Showa “Dual Bending Valve” front end technology for Harley Tourers
Best known for their Harley OE front ends, Japanese suspension specialist Showa, one of the largest suspension businesses in the world, started to enter the aftermarket three years ago, and is now a regular exhibitor at the EICMA ‘Milan Show’.
For a Harley retro fit, Showa is offering what it calls its SDBV (Showa Dual Bending Valve) technology for Touring models.
Designed to cater to the widely ranging weight variables that the big, heavy tourers have to contend with, SDBV is a newly developed valve unit, comprising disc and check valves, that are said to deliver “the same levels of high performance and stable damping characteristics associated with cartridge type set-ups, but with a simpler structure that is closer to that of free-valve design suspensions.”
It is claimed the technology improves response to braking and use of the throttle, reducing dive and improving stability, especially under heavy load.
reduced dive and improved stability
The ability of a front end to cope with the weight issues on Harley Tourers is especially important where ABS is used – the potential for heavy bikes to experience sudden nose diving is accentuated with the kind of braking response dynamics associated with ABS.
The structure of the conventional free-valve design makes it difficult for the suspension to generate the compression-side damping force needed at low piston speeds (suspension operational speeds) where nosedive needs to be controlled.
Showa claim their SDBV has solved this issue. “Since SDBV can generate stable damping force characteristics, it has an advantage of being able to supress the floating of the vehicle body caused by uneven road surfaces.
“Because its basic structure is similar to the free-valve type, the SDBV can keep the increase of cost/weight to a minimum because of the economies of scale we have.”
Showa go on to explain that “the free-valve type, the basic structure of the normal type of front fork, has been applied to many different models. However, the issue of the free-valve structure is that it cannot sufficiently compensate for vehicle posture changes, because the damping force rises more steeply than the linear curve with regard to change in piston speed due to the damping characteristics being generated.
check and disc valves
“The ‘SDBV’ uses a valve unit of a new structure in place of the free-valve structure. Check and disc valves are placed in rebound/compression sides independently to control damping forces. This valve unit generates damping force characteristics that change linearly between low and high piston speeds, improving the ride feel, especially on uneven roads.
“The improved responsiveness allows the tires to grip the ground firmly and provides reliable braking and handling performance.”
AMERICAN SHOWA, INC