality from his machine. Be it for touring, cruising or sports riding, a bikes suspension must be set up to suit the needs that its rider requires. It is essential that a quality suspension is fitted.

"Surely it is very complex and very time consuming - just plain too hard.", I hear you say. Unfortunately there is no quick fix I can recommend for the perfect machine set up. Suspension set up is an individual thing, dependent on the rider (riding style), the road conditions and the weather. However, I can give you some small guidelines and ground rules to help you recognise the fundamental problems and optimise your suspension for your needs.

Before starting to adjust your suspension, you should check that the chassis components are in good order and your tyres are the right ones and in good condition. All too often I have come across motorcyclists that complain about the suspension or ill handling of their bikes, yet upon inspection of the tyres, we have found that they have been running on a too low or high tyre pressure, or a tyre that is more like a square slick.

So, be sure to inspect your bike before making any suspension adjustment and check with the owner's manual for correct tyre pressure settings. A good rule of thumb in motorcycle riding is that the suspension is there to help your tyres achieve the best possible grip on the surface. Suspension plays its most crucial part in acceleration, braking and cornering. Nobody has complained about their suspension in a straight line.

 

Below you will find a range of common technical terms to help you understand the terminology used on this page and in your instruction manuals.

Technical Terms:
Reservoir: A reservoir is either fixed on the shock or connected to the shock with a hose. In the reservoir, oil and nitrogen are separated by a piston.
Bleedsystem: An open bleed system to stop hydraulic lock.
Absorption: Energy conversion and dispensation.
Compression: The rate at which the suspension moves downwards.
Rebound: The rate at which the suspension moves upwards.
Suspension Travel: Travel is the distance moved up and down of the suspension.
Fork Height: The amount that the fork is exposed above the top yoke.
Ride Height: The distance between the rear axle and tailpiece.
Preload: The amount of tension on the springs.
Sag: Suspension movement when the bikes weight is lifted off of the suspension.
Loaded Sag: The amount of suspension used with the rider sitting on the bike.
Steering Head Angle: The angle of the forks from vertical.
Clicks: Number of clicks on the adjusters.
High Speed: Speed at which the piston rod moves.
Low Speed: Speed at which the piston rod moves.
Linear Fork Springs: The fork springs which exhibited the same spring rate over the entire coil range.
Progressive Fork Springs: Fork springs with soft beginning and hard end, i.e. with high resistance to prevent bottoming out.

 

Before starting your suspension set up, it's a smart thing to read the owners manual! Write down all the changes you make, and only change one thing at a time. Try to learn what effect each of the changes you make has on the bike and how it handles the road.

 

Sag
The starting point when setting up a bike is to adjust the amount of sag the front and rear suspension has, as this controls ride height and steering geometry.

Front Sag:
Put a zip-tie round one of the fork tubes, with the front brake applied push down on the forks a couple of times to settle them, then slide the zip-tie up against the fork seal. The next step is to lift the bike by the bars until the front wheel is off of the ground then, measure the amount the forks have traveled down. This measurement is the sag and it is adjusted by the spring preload (the greater the spring preload the less sag).
Rear Sag:
Take a point on the rear axle or swing arm and another on the rear bodywork (tailpiece) directly above it. Get a mate to hold the bike upright and measure between the two points. Then lift the back of the bike, so the rear shock can fully extend itself, and measure how much it comes up. This is the sag and it is adjusted by the spring preload.
Loaded Sag:
Sit the rider on the bike with the feet on the foot pegs in riding position and measure the amount that the rear moves down, using the same marks as before. Add this figure to the sag and you have loaded sag. This is changed with the spring preload.
Rough Guideline for Sag:
Front Sag on most bikes should be roughly between 20 - 30 mm.
Rear Sag on most bikes should be roughly between 5 - 10 mm.

 

Suspension Travel
This is easy to check and gives you important information for ironing out problems. Put a zip tie around one of the front fork tubes and the other around the rear shock shaft, and then slide them against the seals. Now go for a ride, but please no wheelie's or stoppies - this will give you wrong measurement. Upon return, check the amount of travel used. The general guideline is 20mm of unused travel on the forks and 5mm on the rear shock. If there is more, reduce compression, if there is less, the reverse applies. If you can't get this in the ball park, then the spring weight or dampening may be wrong for your weight and riding style.

 

Spring Ratio
The result of a too hard rear spring ratio is that the bike gives easy turning into corners but creates traction problems. Too soft rear spring ratio gives good traction in acceleration, but tends to under steer in the entry of a corner and will give the front a light feel. The result of a too hard fork spring ratio shows in the bike with good under braking, but creates under steer and feels harsh in corners. A too soft spring ratio gives easy turning into corners, but creates over steer and can cause the front to tuck-under or dive under braking.

 

Compression Adjustment
This controls how fast the suspension moves downwards. Check in the owners manual where to find the adjusters (normally on forks at the bottom, and on the rear shock reservoir). Adjustment is made by turning the screws all the way in, then counting number of clicks out. First count and note down the number of clicks in. Screwing the adjusters all the way in gives maximum dampening.

Rear Compression:
Too much rear compression can cause the rear wheel to slide under acceleration and gives a hard ride over bumps.
Not enough rear compression can cause the rear wheel to judder sideways under acceleration out of a corner - the bike will squat (rear is too low) and may cause the front to lose grip.
Front Compression:
Too much front compression can make the bike feel harsh over bumps but gives good results during braking. Not enough front compression will cause the bike to dive and under braking.
Adjustment tip: Always test ride the bike after the adjustment has been made, making sure to ride the same stretch of road and write all your adjustments down for your records.

 

Rebound Adjusters
The adjusters are controlling how fast the suspension moves up. They are adjusted the same way as the compression.

Rear Rebound:
Too much rebound can cause the rear to jump on the bumps instead of following the surface - the bike jutters under braking. It holds the rear down, resulting the bike wheel to under steer. This can cause the hydraulic system in the shock absorber to overheat, making it to loose all important dampening when hot. Not enough rebound can cause it to top out too fast under braking, making the rear wheel jump and the bike feels unstable.
Front Rebound:
Too much rebound can cause the bike to over steer and giving the front tyre poor grip. It feels like the front wheel will tuck under in corners. Not enough rebound will cause under steer and the front can feel unstable.

 

Fork Height
This is the position of the forks in the yokes and its measured with a ruler from the top of the yoke to the top of the fork. When making these changes check for clearance between the front tyre and the radiator at full compression. One disadvantage of moving the forks through the clamps is that it reduces ground clearance and if the pegs and exhaust are already scraping, this will make it worse. Raising the rear end has the same effect on the steering and increases ground clearance - if possible, this is a better option.

 

Rear Height Adjustment
If your shock has a ride height adjustment and you wish to use it, you must measure the ride height (as for Rear Sag). We are recommending to make adjustments of only 5 to 10mm increments at a time. Larger changes will cause the bike to steer considerably quicker, and if you're not ready for it, you may find yourself in trouble! Raising the rear ride height will put more load on the front and may make it necessary to tighten up the front to compensate.