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Late C3 Suspension / Handling- Biggest Bang-for-the-Buck Improvement?

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Late C3 Suspension / Handling- Biggest Bang-for-the-Buck Improvement?

 
Old 02-14-2018, 10:23 PM
  #41  
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Originally Posted by Metalhead140 View Post
What are you wanting to measure? Fundamentally, increased load/weight on a tyre results in increased grip from that tyre, but not as much of an increase as the increase in load. This is why lighter cars are faster around corners and under brakes, all else equal - increasing weight on a tyre increases grip, but to a lesser extent than the increased load.

It's also why drag cars are setup to transfer weight to the rear tyres - increased grip. In that instance the load is constant with the weight of the car vs acceleration, but as the rear wheels do all the work, increasing the weight on the rear tyres increases their traction. With the transfer of weight from front to rear, at the same time you obviously have drastically reduced front end grip.

A sway bar limits roll by transferring additional weight to the outside wheel. This decreases traction at the end of the car that the sway bar is acting on, but increases it at the opposite end, which is maintaining a more equal load across inside and outside tyres due to reduced bodyroll. Stiffer springs can achieve the same benefit without as substantial a reduction in grip as it's not trying to lift the inside wheel and transfer that weight to the outside wheel, it's just reducing wheel travel at the outside wheel. But they have an obvious downside over rougher surfaces...
If playing within the design levels of the spring and rates etc. that we are talking about generally for our cars. But if you start pushing those spring rates upward toward race car levels, they can exceed any body generated force from roll! The roll might still be happening, but your suspension will be less affected by it.

PS if your body is rolling, then the frame is too! Therefore not a fan of soft sprung cars, and on those, the sway bars are essential!

I haven't read all of the replies, but good conversations and like this post from 140, great info and additions.

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Old 02-15-2018, 12:13 AM
  #42  
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Originally Posted by TCracingCA View Post
Toe Curve???????

About 1.5 negative would be about all I would ever run on the street! And that won't suffice to make you one of the top runners for autocross or track. 1.5 camber, I would be pushing out the castor on the front end, or it will be darty as hell!

So someone tell me, what is the movement range on those fancy dancy so called Smart Struts?????
Yup, our trailing arm rear suspensions have bumpsteer, or a toe curve, that can't be eradicated without going away from the trailing arm design (eliminating me from most motorsport classes here in Australia). However there is a sweet spot of minimal change of about 2" travel around where the upper camber arm (which is the half shaft) is level, ~1" above, and ~1" below. Level on the half shaft is the maximum toe in the suspension will see, above and below that point the suspension toes out. If you add an upper link and slip the halfshaft then you can modify (raise) the inner pivot of the upper camber link, such that at ride height the suspension is at the bottom of the 2" sweet spot, and won't toe out more than static until a full 2" of bump. This toe steer in the rear is in my opinion the greatest cause of twitchyness in our cars, particularly when lowered, and is why higher ride heights and/or very stiff suspension in the rear is generally recommended for performance handling.

-1.5 camber is what I run on the front, street and track, and yes I have a bunch of caster, it works very well. At the moment I am only running -0.5 on the rear, and plan to increase that to about the same -1.5 as the front. A lot of the mx5s and other modern cars here are running ~-3 to get the best from their semi slick tyres, with little detriment for street use.

No idea! I'm using the stock arrangement with a spacer to lower it...

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Old 02-15-2018, 06:28 AM
  #43  
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Originally Posted by Metalhead140 View Post
Yup, our trailing arm rear suspensions have bumpsteer, or a toe curve, that can't be eradicated without going away from the trailing arm design (eliminating me from most motorsport classes here in Australia). However there is a sweet spot of minimal change of about 2" travel around where the upper camber arm (which is the half shaft) is level, ~1" above, and ~1" below. Level on the half shaft is the maximum toe in the suspension will see, above and below that point the suspension toes out. If you add an upper link and slip the halfshaft then you can modify (raise) the inner pivot of the upper camber link, such that at ride height the suspension is at the bottom of the 2" sweet spot, and won't toe out more than static until a full 2" of bump. This toe steer in the rear is in my opinion the greatest cause of twitchyness in our cars, particularly when lowered, and is why higher ride heights and/or very stiff suspension in the rear is generally recommended for performance handling.

-1.5 camber is what I run on the front, street and track, and yes I have a bunch of caster, it works very well. At the moment I am only running -0.5 on the rear, and plan to increase that to about the same -1.5 as the front. A lot of the mx5s and other modern cars here are running ~-3 to get the best from their semi slick tyres, with little detriment for street use.

No idea! I'm using the stock arrangement with a spacer to lower it...
Ok more from the old Canyon Racer guy (Mulholland/Turnbull) for what it's worth!

Rear Toe curve and or inherent bump steer is a real hard thing to wrap ones head around. The stock bushing to body gives some compliance and then you have guys like me who want tire tracking and will promote some rotation of the trailing arm or heim link to upright.

A lot of bad can happen back there! I feel the shim design is one of the worst features in our cars! Thus I have eliminated it in all of our cars. Then you don't want in and out movement from any of the Axles in a design without an upper a-arm and on my two fancy Guldstrand and CVC-Apex/Greenwood multi-link units for two cars, I am doing so. I don't like the bushed shocks either and being secured such that the ride up and down (compression/rebound) in it's angled configuration is poor in design (but minimum on our cars, as the unit is mostly vertical) and promotes small toe curve, so have shocks with heims! I don't like the spring end and arc to being bolted up to the rear of the trailing arm, so I designed a heim link to replace the bolt . I don't like the halfshaft being a suspension arm and as it angles up or down, it essentially is trying to narrow the spread of the trailing arms and that essentially is toe out, so I am going to telescoping designs on two cars. I see some dialing in of a bunch of rear end toe-in on the race track!

Exaggerating the effect somewhat to better explain, Why a sway bar in the back can be of positive help, is that as one arm is going up it transfers force to the other side! It essentially helps keep parallel arms and helps to prevent toe out as the halfshafts angle up and down, as the arms are going in opposite directions. If the arms are both going up or down together, then you have influences on toe! A compromised rear suspension or with soft compliant bushings, sometimes a rear bar has a positive effect in essentially stabilizing the rear in an unideal way! But then the rear bar can affect the other end, so people tend to go larger on the front (And I have seen real big ones mount front and rear)! And that can cause a crest of the suspension bell curve in having a positive effect on frame twist and body roll, and hold suspension side to side essentially flat, and as I said in the earlier post about heavy spring rates, it essentially can have a similar effect, but I still am not a fan based on force primarily to the outside handling/grip of the tires to the outside!

Therefore is sway bar handling ideal and/or a sophisticated method of gaining handling. No, but it is essentially a Big Bang for the buck, at the levels of performance our cars are operating in generally. But if you want to really get serious about Corvette handling, you need to fix all of the rear suspension wrongs that I mentioned above!

Diving into sway bar mount, many schools of thoughts on those! Do you pillow block it in solid, thus leaving spring effect and rates from end of bar movement! It definitely helps stabilizes things things side to side and kind of becomes a pseudo panhard bar. Those stock links are fixed and badly bushed! Overall the bar in the rubber or poly or other material (Delrin or even a bearing) can be walking side to side some, as it twists or levers from forces that essentially originate from the dominant handling side of the car. All while the frame of the car is twisting and weighing the bar ends exerting vertical force down, or pull upwards or from frame roll to one side pushing down or pulling up on the other! And this is part of the reason, no bar can be good.

But all of this depends on how fast you are going and on what road, and how heavy into max handling you want to go!

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Old 02-17-2018, 05:12 AM
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Two things I would add to this discussion. First, an earlier post mentioned that C3 Corvettes were front heavy. Absolutely not true. With the mid engine design(engine mounted inboard of either set of axles), it is one of the only cars built in the USA with a nearly 50/50 weight balance. That is the reasoning behind Chevrolet's decision to add a rear sway bar to the FE7 suspension package. It works, I know because I've driven the same year Corvette with and without the optional suspension upgrade. Power oversteer is how you learn to control Corvettes in a turn. It's scary at first, but faster in the end with an experienced driver. Second, having the frame fully welded is one of the best and cheapest things you can do to stiffen the chassis without making the ride harsher. The factory only stitch welded the frame, so there might be a one inch weld every six to twelve inches or so. Fill that in to lessen chassis flex. Just my 2 cents.

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Old 02-17-2018, 06:31 AM
  #45  
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Some really good stuff in the last few posts!

I posted this earlier in the thread about why sway bars, front and rear, are important to fine tune the roll and handling of street vehicles:

http://www.turnology.com/features/la...yre-important/

I have said this before and I'll mention it here again about 2 issues: Chassis flex and properly balanced front AND rear sway bars for a C3.

Since many of us know that the C3 frame is not very rigid (for a host of reasons), anything done to strengthen the frame or eliminate unwanted bushing flex on a C3 is a major bonus! The more diehard amongst us can follow GM's recommendation for chassis reinforcement or a complete frame weld, rather than spot welds. Most people are not going to do the former and latter, but can do what I have done over 35 years, eliminate unwanted suspension flex whenever possible:

Front Spreader bar
Poly sway bar bushings-mounting and endlnks
Poly bushing on the power Power steering ram
Poly shock tower bushings
Heim jointed strut rods
Poly bushings on the composite rear spring
Heim jointed supports from the lower seat belt mount to the upper seat belt mount (floor to birdcage)

The concept of getting max handling from a C3 without a rear bar is foreign to me since running a front only bar creates an imbalance in the anti roll characteristic of the car. All C3's whether BB or SB understeer near the limit of adhesion (BB's more so due to the nose heavy weight bias), both base and gymkhana cars, less so for the sport suspended cars with a rear sway bar. This characteristic is a fact. All GM cars produced after the rear engined Corvair fiasco were mandated to exhibit understeer, sometimes excessive understeer, to protect the driver from himself if the car surpassed normal handling limitations.

Not all C3's had a 50:50 weight distribution, ONLY the SBC C3's had the more ideal weight distribution:

Most C3 SBC's had a weight Distribution of 48-49% Front: 51-52% Rear (THIS is the ideal weight distribution, a slight rear weight bias)
My 78 weight Distribution Stock was 48%F:52% Rear

Most BB C3's had a weight distribution of 54-56%F:44-46% Rear (The BB motor is heavier by 100-125 pounds, sits further forward of the front centerline, and sits higher as well)

Since the BB C3's are clearly nose heavy, running a front bar only would make the inherent understeer worse, so GM logically added a 9/16 inch rear bar (with the unique GM endlink for the time) to reduce this understeer tendency. All early 70's BB C3's came from the factory with the 9/16th rear swaybar, not an option!

The 70's SBC C3 did not come with a rear bar unless it had the gymkhana suspension. Looking at the SBC C3 weight distribution above, you can surmise why they did not have a rear mandatory sway bar like the BB cars. With a near ideal 50:50 weight distribution, the SBC C3's with a front sway bar only, still did exhibit a fair amount of understeer but less so due to the slight rear weight bias. To further reduce the understeer of the SB C3's GM added the optional 7/16th inch rear bar, although there STILL existed the understeer characteristic, but to a lesser extent on the SB gymkhana cars. My 78 L-82 4 speed with the gymkhana suspension required a 3/4 inch rear GM Style sway bar with the stock 1 1/8 inch front sway bar to complete eliminate all understeer, neutral steady state cornering.

Keep in mind that both the BB and SB C3's in the earlier years of C3 production that had a rear bar did have a significantly smaller front sway bar than my stock 1 1/8 bar in 1978, which explains why I needed at least 9/16-3/4 inch rear bar to dial out most of the understeer.

The last 2 points is that GM would never have added a rear sway bar to the SB C3 sport suspended cars or even the BB cars if the rear bar made the handling worse than the base suspension cars...there is no way around this observation! When folks say that they removed the rear bar on a sport suspended car and they claim the car handled better, I scratch my head? Most of the time the reason is that ANY oversteer scares the uninformed driver is my guess.

I also notice that on some videos of C3 cars on road or gymkhana courses, that the oversteer handling observed is not steady state oversteer but power oversteer from healthy SBC/BB motors. Power oversteer and steady state oversteer are not the same things. Any mid engine/front engine car RWD with enough power will power oversteer, rear sway bar or not.

The more finely tuned the car's suspension is with front/rear sway bars or other means, requires a MUCH more refined, smooth driving style. Violent/sudden steering inputs will upset any cars handling adversely. The fastest way around any track is to be the smoothest you can be...ask me how I know.

I recently drove BMW's newest M3 (450 NET HP) for a day on a road course and with the computer assisted handling on, I could literally throw anything at the suspension including violent on and off throttle, crazy steering inputs and the car pretty much went straight. With the active handling off, all bets were off....smoothness and rolling into the throttle were the fastest way around the track. Most times you cannot abuse the throttle and upset the front/back balances of any car with sudden jerky transitions and think that the car will be well behaved. Understeer in these conditions is MUCH easier to control than a steady state/slight oversteer car.

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Old 02-17-2018, 03:17 PM
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Originally Posted by [email protected] View Post
Two things I would add to this discussion. First, an earlier post mentioned that C3 Corvettes were front heavy. Absolutely not true. With the mid engine design(engine mounted inboard of either set of axles), it is one of the only cars built in the USA with a nearly 50/50 weight balance. That is the reasoning behind Chevrolet's decision to add a rear sway bar to the FE7 suspension package. It works, I know because I've driven the same year Corvette with and without the optional suspension upgrade. Power oversteer is how you learn to control Corvettes in a turn. It's scary at first, but faster in the end with an experienced driver. Second, having the frame fully welded is one of the best and cheapest things you can do to stiffen the chassis without making the ride harsher. The factory only stitch welded the frame, so there might be a one inch weld every six to twelve inches or so. Fill that in to lessen chassis flex. Just my 2 cents.
I personally would rather not and try not to oversteer, as sliding is not the fastest way around a turn! True with the application of power, you can cook off the tires at the limit point of adhesion. I have said it in other handling threads, but I am a notorious late apex guy. It suits our beasts to clip a turn late and be back on the power when opening up on a straight section! The Corvette likes to be braked in a straight line, but turn in braking is a delicate dance, while weight is shifting. I tune in a lot of understeer thru tire pressures, bar selection, front to rear track, spring rates, etc. just to give me that extra margin of focus on max adhesion of the fronts and driving it to avoid ultimate plow, prior to losing the back end. I am far more rear weight biased too!
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Old 02-17-2018, 03:39 PM
  #47  
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Originally Posted by jb78L-82 View Post
Some really good stuff in the last few posts!

I posted this earlier in the thread about why sway bars, front and rear, are important to fine tune the roll and handling of street vehicles:

http://www.turnology.com/features/la...yre-important/

I have said this before and I'll mention it here again about 2 issues: Chassis flex and properly balanced front AND rear sway bars for a C3.

Since many of us know that the C3 frame is not very rigid (for a host of reasons), anything done to strengthen the frame or eliminate unwanted bushing flex on a C3 is a major bonus! The more diehard amongst us can follow GM's recommendation for chassis reinforcement or a complete frame weld, rather than spot welds. Most people are not going to do the former and latter, but can do what I have done over 35 years, eliminate unwanted suspension flex whenever possible:

Front Spreader bar
Poly sway bar bushings-mounting and endlnks
Poly bushing on the power Power steering ram
Poly shock tower bushings
Heim jointed strut rods
Poly bushings on the composite rear spring
Heim jointed supports from the lower seat belt mount to the upper seat belt mount (floor to birdcage)

The concept of getting max handling from a C3 without a rear bar is foreign to me since running a front only bar creates an imbalance in the anti roll characteristic of the car. All C3's whether BB or SB understeer near the limit of adhesion (BB's more so due to the nose heavy weight bias), both base and gymkhana cars, less so for the sport suspended cars with a rear sway bar. This characteristic is a fact. All GM cars produced after the rear engined Corvair fiasco were mandated to exhibit understeer, sometimes excessive understeer, to protect the driver from himself if the car surpassed normal handling limitations.

Not all C3's had a 50:50 weight distribution, ONLY the SBC C3's had the more ideal weight distribution:

Most C3 SBC's had a weight Distribution of 48-49% Front: 51-52% Rear (THIS is the ideal weight distribution, a slight rear weight bias)
My 78 weight Distribution Stock was 48%F:52% Rear

Most BB C3's had a weight distribution of 54-56%F:44-46% Rear (The BB motor is heavier by 100-125 pounds, sits further forward of the front centerline, and sits higher as well)

Since the BB C3's are clearly nose heavy, running a front bar only would make the inherent understeer worse, so GM logically added a 9/16 inch rear bar (with the unique GM endlink for the time) to reduce this understeer tendency. All early 70's BB C3's came from the factory with the 9/16th rear swaybar, not an option!

The 70's SBC C3 did not come with a rear bar unless it had the gymkhana suspension. Looking at the SBC C3 weight distribution above, you can surmise why they did not have a rear mandatory sway bar like the BB cars. With a near ideal 50:50 weight distribution, the SBC C3's with a front sway bar only, still did exhibit a fair amount of understeer but less so due to the slight rear weight bias. To further reduce the understeer of the SB C3's GM added the optional 7/16th inch rear bar, although there STILL existed the understeer characteristic, but to a lesser extent on the SB gymkhana cars. My 78 L-82 4 speed with the gymkhana suspension required a 3/4 inch rear GM Style sway bar with the stock 1 1/8 inch front sway bar to complete eliminate all understeer, neutral steady state cornering.

Keep in mind that both the BB and SB C3's in the earlier years of C3 production that had a rear bar did have a significantly smaller front sway bar than my stock 1 1/8 bar in 1978, which explains why I needed at least 9/16-3/4 inch rear bar to dial out most of the understeer.

The last 2 points is that GM would never have added a rear sway bar to the SB C3 sport suspended cars or even the BB cars if the rear bar made the handling worse than the base suspension cars...there is no way around this observation! When folks say that they removed the rear bar on a sport suspended car and they claim the car handled better, I scratch my head? Most of the time the reason is that ANY oversteer scares the uninformed driver is my guess.

I also notice that on some videos of C3 cars on road or gymkhana courses, that the oversteer handling observed is not steady state oversteer but power oversteer from healthy SBC/BB motors. Power oversteer and steady state oversteer are not the same things. Any mid engine/front engine car RWD with enough power will power oversteer, rear sway bar or not.

The more finely tuned the car's suspension is with front/rear sway bars or other means, requires a MUCH more refined, smooth driving style. Violent/sudden steering inputs will upset any cars handling adversely. The fastest way around any track is to be the smoothest you can be...ask me how I know.

I recently drove BMW's newest M3 (450 NET HP) for a day on a road course and with the computer assisted handling on, I could literally throw anything at the suspension including violent on and off throttle, crazy steering inputs and the car pretty much went straight. With the active handling off, all bets were off....smoothness and rolling into the throttle were the fastest way around the track. Most times you cannot abuse the throttle and upset the front/back balances of any car with sudden jerky transitions and think that the car will be well behaved. Understeer in these conditions is MUCH easier to control than a steady state/slight oversteer car.
Frame flex and bushings I treat as two different focus areas! Frame flex can change your desired suspension settings upsetting the critical curve of your suspension movement. The bushing deflection can spike your curve, shift radically, and that is not fun, but they will generally if you can maintain a set at G Force, they will be pushed to the limits of squish, but with road undulations and traction limits coming in and out, they are shifting from deflection to not and you get no consistency like a rigid bushing or heim, with a predictable rotation.

With our cars, the frame flex doesn't rear its ugly head, till you are driving it to the max under loads. Most street tired Corvettes will lose there tire grips prior to having the frame chassis stressed or wound up! True some modern street tires can push the car into 1G territory, and thus stiffening, gusseting, continuous welding, roll caging, etc become a benefit. For street tires car handling, you are better off concentrating on the bushings, if you want to raise your game. I love the Global West units and have ran them longer on cars than anyone else on this or any of the othe CF forums. The simplest Mods that are high bang for buck is the spreader bar, the crossmember rear donuts and I run solid Diff puck, and a roll hoop welding in! I would for safety weld those lower a-arm mountings, weld the sway bar link mounts in the front! And in the back I have toe adjusters, and have gusseted the bushing trailing arm cage. The shock mounts, and have other funky things done that I don't want to share.

The stock Corvette suspensions were all over the place back in the day. Kind of like Cybil was doing the design! Luckily tire technology was advancing!

Most guys do better, more confidence driving it hard with neutral as you have to be on top of your driving to push into the realm of handling at the limits of understeer and oversteer!

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Old 02-17-2018, 03:39 PM
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I am far more rear weight biased too!
The more the car is rear weight biased, the more you have to be very careful with oversteer, especially when racing. The formula cars I raced were rear engined and power oversteer or trailing throttle over steer was ever present!
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Old 02-17-2018, 03:43 PM
  #49  
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Originally Posted by jb78L-82 View Post
The more the car is rear weight biased, the more you have to be very careful with oversteer, especially when racing. The formula cars I raced were rear engined and power oversteer or trailing throttle over steer was ever present!
As to why I purposely try to dial in to the extent of the front tire grip capability, more understeer and I choose to run a stagger on front and rear rim sizes (10 rear/8.5 front) on the race C2. But on our C3 which isn't as purposely rear biased, we were the first in the Country of all of the autocross guys to mount 17 inch 315/335s and ran that pretty square on all four corners. I used to chalk my sidewalls a lot, to get air pressure choices, sway bar tensions, etc

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Old 02-17-2018, 03:52 PM
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PS you really don't want to be oversteering on the streets and freeway ramps or a tight autocross! You can't help but oversteer on high speed tracks or in my Canyons!

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Old 02-19-2018, 03:31 PM
  #51  
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Frame flex and bushings I treat as two different focus areas! Frame flex can change your desired suspension settings upsetting the critical curve of your suspension movement. The bushing deflection can spike your curve, shift radically, and that is not fun, but they will generally if you can maintain a set at G Force, they will be pushed to the limits of squish, but with road undulations and traction limits coming in and out, they are shifting from deflection to not and you get no consistency like a rigid bushing or heim, with a predictable rotation.

With our cars, the frame flex doesn't rear its ugly head, till you are driving it to the max under loads. Most street tired Corvettes will lose there tire grips prior to having the frame chassis stressed or wound up! True some modern street tires can push the car into 1G territory, and thus stiffening, gusseting, continuous welding, roll caging, etc become a benefit. For street tires car handling, you are better off concentrating on the bushings, if you want to raise your game.
PS you really don't want to be oversteering on the streets and freeway ramps or a tight autocross! You can't help but oversteer on high speed tracks or in my Canyons!
I agree that frame flex and bushing deflection are different but most folks, driving on the street, can't do much about frame flex unless you have a Shark bar or spreader bar. The simplest most cost effective way to minimize the impact of frame flex are stiffer bushings or no bushings. The frame will flex to a certain extent but stiffer bushings will minimize the impact on the suspension versus both rubber bushings flexing and the frame flexing which is the reason I mentioned them together previously.

I do have to disagree to an extent concerning frame flex not being an issue until you are generating 1g loads. Just jacking up one side of the car can prevent the doors opening properly on a C3 as well as lifting the whole car up on a lift by the frame with the car running can cause the mechanical fan to rub the fan shroud from the front engine subframe sagging. This frame twisting/flexing occurs just driving down the road with road undulations and bumps which effects the handling and tracking of the vehicle on the street as well as the ride. The front spreader bar has a dramatic effect on the C3 driving on the street precisely since it limits some of the frame flex.

Lastly, you do not want much understeer or oversteer (you want the car to be as neutral handling as possible in most situations ideally) in any vehicle on a highway exit ramp, both can be very dangerous if you over cook the turn, although the understeer is much easier to deal with for the novice driver, crank the wheel and hold on as the car drives straight into the barrier..............

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Old 02-19-2018, 06:51 PM
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Originally Posted by jb78L-82 View Post
I agree that frame flex and bushing deflection are different but most folks, driving on the street, can't do much about frame flex unless you have a Shark bar or spreader bar. The simplest most cost effective way to minimize the impact of frame flex are stiffer bushings or no bushings. The frame will flex to a certain extent but stiffer bushings will minimize the impact on the suspension versus both rubber bushings flexing and the frame flexing which is the reason I mentioned them together previously.

I do have to disagree to an extent concerning frame flex not being an issue until you are generating 1g loads. Just jacking up one side of the car can prevent the doors opening properly on a C3 as well as lifting the whole car up on a lift by the frame with the car running can cause the mechanical fan to rub the fan shroud from the front engine subframe sagging. This frame twisting/flexing occurs just driving down the road with road undulations and bumps which effects the handling and tracking of the vehicle on the street as well as the ride. The front spreader bar has a dramatic effect on the C3 driving on the street precisely since it limits some of the frame flex.

Lastly, you do not want much understeer or oversteer (you want the car to be as neutral handling as possible in most situations ideally) in any vehicle on a highway exit ramp, both can be very dangerous if you over cook the turn, although the understeer is much easier to deal with for the novice driver, crank the wheel and hold on as the car drives straight into the barrier..............
Basically true the frame will be flexing at the .75 thru whatever range of Gforces, but honestly anything under 1 G affects the psychology of the Driver far more, than the grip capability of these modern tires. Thus if you get a good bolstered seat to hold you in place, then the car will still go around the turn within the capabilities of your tires, if you have a good alignment and suspension setup. Most people could probably drive faster with just a bucket seat installed! And yes a door popping open would not be a good idea, someone should shim it and adjust the latch. The suspension travel and resultant roll from that, is the real killer in most street cars, that aren't capable of flat handling. And with that at the max travel, comes frame and body roll, and increasing chassis flexing. I have seen a few tip over, but not that often unless they leave the course or hit something, or someone else. The Corvette has a lower center of gravity, than many vehicles (talking with performance tires/rims and not talking to the balloon high aspect ration crowd.

Chassis flex could honestly vary greatly from car to car, as they were spot welded, etc. But these new tires can even make something that looks like it is going to tip over, handle!

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Old 02-19-2018, 06:54 PM
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Originally Posted by TCracingCA View Post
Basically true the frame will be flexing at the .75 thru whatever range of Gforces, but honestly anything under 1 G affects the psychology of the Driver far more, than the grip capability of these modern tires. Thus if you get a good bolstered seat to hold you in place, then the car will still go around the turn within the capabilities of your tires, if you have a good alignment and suspension setup. Most people could probably drive faster with just a bucket seat installed! And yes a door popping open would not be a good idea, someone should shim it and adjust the latch. The suspension travel and resultant roll from that, is the real killer in most street cars, that aren't capable of flat handling. And with that at the max travel, comes frame and body roll, and some chassis flexing.

Chassis flex could honestly vary greatly from car to car, as they were spot welded, etc. But these new tires can even make something that looks like it is going to tip over, handle!
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Old 02-20-2018, 10:57 AM
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Many might have been around, but most hardcore Autocross cars from back in the day had no roll bars or rollcage and were running respectfully without worry of frame flex. When the Solo I level, the old time trialing formats started up with SCCA, then they upgraded the GCR to add more safety, since those events were being held on sections of race tracks around the Country. Therefore faster speeds, and many of these cars are mistaken for actual race track cars, but weren't. They were still just weekend warriors with race type improvements. Additionally many a Vintage Corvette has navigated freeway on and off ramps and Twisty roads at speed and without added stiffening and survived (some didn't). Therefore gusseting and rollcages, true will improve the car, but at the level of performance most will drive, chassis stiffening is an excessive mod for most and the bolt on stuff is adequate. And if you plan on pushing up to 1 G and over on race rubber, you should then do those Mods.

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Old 02-20-2018, 12:04 PM
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Originally Posted by TCracingCA View Post


Ok more from the old Canyon Racer guy (Mulholland/Turnbull) for what it's worth!

Rear Toe curve and or inherent bump steer is a real hard thing to wrap ones head around. The stock bushing to body gives some compliance and then you have guys like me who want tire tracking and will promote some rotation of the trailing arm or heim link to upright.

A lot of bad can happen back there! I feel the shim design is one of the worst features in our cars! Thus I have eliminated it in all of our cars. Then you don't want in and out movement from any of the Axles in a design without an upper a-arm and on my two fancy Guldstrand and CVC-Apex/Greenwood multi-link units for two cars, I am doing so. I don't like the bushed shocks either and being secured such that the ride up and down (compression/rebound) in it's angled configuration is poor in design (but minimum on our cars, as the unit is mostly vertical) and promotes small toe curve, so have shocks with heims! I don't like the spring end and arc to being bolted up to the rear of the trailing arm, so I designed a heim link to replace the bolt . I don't like the halfshaft being a suspension arm and as it angles up or down, it essentially is trying to narrow the spread of the trailing arms and that essentially is toe out, so I am going to telescoping designs on two cars. I see some dialing in of a bunch of rear end toe-in on the race track!

Exaggerating the effect somewhat to better explain, Why a sway bar in the back can be of positive help, is that as one arm is going up it transfers force to the other side! It essentially helps keep parallel arms and helps to prevent toe out as the halfshafts angle up and down, as the arms are going in opposite directions. If the arms are both going up or down together, then you have influences on toe! A compromised rear suspension or with soft compliant bushings, sometimes a rear bar has a positive effect in essentially stabilizing the rear in an unideal way! But then the rear bar can affect the other end, so people tend to go larger on the front (And I have seen real big ones mount front and rear)! And that can cause a crest of the suspension bell curve in having a positive effect on frame twist and body roll, and hold suspension side to side essentially flat, and as I said in the earlier post about heavy spring rates, it essentially can have a similar effect, but I still am not a fan based on force primarily to the outside handling/grip of the tires to the outside!

Therefore is sway bar handling ideal and/or a sophisticated method of gaining handling. No, but it is essentially a Big Bang for the buck, at the levels of performance our cars are operating in generally. But if you want to really get serious about Corvette handling, you need to fix all of the rear suspension wrongs that I mentioned above!

Diving into sway bar mount, many schools of thoughts on those! Do you pillow block it in solid, thus leaving spring effect and rates from end of bar movement! It definitely helps stabilizes things things side to side and kind of becomes a pseudo panhard bar. Those stock links are fixed and badly bushed! Overall the bar in the rubber or poly or other material (Delrin or even a bearing) can be walking side to side some, as it twists or levers from forces that essentially originate from the dominant handling side of the car. All while the frame of the car is twisting and weighing the bar ends exerting vertical force down, or pull upwards or from frame roll to one side pushing down or pulling up on the other! And this is part of the reason, no bar can be good.

But all of this depends on how fast you are going and on what road, and how heavy into max handling you want to go!
Thank you for this. I am very well versed in motorcycle chassis geometry but cars are a new thing to me. It is very interesting for me to see where the similarities and differences lie between the two.

I don't expect that I will ever drive this car anywhere near the point where the above would matter but I do enjoy the intellectual stimulus.
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Old 02-21-2018, 01:24 AM
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I've been following all the information in this thread and it's all excellent.
Thanks to everyone who is posting.
I would like to add that the best suspension in the world is a waste if you don't know how to drive your car.
Take a professional driving course.
A little training with a professional in the passenger seat is priceless.
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Old 02-21-2018, 06:30 AM
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Originally Posted by OldCarBum View Post
I've been following all the information in this thread and it's all excellent.
Thanks to everyone who is posting.
I would like to add that the best suspension in the world is a waste if you don't know how to drive your car.
Take a professional driving course.
A little training with a professional in the passenger seat is priceless.
Exactly! I agree and have been saying the same for some time. Much of what I read and witness on videos of C3's being driven on autocross courses indicates a high performance driving school would be very beneficial for the driver and the handling of the C3!

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Old 02-21-2018, 09:56 AM
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I just like to be different and come at people with my own unique perspectives!

I pursued my IMSA Credentials back when I was 19 years old and now pushing 60. I took the IMSA/SCCA level License qualifying course and as a young fresh out of High School guy who was already getting an education at places like Turnbull Canyon (I was Club President of our Group), Mulholland, Fullerton Road, Glendora into the mountains, jaunts down Carbon Canyon and others, I thought the school was too uptight. Basically felt Bondurant taught how to play follow the leader. The exercises from classroom to the different car levels they walked you through work the same apex points, brake entry technique, etc. Maybe it was the instructors and Bondurant himself, who back then did a ride along with as many students as he could, but at 19, I didn't personally walk away thinking of any of them as great drivers (Bondurant I felt didn't show me his stuff!!!!!). I felt I developed my own style of like turn in braking, advantage apexing, tire preservation driving etc. The three day Course, they basically taught me the flags! I graduated the fastest in my class and have a nice Bondurant signed personal Graduation plaque for that experience! That is posted up on the Porsche Pelican forum on either my Page 339 or 340 of the Million hit Mulholland RSR thread.

I do not feel I am the greatest driver! One of my own brothers actually beats me in like autocross and Malibu GP (plus he is kind of crazy) and we don't know on a big track, as I think I shift at RPM way more effectively. . I personally don't think driving good is that challenging if you have a brain and some *****, but I do think there are people that are naturals at it and don't need schooling. I had learned to get faster from driving the tach! I would work to hit points on the course at a higher rate of rpms and the coinciding speed. I was varying my lines for conditions, whether track or tires. I work alternative lines for passing or allowing someone to pass. I don't think a School is for everyone. I ended up in our military, and never got my dream of being a race car driver. But I had the course that qualified me for a Pro License and if I had the ride or money could have entered Daytona or Sebring back in the day!

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Old 02-23-2018, 11:41 AM
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Originally Posted by TCracingCA View Post
Many might have been around, but most hardcore Autocross cars from back in the day had no roll bars or rollcage and were running respectfully without worry of frame flex. When the Solo I level, the old time trialing formats started up with SCCA, then they upgraded the GCR to add more safety, since those events were being held on sections of race tracks around the Country. Therefore faster speeds, and many of these cars are mistaken for actual race track cars, but weren't. They were still just weekend warriors with race type improvements. Additionally many a Vintage Corvette has navigated freeway on and off ramps and Twisty roads at speed and without added stiffening and survived (some didn't). Therefore gusseting and rollcages, true will improve the car, but at the level of performance most will drive, chassis stiffening is an excessive mod for most and the bolt on stuff is adequate. And if you plan on pushing up to 1 G and over on race rubber, you should then do those Mods.
The C3 small blocks have a unique way of handling in regard to oversteer. It is something that you have to get used to, for sure. Once you get on top of it, you realize that these C3's can be made to handle really well, considering they have 1960's suspension technology. With a rigid frame, 18" wheel and wide tires, along with poly bushings and the Gymkhana upgrade, they can be made to oversteer perfectly on command through turns. Be careful though, a bit too much and you'll have to hold on and wait for the sliding to stop! Kinda reminds me of my Formula Ford D-mod SCCA car. I raced SCCA for about six years, up to the regional championship level at Sebring back then. All or nothing, push it until it breaks loose and it cannot be righted again until the slide is over! The C3 is not as "all or nothing" as my Formula car was, but if you do all the correct things to improve stiffness and grip, it will handle at or over 1G on good street rubber. I really love my Corvette. I wanted one since I was 5 years old. I have had it for 10 years now, and I still get a thrill just looking at it in my garage. But driving it is so much better! Thanks to everyone involved in this thread. It is one of the most informative and useful discussions I've seen on the forum lately.

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