SLAM IT BRO Large Roll Couples = bad4pussies High Roll Centers = INSIDE LIFT MORE BAD
06-16-2011, 09:30 PM
#42
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@Jason, if the spring is just flat-out too hard and you hit a bump it's going to upset the chassis beyond the point of where it could be practically "calmed down", so what really determines how hard of a spring you can use while dealing with bumps will be in the high speed damping of the shock right? If expecting to encounter bumps on hard springs, less high speed compression damping (the harder spring should help to slow the momentum of the sprung mass) and a bit more damping on HS rebound would be effective? negatives to that?
The *bounce frequency* aka spring stiffness should be as soft as possible that keeps you off or in a reasonable part of the bumpstop while cornering while having enough remaining bump travel to absorb bumps. The conflicting requirement is that you want the car as low as possible to lower the CG as much as possible.
Softer springs is better BUT the conflicting requirement is you don't want a **** ton of body roll because that adversely affects the tire's camber while cornering, and said body roll also compresses the outside suspension reducing remaining available bump travel.
Softer springs is better because the tires will have more grip on bumps. This is the only reason softer springs is better.
With the conflicting requirements there is a compromise that depends on the road surface primarily. The smoother the surface the lower and stiffer you can run. For bumpy backroads you will need a softer taller setup.
For lower grip conditions (e.g. rain) you will have less body roll generated so you can make the setup softer but also lower. Additionally in the wet tires lose more grip when they pass their peak grip point (in their slip angle curve). This means when you get in a slide it takes longer to regain grip. So you don't want to lose grip in the first place, so the setup needs to be softer than dry conditions.
That's the general guidelines. As to the optimal setup, you would have to look at who's fast. 949 seems to have found a fast track setup. Fatcat has nice setups for autox and backroads. It is 949 that has found that very low and very stiff works well for the track.
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06-16-2011, 11:43 PM
#43
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Not yet, I was so close to just buying the EFR6258 so I could stare it, but I spent most of the "turbo setup" money on more tooling and a TIG welder instead. 
That phone picture is huge..., but if I can get just a little better than that, I should be able to make money with it.
That phone picture is huge..., but if I can get just a little better than that, I should be able to make money with it.
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06-17-2011, 02:07 AM
#45
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Mechanical grip
Compared to aerodynamics, understanding the dynamics of tire grip is more elusive and the perceived rules change from one type of tire to another. It seems tire grip is created when the tire is pressed into the track surface enough to cause the rubber to interlock with the grain of the pavement. Not
enough compression damping allows the tire to move freer and ride up on top of the pavement grain, metaphorically similar to “dry aquaplaning”. As the compression damping is increased, the tire will interlock with the pavement and grip will increase. If the damping is further increased incrementally, eventually the grip will stop improving and begin to go down. This is mainly caused by too much pressure from the suspension that overheats the tire or compresses it too much, giving unduly high tire load variations. Keep in mind that the suspension pressure the tire feels is the sum of the compression damping, the spring rate, the sway-bar rate and possibly the torsional rigidity of the chassis.If the pressure sum seems to be optimised for grip but for other reasons it is indicated that one component of the sum needs to be increased, another component may need to be reduced. For instance, a higher spring rate may be necessary to reduce fore and aft pitching. In order to make the stiffer spring work properly, the compression damping may need to be reduced. In another case, one car might have less torsional stiffness in its chassis than another. To compensate for this, the car with lower chassis
stiffness will require more compression damping to make the suspension pressure sum high enough. An indicator of too much suspension pressure is controllable sliding at all speeds and all phases throughout the turns (flat sliding).
Compared to aerodynamics, understanding the dynamics of tire grip is more elusive and the perceived rules change from one type of tire to another. It seems tire grip is created when the tire is pressed into the track surface enough to cause the rubber to interlock with the grain of the pavement. Not
enough compression damping allows the tire to move freer and ride up on top of the pavement grain, metaphorically similar to “dry aquaplaning”. As the compression damping is increased, the tire will interlock with the pavement and grip will increase. If the damping is further increased incrementally, eventually the grip will stop improving and begin to go down. This is mainly caused by too much pressure from the suspension that overheats the tire or compresses it too much, giving unduly high tire load variations. Keep in mind that the suspension pressure the tire feels is the sum of the compression damping, the spring rate, the sway-bar rate and possibly the torsional rigidity of the chassis.If the pressure sum seems to be optimised for grip but for other reasons it is indicated that one component of the sum needs to be increased, another component may need to be reduced. For instance, a higher spring rate may be necessary to reduce fore and aft pitching. In order to make the stiffer spring work properly, the compression damping may need to be reduced. In another case, one car might have less torsional stiffness in its chassis than another. To compensate for this, the car with lower chassis
stiffness will require more compression damping to make the suspension pressure sum high enough. An indicator of too much suspension pressure is controllable sliding at all speeds and all phases throughout the turns (flat sliding).
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06-17-2011, 03:47 AM
#47
Not yet, I was so close to just buying the EFR6258 so I could stare it, but I spent most of the "turbo setup" money on more tooling and a TIG welder instead. 
That phone picture is huge..., but if I can get just a little better than that, I should be able to make money with it.
That phone picture is huge..., but if I can get just a little better than that, I should be able to make money with it.
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06-17-2011, 08:44 AM
#48
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The damping "level" is described in terms of Q, for quality. High Q, less loss, less damping; Low Q, more loss, more damping.
"A system with low quality factor (Q < ½) is said to be overdamped. Such a system doesn't oscillate at all, but when displaced from its equilibrium steady-state output it returns to it by exponential decay, approaching the steady state value asymptotically. It has an impulse response that is the sum of two decaying exponential functions with different rates of decay."
"A system with high quality factor (Q > ½) is said to be underdamped. Underdamped systems combine oscillation at a specific frequency with a decay of the amplitude of the signal. Underdamped systems with a low quality factor (a little above Q = ½) may oscillate only once or a few times before dying out."
"A system with an intermediate quality factor (Q = ½) is said to be critically damped. Like an overdamped system, the output does not oscillate, and does not overshoot its steady-state output (i.e., it approaches a steady-state asymptote). Like an underdamped response, the output of such a system responds quickly to a unit step input. Critical damping results in the fastest response (approach to the final value) possible without overshoot. Real system specifications usually allow some overshoot for a faster initial response or require a slower initial response to provide a safety margin against overshoot."
Q=1/2 would be a balanced system, having a linear response.
A significant difference between a spring&mass system in comparison to an LC circuit exists and should be noted since it appears to be relevant to our suspensions. Although "0.5kx^2 and 0.5mv^2" are equivalent in that they're both simple integrals of force in respect to distance, the concerning difference is between x^2, where x=displacement, and v^2, where v=velocity. In the event a large "unexpected" force is applied to the wheel, such as a bump, it works out to where there will be a larger imbalance of stored energy between the sprung mass and the spring. The larger the force, the faster the sprung mass will travel, and the kinetic energy will build as the square of the velocity. I'm nearly positive this is why "high speed" damping adjustment exists, because you want to transfer that energy imbalance into the spring more quickly in order to maintain tire compliance you will need less damping to maintain a linear response. I think that a slightly underdamped shock compression going over a bump, responding quickly and exponentially in position/time (aka overshoot) will upset the chassis the least in the event of a bump (noting that our spring&mass system has a frequency too low to oscillate or repeat itself at all in the short timeframe of this event) and a slightly "overdamped" shock rebound will then respond with an inversely-exponential position/time, which would make the resultant wheel position/time graph very closely mimic a bump.
Seriously though, the amount of damping needed varies with the "unpredictable force" dependent velocity of the sprung mass and being slightly underdamped improves response time and being a little further from "correct damping" appears to more effectively deal with a "bump". It almost makes you want to feed a linear pot value divided by sampling interval into a PID loop controlling a solenoid field around a damper full of ferrofluid 0_0
Last edited by NickC; 06-18-2011 at 08:10 PM.
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06-17-2011, 11:43 AM
#50
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"An indicator of too much suspension pressure is controllable sliding at all speeds and all phases throughout the turns (flat sliding). "
*****..... my stock bilsteins on my 94 R are blown, I "flat slide" pretty easily.... :(. They are at 175k miles, though.
*****..... my stock bilsteins on my 94 R are blown, I "flat slide" pretty easily.... :(. They are at 175k miles, though.
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06-17-2011, 12:50 PM
#51
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What year BTW is that manual, and does the current one still have that paragraph?
Big companies can have one department designing hot **** stuff, then a newbie in a pissant department writing documentation... I've seen it many times.
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06-17-2011, 12:54 PM
#52
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Well, if you reduce compression with a single ****, the amount of rebound is increased relatively Seriously though, the amount of damping needed varies with the "unpredictable force" dependent velocity of the sprung mass and being slightly underdamped improves response time and being a little further from "correct damping" appears to more effectively deal with a "bump". It almost makes you want to feed a linear pot value divided by sampling interval into a PID loop controlling a solenoid field around a damper full of ferrofluid 0_0
Seriously though, the amount of damping needed varies with the "unpredictable force" dependent velocity of the sprung mass and being slightly underdamped improves response time and being a little further from "correct damping" appears to more effectively deal with a "bump". It almost makes you want to feed a linear pot value divided by sampling interval into a PID loop controlling a solenoid field around a damper full of ferrofluid 0_0
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06-17-2011, 08:02 PM
#53
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Think about this. If you have a linear spring, and if the car doesn't hit the bumpstops, the mass/spring/damper system is linear. Why should the bump and rebound be asymmetric? Then, think. What is the asymmetry in the system, or desired asymmetric behavior, that justifies asymmetric damper curves?
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06-17-2011, 08:05 PM
#54
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As another example, I'm reminded of the fellow who apologized to a valued friend for not taking the time to write a shorter letter. He was too rushed to cull out the unnecessary bullshit and so his friend was forced to wade through it to get his meaning, hence, the apology. Cull out the unnecessary bullshit.
And btw, that sentence I quoted of yours is an example of why you should write less, but better. Read it and you'll see you've said "short/concise communication can lack unintentional implications". I'm pretty sure you didn't really mean that, but with all the other nonsense I can't be sure.
I'm sure you've got lots to say without quadrupling it. We're not idiots, usually, and can read between the lines; just leave some room between the lines and we'll do the rest. And edit a bit for God's sake! Oy!
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06-17-2011, 08:18 PM
#55
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Being an old bastard I have to google this **** to see what you young'ens are talking about. I left out the semi-colon and got, "Tenderloin District". Knowing Hustler's ways I thought this was his way of telling the OP he was going to take him down to the Tenderloin and, you know, teach him the ropes. With the ";" I get a completely different result.
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06-17-2011, 08:36 PM
#56
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The energy transfer occurring between the stored kinetic energy of the sprung mass and potential energy of the spring reminded me of, in a frictionless world, the mechanical equivalent of a lossless resonant LC circuit, where an E&M instead of K&P conversion takes place between a capacitor and an inductor (like mass&spring) and a resistor damps the oscillatory transfer.
The damping "level" is described in terms of Q, for quality. High Q, less loss, less damping; Low Q, more loss, more damping.
"A system with low quality factor (Q < ½) is said to be overdamped. Such a system doesn't oscillate at all, but when displaced from its equilibrium steady-state output it returns to it by exponential decay, approaching the steady state value asymptotically. It has an impulse response that is the sum of two decaying exponential functions with different rates of decay."
"A system with high quality factor (Q > ½) is said to be underdamped. Underdamped systems combine oscillation at a specific frequency with a decay of the amplitude of the signal. Underdamped systems with a low quality factor (a little above Q = ½) may oscillate only once or a few times before dying out."
"A system with an intermediate quality factor (Q = ½) is said to be critically damped. Like an overdamped system, the output does not oscillate, and does not overshoot its steady-state output (i.e., it approaches a steady-state asymptote). Like an underdamped response, the output of such a system responds quickly to a unit step input. Critical damping results in the fastest response (approach to the final value) possible without overshoot. Real system specifications usually allow some overshoot for a faster initial response or require a slower initial response to provide a safety margin against overshoot."
Q=1/2 would be a balanced system, having a linear response.
A significant difference between a spring&mass system in comparison to an LC circuit exists and should be noted since it appears to be relevant to our suspensions. Although "0.5kx^2 and 0.5mv^2" are equivalent in that they're both simple integrals of force in respect to distance, the concerning difference is between x^2, where x=displacement, and v^2, where v=velocity. In the event a large "unexpected" force is applied to the wheel, such as a bump, it works out to where there will be a larger imbalance of stored energy between the sprung mass and the spring. The larger the force, the faster the sprung mass will travel, and the kinetic energy will build as the square of the velocity. I'm nearly positive this is why "high speed" damping adjustment exists, because you want to transfer that energy imbalance into the spring more quickly in order to maintain tire compliance you will need less damping to maintain a linear response. I think that a slightly underdamped shock compression going over a bump, responding quickly and exponentially in position/time (aka overshoot) will upset the chassis the least in the event of a bump (noting that our spring&mass system has a frequency too low to oscillate or repeat itself at all in the short timeframe of this event) and a slightly "overdamped" shock rebound will then respond with an inversely-exponential position/time, which would make the resultant wheel position/time graph very closely mimic a bump.
The damping "level" is described in terms of Q, for quality. High Q, less loss, less damping; Low Q, more loss, more damping.
"A system with low quality factor (Q < ½) is said to be overdamped. Such a system doesn't oscillate at all, but when displaced from its equilibrium steady-state output it returns to it by exponential decay, approaching the steady state value asymptotically. It has an impulse response that is the sum of two decaying exponential functions with different rates of decay."
"A system with high quality factor (Q > ½) is said to be underdamped. Underdamped systems combine oscillation at a specific frequency with a decay of the amplitude of the signal. Underdamped systems with a low quality factor (a little above Q = ½) may oscillate only once or a few times before dying out."
"A system with an intermediate quality factor (Q = ½) is said to be critically damped. Like an overdamped system, the output does not oscillate, and does not overshoot its steady-state output (i.e., it approaches a steady-state asymptote). Like an underdamped response, the output of such a system responds quickly to a unit step input. Critical damping results in the fastest response (approach to the final value) possible without overshoot. Real system specifications usually allow some overshoot for a faster initial response or require a slower initial response to provide a safety margin against overshoot."
Q=1/2 would be a balanced system, having a linear response.
A significant difference between a spring&mass system in comparison to an LC circuit exists and should be noted since it appears to be relevant to our suspensions. Although "0.5kx^2 and 0.5mv^2" are equivalent in that they're both simple integrals of force in respect to distance, the concerning difference is between x^2, where x=displacement, and v^2, where v=velocity. In the event a large "unexpected" force is applied to the wheel, such as a bump, it works out to where there will be a larger imbalance of stored energy between the sprung mass and the spring. The larger the force, the faster the sprung mass will travel, and the kinetic energy will build as the square of the velocity. I'm nearly positive this is why "high speed" damping adjustment exists, because you want to transfer that energy imbalance into the spring more quickly in order to maintain tire compliance you will need less damping to maintain a linear response. I think that a slightly underdamped shock compression going over a bump, responding quickly and exponentially in position/time (aka overshoot) will upset the chassis the least in the event of a bump (noting that our spring&mass system has a frequency too low to oscillate or repeat itself at all in the short timeframe of this event) and a slightly "overdamped" shock rebound will then respond with an inversely-exponential position/time, which would make the resultant wheel position/time graph very closely mimic a bump.
Don't take this wrong, Nick, I'm saying this for your own good. Someday you'll thank me.
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06-18-2011, 01:29 AM
#59
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This is the most pedantic bullshit I've possibly EVER read. When you get your head out of your *** you'll realize this too. I'm normally a mild mannered man, but I really want to bitch slap you right now, Nick.
Don't take this wrong, Nick, I'm saying this for your own good. Someday you'll thank me.
Don't take this wrong, Nick, I'm saying this for your own good. Someday you'll thank me.
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