V-Twin Motorcycle Suspension Guide

High performance suspension isn’t just for racing, it is the secret to getting off your massive touring machine after hours of riding and feeling like you just stepped out of a car. Performance suspension and touring/cruisers are not often spoken in the same sentence. For the most part, cruiser and touring riders have gone without improving suspension performance. Lowering kits and style components have always been available but now finally over the past few years V-Twin owners can get their hands on suspension that will improve the comfort and safety of their ride.

Progressive Suspension 944 Ultra-Low Standard Duty Shocks | 163-582

Progressive Suspension 944 Ultra-Low Standard Duty Shocks | 163-582

Suspension is key. If you have spent time around or are familiar with racing, you’ve probably had that phrase over and over. The saying is absolutely true but not just for racers, the right suspension set up will improve the quality, comfort, and safety of your ride. How your bike handles in turns and absorbs bumps will be determined by your suspension. Also the right set up will keep you out of harm’s way by avoiding potentially disastrous situations like losing control of the bars from head shake. Suspension is made to increase handling confidence when tuned correct for the individual. So whether you’re an aggressive rider looking to get the most out of your bike or you like to cruise, the right suspension will help you enjoy your ride more than ever before.

The first step to getting your suspension dialed is to have a basic understanding of the seemingly elusive inner workings of motorcycle suspension. The function of the spring itself is easily seen from observation. What eludes many riders is how the spring rate, sag, and inner components of the shock and forks actually pave the way to better suspension.

Springs

A spring can be defined by wound steel that is rated by the measurement of force required for the spring to compress. The simplified function of the spring is to bear the load and absorb impact. The spring rate is typically expressed in lbs per inch. There are two commonly used types of spring rates, linear and progressive. The linear spring rate is basic in that every inch of the spring requires the same amount of force to compress. Progressively wound springs on the other hand require more force for each inch the spring is compressed, so the spring becomes stiffer as it is compressed. The advantage of a progressively wound spring is that the spring is able to soak up small bumps but deeper in the stroke the spring is stiff enough to handle a big hit.

Dampers

The damper works to dissipate the energy created from the compression of the spring and the following rebound.

While you’re riding down the road, hit a small bump and your spring compresses to absorb the bump like explained above, but that is not all that will happen. Now the compressed spring has stored energy that needs to be released. If the spring were to release this stored energy without a damper your bike would essentially bounce down the road. As the spring released the bound up energy extending past its original static length and cycling through until the energy dissipated. The damper slows this release of stored energy so you can keep on riding after absorbing the bumps on the road. Dampers use two separate chambers, one with heat tolerant gas such as nitrogen and one with oil, to allow the oil to expand without impacting damping. Without the nitrogen the shock would likely stop moving from raid damper movement.

Preload Adjusters

Although a shock may be designed to fit your bike it may not be adjusted properly to fit you right out of the factory. Any rider can vary greatly in weight but also the shock will need to be adjusted on the fly if you plan on carrying a passenger. The solution to this problem? Preload adjustment. Preload is the amount in which the spring is pre-compressed at a resting rate. Preload adjusters work by slightly compressing or uncompressing the shock so the rider can tune to varying conditions. Remember you always want to have the preload adjusted equally on twin shock bikes.

Shock Sag Adjustment

Now you understand the basics of suspension! So you want to buy a new set of shocks. Where should you start when setting in your new suspension? The first thing you should do is set the recommended amount of “sag” which is the amount your shock will compress under the bike and rider weight. To measure your sag make sure you have a reliable helper or two and your owner’s manual, this will tell you what magic number you are looking for when you take the difference between measurements. There are two measurement you will need to determine the sag, first the free sag and second rider sag.

To measure the free sag select any point directly above the rear axle. Lift the rear fender as far as you can to free any compression on the shock and measure from the axle to your selected point.

To measure rider sag grab your two helpers to support your bike, you will need to be standing on the foot pegs with your hands on the bars. Take the measurement from the rear axle to the same point used for free sag.

The sag is the difference between these two measurements. This is where your owner’s manual comes in handy if you want to get the sag just right. Typically the recommended sag for cruiser and touring bikes is between .75” to 1.25” depending on the bike. If your number falls below the range specific for your model the bike will need less preload where as if your number falls above the range your bike will need more preload. Remember to adjust the preload equally on both sides when you have twin shocks!

What do the techs at J&P Cycles recommend?

Progressive Suspension has been a leader in the aftermarket motorcycle suspension market since they started in 1982 and for good reason. Their team of engineers use state of the art computers, shock dynos, and real world testing to design the ideal suspension for your ride. Most units are dyno tested before leaving the factory and Progressive has outstanding quality control that each component touches before getting to your doorstep.

So what do our techs recommend? See the 944 Series from Progressive Suspension for standard, low, and heavy-duty shocks for superior ride quality. Want more? The 977 series offers high performance ride quality. Check out our selection of Progressive Suspension for your ride here jpcycles.com/progressivesuspension.

About the Author:

J&P Cycles Social Engagement and Content Specialist. Motocross racer and motorcycle enthusiast.

2 Comments

  1. Dave March 17, 2016 at 9:44 pm

    The stock suspension on my ’15 Street Glide Special was awful. Even with the Special’s upgraded rear shocks, the cheap Harley shocks. limited rear suspension travel (2″), and primitive pushrod forks are punishing on bumpy roads. I installed Proaction Suspension 13″ Bagger rear shocks which helped the rear with an added 1″ rear travel & much better multi-adjustable nitrogen charged shocks. They are not cheap ($900) but make a big difference. We also had Progressive suspension fork springs installed but unfortunately they made the front end even stiffer than stock; not the plush ride improvement we were after. My bike is having the Harley cartridge fork kit installed right now (using thinner than recommended Redline oil) and hopefully it will smooth out these eastern Ohio / western Pennsylvania roads. Harley really needs to up their game; they’ve got the looks, they’ve got the drivetrain, they’ve got the dealer & customer support; but their suspension is sub par. Compared to the ’14-16 Indians, the Indian is by far a plusher, more comfy ride with stock Fox nitrogen shocks & stock cartridge forks.

    • J&P Cycles March 18, 2016 at 8:17 am

      Dave,
      I agree Harley Davidson is up on everything else it seems like other than suspension. Over the past three to five years we have seen a huge change in how the market views suspension so hopefully we will be seeing better stock suspension in the near future. They will have to if they want to compete with other brands.

      Kaitlyn

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