The spring effect of a shock is there and is very real and as long as we run single rod dampers charged with nitrogen this will be the case. An ideal damper will exhibit a force output that varies strictly with velocity, which is what I think you desperately want to believe you have. However, the single rod charged dampers we use are actually an ideal damper and small gas spring in parallel. The spring effect is a by-product of the damper and doesn't effect the velocity dependent characteristics of that damper, it's just a necessary component of the system. If your charge is high enough you better factor it into your suspension setup and possible choice of springs. What matters in the end is the total spring rate acting at the wheel and if you add a bunch via your damper you may want to remove some via your spring to maintain your operating point.
There is a real reason base valves and the like were invented. There's a real reason guys prefer to minimize damper charge pressure as much as possible. If the gas spring effect in the damper never made a difference we'd never need base valves and we'd never worry about keeping charge pressures low. We'd just charge dampers with 500 psi with no ill effects and no worry of cavitation. But this isn't the case. 500 psi is going to manifest itself as a huge gas spring that will likely be unwanted in our setup. Therefore we spend time with basevalves, anti-cavitation devices, and achieving low charge pressures. It keeps our damper as close to the ideal damper as possible.
Supporting a car with dampers is far from ideal and not most efficient. However, if rules pigeon hole you into that corner and using the shocks in that manner is the only way to achieve an effect that net makes your car faster would you not use it then?
Belatti wrote: It can even go from linear to digressive using the same piston although with different shim config.
speedsense wrote:I'm not disputing that there's a spring effect in a shock.But a 45 pound measured spring force on a stationary shock is not the same as the "same" 45 pound spring force on a moving shock piston that is producing flow across the piston that is in constant chaotic motion. Depending on the piston design and the valving, the flow will reduce that number to one that may or may not have the same ride change effect that one would see on a stationary car/shock. The author of the article presented states that a spring change may be necessary to compensate for the spring rate of the shock. I believe he's incorrect (actually flat wrong) in prescribing such a change.
speedsense wrote: Being "pigeon holed" is a matter of experience and knowledge, there's plenty of ways to avoid it instead of making a shock act like something it isn't. A balanced car with an capable driver will win more times than a "tricked car" with the same capable driver who's unsure of what the car will do. IMHO
Not go away, but reduces from the stationary measured/calucated amount. The stationary position has no measureable stiction, a moving one does have a measurable amount. As pressure effects the piston seals and increases the stiction amount (along with other influences), one can ascertain that spring rate is the cause of ride change due to pressure but cannot ignore the other acting properties, such as stiction.RideRate wrote:You've got to explain to me how a 45 lbf spring force is not the same as the "same" 45 lbf spring force. You really seem to believe the spring force (aka spring effect or spring characteristic) goes away when the damper moves. Is this correct? Is this what you believe?
With no consideration for the shock piston?We've already explained how this is not the case. That spring force in the shock is going to always affect the height of the car just like a normal small spring. The hope is the force stays so low it's mostly negligible, but this isn't always the case.
All I can say is take your favorite pressure tapped shock. Run it on a dyno with a sine wave, track file, or whatever you want. If you don't believe a dyno collect some data on the shaker rig or at the track. Look at your compression chamber pressure data. Multiply that pressure by the area of your shock shaft.
If you run a basevalve remove the pressure drop across the basevalve from the compression chamber pressure. Subtract from this the area of the shaft times atmospheric pressure. Plot as a math channel vs time, track position, shock displacement, or whatever just as long as you know it's data from a constant chaotic motion event. What you see live and in front of you is damper force that is independent of velocity of the damper and only occurs due to the position of the damper's displacement (and the acceleration, but that's small and you can remove it too if you like). Look at that data. It's the spring in real life acting on your car straight from your damper and during constant chaotic motion. It's not going anywhere. Sure, there is some lag in it, but every spring exhibits some level of frequency sensitivity which is a totally different topic. It's still a fundamental spring and you can see it for yourself.
Sure there are ways to avoid it, some or all of which may not be legal, affordable, or beneficial. But if a method using shocks or anything else not as intended is faster than using the "proper" method, who wins? Not saying it's right, but one method will dominate until the other is proven out to be net faster for whatever reason.
Belatti wrote:When weight and packaging is not a big problem, for some specific racing cars you could use oversized remote reservoirs in the dampers. This would make a "not so progressive" gas spring, please correct me if Im wrong.
speedsense wrote:The stationary position has no measureable stiction, a moving one does have a measurable amount. As pressure effects the piston seals and increases the stiction amount (along with other influences), one can ascertain that spring rate is the cause of ride change due to pressure but cannot ignore the other acting properties, such as stiction.
speedsense wrote: Can the author of the article, be sure of a spring rate change to the car as a result of can pressure of the shock as an addition to the overall spring of the car? Higher pressure raises the stiction amount of the shock piston and is not a result of the internal spring rate of the said shock.
Or even the coil spring itself also contains stiction rates. Hyperco makes a hydraulic platform for the coil spring to reduce this stiction amount. As someone who tested these platforms (during their introduction) with live suspension data from a car, the addition of the platforms, reduced the stiction rate of the coil spring and resulted in a drop in spring rate to achieve the same performance of the higher rate springs. This was done with the exact same shock settings. The addition of the platform changed the shock velocities as well, and it was presumed it reduced the shock shaft's (from the coil spring acting on it) stiction as well.
The shock changed it's character without any changes to it's internal workings or pressure.
How can the author be sure, it's not stiction affecting the internal spring rate or whether it's the pressure?
speedsense wrote: A racecar body exhibits some of the same restraints as shock pressure, as it also moves in liquid that is under constant pressure (atmospheric), yet there are differences in how that constant pressure affects......
speedsense wrote:With no consideration for the shock piston?
speedsense wrote: The question isn't whether there is a spring rate in the shock with say 45lbs measured rate. The question is: How much is the reduced effect by piston design/valving and a reduction of stiction of the piston seals (by design), reducing the impact of the 45lbs of spring rate to a number low enough to not be a consideration as an acting spring or influence on the car's sprung mass?
speedsense wrote: I guess at that point we should rename the dampener to something else.....
PhillipM wrote:Belatti wrote: It can even go from linear to digressive using the same piston although with different shim config.
You can do that with pretty much any piston with the right shims
How far you can go towards a full digressive setup is the trick I suppose...
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