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Steel Thunder Custom Cycles
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|SHOCK INFORMATION AND TECH (Provided by PROGRESSIVE SUSPENSION INC. U.S.A.)|
Definition of Terms :
Rear suspension on a motorcycle is comprised of a damper and a spring. This combination is commonly referred to as the shock absorber.
Damping is divided into two parts: Compression Damping and Rebound Damping.
Compression Damping comes into play when the shock is compressed and helps absorb the impact when a bump is encountered and the wheel goes up.
Rebound Damping controls the return of the shock absorber and wheel to its original position. If this occurs too quickly, the wheel may bounce back (pogo). If it returns too slowly the shock absorber may not allow the wheel to return to its correct position for the next bump causing the tire to lose contact with the road surface. Control is the key word. Rebound damping controls the speed is which the spring and damper combination return to its original position.
Spring rates are selected by Progressive Suspension to match each motorcycle application. Leverage ratio (wheel travel vs shock travel), wheel travel and load determine the required spring rate for your motorcycle. On those applications where you have a choice of a standard spring or a heavy duty spring, the heavy duty spring should be selected for a load weight over 200 lbs, not by how fast you ride. There are four common types of springs.
Straight wound springs of 100 lb/in. require 100 lbs of force to compress each inch of travel. A progressively wound spring will usually have coils closer together on one end producing a progressively stiffer spring rate. At the beginning of compression, less force is required. As the spring is compressed, more force per inch is required to compress the spring. Two springs are stacked to produce a "dual rate". When the softer rate is used up, the springs jump to the higher rate (i.e.; 70-100).
Air spring When air in a shock absorber is compressed the pressure increases. This increase in air pressure acts the same as a spring rate. The purpose of adding air to the shock is to easily set the correct ride height for changes in load. For safety reasons, Progressive air shocks feature a combination of a steel spring used for the standard load capacity, air is then added to adjust the correct ride height.
Types of Shock Absorbers
There is a shock absorber available for each type of riding and every type of motorcycle. Determine which type of shock absorber will best fit your riding style.
Conventional Steel Spring - The rider who has a fairly consistent load from one trip to another and is looking for outstanding performance will choose Progressive Suspension's conventional steel spring shocks.
Adjustable Damping - The high performance rider will want to choose the Progressive Suspension adjustable damping shock for outstanding performance, damping adjustability and a reasonable price.
Air Shocks - A touring rider with widely varying loads from one trip to another should consider our famous Progressive Suspension air shocks. The correct ride height is easily adjusted by adding or subtracting air pressure. These shocks offer exceptional control and comfort.
Progressive Suspension's spring shocks have a mechanical spring preload adjustment feature. This adjustment is used for setting the correct ride height when you have changes in load. When the preload adjuster is raised to a higher notch, it will increase the beginning spring load and raise the ride height of the motorcycle. Ride height is very important. Most complaints of a harsh ride can be traced to incorrect ride height adjustment. If the motorcycle is sagging too much, there will not be enough wheel travel to absorb big bumps and one will get the feeling that the suspension is too stiff but in reality it is too soft. Stability and safety of the motorcycle is impaired when excessive bottoming occurs. Tire wear and damage is also effected by excessive bottoming. When the shock bottoms out the tire must try to absorb the remaining force of the bump. This causes excessive side wall flex in the tire which can weaken the tire and possibly cause premature tire failure.
If one needs to lower a motorcycle it must be done by choosing the correct shock and spring for that particular motorcycle. There must be sufficient clearances of the wheel and other components. Choosing a shock that is designed for another motorcycle can be dangerous. Generally when you lower a motorcycle by utilizing a shorter shock you will lose the equivalent amount of wheel travel (or more depending on the ratio of shock travel to wheel travel). For example if you lower the motorcycle 1" you will lose 1" of wheel travel. A motorcycle with 4" of wheel travel that is lowered 1" will lose 25% of the ability to absorb bumps. Decreased wheel travel will increase bottoming and decrease ride quality. Lowered shocks will generally have stiffer spring rates and damping to help compensate for the loss of travel. Initial cornering clearances will also be affected and care must be taken in making turns at any speed. Lowering motorcycles that are heavily loaded is not recommended.
We NEVER recommend lowering blocks on any motorcycle. The use of lowering blocks changes the angle of the shock. This can cause shock failure and the spring and damping requirements will be incorrect due to a change of leverage of the shock. The use of lowering blocks voids most aftermarket shock warranties including ours.
Front forks should be taken apart, inspected, cleaned and fresh oil installed every 20,000 miles or once a year for optimum performance and minimum wear. Many complaints of a harsh ride can be traced to the front forks, including weak springs, worn internal parts, misaligned aftermarket fork braces (which causes binding) and fork tubes that are bent or misaligned to each other (causing binding).
Fork Oil Volume
When installing fork oil we recommend the stock volume of oil listed in your shop manual.
Fork Oil Viscosity
Most motorcycle manufacturers recommend ATF (automatic transmission fluid) for fork oil. This has excellent lubricating and cleaning qualities but we do not recommend ATF oil for one main reason. When it is manufactured it has no viscosity specification other than it must fall between 5 wgt and 17 wgt. One time you buy ATF it might be 5 wgt and the next time it could be 17 wgt. We do not feel that this is acceptable for motorcycle forks. Therefore we recommend most major brands of motorcycle fork oil. As a general recommendation 10 wgt works well for most motorcycles.
Aftermarket fork braces are another problem. There are good and bad braces on the market. A good quality brace, properly installed, will help stabilize the forks, especially at slow speeds. A poor quality brace, or one that is improperly installed, will cause many problems in fork performance, ride quality and handling.
Things that affect suspension
Wheel bearings, swing arm bearings and steering head bearings all affect the handling of the motorcycle. Adjust steering head bearings and swingarm bearings to the factory specifications. Do not over torque the steering head bearings. Over torquing bearings to try to correct a wobble is a common mistake that well meaning mechanics make. Under no circumstances should this be done, it will cause even more handling problems and premature wear. If your mechanic suggests this, immediately take your motorcycle out of there!
Good quality tires of the correct size and profile are very important. Below are some of the more common tire problems that adversely affect handling.
• Wrong tire size (width) for the rim size
• Tire not sealed on the rim correctly.
• Incompatible front and rear tires (mixing makes or profiles is not recommended).
• Incorrect tire pressure - This is the #1 cause of excessive tire wear and bad handling! Do not try to improve your ride comfort by letting air out of the tires! Under inflated tires overheat, cause handling problems and are more likely to blow out!
• Worn or poor quality suspension will cause excessive tire wear, especially cupping.
• Weight - Some accessories when bolted to a motorcycle may cause handling problems. The most common causes of the problem are: Added weight of additional accessories Overloaded travel trunks and saddlebags Overloaded trailers Trailers with the wrong hitch ball height and/or weight Incorrect distribution of weight (too much weight to the rear of the motorcycle.
(Q) What is the advantage of air over steel springs?
(Q) What is preload?
(Q) What are spring rates?
(Q) Why progressive rate?
(Q) Why should I buy your 420 Single Shock?
(Q) Why should I upgrade my suspension?
(Q) Why do OEM shocks wear out so fast?
(Q) Why do I need aftermarket shocks?
(Q): On my 5th Element Air Shock, is the air valve on the small end of the shock "negative air"?
The control valve controls position sensitive compression damping. In other words, the shock senses how far it is compressed and responds with varying compression damping throughout the shock’s travel. The higher the IFP pressure, the sooner the control valve starts to close as the shock is compressed, increasing compression damping.
The correct normal range of pressure is 50psi – 100psi for the 5th Element Air Shock IFP chamber and 75psi – 150psi for the 5th Element Coil Shock IFP chamber.
(Q): Why does my shock seem to have lost air every time I pump it up?
To really tell if the shock is leaking air, you can dunk the shock underwater, just like testing for a puncture in a tube.
(Q): Why does my 5th Element Air Shock seem to be leaking oil?
©2003 Progressive Suspension, Inc. --- All Rights Reserved.
Progressive Suspension Literature - Catalogs and Brochures on PDF
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Steel Thunder Custom Cycles
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Marshfield, MO 65706
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