'SPEED BUMPS'

Motorcycle Chassis and Suspension Specialists

MOTORCYCLE DYNAMICS RIDER MATCHED

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Editor: Greg Leech - Australian Motorcycle Trader

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Speed Bumps

The first step in setting up your suspension is determining if the fork and shock springs match your weight. The second step is finetuning the suspension adjustors or "clickers'. As ProMechA's PETER CLEMENTS explains, if you follow this procedure you'll eliminate some of the variables, and be well on the way to making the most of your bike's standard suspension.

Suspension set-up in a motorcycle, for dirt or road, is set for Joe Average, a fictitious individual of standard weight, size and riding style. There are many variables in suspension sensitivity - rider weight, rider/bike weight, weight distribution, the addition of pillion passenger and luggage, and so on, and every adjustment you make affects another aspect of suspension performance.

Nevertheless, you can adjust the suspension to make your bike behave and handle the way you'd like, and we don't simply mean by jacking up the preload to take a pillion.

If you want to ride like this, the first thing you need is good suspension. The way to get it is to dial in your basic compression, rebound and ride height settings.

What we're doing here is matching the spring rates to the rider, then fine-tuning the damping through the suspension adjustors to get maximum control over the springs and the rider-bike combination.

There are three steps in setting up motorcycle suspension front and rear, if you include adjustment of both rebound and compression, and three tests for each of these steps. It's quite simple and here's how it works.

# 1. THE SPRINGS

The first step in determining whether or not the springs suit your weight is to carry out a 'sag' test. This particular sag test will also indicate how the spring(s) will control the weight of the bike.

The first test is for 'bike sag' or 'static sag' and tells us how far the bike will drop under its own weight. You find this out by taking two measurements, one with the bike on a stand, then again with the bike on the ground. The amount of sag will vary, because of the many influencing factors involved but generally speaking, it should be between 0 percent and 15 percent of the bike's wheel travel.

To carry out this procedure accurately, sag measurements should be taken from the front and rear of the bike, not merely the rear as most riders do. Measuring fork sag is more difficult so do it carefully. You can measure the length of the fork boot in the different positions, if your bike has a fork boot, or fit a zip-tie to the fork leg and use that as a reference point. Here's how to do it:

With the bike on a stand, measure from a point on the top of the fork to the zip-tie. Write that figure down. Now do the same at the rear of the bike, running the tape from the centre of the rear axle in a vertical line to the underside of the rear. Write that figure down too.
Now take the bike off the stand, make the same measurements again and write these figures down.
With a bike like the Yamaha WR450 your measurements should end up something like this:

Bike sag: Front - 20 to 35mm
Bike sag: Rear - 25 to 45mm

Now we measure 'rider sag' or how far the bike's suspension will drop with a clothed rider on the bike. This test will show how the spring will control the weight of the bike. The rider should stand with his weight centred, because weight distribution can influence the outcome, and lean with one hand against a wall so the bike takes all his weight. The test should mimic normal riding conditions so try to make sure the fuel tank is about half full when you're doing this. Rider sag is usually between 20 percent to 30 percent of total suspension travel. Here's what the numbers should look like if the standard springs are okay for your weight:

Rider sag: Front 90 to 100mm
Rider sag: Rear - 90 to 110mm

If the springs are too soft you'll get more sag and if they're too hard you'll get less sag. The numbers tell it all. You can't compensate for having the wrong springs with the suspension adjusters either, so if the numbers are outside this range you'll be visiting your dealer or suspension specialist for harder or softer springs.

# 2. REBOUND ADJUSTMENT

Having confirmed that the standard springs suit your weight, we now turn our attention to the suspension adjusters or 'clickers' that control rebound and compression damping. Bergin this part of the sequence with the clicker settings on standard position; in other words, the positions they were in when you picked up your new bike.

This sounds odd I know, but assume this setting to be "soft" even if it's not. Test ride the bike, then try a slightly too firm setting, three or four clicks towards the Hard position, then test ride again. Doing this will help teach you what too hard and too soft feel like.

You can then judge where the third setting, what I call the baseline setting should be. Continue testing to find the setting either side of your baseline that gives you the most feel and control for the conditions you ride most.

WHAT'S A GOOD BASELINE SETTING?

You can't make a decision on a clicker change from just one setting. But with two settings you can. If the 'soft' feels too soft then your change needs to be moved closer to the firm setting. Alternatively, if the firm setting feels too firm, then do the opposite and go towards the softer setting. A good example is to imagine the two settings as goalposts. You've just set them a distance apart, now you're going to kick the ball through the best spot; that is to find the best setting, which we call the baseline setting.

# 3. COMPRESSION ADJUSTMENT

Again, start by assuming the standard setting to be too soft, then go too firm, three or four clicks in, which should feel too hard. Now you can judge where to set your baseline setting, as you did with the rebound test. Continue adjusting and testing until you get the feel and control you like.

It's important to arrive at the correct blend of the above three steps. Be aware that there'll be a major change in the way your bike feels and that you should ride carefully to test those changes. Don't ride too hard too soon. Remember too, that unless your suspension has high as well as low speed adjustment, changing clicker settings will affect only low speed suspension performance, not high speed performance. And, by the way, "high speed" doesn't mean high bike speed but the speed at which the fork and shock move through their travel.

REGULAR SUSPENSION MAINTENANCE

The above are tests and changes can be done by anyone. It's not rocket science. However, other factors affect suspension performance. We recommend regular maintenance to make sure that suspension action remains constant. Regularly check the bike for worn seals that may leak oil, and marks and scratches on the chrome-plating. To service or repair these you'll need a suspension check-up and fork or shock oil change and service at the minimum. Motorcycles and ATV's are most sensitive to suspension changes and need to be serviced regularly. Dirt bikes, such as the WR450, should be serviced more regularly than a road bike since dirt and grit can etch into suspension components causing damage and wear.

Oil weight, oil height and viscosity also have an effect on how suspension works.

THE ULTIMATE IN SUSPENSION PERFORMANCE

We recommend matching spring rates to the rider and then setting damping rates to achieve the best control over the springs and bike/rider combination. Changes to standard suspension will always produce huge differences in performance, especially when matched to the bike, the rider and the type of terrain.

For blokes who want the best suspension for their riding, we sell, service, manufacture and install highly technical suspension components, for example, fork and shock kits, springs and hi-tech adjusters, many regularly used by top riders in motocross, supercross, enduro and road racing. These components give the most adjustability in suspension performance, reduce arm pump, fatigue and help improve your riding skills more quickly.

Note: Peter Clements owns ProMechA Chassis and Suspension. He's a nice bloke and he knows it all. If you want advice, or you want him to fix your WR450, call Pete on (03) ~~9574 1164~~ 9560 2770. © 2005

Reprint courtesy of Australian Motorcycle Trader Magazine