Nobody in the Suspension forum has answered this one at all !!!! Help, btw I'm a recent ME grad.
Just wondering if any of you suspension nuts could give me a simple answer as to how a stiff spring coupled with a light shock will wear out the shock more quickly...(this "fact" has been gathered from reading through many a thread on suspension here at NICO)
In my logic, upon compression, the stiffer spring will resist more travel, and thereby lessen the stress on the shock.
The only thing I can see that is damaging, would be upon rebound, the stiffer spring will push much harder to return to static height, thus working the shock more.
I do understand that this kind of setup will suck terribly for handling, but I just want to know how the shock will wear out quicker. Also, do not comment on lowering (as this is obviously bad for the shock), just a mega stiff spring at stock height.
Me trying to understand, thanks.
underdamped
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Q45tech
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- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
The rebound stiffness [in pounds per inch at a certain velocity] is usually 2.5-3 times more than the shocks compression stiffness.
Rear bobbing up and down and front sway are the usually culprits in rebound wear.
As the number of cycles per second increases the internal temperature rises and this raises the Nitrogen pressure which leaks out faster [wear defined as failure to self expand at as new rate]. Rebound seals deform from heat/orifice wear
The seals are rated for only so many cycles.
Most can't test rebound on car as pulling the car bumper up 3" in less than a second is beyond the strength of humans.
Rear bobbing up and down and front sway are the usually culprits in rebound wear.
As the number of cycles per second increases the internal temperature rises and this raises the Nitrogen pressure which leaks out faster [wear defined as failure to self expand at as new rate]. Rebound seals deform from heat/orifice wear
The seals are rated for only so many cycles.
Most can't test rebound on car as pulling the car bumper up 3" in less than a second is beyond the strength of humans.
Quote »The rebound stiffness [in pounds per inch at a certain velocity] is usually 2.5-3 times more than the shocks compression stiffness.[/quote]
So.....I was on the right path, i think. The stiffer spring pushing the shock back up to static height faster, wears more on the rebound resistance...ok.
Quote »Rear bobbing up and down and front sway are the usually culprits in rebound wear.[/quote]
I would think bobbing would occur after the shock is blown...just trying to understand. sway? not really a wear factor on a shock i would say. It's only a slow compression to a new static point (around a turn), nothing compared to road imperfections.
Quote »As the number of cycles per second increases the internal temperature rises and this raises the Nitrogen pressure which leaks out faster [wear defined as failure to self expand at as new rate]. Rebound seals deform from heat/orifice wear[/quote]
I see how a stiffer spring could follow smaller/higher frequency bumps in the road. But we're not changing the road, same frequency input. (assuming the tires stay in contact)
So.....I was on the right path, i think. The stiffer spring pushing the shock back up to static height faster, wears more on the rebound resistance...ok.
Quote »Rear bobbing up and down and front sway are the usually culprits in rebound wear.[/quote]
I would think bobbing would occur after the shock is blown...just trying to understand. sway? not really a wear factor on a shock i would say. It's only a slow compression to a new static point (around a turn), nothing compared to road imperfections.
Quote »As the number of cycles per second increases the internal temperature rises and this raises the Nitrogen pressure which leaks out faster [wear defined as failure to self expand at as new rate]. Rebound seals deform from heat/orifice wear[/quote]
I see how a stiffer spring could follow smaller/higher frequency bumps in the road. But we're not changing the road, same frequency input. (assuming the tires stay in contact)
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
The purpose of shock is to convert the springs energy into heat, a 20% stiffer spring will have 20% more energy after compression during rebound [expansion] for the shock to dissapate.
Shocks must be matched to unsprung weight. Using 5-10 pound heavier than oem tires/wheels will affect the shocks life just as much if not more than 20% stiffer springs. Shock compression [rate/stiffness] only controls the oscillation of the unsprung weight. Rebound/expansion rate is affected by the sprung rate which varies with loading of vehicle.
There is an ideal compression rate which doesn't vary while the rebound rate is always wrong because of trunk/gas/passenger weight changes.........not to mention cornering changes. The front varies much less than the rear weight.
Instantly does the rear shock see 500 or 1500 pounds.On a Q the rear shock is specified at a velocity of 1ft per second to have 46-77 pounds of compression resistance but on rebound [expansion] the resistance rises to 185-251 pounds............all on a spring which only has 123 pounds per inch of stiffness.
The major problem is shocks only have 7" of total travel and lowering springs reduce that by 1" so you are asking the shock to control more energy in less travel, so shocks should actually be 20% x 114%=25% stiffer and be designed to work over the shorter range.
Easy test measure the temperature of shocks on the road, you will be surprised how hot they get in action!
Even the Tokicio blue aftermarket are not up to the task of rebound control on a Q weight car lowered.......they wear out fast from over heats.
http://www.dmsamericas.com/docs/feature ... 7/...t.htm
Shocks must be matched to unsprung weight. Using 5-10 pound heavier than oem tires/wheels will affect the shocks life just as much if not more than 20% stiffer springs. Shock compression [rate/stiffness] only controls the oscillation of the unsprung weight. Rebound/expansion rate is affected by the sprung rate which varies with loading of vehicle.
There is an ideal compression rate which doesn't vary while the rebound rate is always wrong because of trunk/gas/passenger weight changes.........not to mention cornering changes. The front varies much less than the rear weight.
Instantly does the rear shock see 500 or 1500 pounds.On a Q the rear shock is specified at a velocity of 1ft per second to have 46-77 pounds of compression resistance but on rebound [expansion] the resistance rises to 185-251 pounds............all on a spring which only has 123 pounds per inch of stiffness.
The major problem is shocks only have 7" of total travel and lowering springs reduce that by 1" so you are asking the shock to control more energy in less travel, so shocks should actually be 20% x 114%=25% stiffer and be designed to work over the shorter range.
Easy test measure the temperature of shocks on the road, you will be surprised how hot they get in action!
Even the Tokicio blue aftermarket are not up to the task of rebound control on a Q weight car lowered.......they wear out fast from over heats.
http://www.dmsamericas.com/docs/feature ... 7/...t.htm
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Notice that the inexpensive [$150 each] adjustable shocks focus on having at least a mius 20% to plus 220% variable rebound adjustment range............too compensate for wear after they are dialed in new........................unfortunately the Nitrogen still goes into solution and migrates out.
But throught the 60-100k life they can be adjusted to be the same new and used.
But throught the 60-100k life they can be adjusted to be the same new and used.
speaking of <150$ adjustables, I was wondering if you had any links to any REAL tech info on the KYB AGX. It's nice to be able to adjust mine, but have no real idea on how much dampening is optimum for my springs (given a road condition). Just trial and error. I assume that too much dampening is a bad thing as well.
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Un likely that you can get too much rebound dampening on a low cost shock.
"All Shock values are wheel rate too, like the springs. The dampening values are in newtons/meter/second - which means if you have a 1000 bump newtons setting in the garage, the shock will provide 1000 newtons of resistance when the shock is traveling at 1 meter/second (1000mm/sec). Most race cars of the GT type operate the shocks from 0-100mm/second at low speed (driver inputs) and up to 500mm/second at high-speed (bumps and curbs). Typical bumpy sections will be in the 200-400mm/sec range. Now, the telemetry graphs need to be setup to display this properly or you won’t get much use out of them. As shipped they seriously under-graphed and shouldn’t be filtered (except for histograms). Also the sampling rate should be set to 40 in the .PLR file (from the default 10). Use the graphs I've included (should have been installed for you), which sets the shock velocities from 0-500mm/sec and takes out the filtering – you need to know the peaks with shocks. Anything under 100mm per second is considered “low-speed” and is mostly your driver inputs, and over that is considered “high-speed” - bumps and curbs. So if you have a problem at a certain part of the track, or a persistent problem with something like corner entry understeer, look at the shock velocity graph at that point of the track and pick out the shock speeds. If it’s all under 100mm/sec then you want to change the low-speed dampening, if you see higher speeds going on (maybe bumps you don’t feel) than adjust the high-speed – or sometimes both. High-speed rebound dampening is typically at least double the fast bump because it is damping the main sprung mass in addition to the energy built up in the spring. On the other hand, the bump is only damping the unsprung mass (wheel, tire, spindle, brakes, and suspension arms) and the spring oscillations.
Slow speed dampening is not as cut and dry for the initial setting. I usually start slightly higher than the low-speed numbers and go from there. Here’s a chart I did way back for GP2, but it’s still relevant and is based entirely on real world settings and effects. I’ve included the intro tests, but the most useful is the corner phase descriptions and the chart for adjusting them … (please ignore the specific GP2 references):
1.3.1 General
At all times cornering balance is affected by the weight distribution on the four tires. Springs, sway bars and wings give constant resistance or affect weight distribution through the ENTIRE length of a turn. Dampers however, and their amount of resistance, can affect the balance at different _parts_ of a turn. This occurs because at different parts (or what are called "phases") of a corner, different dampers and their travel are dominant at that point. This makes for a excellent way to adjust the corner entry and exit independent of each other, or to take a corner that is unbalanced from entry to exit, to one that is balanced (ie: understeer on the way in - oversteer on the way out).
1.3.2 Fast-Damping
Fast damping is what the tires see and feel i.e.: reactions over bumps or kerbs. Its job is to keep the rubber on the ground over the various surface undulations. Traveling over a bump at speed causes a relatively large and “fast” movement of the damper shaft, and hence it's name. If the front of your car is “overdamped” in the fast bump direction, then you will experience UNDERSTEER on the bumpy sections of turns. If the rear is overdamped you will experience OVERSTEER.
For fast speed adjustments, pick a bumpy turn at the particular track you're working on. Start with bump at 0 and rebound at 2 and work your way up until the front UNDERSTEERS over the bumps, then back off 1 or 2 clicks. Then do the same for the rear until it OVERSTEERS over bumps, again back off 1 or 2 clicks. Always keep the fast rebound higher than the bump - 1.5 to 3 times so. The stiffer the spring the stiffer the rebound setting. It is the fast rebound's job to resist spring pressure and unsprung weight (wheel, tire, hubs, brakes etc) when the suspension oscillates. Usually a setting of 2 times the fast bump works well in GP2. Make sure the car likes "usable" kerbs, too. This may require softer settings than done in your bumpy turn test - everything is a compromise."
The problem with inexpensive shocks is that they have only one rebound adjustment, so you can't set slow rebound different from fast velocity [bump recovery] rebound!
"1.3.3. Slow-Damping
Slow damping is what the driver feels ie: turn-in throttle-out, and mid-corner transitions (chicanes). It controls the dynamic weight transfer and overall motion of the main chassis relative to the track surface as the car is turned, slowed, and accelerated. These motions cause “slow” and small movements of the damper shaft, again the name. The slow rebound usually ends up being higher than the bump, but can be at times 1:1.
Most fiddling will be done with the slow speed settings. First settle on a spring and roll bar setting using a constant radius neutral throttle corner. Next do the “fast” bump adjustments as described previously, then fine tune with slow speed adjustments. First we’ll need to understand the different cornering “phases” before we can make a decision as to what slow speed adjustments to make.
Entry type 1: Increasing braking + increasing steering
This phase is the first part of a fast decreasing radius turn. This phase will not occur at all if you get all your braking done before you turn-in. Since weight is being transferred both forward and outboard, the outside front damper moves in bump and the inside rear damper moves in rebound. These are the dominant two dampers in this phase of turn-in. The other two have minimal effects during this phase.
Entry type 2: Decreasing braking + increasing steering
This is the turn-in phase of a slow corner. This phase may or may not occur depending on the type of turn or driving technique. Weight is being transferred outboard and to the rear, so the outboard rear damper moves in bump and the inside front damper moves in rebound. The other two dampers are considered stationary.
Entry type 3: Increasing steering at constant throttle
This phase can be a chicane turn-in or a turn entry taken at full throttle. Weight is being transferred outboard only, so both outside dampers are moving in bump and both inside dampers are moving in rebound.
Mid-corner Transition: Decreasing steering back to zero at constant throttle
This is really the opposite of a type 3 entry. It’s what happens in the middle of a chicane, as you flick the steering back away from the current cornering direction. As soon as the lateral acceleration passes back through zero, the turn reverts to a type 3 entry again.
Exit: Decreasing steering + increasing throttle (or decreasing braking)
This is the apex-to-exit phase. Weight is being transferred inboard and to the rear. The outside front damper moves in rebound and the inside rear moves in bump. The others are considered stationary. "
"All Shock values are wheel rate too, like the springs. The dampening values are in newtons/meter/second - which means if you have a 1000 bump newtons setting in the garage, the shock will provide 1000 newtons of resistance when the shock is traveling at 1 meter/second (1000mm/sec). Most race cars of the GT type operate the shocks from 0-100mm/second at low speed (driver inputs) and up to 500mm/second at high-speed (bumps and curbs). Typical bumpy sections will be in the 200-400mm/sec range. Now, the telemetry graphs need to be setup to display this properly or you won’t get much use out of them. As shipped they seriously under-graphed and shouldn’t be filtered (except for histograms). Also the sampling rate should be set to 40 in the .PLR file (from the default 10). Use the graphs I've included (should have been installed for you), which sets the shock velocities from 0-500mm/sec and takes out the filtering – you need to know the peaks with shocks. Anything under 100mm per second is considered “low-speed” and is mostly your driver inputs, and over that is considered “high-speed” - bumps and curbs. So if you have a problem at a certain part of the track, or a persistent problem with something like corner entry understeer, look at the shock velocity graph at that point of the track and pick out the shock speeds. If it’s all under 100mm/sec then you want to change the low-speed dampening, if you see higher speeds going on (maybe bumps you don’t feel) than adjust the high-speed – or sometimes both. High-speed rebound dampening is typically at least double the fast bump because it is damping the main sprung mass in addition to the energy built up in the spring. On the other hand, the bump is only damping the unsprung mass (wheel, tire, spindle, brakes, and suspension arms) and the spring oscillations.
Slow speed dampening is not as cut and dry for the initial setting. I usually start slightly higher than the low-speed numbers and go from there. Here’s a chart I did way back for GP2, but it’s still relevant and is based entirely on real world settings and effects. I’ve included the intro tests, but the most useful is the corner phase descriptions and the chart for adjusting them … (please ignore the specific GP2 references):
1.3.1 General
At all times cornering balance is affected by the weight distribution on the four tires. Springs, sway bars and wings give constant resistance or affect weight distribution through the ENTIRE length of a turn. Dampers however, and their amount of resistance, can affect the balance at different _parts_ of a turn. This occurs because at different parts (or what are called "phases") of a corner, different dampers and their travel are dominant at that point. This makes for a excellent way to adjust the corner entry and exit independent of each other, or to take a corner that is unbalanced from entry to exit, to one that is balanced (ie: understeer on the way in - oversteer on the way out).
1.3.2 Fast-Damping
Fast damping is what the tires see and feel i.e.: reactions over bumps or kerbs. Its job is to keep the rubber on the ground over the various surface undulations. Traveling over a bump at speed causes a relatively large and “fast” movement of the damper shaft, and hence it's name. If the front of your car is “overdamped” in the fast bump direction, then you will experience UNDERSTEER on the bumpy sections of turns. If the rear is overdamped you will experience OVERSTEER.
For fast speed adjustments, pick a bumpy turn at the particular track you're working on. Start with bump at 0 and rebound at 2 and work your way up until the front UNDERSTEERS over the bumps, then back off 1 or 2 clicks. Then do the same for the rear until it OVERSTEERS over bumps, again back off 1 or 2 clicks. Always keep the fast rebound higher than the bump - 1.5 to 3 times so. The stiffer the spring the stiffer the rebound setting. It is the fast rebound's job to resist spring pressure and unsprung weight (wheel, tire, hubs, brakes etc) when the suspension oscillates. Usually a setting of 2 times the fast bump works well in GP2. Make sure the car likes "usable" kerbs, too. This may require softer settings than done in your bumpy turn test - everything is a compromise."
The problem with inexpensive shocks is that they have only one rebound adjustment, so you can't set slow rebound different from fast velocity [bump recovery] rebound!
"1.3.3. Slow-Damping
Slow damping is what the driver feels ie: turn-in throttle-out, and mid-corner transitions (chicanes). It controls the dynamic weight transfer and overall motion of the main chassis relative to the track surface as the car is turned, slowed, and accelerated. These motions cause “slow” and small movements of the damper shaft, again the name. The slow rebound usually ends up being higher than the bump, but can be at times 1:1.
Most fiddling will be done with the slow speed settings. First settle on a spring and roll bar setting using a constant radius neutral throttle corner. Next do the “fast” bump adjustments as described previously, then fine tune with slow speed adjustments. First we’ll need to understand the different cornering “phases” before we can make a decision as to what slow speed adjustments to make.
Entry type 1: Increasing braking + increasing steering
This phase is the first part of a fast decreasing radius turn. This phase will not occur at all if you get all your braking done before you turn-in. Since weight is being transferred both forward and outboard, the outside front damper moves in bump and the inside rear damper moves in rebound. These are the dominant two dampers in this phase of turn-in. The other two have minimal effects during this phase.
Entry type 2: Decreasing braking + increasing steering
This is the turn-in phase of a slow corner. This phase may or may not occur depending on the type of turn or driving technique. Weight is being transferred outboard and to the rear, so the outboard rear damper moves in bump and the inside front damper moves in rebound. The other two dampers are considered stationary.
Entry type 3: Increasing steering at constant throttle
This phase can be a chicane turn-in or a turn entry taken at full throttle. Weight is being transferred outboard only, so both outside dampers are moving in bump and both inside dampers are moving in rebound.
Mid-corner Transition: Decreasing steering back to zero at constant throttle
This is really the opposite of a type 3 entry. It’s what happens in the middle of a chicane, as you flick the steering back away from the current cornering direction. As soon as the lateral acceleration passes back through zero, the turn reverts to a type 3 entry again.
Exit: Decreasing steering + increasing throttle (or decreasing braking)
This is the apex-to-exit phase. Weight is being transferred inboard and to the rear. The outside front damper moves in rebound and the inside rear moves in bump. The others are considered stationary. "