WHAT IS A SHOCK DYNO?
There is a wealth of misinformation on the Internet and forums concerning shock dynos. First we must understand that a shock dyno is not the quintessential element of ride quality and performance.
A Shock dyno is only a tool to help determine how good a shock is in theory. Real world testing is also necessary to determine how a shock rides and performs. Shock dyno results primarily aid in determining hysteresis & cavitation. We also use a shock dyno for shock matching, durability tests and confirming damper adjustments. At Fortune Auto North America we use a shock dyno in our daily operations for all of these tests. This helps us offer the client a consistent and thoroughly tested product.
Many manufacturers shy away from displaying shock dynos because either they do not have have access to a dynometer or they may be trying to hide their shocks' characteristics. When we build all of our shocks we use a CVP graph to confirm that the shock was built properly. At Fortune Auto you can request a shock dyno when purchasing your shocks for an additional $100. We supply you with a PVP sweep graph. We normally do not provide this service free of charge because it takes about 45 minutes per shock to conduct a PVP sweep graph.
CVP SHOCK DYNO PLOT:
This plot helps a shock builder or manufacturer determine if a newly assembled shock is performing within its defined parameters. It also helps determine if there is excess cavitation (usually due to lack of nitrogen pressure) and more importantly hysteresis.
Hysteresis is shown by the separation of the 2 lines in the graph and is the result of seal drag. Generally a shock with extremely low seal drag (a good thing for performance) has a lower life span and will need to be rebuilt more often. A shock with higher seal drag (think oem strut) can go longer with out rebuilds. Its important to find a balance between the two. A damper exhibiting a good balance between low hysteresis & seal drag generally requires rebuilding every 2-5 years.
The graph below is of a BWS / Fortune Auto shock. The minimal gap between the 2 lines shows fairly low hysteresis. This test was conducted at 250 degrees, the maximum heat that would be seen on a race or drift car.
The graph below is of a competitors shock that is similarly priced to ours. This damper exhibits poor shock operation and is unacceptable in terms of hysteresis. Its actually worse then an oem shock. This shock was also tested at 250 degrees.
PVP SHOCK DYNO PLOT:
At Broadway Static we like to use the PVP plot in determining the ride quality and ride performance of a shock. It also helps determine how linear or digressive a shock is.
Below is a graph of a 510 damper. The graph is separated into 4 quadrants. The top of the graph displays compression force and the bottom of the graph displays rebound force. The left side of the graph represents low shaft speed and the right side represents high shaft speed. A common misconception of the low speed and high speed variables is that the measured velocity is referring to the speed of the car. Low shaft speed represents driver inputs such as roll, pitch, squat and dive. High shaft speed represents bumps, pot holes, rumble strips etc.
High shaft speed results will generally give you an idea of how comfortable a shock is and low shaft speed results help give the driver confidence. A linear shock has very little low speed force and will not handle roll, pitch, squat and dive situations as well as a digressive shock that has greater lower speed force.
Generally everything under 2-3 inches per second is considered low shaft speed and anything over 2-3 inches per second is considered high shaft speed. The graph below is of a linear shock. Again this shock is a competitor's shock. As you can see there is very little low speed force.
The graph below is of a 510 series shock. As you can see the graph has a knee in it. The shock exhibits much lower shaft speed force...again more control in roll and dive/squat situations.