C3 Suspension Dynamics
06-16-2017, 11:49 PM
#1
Safety Car
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C3 Suspension Dynamics
For those of us who like into get deep into the dynamics of our cars, I found this slide show that uses the C3 parameters for a good part of the exposition. Apologies if anybody has posted this in the past, but I've been following discussions on this subject whenever they pop up and haven't seen this. I've bookmarked it on my laptop.
Here you go:
https://www.slideshare.net/billharbi...parts-iiimar13
____________________
This second slide show discusses lateral (i.e. cornering) forces on the car with particular attention paid to anti-roll bar stiffness
https://www.slideshare.net/billharbi...arts-iiiimar13
Here you go:
https://www.slideshare.net/billharbi...parts-iiimar13
____________________
This second slide show discusses lateral (i.e. cornering) forces on the car with particular attention paid to anti-roll bar stiffness
https://www.slideshare.net/billharbi...arts-iiiimar13
Last edited by ignatz; 06-23-2017 at 12:31 PM. Reason: lateral load transfer
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06-17-2017, 06:04 PM
#3
Drifting
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C3 of Year Finalist (track prepared) 2019
Nothing particularly new, but lots of well laid out information and detail. Thanks for sharing! Those who have disagreed with the fact that swaybars result in an overall loss of grip at the end they are fitted should have a look at slide 24:
"The effect is a reduction of body roll and an increase in load transfer at the end of the chassis that has the anti-roll bar."
Good diagrams to illustrate why too. Of course neither the author or I are against anti-roll bars, they're important, but like all things, a balanced system is best. There's some other information there by the same author on c3 corvette suspension too. Well worth a look and read.
"The effect is a reduction of body roll and an increase in load transfer at the end of the chassis that has the anti-roll bar."
Good diagrams to illustrate why too. Of course neither the author or I are against anti-roll bars, they're important, but like all things, a balanced system is best. There's some other information there by the same author on c3 corvette suspension too. Well worth a look and read.
06-17-2017, 06:43 PM
#4
Le Mans Master
Good stuff.............roll bars front and rear in a balanced set are priceless for optimizing handling....it is very difficult to balance the handling front to rear using a front bar only, as I have always said..GM thought so as well with the C3 since all BB C3's had a rear bar and ONLY the SB C3's with the handling package for maximum grip.
As I have said countless times now, just about every car on the road in the last 15 years, all have a front AND a rear sway bar regardless of whether FWD, RWD, mid engine, rear engine, or front engine cars. All these manufacturers must know something about how to balance a chassis using springs and sway bars..does not seem to make sense to attempt the same using only a front bar only with a C3 or most cars...just logic.
As I have said countless times now, just about every car on the road in the last 15 years, all have a front AND a rear sway bar regardless of whether FWD, RWD, mid engine, rear engine, or front engine cars. All these manufacturers must know something about how to balance a chassis using springs and sway bars..does not seem to make sense to attempt the same using only a front bar only with a C3 or most cars...just logic.
06-17-2017, 08:39 PM
#5
Melting Slicks
Good stuff.............roll bars front and rear in a balanced set are priceless for optimizing handling....it is very difficult to balance the handling front to rear using a front bar only, as I have always said..GM thought so as well with the C3 since all BB C3's had a rear bar and ONLY the SB C3's with the handling package for maximum grip.
As I have said countless times now, just about every car on the road in the last 15 years, all have a front AND a rear sway bar regardless of whether FWD, RWD, mid engine, rear engine, or front engine cars. All these manufacturers must know something about how to balance a chassis using springs and sway bars..does not seem to make sense to attempt the same using only a front bar only with a C3 or most cars...just logic.
As I have said countless times now, just about every car on the road in the last 15 years, all have a front AND a rear sway bar regardless of whether FWD, RWD, mid engine, rear engine, or front engine cars. All these manufacturers must know something about how to balance a chassis using springs and sway bars..does not seem to make sense to attempt the same using only a front bar only with a C3 or most cars...just logic.
Mike
Last edited by v2racing; 06-17-2017 at 08:55 PM.
06-17-2017, 09:12 PM
#6
Le Mans Master
Yes, I agree with that statement and stated such many times in the past!
My 78 C3 with the gymkhana suspension understeered from the factory and this fact was well documented from car magazines at the time and had the 7/16 inch rear bar. All GM cars understeered after the Ralph Nader fiasco in the 60's with the Corvair.
I replaced the 7/16 rear bar with a 3/4 inch GM Style rear sway bar about 12 years ago to dial out this understeer with great success. Most SB C3's will never achieve optimal handling with a front bar only....
06-18-2017, 01:27 AM
#7
Le Mans Master
Yep, seen it before, but definitely worth your having shared for those who haven't. 
As to the complex relationship between bars, springs and anti-roll stiffness which has come up once again, please to forgive this sidebar which I would hope clears up some ever-present misconceptions...
While a combination of softer springs and bigger bars are often necessitated by less than billiard table smooth surfaces - and which definitely played a roll in the General resorting to rear bar - this should NOT be misread to conclude that bars at both ends are an absolute necessity. Thing is, the smoother is the road/track surface in question, the higher spring frequencies can be run without loosing the ability to keep the tires in contact with the ground. Wherever higher spring rates are thus practical, the more anti-roll is inherently provided by spring, and the less supplemental anti-roll stiffness is required from any bar(s). Adding bar beyond the point at which sufficient anti-roll can be provided at an axle with spring alone is a fundamental step backwards, as doing so will result in excess lateral weight transfer (reducing cornering capacity at that axle). And, since a significantly higher roll couple distribution percentage is typically required up front, it's the rear bar which can more often be made redundant, should the surface in question permit.
In any event, IMCO advice about spring rates is too often given/read from the opposite end of the equation, at least from a performance perspective, than it probably should. Rather than automatically defaulting to soft/softer/softest springs which require big/bigger/biggest supplemental bars (read, "crutches"), many a would be chassis tuner would be better served by viewing things from the perspective of "How much spring can I get away with to minimize reliance on bar(s)?" Of course, this all makes better sense if one grasps somewhat the concepts of how bars work and what impact that has on a tire's cornering capacity relative to load sensitivity.
FWIW, not flaming on anyone here. Just trying to help others piece together what can be a considerable puzzle. ...one with which even F1 engineers contend to this day.
As to the complex relationship between bars, springs and anti-roll stiffness which has come up once again, please to forgive this sidebar which I would hope clears up some ever-present misconceptions...
While a combination of softer springs and bigger bars are often necessitated by less than billiard table smooth surfaces - and which definitely played a roll in the General resorting to rear bar - this should NOT be misread to conclude that bars at both ends are an absolute necessity. Thing is, the smoother is the road/track surface in question, the higher spring frequencies can be run without loosing the ability to keep the tires in contact with the ground. Wherever higher spring rates are thus practical, the more anti-roll is inherently provided by spring, and the less supplemental anti-roll stiffness is required from any bar(s). Adding bar beyond the point at which sufficient anti-roll can be provided at an axle with spring alone is a fundamental step backwards, as doing so will result in excess lateral weight transfer (reducing cornering capacity at that axle). And, since a significantly higher roll couple distribution percentage is typically required up front, it's the rear bar which can more often be made redundant, should the surface in question permit.
In any event, IMCO advice about spring rates is too often given/read from the opposite end of the equation, at least from a performance perspective, than it probably should. Rather than automatically defaulting to soft/softer/softest springs which require big/bigger/biggest supplemental bars (read, "crutches"), many a would be chassis tuner would be better served by viewing things from the perspective of "How much spring can I get away with to minimize reliance on bar(s)?" Of course, this all makes better sense if one grasps somewhat the concepts of how bars work and what impact that has on a tire's cornering capacity relative to load sensitivity.
FWIW, not flaming on anyone here. Just trying to help others piece together what can be a considerable puzzle. ...one with which even F1 engineers contend to this day.
Last edited by TheSkunkWorks; 06-18-2017 at 01:33 AM.
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Metalhead140 (06-18-2017)
06-18-2017, 07:21 AM
#8
Le Mans Master
Yep, seen it before, but definitely worth your having shared for those who haven't.
As to the complex relationship between bars, springs and anti-roll stiffness which has come up once again, please to forgive this sidebar which I would hope clears up some ever-present misconceptions...
While a combination of softer springs and bigger bars are often necessitated by less than billiard table smooth surfaces - and which definitely played a roll in the General resorting to rear bar - this should NOT be misread to conclude that bars at both ends are an absolute necessity. Thing is, the smoother is the road/track surface in question, the higher spring frequencies can be run without loosing the ability to keep the tires in contact with the ground. Wherever higher spring rates are thus practical, the more anti-roll is inherently provided by spring, and the less supplemental anti-roll stiffness is required from any bar(s). Adding bar beyond the point at which sufficient anti-roll can be provided at an axle with spring alone is a fundamental step backwards, as doing so will result in excess lateral weight transfer (reducing cornering capacity at that axle). And, since a significantly higher roll couple distribution percentage is typically required up front, it's the rear bar which can more often be made redundant, should the surface in question permit.
In any event, IMCO advice about spring rates is too often given/read from the opposite end of the equation, at least from a performance perspective, than it probably should. Rather than automatically defaulting to soft/softer/softest springs which require big/bigger/biggest supplemental bars (read, "crutches"), many a would be chassis tuner would be better served by viewing things from the perspective of "How much spring can I get away with to minimize reliance on bar(s)?" Of course, this all makes better sense if one grasps somewhat the concepts of how bars work and what impact that has on a tire's cornering capacity relative to load sensitivity.
FWIW, not flaming on anyone here. Just trying to help others piece together what can be a considerable puzzle. ...one with which even F1 engineers contend to this day.
As to the complex relationship between bars, springs and anti-roll stiffness which has come up once again, please to forgive this sidebar which I would hope clears up some ever-present misconceptions...
While a combination of softer springs and bigger bars are often necessitated by less than billiard table smooth surfaces - and which definitely played a roll in the General resorting to rear bar - this should NOT be misread to conclude that bars at both ends are an absolute necessity. Thing is, the smoother is the road/track surface in question, the higher spring frequencies can be run without loosing the ability to keep the tires in contact with the ground. Wherever higher spring rates are thus practical, the more anti-roll is inherently provided by spring, and the less supplemental anti-roll stiffness is required from any bar(s). Adding bar beyond the point at which sufficient anti-roll can be provided at an axle with spring alone is a fundamental step backwards, as doing so will result in excess lateral weight transfer (reducing cornering capacity at that axle). And, since a significantly higher roll couple distribution percentage is typically required up front, it's the rear bar which can more often be made redundant, should the surface in question permit.
In any event, IMCO advice about spring rates is too often given/read from the opposite end of the equation, at least from a performance perspective, than it probably should. Rather than automatically defaulting to soft/softer/softest springs which require big/bigger/biggest supplemental bars (read, "crutches"), many a would be chassis tuner would be better served by viewing things from the perspective of "How much spring can I get away with to minimize reliance on bar(s)?" Of course, this all makes better sense if one grasps somewhat the concepts of how bars work and what impact that has on a tire's cornering capacity relative to load sensitivity.
FWIW, not flaming on anyone here. Just trying to help others piece together what can be a considerable puzzle. ...one with which even F1 engineers contend to this day.
Every sway bar application is different for each car and for a C3 this rule applies as well.
The beauty of sway bars for street cars is that generally speaking a street car cannot achieve the high anti roll characteristics with springs alone since the spring necessary for such handling behavior are too high to achieve without a punishing ride profile. If you take a look at the suspension of just about any car made in the last 25 years, you will find a front and rear sway bar coupled with springs that will give a somewhat compliant ride for most road conditions regardless of the engine location, FWD, RWD etc.
GM hardly used any rear sway bars on the C2 corvettes (I don't believe any but would have to look this up) and it wasn't until the late 60's/early 70's that rear sway bars began showing up on the BB C3's to allow soft enough springs for a compliant ride and the need to control anti-roll up front and to counter the natural tendency of the front heavy BB cars to understeer. (using a rear sway bar countered this dynamic). In fact, almost every GM car from this era did not have a rear sway bar. C3 corvettes were like many things with the corvette, one of the first to come from the factory with rear bars and even then the rear sway bar cars would understeer at the limit which was a corporate mandate derived from the Corvair rear engine car fiasco.
Beginning in the mid 70's, The C3 handling SB corvettes, gymkhana cars, were offered with a rear sway bar AND stiffer springs to improve the handling of the SB C3's but they too still understeered at the limit. GM must have known that the springs offered at the time on the SB C3's were the stiffest they were willing to offer to the public with a rear bar for anti roll control and still able to achieve a somewhat acceptable ride but clearly stiffer springs would have been necessary to achieve the handling level at that time if no rear bar was offered but they were unwilling to make that compromise with even stiffer springs for street cars.
During the late 70's, GM began using rear bars on the handling sedans/coupes more widely such as the SS models, Firebird/Camaros, etc using softer springs and bigger bars to control roll.
Interestingly, the concept on the track of using springs only to control roll seems to have also been abandoned to some degree since the rear engine formula cars I race on billet smooth tracks also use both front and rear sway bars for anti roll control and F1 cars (which employ the highest automotive technology of any race car type) that are very stiffly sprung also employ front and rear sway bars where it would appear the same anti roll could be achieved with stiffer springs alone on billet smooth tracks....
Either way, it appears both on the track and on the street, almost every car uses the combination of springs, dampers, and sway bars to find the sweet spot between ride quality and handling.
My belief in sway bars to control anti roll goes way back to 1979 with my first car, a 1973 Nova SS, that had a 3/4 inch front sway bar and no rear bar. The car handled like a boat! My 1978 high School AP physics teacher would be proud since at that time, knowing very little about car mechanics, I purchased an ADDCO 1 inch front sway and an ADDCO 1/2 inch rear sway bar and installed them on the Nova SS...transformed the handling of the car............
I am a firm believer that you should run the stiffest springs that allow for an acceptable ride and then fine tune the anti roll with the sway bars front and rear....as the 92-98 BMW McLaren F1 designers and engineers stated in the quote from the recent addition of Road and Track, it is very difficult to get the handling dynamics right with a front bar only with no rear bar....especially on the street.
Last edited by jb78L-82; 06-18-2017 at 07:59 AM.
06-18-2017, 02:22 PM
#9
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Appreciate the anti-roll discussion. I've arrived at a configuration which I'm reasonably happy with.
Just to keep this alive which I've at least partially posted for self-serving reasons, let me try you guys on this subject. Possibly you guys can weigh in on turn-in dynamics? As a forinstance, tuning the shock settings front and rear. I've gotten to a mostly neutral car with my anti-roll bars and with torque as the frosting on the cake for mild driver induced oversteer. But for the dynamics I really have no idea.
It has always bothered me that shocks, adjustable or otherwise, are never sold with a damping rate numerical characterization, bolt them in and try them out with different settings. Anybody got any tips on how to approach critical damping or some desirable damping ratio?
Also just as an aside the frequency vs. deflection graph in fig 34 completely mystifies me.
Just to keep this alive which I've at least partially posted for self-serving reasons, let me try you guys on this subject. Possibly you guys can weigh in on turn-in dynamics? As a forinstance, tuning the shock settings front and rear. I've gotten to a mostly neutral car with my anti-roll bars and with torque as the frosting on the cake for mild driver induced oversteer. But for the dynamics I really have no idea.
It has always bothered me that shocks, adjustable or otherwise, are never sold with a damping rate numerical characterization, bolt them in and try them out with different settings. Anybody got any tips on how to approach critical damping or some desirable damping ratio?
Also just as an aside the frequency vs. deflection graph in fig 34 completely mystifies me.
06-18-2017, 02:27 PM
#10
Le Mans Master
Actually, I entirely agree that bars are quite often necessary due to conditions in which higher spring rates are not practical. My point is that running overly soft spring rates forces reliance on more bar than otherwise desirable for max cornering capacity, and that there are certain situations where enough rear spring is, in fact, practical so as to eliminate the need for rear bar. In the great scheme of things, spring selection appropriate for the conditions at hand should be determined before one decides just how much bar is or isn't necessary. Not the other way round. Despite their usefulness as may be necessitated by a given set of conditions, I stand behind my view that bars should be thought of a as a supplemental crutch on which reliance is best minimized. YMMV...
FWIW, unless they've changed how they go about doing so, SBRS school/racing cars have historically been sprung for Sebring (America's roughest road course), and subsequently tuned from that baseline with bar and/or shocks as necessary to suit other circuits prior to each race weekend. However, such tuning/"BOP" checks done prior to each race weekend are performed to level the field of cars instead of lowering lap times. In any event, having done a stint of testing in their B1 chassis for feedback on a handling issue being chased during its development, you might say I'm at least a tad familiar with the program...
I'll have to get back to the OP's inquiry on turn-in, shocks and the freq/deflection matter. Got some family things to do.
FWIW, unless they've changed how they go about doing so, SBRS school/racing cars have historically been sprung for Sebring (America's roughest road course), and subsequently tuned from that baseline with bar and/or shocks as necessary to suit other circuits prior to each race weekend. However, such tuning/"BOP" checks done prior to each race weekend are performed to level the field of cars instead of lowering lap times. In any event, having done a stint of testing in their B1 chassis for feedback on a handling issue being chased during its development, you might say I'm at least a tad familiar with the program...
I'll have to get back to the OP's inquiry on turn-in, shocks and the freq/deflection matter. Got some family things to do.
Last edited by TheSkunkWorks; 06-18-2017 at 02:30 PM.
06-18-2017, 03:47 PM
#12
Le Mans Master
Actually, I entirely agree that bars are quite often necessary due to conditions in which higher spring rates are not practical. My point is that running overly soft spring rates forces reliance on more bar than otherwise desirable for max cornering capacity, and that there are certain situations where enough rear spring is, in fact, practical so as to eliminate the need for rear bar. In the great scheme of things, spring selection appropriate for the conditions at hand should be determined before one decides just how much bar is or isn't necessary. Not the other way round. Despite their usefulness as may be necessitated by a given set of conditions, I stand behind my view that bars should be thought of a as a supplemental crutch on which reliance is best minimized. YMMV...
FWIW, unless they've changed how they go about doing so, SBRS school/racing cars have historically been sprung for Sebring (America's roughest road course), and subsequently tuned from that baseline with bar and/or shocks as necessary to suit other circuits prior to each race weekend. However, such tuning/"BOP" checks done prior to each race weekend are performed to level the field of cars instead of lowering lap times. In any event, having done a stint of testing in their B1 chassis for feedback on a handling issue being chased during its development, you might say I'm at least a tad familiar with the program...
I'll have to get back to the OP's inquiry on turn-in, shocks and the freq/deflection matter. Got some family things to do.
FWIW, unless they've changed how they go about doing so, SBRS school/racing cars have historically been sprung for Sebring (America's roughest road course), and subsequently tuned from that baseline with bar and/or shocks as necessary to suit other circuits prior to each race weekend. However, such tuning/"BOP" checks done prior to each race weekend are performed to level the field of cars instead of lowering lap times. In any event, having done a stint of testing in their B1 chassis for feedback on a handling issue being chased during its development, you might say I'm at least a tad familiar with the program...
I'll have to get back to the OP's inquiry on turn-in, shocks and the freq/deflection matter. Got some family things to do.
1. Almost every single car on the road today made in the last 20 years has a rear anti roll bar whether FWD, RWD, mid engine, rear engine, front engined from Ferrari to Hyundai. I just don't believe that all these companies would be running front and rear bars if the same result could be achieved with springs only, front or rear ...highly unlikely.
2. I have yet to drive a car of any vintage with no rear bar that maximized its handling. Suspension dynamics to achieve very good grip, not maximum grip, with a front bar only is VERY difficult to do on the street especially and as stated above is almost nonexistent with todays modern cars. You have to ask yourself, why is that? The answer is not that modern cars of all types use soft springs with the sway bars since all cars today are fairly stiffly sprung, much more so than even 20 years ago.
SBRS formula cars that I drive are at Lime Rock which was resurfaced several years ago and is billet smooth...their cars run front and rear bars as stated before.
Last edited by jb78L-82; 06-18-2017 at 03:51 PM.
06-18-2017, 05:43 PM
#13
Melting Slicks
Danny Popp ran a 1 1/4" Rancho bar up until a few years ago. I think he is running a hollow splined end bar now. And he was alternating between the 3/4" Rancho rear bar and the stock 9/16". Nuff said.
06-18-2017, 07:48 PM
#14
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My car
- 1-1/4" hollow front bar, 3/4" OE style rear bar, poly bushings, Guldstrand style front links
- GW front and rear arms, SPC control arms, Delrin bushings, rear arms have ball type attachment
- Heim jointed strut rods with camber gain set as high as I can get it, lots of caster up front
- zero toe all around, camber 2-1/4 degrees everywhere, near zero bump steer
- 460# front spring with one coil cut off, 360# rear FG spring
- single adjustable shocks, rears on the soft side, fronts on the hard side
- empty weight F/R 1458/1538, total weight is w/o driver at 2996#'s
My thinking was to get every possible source of binding reduced as much as possible. The rear seems to be the more upsetting part of the handling for these cars, so my thinking there is to get it settled as fast as possible, hence the shock setting. It would be kind of neat to analyze my car's dynamic behavior somehow. I suppose video is a possibility.
- 1-1/4" hollow front bar, 3/4" OE style rear bar, poly bushings, Guldstrand style front links
- GW front and rear arms, SPC control arms, Delrin bushings, rear arms have ball type attachment
- Heim jointed strut rods with camber gain set as high as I can get it, lots of caster up front
- zero toe all around, camber 2-1/4 degrees everywhere, near zero bump steer
- 460# front spring with one coil cut off, 360# rear FG spring
- single adjustable shocks, rears on the soft side, fronts on the hard side
- empty weight F/R 1458/1538, total weight is w/o driver at 2996#'s
My thinking was to get every possible source of binding reduced as much as possible. The rear seems to be the more upsetting part of the handling for these cars, so my thinking there is to get it settled as fast as possible, hence the shock setting. It would be kind of neat to analyze my car's dynamic behavior somehow. I suppose video is a possibility.
Last edited by ignatz; 06-18-2017 at 07:54 PM.
06-18-2017, 09:02 PM
#15
Melting Slicks
06-18-2017, 09:35 PM
#16
Safety Car
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I just noticed another thread on anti-roll bars here. What I have it seems many have similar setups. I'm OK with mine and my inquiry was about shock settings and how to get to critical damping and/or something else.
Last edited by ignatz; 06-18-2017 at 09:41 PM.
06-19-2017, 06:32 PM
#17
Le Mans Master
Appreciate the anti-roll discussion. I've arrived at a configuration which I'm reasonably happy with.
Just to keep this alive which I've at least partially posted for self-serving reasons, let me try you guys on this subject. Possibly you guys can weigh in on turn-in dynamics? As a forinstance, tuning the shock settings front and rear. I've gotten to a mostly neutral car with my anti-roll bars and with torque as the frosting on the cake for mild driver induced oversteer. But for the dynamics I really have no idea.
It has always bothered me that shocks, adjustable or otherwise, are never sold with a damping rate numerical characterization, bolt them in and try them out with different settings. Anybody got any tips on how to approach critical damping or some desirable damping ratio?
Also just as an aside the frequency vs. deflection graph in fig 34 completely mystifies me.
Just to keep this alive which I've at least partially posted for self-serving reasons, let me try you guys on this subject. Possibly you guys can weigh in on turn-in dynamics? As a forinstance, tuning the shock settings front and rear. I've gotten to a mostly neutral car with my anti-roll bars and with torque as the frosting on the cake for mild driver induced oversteer. But for the dynamics I really have no idea.
It has always bothered me that shocks, adjustable or otherwise, are never sold with a damping rate numerical characterization, bolt them in and try them out with different settings. Anybody got any tips on how to approach critical damping or some desirable damping ratio?
Also just as an aside the frequency vs. deflection graph in fig 34 completely mystifies me.
As to fig 34, that particular graph is "only" a representative illustration of vibration inherent to an example chassis & suspension, if left undampened. Shock engineers take these vibration frequency and amplitude characteristics into account when calculating the valving for a given application. Unless building your own from scratch (or writing a thesis), from an end-user's perspective the kernel most worth grasping here is that the impact had on 1) maintaining tire contact with the road and 2) acceptable ride quality both vary directly from the relationship between the magnitude of wheel upsets being encountered and the specific spring frequencies in play.
FWIW, those manufacturers who offer custom valving services will crunch the necessary maths for you, but assuming 4+ posting your chassis isn't in the budget they'll ask for your CGxyz, corner weights, sprung vs. unsprung weights, spring rates, motion ratios at the shocks & springs, and etc.. From that info they'll formulate a baseline valving and adjustment range profile much as a tailor would fit you a suit. And, if you happen to have field re-buildable shocks, you have the option of re-valving them should the profile they've provided prove lacking, tho you'll need that dyno mentioned earlier.
In any event, given the complexities involved, IMCO no amount of theoretical maths can replace actually testing and quantifying results for arriving at an optimal setup in a given car driven by a given driver on a given course on a given day. That said, rather than referring to it as "trial and error", I prefer to think of it as applying good ole scientific method. The casual observer is likely oblivious as to how much effort is focused by serious racing efforts on shock tuning. Anyway, I'd be interested in knowing what about your car's characteristics isn't working, and in what circumstance, in case there's a shock adjustment I could recommend that might help.
Lastly (and I apologize for feeling compelled to respond), that I and a good many others I've known thru my years on and off track don't adhere to a strict BBSS (Big Bars, Soft Springs) philosophy is in no way shape or form meant as an indictment of going down that path when it best suits the specific application at hand. Fact remains, just as much as it is possible to run too much spring, so too is there such a thing as running too little; either way, potential performance is left on the table. Thus, I respectfully submit the concept of keeping an open approach to chassis tuning and not becoming entrenched in the far corner of any one school of thought has merit, and doesn't require my "winning" a debate for validation. If anyone is satisfied with their setup, I'm happy for you. But, please do bear in mind that there is no such thing as a one-size-fits-all optimum setup. Thank you.
Last edited by TheSkunkWorks; 06-19-2017 at 06:36 PM.
06-20-2017, 01:08 AM
#18
Team Owner
I think sway bars are a necessary evil on the street, where heavier springs in general aren't practical! I just generally don't like sway bars, because it is an uncontrolled spring basically! I like them as tuning devices and to control body roll, but not necessarily suspension control. I like them in rotating type mounts and ends that don't bind or lock. When they come into play, the suspension eases into the bar and out of the bar without snap! Depends to on what surfaces you are running over! I go heavy shocks on smooth surfaces but with focus to not cause lifting of a corner and lighten up the shock on rougher surface for focus on maintaining contact patch and sometimes I just swap out the springs. So where do you bring in the sway bar would be the important factor. I usually have my shock tuning Range heavier than what the springs need for control and if the spring is compressing heavy in a turn, as I get lean, the sway bar comes in to supplement the overall spring action on the corner, but still within the ability of the shock to maintain control.
Last edited by TCracingCA; 06-20-2017 at 01:16 AM.
06-20-2017, 01:46 PM
#19
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Thanks for the discussion guys, but let me put the question about tuning the shocks in simple terms: where do I start and when do I stop?
My thinking about where I start (given I am pretty happy with my spring/roll bar setup) is that I probably shouldn't have wheel inputs that want to twist the frame overly much. Especially on these cars with their semi-rigid frame which I imagine stores some energy. So with a front setup that is comparatively stiff relative to the rear, I now have a shock setting with more damping up front and less in the rear. But that's just a SWAG. Ideally (in my mind) front and back would be critically damped so the spring/shock combination gets settled as quickly as possible at both ends of the car without putting energy into the frame. At present I only have single adjustable shocks so tuning requires less parameters to mess with.
That raises some questions:
1) If critical damping all around is a sensible goal, how do I find it and balance the front and back?
2) If such a condition is not the best, how do I start to find better settings?
3) Would the car be a lot better if I could tune compression and rebound separately?
At present the car is neutral, I can kind of feel where the edge is and stay close to it, but it feels like I could do better. TC, for instance you describe things like "where do you bring in the sway bar" and "spring is compressing heavy". Sounds like you have a highly developed subjective sense for what is going on at each wheel. Me I don't have that. I just want to get the car to an eighty or ninety percent condition.
After thinking about this enough to where I could write something down, question #3 is the most on my mind.
My thinking about where I start (given I am pretty happy with my spring/roll bar setup) is that I probably shouldn't have wheel inputs that want to twist the frame overly much. Especially on these cars with their semi-rigid frame which I imagine stores some energy. So with a front setup that is comparatively stiff relative to the rear, I now have a shock setting with more damping up front and less in the rear. But that's just a SWAG. Ideally (in my mind) front and back would be critically damped so the spring/shock combination gets settled as quickly as possible at both ends of the car without putting energy into the frame. At present I only have single adjustable shocks so tuning requires less parameters to mess with.
That raises some questions:
1) If critical damping all around is a sensible goal, how do I find it and balance the front and back?
2) If such a condition is not the best, how do I start to find better settings?
3) Would the car be a lot better if I could tune compression and rebound separately?
At present the car is neutral, I can kind of feel where the edge is and stay close to it, but it feels like I could do better. TC, for instance you describe things like "where do you bring in the sway bar" and "spring is compressing heavy". Sounds like you have a highly developed subjective sense for what is going on at each wheel. Me I don't have that. I just want to get the car to an eighty or ninety percent condition.
After thinking about this enough to where I could write something down, question #3 is the most on my mind.
Last edited by ignatz; 06-20-2017 at 09:04 PM.
06-21-2017, 04:17 AM
#20
Le Mans Master
Shocks 102, vastly oversimplified: Beyond their obvious task of dampening suspension oscillations, "shocks" also regulate weight transfer rates. Thus, manipulating bump and/or rebound valving (within the confines of maintaining suspension control) can be quite an effective tool for tuning transitional phases into and out of corners. This advanced facet of chassis tuning is lost on many an enthusiast, but show me a professional racer who doesn't put much work into solving this part of the puzzle, and I'll almost certainly be able to show you a back-marker.
Unfortunately, single adjustables typically come either rebound only or combine both bump and rebound into a single adjustment; either drastically limiting how much tuning of transitional characteristics can be accomplished. Doubles provide separate low-speed bump and rebound adjustments (which is where we most often want to work when tuning transitions), but usually come with pre-set high-speed/blow off valving for handling faster/larger wheel upsets. Doubles will give the majority of serious enthusiasts plenty of latitude for transitional tuning (which should answer #3). Then there is the complex world of multi-adjustables, from 3-ways up to 6-ways and higher, which permit a number of adjustment profiles for various motion/speed ranges. However, I wouldn't recommend multies to anyone not already somewhat familiar with tuning doubles.
As for a starting point, assuming current settings adequately maintain tire contact with the road, first you need to accurately identify one or more things occurring during any transitional phase of cornering that you'd like to improve. (Once a car "takes a set" into steady state cornering, there is no weight transference to actively regulate.) If you're completely happy, no flames intended, but you're likely either not pushing hard enough to uncover an otherwise latent issue, or have simply yet to encounter a sufficient variety of bends. This is where I typically remind everyone that things are often different out at the limits than they might assume, and to carefully creep up on them in a safe environment if not already dead certain what characteristics lay out there. Also, one shouldn't make changes to improve lesser corners in compromise of those of greater importance to lap time.
If/when an issue presents itself, you'll need to identify not only what's wrong, but also during what transitional phase and in what type of corner it is happening. In addition, be sure it's not something which can be readily addressed by altering driving technique without loosing performance. (Poor man's data acquisition is to always check the tachometer at the same track-out point.) Then, it's time to consider shock tweaks which might help. And, only then if the shocks at hand offer an adjustment appropriate to the problem, so we'd need to know if they're rebound only or bump/rebound.
Sorry if the above doesn't satisfy your appetite for analyzing the maths. I have one also, but in no way, shape or form am I qualified to delve deeply enough into that can of worms. I honestly understand quark spin better. What practical knowledge I've managed to gain about shock tuning has come mostly from real-world, hands-on experience, attending Penske racing shock seminars and listening closely to advice given by race engineers I've had the privilege to enlist privately.
Reading material: Of the texts out there on the topic, very few appear to come from people actually practicing the trade of racing shock development. (Remember the old adage, "Those who can't, teach.") However, if you're up for a difficult read that nevertheless has a few nuggets worth the challenge, you might be interested in Vehicle Dynamics and Damping by Jan "You Need More Bump" Zuijdijk, but I'd take two Tylenol beforehand. And, if it's applicable info you're looking for, IMHO you'll probably pick up more from studying (over and over) Carroll Smith's Tune to Win than from most any graduate theses posted online or from the fsae forums, tho it only scratches the surface on the subject of transitional shock tuning.
Sorry if I seem to have referenced racing too often, but IMHO there is no better crucible in which to find and work out a car's handling ills than when seriously hammering one's way thru the twisty bits.
Anyway, I hope you've found at least a couple of general, if not specific, answers somewhere in there.
Unfortunately, single adjustables typically come either rebound only or combine both bump and rebound into a single adjustment; either drastically limiting how much tuning of transitional characteristics can be accomplished. Doubles provide separate low-speed bump and rebound adjustments (which is where we most often want to work when tuning transitions), but usually come with pre-set high-speed/blow off valving for handling faster/larger wheel upsets. Doubles will give the majority of serious enthusiasts plenty of latitude for transitional tuning (which should answer #3). Then there is the complex world of multi-adjustables, from 3-ways up to 6-ways and higher, which permit a number of adjustment profiles for various motion/speed ranges. However, I wouldn't recommend multies to anyone not already somewhat familiar with tuning doubles.
As for a starting point, assuming current settings adequately maintain tire contact with the road, first you need to accurately identify one or more things occurring during any transitional phase of cornering that you'd like to improve. (Once a car "takes a set" into steady state cornering, there is no weight transference to actively regulate.) If you're completely happy, no flames intended, but you're likely either not pushing hard enough to uncover an otherwise latent issue, or have simply yet to encounter a sufficient variety of bends. This is where I typically remind everyone that things are often different out at the limits than they might assume, and to carefully creep up on them in a safe environment if not already dead certain what characteristics lay out there. Also, one shouldn't make changes to improve lesser corners in compromise of those of greater importance to lap time.
If/when an issue presents itself, you'll need to identify not only what's wrong, but also during what transitional phase and in what type of corner it is happening. In addition, be sure it's not something which can be readily addressed by altering driving technique without loosing performance. (Poor man's data acquisition is to always check the tachometer at the same track-out point.) Then, it's time to consider shock tweaks which might help. And, only then if the shocks at hand offer an adjustment appropriate to the problem, so we'd need to know if they're rebound only or bump/rebound.
Sorry if the above doesn't satisfy your appetite for analyzing the maths. I have one also, but in no way, shape or form am I qualified to delve deeply enough into that can of worms. I honestly understand quark spin better. What practical knowledge I've managed to gain about shock tuning has come mostly from real-world, hands-on experience, attending Penske racing shock seminars and listening closely to advice given by race engineers I've had the privilege to enlist privately.
Reading material: Of the texts out there on the topic, very few appear to come from people actually practicing the trade of racing shock development. (Remember the old adage, "Those who can't, teach.") However, if you're up for a difficult read that nevertheless has a few nuggets worth the challenge, you might be interested in Vehicle Dynamics and Damping by Jan "You Need More Bump" Zuijdijk, but I'd take two Tylenol beforehand. And, if it's applicable info you're looking for, IMHO you'll probably pick up more from studying (over and over) Carroll Smith's Tune to Win than from most any graduate theses posted online or from the fsae forums, tho it only scratches the surface on the subject of transitional shock tuning.
Sorry if I seem to have referenced racing too often, but IMHO there is no better crucible in which to find and work out a car's handling ills than when seriously hammering one's way thru the twisty bits.
Anyway, I hope you've found at least a couple of general, if not specific, answers somewhere in there.
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ignatz (06-21-2017)
