gas pressures for shocks
Posted: November 9th, 2010, 3:35 pm
I decided to start a new thread on tthe issue I raised regarding pressures. Brian mentioned that testing his shock on a scale did not disclose any changes when pressures were changed and that's probably right since he was testing the slow speed circuit of the shock. Long strokes in the shock are the domain of the low speed curcuit. In my previous post i mentioned gas pressures effected "high speed bleed" behavior. If you put a shock on a dyno and change pressures you will see a change in the high speed behavior. Specifically, the high speed blowoff, the point at which the bleed is overloaded and the shims begin to work, will change. My butt translates the high speed circuit as the jiggily feeling you get from the car. It kinda feels that its bouncing across the bumps rather than flowing over them. The high speed circuit really determines how a car will react to curbs as well.
The triple adjustable Penskes have an adjustable high speed circuit that changes the preload of the shims which will change when the shims will blowoff. It is felt that on a shock like the small black fronts or with the relative low spring rates vees use, pressures will have a measurable effect on the high speed behavior.
When we first began using Penskes rears, they came with a recommened 250 psi. Over time, many of us found that 150 worked a lot better. Granted, many of us ran springs that were a lot softer than many today; that will change how pressure changes will alter the behavior of the car. The evolution of drilling bleed holes, pioneered by Joe Stimola in our class, also dealt with the same issue only more drastically than pressures.
Like I said in the previous post, changing pressures on a test day is a very simple quick thing to do and your results may vary but when you don't have time or options, it could make a difference on a rainy day.
The triple adjustable Penskes have an adjustable high speed circuit that changes the preload of the shims which will change when the shims will blowoff. It is felt that on a shock like the small black fronts or with the relative low spring rates vees use, pressures will have a measurable effect on the high speed behavior.
When we first began using Penskes rears, they came with a recommened 250 psi. Over time, many of us found that 150 worked a lot better. Granted, many of us ran springs that were a lot softer than many today; that will change how pressure changes will alter the behavior of the car. The evolution of drilling bleed holes, pioneered by Joe Stimola in our class, also dealt with the same issue only more drastically than pressures.
Like I said in the previous post, changing pressures on a test day is a very simple quick thing to do and your results may vary but when you don't have time or options, it could make a difference on a rainy day.