So I want to upgrade my suspension.

Firstly see the blog re understanding my suspension.

Inside your forks you will find in most modern bikes items called cartridges containing valves (or crudely sometimes called Pistons) and these valves are much the same as whats found in Shocks. So within the OEM suspension and more often that not these valves will be crude and cost effective to produce items. In years previous cartridges were expensive to produce and tended to be the domain of more expensive bikes and many manufacrures used what is called a dampening fork. So called because dampening of the spring energy was by forcing oil through smaller orifices. (holes) These forks (dampening) went through many changes and valves were invented (RaceTech - Paul Thede) that utilized shim stakes that in may cases mimicked a cartridge fork with exceptional results. Later came more advanced methods with improvements to the sealing of the dampening rods and both rebound and dampening control. Kiwis where very active with some of these designs and remain so but the major failing of these forks is cavitation as they returned the oil and bypass back to the fork reservoir. The later cartridge and “upside down fork” requires less oil. Compared to modern day cartridges they use small air gaps and that further encourages the cavitation. Modifications became exspensive and newer cartridge development meant cartridges could be produced way more cheaply and became almost like throw away in there construction.

With cartridges the cartridge could / can be replaced within the fork with way more sophisticated and adjustable units or often the cartridge can be dismantled and the valves replaced or modified with better technology. By replacing these items with modern machining and accuracy (CNC) the parts can be greatly enhanced that allows better oil flow, sealing, cavitation and pressurization. When Suspension Dynamometers were developed so to was the ability to further develop suspension without just trusting the seat of your pants. Workshops could track the development and behavior of there designs and parts without becoming encumbered with exhorbatant costs.

Front and rear suspension went from dampening devices controlled largely by springs to devices controlled by oil flow that made the energy stored within springs so much more controllable. Suspension today uses small piston like bodies with shims to control the spring energy. These bodies through thin flexible shims could control suspension compression and rebound (return of the fork) through the flow of oil through the distorting shims. These shims distort through the force / velocity which modern math has taught us is a constant or squared law. Of course to work all this out effectively and because the possibilities are enormous you need a Suspension Dyno and now the knowledge is just getting started. Then you have pre-load on the spring and that’s as scary a science (another blog) as it effects the sweet spot of the shim stack, now introduce oil flow through the offices or deforming shim stacks, oil flow is measured in centistokes (cSt) and defines an oil's resistance to flow under gravity through a known orifice so don’t be confused by the weight of Oil, like a 10w or 15w as these vary from one manufacturer to another, oh and spring weights.

Today many variations of valves and where they are placed exist, like shims on both sides of the valve body, giving both rebound and compression control through the one valve, Separate compression valves and rebound valves at the top and bottom of the cartridge to one fork being compression and one fork being rebound. This latter system has advantages in that both rebound and dampening can be easily adjusted where when both valves exist in the same fork it was often much harder to adjust without removing the axle.

Shim stacks are interesting in they tend to carry multiple shims that start at a larger diametre (Low force / Velocity - low speed opening of the shims) down to smaller diametre shims that give better high speed control. Then you can gain further control by introducing what is commonly called clickers, these clickers work by just allowing more or less oil to by-pass the shim stacks and so effecting the dampening of the forks speed or hardness. So if you close the clicker off (generally turning in a clockwise direction) you are lessening the oil that can bypass the valve (shims) which now makes the suspension harder or slower as the spring can’t use it’s energy so easily.

Of course the point of all this is to keep the tyre as it rides over the undulations to stay in constant contact with the surface. Oh one last thing if you have had your forks / shocks professionally built and dyno’d by a knowledgeable, experienced technician and unless your last name is Lorenzo you don’t necessarily need clickers.

I hope you are now a little enlightened to how the suspension controls the contact of the rubber with the road. Regards Leigh.