Impact of rebound versus compression damping.
10-13-2003, 06:07 AM
#1
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Impact of rebound versus compression damping.
Aftermarket shocks and coilovers are available as single adjustable for rebound only, single adjustable for rebound and compression together, double adjustable for rebound and compression separately, triple adjustable and in some cases the gas pressure can be set.
I’m still looking for what will better suite my needs and objectives. I take my car to track days and time trials (Four laps of a track for a time. This is attempted four times during a daily event and the best 4-lap time counts.Therefore 16 timed laps per event, plus a warm up lap each time, for a total of 20 laps per day.These, of course, are much more intense than track day laps). My only complaint about the handling of the car is the unpredictability of the rear end, and it’s the only issue I aim to address. I am open to increasing the spring rates if need be, but I still want the car to remain comfortable enough to be a summer daily driver.
Therefore, the purpose of this post is to pick the brains of those who have had experience with different dampers in different venues, who can offer opinions as to how the specific handling characteristics of the S2K are influenced by, to keep it simple: 1) adjusting rebound damping and, 2) adjusting compression damping.
As I understand it presently, in general, adjusting rebound damping has the most significant impact on a car’s handling, whereas adjusting compression is more of a fine tune on most cars. Apparently, however, according to some, the S2K responds well to an increase in rear compression damping, because it limits rear suspension travel (the people who have put forth this opinion run stock spring rates). Comments on this opinion would be welcome. Please remember that I am free to change spring rates, so you would think that compression damping would be less useful in this context, but that’s just my uninformed personal opinion, which begs to be shown the light.
All opinions are more than welcome.Thanks,
Pierre
I’m still looking for what will better suite my needs and objectives. I take my car to track days and time trials (Four laps of a track for a time. This is attempted four times during a daily event and the best 4-lap time counts.Therefore 16 timed laps per event, plus a warm up lap each time, for a total of 20 laps per day.These, of course, are much more intense than track day laps). My only complaint about the handling of the car is the unpredictability of the rear end, and it’s the only issue I aim to address. I am open to increasing the spring rates if need be, but I still want the car to remain comfortable enough to be a summer daily driver.
Therefore, the purpose of this post is to pick the brains of those who have had experience with different dampers in different venues, who can offer opinions as to how the specific handling characteristics of the S2K are influenced by, to keep it simple: 1) adjusting rebound damping and, 2) adjusting compression damping.
As I understand it presently, in general, adjusting rebound damping has the most significant impact on a car’s handling, whereas adjusting compression is more of a fine tune on most cars. Apparently, however, according to some, the S2K responds well to an increase in rear compression damping, because it limits rear suspension travel (the people who have put forth this opinion run stock spring rates). Comments on this opinion would be welcome. Please remember that I am free to change spring rates, so you would think that compression damping would be less useful in this context, but that’s just my uninformed personal opinion, which begs to be shown the light.
All opinions are more than welcome.Thanks,
Pierre
10-13-2003, 10:40 AM
#2
Typically, compression is used to control wheel motion over bumps, and rebound is used to control body motion and tune handling.
If you do it this way, then the ideal compression setting only depends on the spring rate and unsprung weight at each corner. It is set-and-forget. You figure out what damping rate is required for your wheels and springs, and get the shocks valved to provide that damping rate. If you change spring rates, you will want to change the compression setting.
Rebound settings can be used to control corner entry and corner exit handling. The fronts affect corner exit, the rears affect corner entry.
If you do it this way, then the ideal compression setting only depends on the spring rate and unsprung weight at each corner. It is set-and-forget. You figure out what damping rate is required for your wheels and springs, and get the shocks valved to provide that damping rate. If you change spring rates, you will want to change the compression setting.
Rebound settings can be used to control corner entry and corner exit handling. The fronts affect corner exit, the rears affect corner entry.
10-13-2003, 11:11 AM
#3
Originally posted by Pierre'S2k
My only complaint about the handling of the car is the unpredictability of the rear end, and it’s the only issue I aim to address.
My only complaint about the handling of the car is the unpredictability of the rear end, and it’s the only issue I aim to address.
-MSM
10-13-2003, 12:06 PM
#4
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Thread Starter
msm_s2k,
I have a Whiteline swaybar, which is 50% stiffer than stock, much like the bigger Mugen. It has, in my view, reduced the tendency to oversteer (at the expense of more understeer, of course) in many circumstances, but I find it is still there lurking in the handling envelope, and a few times this past summer while lapping, the rear, once again, got ahead of the front.
Looking for more balance....
Pierre
I have a Whiteline swaybar, which is 50% stiffer than stock, much like the bigger Mugen. It has, in my view, reduced the tendency to oversteer (at the expense of more understeer, of course) in many circumstances, but I find it is still there lurking in the handling envelope, and a few times this past summer while lapping, the rear, once again, got ahead of the front.
Looking for more balance....
Pierre
10-13-2003, 01:25 PM
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You have just asked for a 500 page answer. The only short answer is "it depends." Suspension is complex, all parts are interelated, and every change affects the answer for everything else. Get a suspension book and read up. Tune to Win by Carrol Smith is not tto technically overwhelming.
For example, the correct shock rate depends, among other things, on the spring rate. You can never talk sensibly about changing one independently of the other.
Koni Sportshocks (with stock springs), which have a softer rear compression rate than stock, will substantially help the sudden rear bounce out problem. Whether you also need heavier front swaybar depends on the wheels and tires you are running.
Gregg
For example, the correct shock rate depends, among other things, on the spring rate. You can never talk sensibly about changing one independently of the other.
Koni Sportshocks (with stock springs), which have a softer rear compression rate than stock, will substantially help the sudden rear bounce out problem. Whether you also need heavier front swaybar depends on the wheels and tires you are running.
Gregg
10-13-2003, 01:49 PM
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[QUOTE]Originally posted by Orthonormal
Typically, compression is used to control wheel motion over bumps, and rebound is used to control body motion and tune handling.
If you do it this way, then the ideal compression setting only depends on the spring rate and unsprung weight at each corner.
Typically, compression is used to control wheel motion over bumps, and rebound is used to control body motion and tune handling.
If you do it this way, then the ideal compression setting only depends on the spring rate and unsprung weight at each corner.
10-13-2003, 03:09 PM
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Pierre, I don't know how fast the track is you're running on, but for higher-speed stuff it's important to remember the effects of aerodynamics. A stock S2000 develops roughly 88lbs. of lift at the rear axle at 100mph. This means that even if you have the car perfectly balanced in the mechanical sense at 40mph, by the time you reach 100mph, it will develop oversteer.
You have the option of either dialing-in low-speed understeer or doing some sort of aerodynamic modification to minimize (or perhaps even reverse) this trend. If anything, you want the rear to be getting more grip in relation to the front as speeds increase.
And not to pick on you, but I've seen you start a thread for just about every sort of damper and spring there is out there. There is no one "perfect" shock/spring rate pair for the car any more than there is one perfect pair of tits - like Gregg said, "it depends". No amount of words read on a message board or in books can make up for time spent driving, twisting knobs, and feeling the change you just made. Practice and tweaking is a great teacher by itself, especially when combined with reading. It all starts to come together when you can link what you're feeling through the seat with the theory you read in the book, and know where to go from there to make things better.
If there's anybody that can appreciate planning and the pursuit of understanding before making a purchase it's me, but I think you're taking this to the extreme. Dive in to that pool, get yourself a decent pair of DA's (Koni, Penske, Moton, doesn't make as much difference as you might think) and get boxes and boxes of springs. Play around with rates and damper settings, and work out what feels best for you.
Or you could just make one of these and be done with it.
p.s. My apologies if I seem harsh, apparently my attitude is not its best today...
You have the option of either dialing-in low-speed understeer or doing some sort of aerodynamic modification to minimize (or perhaps even reverse) this trend. If anything, you want the rear to be getting more grip in relation to the front as speeds increase.
And not to pick on you, but I've seen you start a thread for just about every sort of damper and spring there is out there. There is no one "perfect" shock/spring rate pair for the car any more than there is one perfect pair of tits - like Gregg said, "it depends". No amount of words read on a message board or in books can make up for time spent driving, twisting knobs, and feeling the change you just made. Practice and tweaking is a great teacher by itself, especially when combined with reading. It all starts to come together when you can link what you're feeling through the seat with the theory you read in the book, and know where to go from there to make things better.
If there's anybody that can appreciate planning and the pursuit of understanding before making a purchase it's me, but I think you're taking this to the extreme. Dive in to that pool, get yourself a decent pair of DA's (Koni, Penske, Moton, doesn't make as much difference as you might think) and get boxes and boxes of springs. Play around with rates and damper settings, and work out what feels best for you.
Or you could just make one of these and be done with it.
p.s. My apologies if I seem harsh, apparently my attitude is not its best today...
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10-14-2003, 03:08 AM
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Pierre,
I'm not competent to answer you're questions, but here is some info from Koni I've recieved that I'd posted in another thread. Hope it helps.
[QUOTE]Perry,
I'm not competent to answer you're questions, but here is some info from Koni I've recieved that I'd posted in another thread. Hope it helps.
[QUOTE]Perry,
10-14-2003, 07:04 AM
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Surface quality also is a factor. Smooth surface found on some race tracks can handle higher compression damping rate.
But I agree that rebound rate is where most tuning is done. And the really expensive shocks with independently adjustable high and low speed rebound rates are more of an issue in SCCA Stock ax rules where you are not allowed to change springs, ride height, or rear swaybar. People are using high rate low speed and low rate high speed settings so that shocks ride over bumps well (high speed rate), while resisting roll in slaloms and offsets (low speed rate) as a swaybar substitute. If you are not bound by AX rules, then this isn't so necessary, since you can change rear swaybar, springs, ride height, tire and wheel size, if that suits you.
An old rule of thumb agreeing with you is that compression rate damps wheels, rebound rate damps the car.
Gregg
[QUOTE]Originally posted by Orthonormal
Typically, compression is used to control wheel motion over bumps, and rebound is used to control body motion and tune handling.
If you do it this way, then the ideal compression setting only depends on the spring rate and unsprung weight at each corner.
But I agree that rebound rate is where most tuning is done. And the really expensive shocks with independently adjustable high and low speed rebound rates are more of an issue in SCCA Stock ax rules where you are not allowed to change springs, ride height, or rear swaybar. People are using high rate low speed and low rate high speed settings so that shocks ride over bumps well (high speed rate), while resisting roll in slaloms and offsets (low speed rate) as a swaybar substitute. If you are not bound by AX rules, then this isn't so necessary, since you can change rear swaybar, springs, ride height, tire and wheel size, if that suits you.
An old rule of thumb agreeing with you is that compression rate damps wheels, rebound rate damps the car.
Gregg
[QUOTE]Originally posted by Orthonormal
Typically, compression is used to control wheel motion over bumps, and rebound is used to control body motion and tune handling.
If you do it this way, then the ideal compression setting only depends on the spring rate and unsprung weight at each corner.