The Dennis Kirk Blog
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How does your bike ride and handle? Chances are, not the best that it can be. A good percentage of riders just accept the way their bike is setup. It’s good enough, right? Well maybe if you’re just into settling for what the factory gives you or if you just happen to fit the mold of what the factory determines is the average rider. Chances are, though, that you don’t fit the mold of the “average” sized rider. Your suspension setup also needs to account for the extra weight of your luggage and a passenger if you ride two-up. All of the different variables make it fairly hard to rely on the stock setup for optimal handling and comfort.
Fortunately, adjusting a motorcycle’s suspension can be done by just about anyone with a few simple tools and a friend or two.
It is important to note that correctly adjusting your suspension won’t necessarily make your bike ride like a dream (that’s what aftermarket upgrades are for). But tuning the suspension will allow you to get the most out of your bike as is. You won’t know if you need to upgrade the parts until you have ridden the bike with it properly set up for you and how you ride.
Before you begin to make any adjustments to the suspension, you first need to ensure that all of your components are fully functional. Check the shocks and forks to see that they are working as they should. The seals should not have any leaks. Also check for any slop in the steering head bearings, swingarm bearings, wheel bearings and bushings. Any wobble in these components will throw off your bike’s handling and can negate any adjustments that you make.
Your tires aren’t technically a part of your motorcycle’s suspension, but they play a crucial role. Your bike will not handle the way it is supposed to if the tires are either under inflated or over inflated. In order to set a solid base line to test your suspension setup, you need to ensure that the tires are properly inflated.
A proper suspension setup starts with properly set ride sag. Ride sag is the amount of “sag” or compression of the shock(s) that occurs when under load from the normal weight of the rider(s), gear and whatever weight is on the bike while riding. The purpose of ride sag is to act as the suspension when your bike travels over cracks, potholes or other depressions. It allows the shock to extend preventing the chassis from being upset. A properly set ride sag will also improve your bike’s handling by being able to properly handle the weight of the bike shifting.
To measure your suspension sag, you will need a tape measure, your owner’s manual and a friend or two. A stand or lift can also make the job a bit easier to complete, especially for heavy bikes.
Start by fully extending the rear suspension. You can do this by lifting the bike by hand if it is light enough, tipping it onto the side stand or by using a lift. With the suspension fully extended, use your tape to measure from the center of the axle to some fixed point directly above, like on the subframe or fender. Record the measurement.
Next, measure the amount of sag that occurs under a normal riding load. This should include the rider, all the gear that is worn and any luggage that may be used. Before taking a measurement, bounce the suspension up and down a few times to help remove any stiction that could prevent the suspension from settling correctly. Now, sit in your normal riding position with all your weight on the bike. Have your assistant measure from the center of the axle to the same point from before and record the measurement.
Now divide your first measurement by the second. The ideal starting point for suspension sag is about 1/3 or 30% of the extended length. If the result of your equation is less than 30%, you will need to reduce the amount of preload on the shocks. If it is more, you will need to increase the amount of preload. Spin the retaining collar on the shock in the appropriate direction to achieve the amount of desired preload. Spinning the collar down increases preload and reduces the amount of sag. Spinning the collar upwards reduces preload and increases sag. Do so until you reach the desired amount of sag. For example, a shock with 9 inches of travel should have 3 inches of sag under a normal riding load.
The forks of your motorcycle can also be adjusted for rider sag, though it is not always necessary. The formula is the same as the rear: fully extended length minus compressed length under normal riding load. Conventional forks should be measured from the bottom of the lower triple tree to the top of the dust seal on the slider. On an inverted fork, measure from the dust seal to the top of the axle clamp. For both, the area being measured is the exposed area of the fork slider.
Not all motorcycle forks can be adjusted in the same way. Many forks have preload adjusters located on top of the forks. Turning the adjuster in will increase the preload, while turning it out will decrease the preload. Some forks do not have adjusters and require the use of preload spacers. The spacers can be swapped out with either shorter or longer spacers to achieve your desired amount of sag on the forks. Longer spacers equate to more preload, while shorter spacers provide less preload.
When you ride with more luggage or a with passenger, you will need to increase the amount of preload to account for the added weight to keep the sag at 30%. It is helpful to do the measurements for those situations at the same time that you take the other measurements. That way, you can record how many turns of the collar it takes to achieve the desired results. That way, you can make the necessary adjustments without having to measure the sag every time.
Ride & Test
With the proper sag set on your motorcycle, it’s time to take it for a ride and test it out. Take note of how your bike handles while cornering, accelerating/decelerating and how it handles road imperfections. If the results are still not what you expected, you can then either fine tune the preload or consider upgrading your suspension with better performing aftermarket components. Also, if your bike’s suspension has damping adjustments, you can play around with those to fine tune the suspension even further.
Damping Adjustment if Applicable
As mentioned above, adjusting the damping on the suspension can further fine tune the setup for a better ride. Rebound damping or “tension” controls the rate at which the shock re-extends after being compressed. When there is too little rebound damping, the suspension will spring back too quickly and not dissipate enough energy from the bump. Too much rebound damping will prevent the suspension from fully extending before you hit the next bump.
The initial compression and upward movement of the suspension after hitting a bump is controlled by compression damping. This helps prevent excessive travel of the suspension, which could cause the suspension to bottom out. It also works to balance out the spring rate to absorb the small bumps as well as the large ones.
Not all motorcycles include damping adjustments, but if you own one that does, you should really consider using them. Every rider is different so there is no one magic setting. Make adjustments in small increments and take notes on how the bike performs. Finding the perfect balance in damping adjustments with a properly set suspension sag can make your motorcycle handle and ride like a completely different machine.
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