Tuesday, September 25, 2007 - 02:08 pm, by: Cara Joseph(Carasky)
For some time lot's of guys have been asking me to explain the differences between a good shock and a bad one, what sophisticated valving really means, why a monotube shock is better than a twin tube etc etc. So this thread is an attempt to answer those questions and any others that might come up in the process.
To kick it off I thought I would start with why a monotube shock is better than a twin tube. Monotube shocks have a larger piston area than a twin tube for the same given outside diameter. This larger piston OD/monotube design means that; 1. There is room for more valves 2. The valves themselves can be bigger 3. More hydraulic fluid is moved for the same stroke, this means superior metering of the fluid transfer though the piston. 4. There is more fluid in the shock, which means higher temperature capacity. The movement of the fluid through the valves generates heat (Newtons law at work) by transforming the kinetic (up and down) energy. 5. The fluid is in direct contact with the shock body meaning rapid transfer of heat to the outside )ambient) atmosphere.
Following is a shock dyno graph (courtesy of Bilstein) showing the effect of heat on dampening of a typical Japanese twin tube shock. As you can see after 2 minutes, yes that's 2 minutes, of running at 550 mm/sec the damping force (the vertical axis) drops off dramatically. For those that haven't seen a shock dyno graph before the vertical axis is the damping force and the horizontal axis is the speed (frequency) of the up and down.
This means is the damping efficiency of shock drops away due to the rapid overheating of the fluid. Because of the twin tube design there is insufficient fluid to absorb the heat and the two tubes slow down the heat transfer to outside atmosphere. What you feel in real life is a gradual decrease in damping effect, the shock slowly ceases to control the spring and the chassis. You get move vertical/roll movement, the shock no longer helps to keep the tyre in contact with the road.
Hope that was in some way informative, the next subject (with pictures) will be a comparison of the design of the shock piston and the valve pack.
I Got this information of a very experienced and knowledgable person whom which I cant name that works at whiteline. Enjoy peoples.
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