Enter your username:
Do you want to login or register?
  • Forgot your password?

    Login / Register



    Page 3 of 3 FirstFirst 1 2 3
    Results 41 to 58 of 58
    1. #41
      Join Date
      Sep 2010
      Location
      Beach Park IL
      Posts
      2,586
      Country Flag: United States
      How does stiffening the rear bar differ greatly from raising the rear RC?
      When you add roll rate from either more spring or the ARB, you load the outside tire......and I think the inside front to some degree.

      That doesn't happen when you raise the roll center
      Donny

      Support your local hot rod shop!

    2. #42
      Join Date
      Nov 2014
      Location
      East Tennessee
      Posts
      145
      Country Flag: United States
      Quote Originally Posted by dontlifttoshift View Post
      When you add roll rate from either more spring or the ARB, you load the outside tire......and I think the inside front to some degree.

      That doesn't happen when you raise the roll center
      Raising a RC will load the outside tire of that end of the car, as will an increase in roll rate (ARB or ride springs). The difference is mainly that an increase in roll rate of an end increases the total roll rate of the system (i.e. the car). A RC change will merely "move around" the weight transfer you already have. A rear RC moved up will load the outside rear more, the inside rear less, and will reduce front weight transfer which unloads the outside front and loads the inside front. Just as you said.

      From Dennis Grant:

      "Weight transfer has two components:

      Unsprung Weight Transfer: This is the contribution to weight transfer from the unsprung mass of the car.
      Sprung Weight Transfer: This is the contribution to weight transfer from the sprung mass of the car, which itself is broken into two sub-components:

      Geometric Weight Transfer: This is the contribution to weight transfer from the lever that comes of the difference between where the suspension naturally wants the sprung mass to roll (the roll centre) and where the sprung mass naturally wants to roll on its own (the projection of thecentre of gravity onto the ground plane)
      Elastic Weight Transfer: This is the contribution to weight transfer from the reaction force of the springs and bars as they attempt to resist the spring mass roll.
      These three components are additive, meaning that total weight transfer is the sum of all three components.

      As a first guess, one might assume that the sprung mass works effectively the same as the unsprung mass, so weight transfer would be the sprung mass (Ms) times the lateral acceleration (LatA) times the height of the CG of the sprung mass (CGhs) divided by the track - and you'd almost be right.

      The problem is determining the length of the lever through which the cornering force acts. For the unsprung mass, it's the projection of the CG on the ground (the ground on the tires being the centre of rotation). But for an articulated suspension, the point around which the suspension wants to roll is controlled by the interaction of the suspension links and pivots with each other.

      Think of it this way - if you push a door on the handle, it will pivot around the hinges. If you take the door off the hinges and stand it up on an ice rink and then push the handle, it will (assuming it doesn't fall over) pivot in place, somewhere near the centre (where the projection of the CG onto the ice surface is). The suspension works the same way as the door hinges.

      The trick then becomes figuring out where that pivot point - the roll centre lies. And that's where things start to get REALLY complicated.

      Firstly, because locating the roll centre is really not a straightforward process. Secondly, because there is an intrinsic amount of weight transfer that is a function of the difference in height between the roll centre and the ground (the pivot point for the unsprung mass) and a second component based on the difference in height between the height of the roll centre (RCh) and the height of the CG of the sprung mass.

      So to help calculate these sub-components, we call the first the Geometric Weight Transfer and the second the Elastic Weight Transfer.

      Some textbooks refer to the Geometric Weight Transfer as "jacking force" and it can be helpful to keep that term in the back of your mind - because based on where the roll centre lies, that jacking force can be positive, negative, or neutral. And to further muddy the waters, the roll centre can (probably will!) move as the suspension articulates!

      Breaking these down into equations, we get:

      WTg = Ms * LatA * RCh / T

      WTe = Ms * LatA * (CGhs - RCh) / T

      Now if you pay attention to these equations, you can see that the location of the roll centre is really very important:

      If the roll centre height is on the ground (0) then the geometric weight transfer is zero (no jacking force) and the elastic weight transfer is maximum;
      If the roll centre height is on the CG, then jacking force is maximum and the sprung mass won't roll (the car will try and flip over the outside tire);
      In between these two extremes, you get an intermediate result; and
      If the roll centre is below the ground, you get "anti-jacking";"
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    3. #43
      Join Date
      Nov 2008
      Location
      Lawrenceburg, TN
      Posts
      4,057
      Country Flag: United States

    4. #44
      Join Date
      Nov 2014
      Location
      East Tennessee
      Posts
      145
      Country Flag: United States
      Quote Originally Posted by Rod View Post
      fun thread .....
      What are your thoughts Rodney?

      Also, didn't see you at the TRSCCA Borderwars event, was hoping to.
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    5. #45
      Join Date
      Nov 2014
      Location
      East Tennessee
      Posts
      145
      Country Flag: United States
      Slight improvement in driving. CAMT turnout was 2 cars so I ran an "open" class called STM (street tire modified). Took 1st by 0.418s of a field of 8 .

      Fastest run, 44.281 s , 5th run of 6, ETRSCCA, Bristol Motor Speedway:

      https://youtu.be/OQcu2xM2zko

      http://live.etrscca.org/STM.htm

      Open to any thoughts.

      I will hopefully have pictures of what the car was doing in corners in a couple days. I think think the roll couple is off...working on a way to stiffen the rear easily. A rear spring change is a major pain (and expensive), softening the front is not the solution IMO.
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    6. #46
      Join Date
      Aug 2012
      Location
      Peoria, AZ
      Posts
      1,734
      Country Flag: United States
      Holey long soft FAST course design!! Kind of hard to diagnose how the car is doing in turns when there aren't any!! :D
      Lance
      1985 Monte Carlo SS Street Car

    7. #47
      Join Date
      Nov 2014
      Location
      East Tennessee
      Posts
      145
      Country Flag: United States
      Quote Originally Posted by SSLance View Post
      Holey long soft FAST course design!! Kind of hard to diagnose how the car is doing in turns when there aren't any!! :D
      The course was definitely friendly to putting down power, but there were certainly places where alot of cornering force was being generated.

      Here's a picture showing the front suspension compressing as it should.
      Attached Images Attached Images  
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    8. #48
      Join Date
      Nov 2014
      Location
      East Tennessee
      Posts
      145
      Country Flag: United States
      Been awhile since my last post. I figured I would document my tuning progression to help others with the same type of issues I have been having.

      The event after the one above was in Georgia at a CRSCCA event. Tight but fun course. Prior to the event I made a change to the car to reduce understeer (increase oversteer) by stiffening the rear via the use of rod end turnbuckles anti roll bar endlinks as opposed to the polyurethane bushed endlinks I had been using. In addition to this I increased the camber angle to -2.2 from -1.5. Toe was set at 1/8" out (total toe). Car did great. helped alot with the understeer but still had slight turn in understeer. Ended up 5th PAX with a big heavy car. Link to video below:

      https://youtu.be/g3PCvbclDA0

      After the CRSCCA event I went to an event pretty far away from home (5hrs). That was the first time the car was on a trailer in 6 years. Car made it two runs before blowing the muncie trans. Good thing it was trailered. Next event not until 2021....

      Event #1 in 2021 was a local ETRSCCA event at Bristol. Very cold, had alot of trouble getting the rivals up to temperature. Highs in the mid 40s when I was running. Car did decent but had to baby it due to the cold tires. Placed 2nd in CAMT. Link to video below.

      https://youtu.be/3KSN1t5oynk

      Event #2 in 2021 was an autocross guys event. Tighter course. Car did well but still had some understeering issues. Mid corner and corner entry. No change from previous setup.

      https://youtu.be/ZZLDgcWE1Io

      Event #3 in 2021 was at Bristol again, ETRSCCA. Just before the event I made a change. Moved the battery to the passenger side of the trunk, removed the front bumper, and lowered the front RC about 0.5". RC movement was achieved by changing the upper ball joint pin to a 0.5" tall version from a 0.9" tall version. Bumpsteer was corrected after the change. Alignment set at -2.0 camber, +6.5 castor, 1/8" toe out. Won CAMT by 0.57sec. 14th PAX.

      https://youtu.be/NAzwijUgC04

      Event #4 was a very tight course at Smokies Stadium with ETRSCCA this past weekend. Prior to the event I installed some double adjustable rear dampers from Varishock I had. The dampers I had been using previously were also varishocks but they were non-adjustable. The doubles are capable of much more damping force than the non adjustable versions. I set the bump damping as close to the non adjustable shocks as I could. For rebound I went approx. 2 clicks stiffer as far as I could tell. Did some street slalom testing and set the rear rebound where the turn-in understeer was reduced to a minimum without making the car overly loose. Placed 1st in CAMT by 0.082s and 20th PAX. My driving was pretty sloppy and on my fastest run I messed up the hairpin badly. I think the shocks improved the braking initial "bite" of the car alot but I was timid on the brakes as to not lockup. Need to drive the car harder with more conviction, trust it more, and be more smooth. This should help me keep a better and more consistent line and stay tighter to cones that need staying tight to. I also need to brake harder. Video below.

      https://youtu.be/haloDI0p5Bs

      Please feel free to critique driving and car behavior. Additionally I am open to any and all suggestions.

      Thank you
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    9. #49
      Join Date
      Nov 2014
      Location
      East Tennessee
      Posts
      145
      Country Flag: United States
      More updates. After Event #4 I found that the bushings in the rear dampers were virtually destroyed. This seemed to happen because the the shock was initially mounted "cantilever style" which put the bushing in a big bind. I did not run the car like this but only mocked it up. Ended up making clevis mounts to keep the bushing from binding but the bushings were old and the damage was done. Got new bushings after the event. One was beaten out of the shock and the other was almost gone.

      Event #5 was also an SCCA event @ Bristol Motor Speedway. Very fast course, placed 2nd in CAMT, 18th PAX, 52.872s Car felt alot better here but still pushes. I found that I can get the car to rotate is some situations with throttle, but in others it wants to push.

      https://www.youtube.com/watch?v=W4fypAEUd48

      Event #6: SCCA National Champ Tour @ Bristol. Day 1 was rough. Car pushed alot, could not get heat in the tires in 3 runs, and my driving sucked. I was way too timid. 7th out of 11 in CAMT, 208th PAX, 59.601s.

      https://www.youtube.com/watch?v=3MTUs7z9aJA

      Day 2 I did alot better but stayed in 7th of 11 due to the addition of time from both days. I bumped up the rear tire pressure 2psi and stiffened rear rebound 2 clicks. This reduced the grip in the rear (not what I wanted to do but was forced to at the time) but made the car alot easier to drive. It turned in alot better. Additionally I drove the car a lot harder and used the throttle more.

      https://www.youtube.com/watch?v=p9eYX6oQzeA

      At the latest event I worked on my driving. No setup changes. 1st in CAMT, 12th PAX, 17th RAW.

      https://www.youtube.com/watch?v=6rFlDfnxd40

      The next event is this coming weekned. I did some thinking over the past few weeks and came up with an idea, that alot of others have talked about, to use jounce bumpers (aka bump stops) to tune the front end stiffness easily since I am on leaf springs and regular, factory style front springs. I purchased an array of bumpers of varying stiffnesses to test out.

      The first thing I am going to try it to remove the front jounce bumpers completely. Looking at pictures of the car mid corner it became clear that the car was in some way pivoting on the outside front tire to some degree. My theory is that this is due in part to the jounce bumper being loaded, not allowing the front end to articulate as much as I would like and thus not taking advantage of the "improved" camber curve as described in previous posts. The distance between the bumper and the bumper "landing" pad is about 1/2" - 3/4" at ride height. Not alot of movement allowed. You can see this somewhat in the attached picture. Outside front tire appears heavily loaded and camber relative to ground plane is poor - possibly even positive. Alignment is -2.0 Camber +6.5 Castor 1/8" total toe out. Tire pressures 33.5psig front 33.0psig rear on 275/35R18 BFG Rival S 1.5s.
      Attached Images Attached Images    
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    10. #50
      Join Date
      Apr 2007
      Posts
      175
      I'm reading, watching, but off the top of my head pre morning coffee, I don't have much input.

      Thought experiment- what happens if you go to a stiffer front spring, and hold the car-as-a whole, flatter with that. Theory says should increase push, right? What if it doesn't actually do so in practice? I think your odds are better than 50-50.
      Can you explain your taking out the .9" tall balljoint in favour of a .5" tall one? I trust you give your set up much more thought than I can just walking in here, but it is also true that you felt (and I agree) that that meant a need for more static neg camber, and also that you now note the outer tire is in need of more neg from somewhere ( maybe caster is a last grasp option?). Basically, in following the saying, "you don't understand something fully until you have to explain it", can you throw out a few sentences on what change in feel you aimed for, and consider if you got it?
      I'd have lowered the front end at that point- cut say a quarter of a coil off- you'd change the turn in, get your rear end looser, and get deeper into the camber curve. Not by large amounts of any, but all factors are directionally the same so add up. That is definitely "hack"..., but this is a car that despite all the work and thinking we do in this "niche" of performance, has only a fair to middling and largely unchangeable geometry set, by definition. At an OE or custom suspension level, I think playing with rear roll center at that point might have helped, so what do you have you can do with stock rear parts? I'm not a Camaro guy- you do have a panhard bar in these, right?

    11. #51
      Join Date
      Nov 2014
      Location
      East Tennessee
      Posts
      145
      Country Flag: United States
      Thank you for the reply iadr; I appreciate it. To answer your questions:

      Quote Originally Posted by iadr View Post
      Thought experiment- what happens if you go to a stiffer front spring, and hold the car-as-a whole, flatter with that. Theory says should increase push, right? What if it doesn't actually do so in practice? I think your odds are better than 50-50.
      Keeping with the theory I have, the car would push more, likely everywhere. Not particularly easy to do on my car; however, with easily changeable jounce bumpers (instead of ride springs) I could try a stiffer front end. Not sure what you mean by the odds are better than 50-50 - towards more understeer or towards more oversteer with more front spring?

      Quote Originally Posted by iadr View Post
      Can you explain your taking out the .9" tall balljoint in favour of a .5" tall one? Basically, in following the saying, "you don't understand something fully until you have to explain it", can you throw out a few sentences on what change in feel you aimed for, and consider if you got it?
      SETUP 1: The first significant front RC change I did was achieved by going to a 0.9" tall upper ball joint from a factory one on otherwise stock geometry (raised roll center ~ 1.25" and made camber gain negative instead of positive - 0.3/in). This was in 2015. -3.0 camber , +6.0 castor , 0.0" toe

      SETUP 2: The second front RC change was done in 2020 by lowering the inner pivot of the upper control arm about 1/2" rear hole 5/8" front hole (raised front roll center ~1.1" and made camber gain more aggressive 0.8/in). This also had the effect of reducing front anti-dive since it is fairly excessive in first gen camaros. The reason for the second change was because I found I had to run alot of front camber (2.7-3.0 neg) to keep the front tires happy but this came at the cost of poor front end grip in braking. I attributed this poor braking performance to the excessive static camber after playing with brake pressure proportion (ended up with full bias to rear tires in braking, still locked up front tires with even small amounts of trail brake). The idea was to increase camber gain and thus reduce the need for static camber. The inadvertent effect was a stiffer front end due to the higher front roll center. -1.5 camber , +6.5 castor , 0.0" toe.

      SETUP 2.5: Rear RC moved up to 13.5" from 12.5". Rear ARB endlinks changed to rod end style from polyurethane-bushed style. -2.0 camber , +6.5 castor , 1/8" total toe out

      SETUP 3: The third front RC change was performed in 2021 by going to a 0.5" tall upper ball joint from 0.9" tall (lowered front roll center ~0.5" and made camber gain less aggressive - 0.6/in). This change was made in an attempt to "split the difference" between change one and two. This height jived with the rear RC height of 13.5" quite well for the roll stiffness's I have been able to achieve with my current springs and bars. The rear is as stiff as I can get it with the bars, leaf springs, and rear RC I have. -2.1 camber , +6.7 castor , 1/8" total toe out.

      As far as I can tell, each time I raised the front RC, the car pushed more, anf the front was stiffer. Each time I raised the rear RC, the car pushed less and the rear was stiffer. The time I lowered the front RC, the car pushed less and the front was softer - up to a point. The point appears to be where the outside front jounce bumper starts to really "come on" and become really stiff. The jounce bumpers can be thought of as progressive rate springs.

      Quote Originally Posted by iadr View Post
      I trust you give your set up much more thought than I can just walking in here, but it is also true that you felt (and I agree) that that meant a need for more static neg camber, and also that you now note the outer tire is in need of more neg from somewhere ( maybe caster is a last grasp option?).
      The car wanted a certain amount of dynamic camber relative to the ground. The RC adjustments were preformed in an attempt to achieve this dynamic camber setting with LESS static camber. So far the adjustments have been semi-successful, but I appear to have been limited by the lack of rear roll stiffness - mainly due to a lack of rear ride stiffness (approx 1.4Hz / 175lb/in rear, front is 1.5Hz / 600lb/in).

      Quote Originally Posted by iadr View Post
      I'd have lowered the front end at that point- cut say a quarter of a coil off- you'd change the turn in, get your rear end looser, and get deeper into the camber curve. Not by large amounts of any, but all factors are directionally the same so add up. That is definitely "hack"..., but this is a car that despite all the work and thinking we do in this "niche" of performance, has only a fair to middling and largely unchangeable geometry set, by definition.
      What is your rationale that lowering the front end will get the rear looser other than increasing front dynamic camber? I have heard other people mention lowering the front to help with push. Unfortunately, the car would be very low and would scrape everywhere if I lowered the front much more. Could the same thing be achieved by raising the rear?

      Quote Originally Posted by iadr View Post
      At an OE or custom suspension level, I think playing with rear roll center at that point might have helped, so what do you have you can do with stock rear parts? I'm not a Camaro guy- you do have a panhard bar in these, right?
      The car has a rear Watt's link. They (1st gen camaros) do not come with a lateral axle locating device from the factory actually. This is a aftermarket unit from Jim Fay (Fays2). I did actually adjust the rear RC in proportion to the movement of the front RC from setup one to setup two and it helped but was not enough. The rear RC is as high as it will go without some fairly significant fabrication.

      Thanks again for the reply. Love to have discussions like these. Other people's perspectives can really open your eyes.
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    12. #52
      Join Date
      Sep 2010
      Location
      Beach Park IL
      Posts
      2,586
      Country Flag: United States
      You are giving away all of your camber gain in roll. A tire will make the most grip in negative camber, not flat.

      Your wheel rate is too low so you get the above. Spring rubbers are cheap and easy.

      Once the suspension bottoms on the stop and the inside starts to lift, your new roll center is the contact patch of the outside tire. Removing the bumpstop is going to make that significantly worse. Stay off the stop and enjoy better turn in.

      Roll rates, roll axis distribution, and the rest of the science and math really only matters in steady state cornering. How much of that is there in autocross? You are trying to math your way into a perfect setup for a situation that exists for less than 5% of a run.

      Back at the top of this page, read my post and reconcile it with what you just said.

      As far as I can tell, each time I raised the front RC, the car pushed more, and the front was stiffer. Each time I raised the rear RC, the car pushed less and the rear was stiffer.
      The front pushed after raising the roll center because you weren't loading the tire. The front wasn't stiffer, it just felt that way because you shortened the lever arm between CoG and the RC, but you loaded the tire less. Same in the back. You will have more total grip if you drop the rear roll center. Yes, the car will feel tight because you made your rear traction circle bigger so now we have excess traction in the rear. That brings me to me final random thought.

      If we have excess traction, or grip, available in the rear, what can we do? Lets look at the circle.

      Name:  traction-circle-copy-1.jpg
Views: 125
Size:  51.0 KB

      A tire gives us 100% available traction in any given direction but if we ask the tire to multi task it has to split up that 100%. So there we sit in our rear wheel drive car as the front tires grind away wondering what can we do to loosen the car up. The answer is underneath your right foot. By using the rear tires to accelerate the car, we remove available lateral grip from the rear tires and then we achieve balance. You can pick up the throttle earlier and harder and will carry more speed to the next element.

      TL;DR More front spring, lower rear roll center, step on the gas.
      Donny

      Support your local hot rod shop!

    13. #53
      Join Date
      Nov 2014
      Location
      East Tennessee
      Posts
      145
      Country Flag: United States
      Had an event this past weekend. Tried softening the front jounce bumpers by running a 3/4" hole saw through the center of them. It reduced the effective rate by about a factor or 2. Numbers posted below, compression is in inches and reaction force is in pounds.

      Compression...OLD...NEW.....DRILLED

      0".................0.........0.........0
      0.5"..............30.......75........20
      1.0"..............75.......150......40
      1.25"............120.....225.......60
      1.5"..............200.....350......110
      1.75"............325.....650.......215

      The car felt better but the problem is not fully solved. The next thing I am going to try is a bit more drastic....Adding a leaf to the rear springs with the help of a spring shop that makes custom springs and rebuilds leaf springs. Additionally, I am going to change out the front leaf spring bushings from rubber to aluminum or Delrin to increase the torsion on the spring in roll and thus increase the rear roll stiffness. Hopefully this extra rear ride and roll rate will allow me to get the rear sway bar off of full stiff and somewhere in the middle.

      Here's a vid of my fastest. The accelerometer data is offset right, I forgot to recalibrate it that day. Car still pushes sometimes, especially in sweepers but the turn in is way better and I am able to get the car to rotate with the throttle now, whereas before it would tend to push with heavy throttle application. All indications point to the need for more rear stiffness or less front stiffness. Since the front is decently soft (1.5Hz undamped) I have opted to stiffen the rear (currently 1.2-1.4Hz undamped).

      https://youtu.be/H_XrWLbo4r8

      Thanks to all. Still open to driving critiques. I was pretty sloppy here.
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    14. #54
      Join Date
      Nov 2014
      Location
      East Tennessee
      Posts
      145
      Country Flag: United States
      Another update, and good news for that matter:

      I changed out the leaf springs' front eyelet bushing to a Delrin-aluminum bushing/bearing from rubber this weekend. Made a fairly significant difference in terms of how the car drives. Now turn in is more precise, at least as far as I can perceive. The car also feels more neutral mid corner. All of this testing was performed at 80% max effort and with the new, stiffer front jounce bumpers. It is my hypothesis that the reason the car is turning better is becuase the balance is better (the rear is now stiffer since the bushing no longer flexes like it did and the leaf springs are forced to flex more torsionally).

      I was able to induce yaw better than I had felt before the front roll center change without heavy throttle application. Light (maybe 20-30%) throttle while cornering hard would get the car to rotate around better while also accelerating. Additionally I was able to feel lift-off oversteer mid corner if I tried to induce it. Before lift-off would usually cause transient understeer until the front tires "caught up" after the car slowed down enough to stop understeering, causing me to have to wait for what seemed like an eternity. Also, like before, the car has tons of rear grip while accelerating. If I find the car is over rotating for what I want at the time I can apply throttle or counter-steer to get the car going straighter.

      Quote Originally Posted by dontlifttoshift View Post
      You are giving away all of your camber gain in roll. A tire will make the most grip in negative camber, not flat.

      Your wheel rate is too low so you get the above. Spring rubbers are cheap and easy.

      Once the suspension bottoms on the stop and the inside starts to lift, your new roll center is the contact patch of the outside tire. Removing the bumpstop is going to make that significantly worse. Stay off the stop and enjoy better turn in.
      I agree, this was (is still possibly?) part of the issue. The front end was pivoting on the outside front tire (not compressing the front suspension adequately thus gaining little camber relative to the chassis but losing chamber relative to the ground because of the chassis roll about the outside front tire). I believe car was understeering for two reasons: 1. Jounce bumpers engaging causing pivot and roll center change 2. weight transfer distribution was off. The front was carrying more weight transfer than it should have and the rear was carrying less than it should have - causing the rear to have more grip (less weight transfer) and the front to have less grip (more weight transfer)


      Quote Originally Posted by dontlifttoshift View Post
      Roll rates, roll axis distribution, and the rest of the science and math really only matters in steady state cornering. How much of that is there in autocross? You are trying to math your way into a perfect setup for a situation that exists for less than 5% of a run.
      I think the prime issue is the car's balance being poor in steady state - and even though steady state is rarely "purely" achieved in autocross, it's contribution is present any time the car is cornering, which is virtually always in autocross. I think it really comes down to making the car corner better. More front grip is better even if I reduce rear grip since the front was the limiting factor. Now the front and rear tires break loose at more or less the same time (neutral balance).

      Quote Originally Posted by dontlifttoshift View Post
      The front pushed after raising the roll center because you weren't loading the tire. The front wasn't stiffer, it just felt that way because you shortened the lever arm between CoG and the RC, but you loaded the tire less. Same in the back. You will have more total grip if you drop the rear roll center. Yes, the car will feel tight because you made your rear traction circle bigger so now we have excess traction in the rear. That brings me to me final random thought.
      I disagree. The front pushed after raising the roll center because doing so made the front stiffer, which made it carry more weight transfer, which loaded the outside front more and inside front less, reducing mechanical grip. It also increased front jacking force, which reduced chassis roll for the same lateral acceleration. However, since the front was carrying more weight transfer because it was so much stiffer than the rear, it had less grip and rolled less, reducing suspension compression and thus dynamic camber relative to the ground. The jounce bumpers definitely didn't help.

      Quote Originally Posted by dontlifttoshift View Post
      If we have excess traction, or grip, available in the rear, what can we do? Lets look at the circle.

      A tire gives us 100% available traction in any given direction but if we ask the tire to multi task it has to split up that 100%. So there we sit in our rear wheel drive car as the front tires grind away wondering what can we do to loosen the car up. The answer is underneath your right foot. By using the rear tires to accelerate the car, we remove available lateral grip from the rear tires and then we achieve balance. You can pick up the throttle earlier and harder and will carry more speed to the next element.

      TL;DR More front spring, lower rear roll center, step on the gas.
      Yes, the traction circle tells us there is meat left on the bones in the rear; however, I am mainly having understeer issues on corner entry and mid corner, no corner exit. It is difficult to use the throttle to induce less understeer (more oversteer) in the middle and entrance of a corner. I do understand your point regarding conserving rear grip for throttle application since the car is RWD, but as of now I have plenty of rear bite.

      As you and many others have said before, loose (oversteer biased, more front grip than rear) is fast because the car rotates. The car was very tight. Making it tighter will make it - and me - slower, in my opinion.

      More front spring does not appear to be the solution, in and of itself at least, from what testing has shown. The rear is too soft - or the front is too stiff depending on how you look at it. Either way the two axles weren't working together before, and now they are working better with one another.

      I have an event on the 19th and 26th where I will be able to test out the leaf spring bushing change better. Will report back with my findings.

      Thanks again to all who have contributed to this discussion thus far. Please feel free to continue to discuss. I really appreciate it and I think we have all learned something - I know I have.
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    15. #55
      Join Date
      Apr 2009
      Location
      Michigan
      Posts
      285
      Country Flag: United States
      Quote Originally Posted by Sleeper68 View Post
      All indications point to the need for more rear stiffness or less front stiffness. Since the front is decently soft (1.5Hz undamped) I have opted to stiffen the rear (currently 1.2-1.4Hz undamped).
      Are those measured ride frequencies, or calculated? When I actually measured my ride frequencies, I was surprised to find they were quite a bit higher than calculated, especially in the rear. My car (1968 Firebird, 3410 lb, 58% front) has a rear ride frequency of 1.75 Hz with stock 5 leaf rear springs, which have a published rate of 110 lb/in.

      To measure the ride frequencies, I took the shocks off one end of the car, put the other end on full stiff (to minimize coupling effects), and bounced it. It'll be kind of like pushing a swing - it's fairly easy to feel the natural frequency. The quick and dirty way is to count bounces in like a 30 sec timespan, but I got fancy and used the accelerometer on my phone and then analyzed the data in Matlab. I think it's worth measuring (if you haven't already) to give you a baseline.
      - Ryan

    16. #56
      Join Date
      Nov 2014
      Location
      East Tennessee
      Posts
      145
      Country Flag: United States
      Quote Originally Posted by stab6902 View Post
      Are those measured ride frequencies, or calculated?
      Calculated, using measured values - namely corner weight, motion ratio, and spring rate (normalized) using the std. equation for natural frequency ω=√(k*MR/m) , where ω is the natural frequency of the sprung mass, k is the spring rate, MR is the motion ratio, and m is the sprung mass.

      Quote Originally Posted by stab6902 View Post
      When I actually measured my ride frequencies, I was surprised to find they were quite a bit higher than calculated, especially in the rear. My car (1968 Firebird, 3410 lb, 58% front) has a rear ride frequency of 1.75 Hz with stock 5 leaf rear springs, which have a published rate of 110 lb/in.

      To measure the ride frequencies, I took the shocks off one end of the car, put the other end on full stiff (to minimize coupling effects), and bounced it. It'll be kind of like pushing a swing - it's fairly easy to feel the natural frequency. The quick and dirty way is to count bounces in like a 30 sec timespan, but I got fancy and used the accelerometer on my phone and then analyzed the data in Matlab. I think it's worth measuring (if you haven't already) to give you a baseline.
      That is very interesting. Your measured value and theoretical value for natural frequency vary quite drastically in the rear. My calcs show you should have been in the 1.56Hz range for rear ride frequency (assuming a motion ratio of 1.0), however with a motion ratio of ~0.7 (the actual leaf spring simplified motion ratio in roll) you get 1.1Hz. This brings up an interesting point - the wheel:spring motion ratio for a solid axle changes depending if the sprung mass is moving in heave or roll, or some combination of the two. This may be why you got a higher measured value than "expected", you were moving the sprung mass in heave. Additionally, as you probably already know, leaf springs have a progressive rate when installed with shackles like G1 and G2 F bodies have. This may have contributed to the higher measured ride rate/frequency as well.

      To be clear, my estimate of my rear ride frequency (1.3Hz) actually uses the measured "pure" roll motion ratio of ~0.7:1. Using a heave motion ratio of 1.0:1 I get 1.85Hz rear ride freq for my car.

      I will check the rear ride frequency using your method on my car when I have a chance and report back.
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    17. #57
      Join Date
      Apr 2009
      Location
      Michigan
      Posts
      285
      Country Flag: United States
      Quote Originally Posted by Sleeper68 View Post
      Calculated, using measured values - namely corner weight, motion ratio, and spring rate (normalized) using the std. equation for natural frequency ω=√(k*MR/m) , where ω is the natural frequency of the sprung mass, k is the spring rate, MR is the motion ratio, and m is the sprung mass.



      That is very interesting. Your measured value and theoretical value for natural frequency vary quite drastically in the rear. My calcs show you should have been in the 1.56Hz range for rear ride frequency (assuming a motion ratio of 1.0), however with a motion ratio of ~0.7 (the actual leaf spring simplified motion ratio in roll) you get 1.1Hz. This brings up an interesting point - the wheel:spring motion ratio for a solid axle changes depending if the sprung mass is moving in heave or roll, or some combination of the two. This may be why you got a higher measured value than "expected", you were moving the sprung mass in heave. Additionally, as you probably already know, leaf springs have a progressive rate when installed with shackles like G1 and G2 F bodies have. This may have contributed to the higher measured ride rate/frequency as well.

      To be clear, my estimate of my rear ride frequency (1.3Hz) actually uses the measured "pure" roll motion ratio of ~0.7:1. Using a heave motion ratio of 1.0:1 I get 1.85Hz rear ride freq for my car.

      I will check the rear ride frequency using your method on my car when I have a chance and report back.
      I was assuming you were talking about heave ride frequencies all along, so things make more sense now. I'm not used to people talking about roll ride frequencies, but I can see why you were thinking along those lines given the problem you're trying to solve.

      For what it's worth, my measured front ride frequency was also higher than calculated, as were the ride frequencies on both ends of my 1972 Skylark. The biggest delta was with the leaf springs though. They are progressive of course, but I couldn't measure a difference between light bouncing (+/- 0.5") and heavy bouncing (+/- 1"). I'm using the same standard equation as you, but always for heave as I'm trying to dial in ride comfort. More caveats - I'm running rubber bushings everywhere , which could add a very slight amount of wheel rate, and there's some estimation involved in my unsprung weights (I'm not taking into account half the weight of the control arms etc), but I think they're close.

      Anyway, I'm curious what you measure. Sorry I'm not more help on your specific issue - I'm kind of on the opposite end of the spectrum, trying to improve handling performance on street cruisers while still maintaining a comfortable ride.
      - Ryan

    18. #58
      Join Date
      Nov 2014
      Location
      East Tennessee
      Posts
      145
      Country Flag: United States
      Thank you for the contribution Ryan, I appreciate it.

      Quote Originally Posted by stab6902 View Post
      I was assuming you were talking about heave ride frequencies all along, so things make more sense now. I'm not used to people talking about roll ride frequencies, but I can see why you were thinking along those lines given the problem you're trying to solve.



      For what it's worth, my measured front ride frequency was also higher than calculated, as were the ride frequencies on both ends of my 1972 Skylark. The biggest delta was with the leaf springs though. They are progressive of course, but I couldn't measure a difference between light bouncing (+/- 0.5") and heavy bouncing (+/- 1"). I'm using the same standard equation as you, but always for heave as I'm trying to dial in ride comfort. More caveats - I'm running rubber bushings everywhere , which could add a very slight amount of wheel rate, and there's some estimation involved in my unsprung weights (I'm not taking into account half the weight of the control arms etc), but I think they're close.

      Anyway, I'm curious what you measure. Sorry I'm not more help on your specific issue - I'm kind of on the opposite end of the spectrum, trying to improve handling performance on street cruisers while still maintaining a comfortable ride.
      I have not been able to measure the front and rear heave or roll rates yet. I will do so as soon as I can. I am still unsure how to easily measure the front and rear roll rates, those are a little more tricky.

      Good news: the aforementioned leaf spring front eyelet bushing change did seem to net a benefit on course. I tried it out Sunday at a new (to me) venue with the Highlands Sports Car Club HSCC. This was a tight course. I found that front grip while braking, turn in feel, roll response rate (total), yaw rate (velocity), and front tire outer edge wear were improved. These improvements were really only qualitative in nature. This was the first time the car had been on this surface and temps were lower than usual. Next weekend I have an event on a familiar surface so we should be able get some more quantitative data. I can say this, the car definitely feels better than it was, and maybe better than it ever has been. Part of that may be driving, part of it may be real , and part of it may be placebo. It is also important to note that I used the new-stiff front jounce bumpers at this event.

      Here is the video from this last Sunday, 5th PAX, 6th RAW:

      https://youtu.be/a_rXDVMWofE

      My theory is that the TLLTD (Total Lateral Load Transfer Distribution) and the roll couple were not playing well together after I moved the front roll center up (a consequence of making the front camber gain curve more aggressive). What I mean by this is that the front roll rate was too high compared to the roll couple to allow proper front suspension compression while accelerating laterally and by extension reducing dynamic camber to the ground plane (car pivoting on outside front tire). By moving the front roll center up, the car experienced increased front jacking forces, increased front load transfer (also reduced rear load transfer), and flattened the roll axis inclination. Other dynamic effects such as roll understeer induced by leaf spring rake may have affected this as well since rear roll increased due to the stiffer front axle. Stiffening the rear and reintroducing inclination to the roll axis increased rear weight transfer and reduced front weight transfer. What I have yet to be able to check is front/rear roll suspension compression ratio. Setup 2, 2.5, and 3 exhibited little front suspension compression. I would like to see what the front end is doing now. It feels like it is compressing more and the car is starting to yaw more quickly after steering input but I need better data.

      For completeness, the suspension tuning progression:

      SETUP 1: The first significant front RC change I did was achieved by going to a 0.9" tall upper ball joint from a factory one on otherwise stock geometry (raised roll center ~ 1.25" and made camber gain negative instead of positive - 0.3/in). This was in 2015. -3.0 camber , +6.0 castor , 0.0" toe

      SETUP 2: The second front RC change was done in 2020 by lowering the inner pivot of the upper control arm about 1/2" rear hole 5/8" front hole (raised front roll center ~1.1" and made camber gain more aggressive 0.8/in). This also had the effect of reducing front anti-dive since it is fairly excessive in first gen camaros. The reason for the second change was because I found I had to run alot of front camber (2.7-3.0 neg) to keep the front tires happy but this came at the cost of poor front end grip in braking. I attributed this poor braking performance to the excessive static camber after playing with brake pressure proportion (ended up with full bias to rear tires in braking, still locked up front tires with even small amounts of trail brake). The idea was to increase camber gain and thus reduce the need for static camber. The inadvertent effect was a stiffer front end due to the higher front roll center. -1.5 camber , +6.5 castor , 0.0" toe.

      SETUP 2.5: Rear RC moved up to 13.5" from 12.5". Rear ARB endlinks changed to rod end style from polyurethane-bushed style. -2.0 camber , +6.5 castor , 1/8" total toe out

      SETUP 3: The third front RC change was performed in 2021 by going to a 0.5" tall upper ball joint from 0.9" tall (lowered front roll center ~0.5" and made camber gain less aggressive - 0.6/in). This change was made in an attempt to "split the difference" between change one and two. -2.1 camber , +6.7 castor , 1/8" total toe out.

      SETUP 4: Change to softer front jounce bumpers. Increased front damper bump travel (reduced rebound travel) by moving the lower damper mount down in relation to the lower control arm. -2.1 camber , +6.7 castor , 1/8" total toe out

      SETUP 5: Front eyelet bushing of leaf springs changed to aluminum/delrin/steel bushing with thrust washers from steel/rubber/steel bushing. This eliminated any appreciable compliance in the bushing and forced the rear leaf springs to comply with roll, effectively increasing the rear roll rate. -2.1 camber , +6.7 castor , 1/8" total toe out.
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black


    Page 3 of 3 FirstFirst 1 2 3