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    1. #21
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      I mean, you're not wrong about "the front changed, so lets make the rear match" I would just prefer to get back the grip that was lost in the front before I took it away from the rear to get the balance back.

      My next step would be to get the car as low as possible, add enough spring to keep from crashing the bumpstops and slam all camber and caster I could into the alignment with maybe a tick of toe out........Then run the biggest front bar I could so the car is slight understeer steady state and then add a little tiny rear sway bar so that I could adjust to oversteer as needed.........but I am a knuckle dragger and would rather drink than do math.

      Like I said earlier, you made a change, lets see what happens. At the same time, like Lance said, your contact patch is broken. You are giving up all of your camber with body roll and so you are stuck riding on the outside edge......it is 100% a front suspension problem and your roll center is only a very small part of that.

      Are you on crazy stiff shocks?

      Donny

      Support your local hot rod shop!


    2. #22
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      I kind of do it the same as Donny. I set my front ride height where I want it making sure to keep the front roll center above ground at a minimum. I then set rear height. I will then set rear roll center to have whatever roll axis inclination I have guessed will work. I will then adjust corners somewhat for corner balance. I add in all the castor I can get which for me is normally 6 degrees. I drive the car and log tire temps. I start adding negative camber to whatever point the temps tell me (different per side). That makes my baseline runs. Then I start playing with wheel rate. I do like having pics of the car in action for tuning but in my opinion the car needs to be close before I start using that.

    3. #23
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      Quote Originally Posted by dontlifttoshift View Post

      You are giving up all of your camber with body roll and so you are stuck riding on the outside edge......it is 100% a front suspension problem and your roll center is only a very small part of that.

      Agree completely. Your car can only go around a corner as fast as the front tires will let it. My personal theory is not much different than Donny's, get the front as good as you can get it and tune the back to balance it to the front.




      Quote Originally Posted by Sleeper68 View Post

      I don't see an additional couple degrees of caster solving the problem. That amount of caster will have no appreciable effect at the steering angles we are dealing with (0-30° or so), in my opinion. It would take a full 90° of steering to get the added 1 or so degrees of camber from the caster/SAI split.

      Your front RC is very low compared to mine. I think that is why your stiff front ARB works. Our rear RC's are comparable.

      What would be your suggested next step?
      What caster do you have in the car now? And what spindles?

      My car static camber is around -1.5*, with 9.75* of caster it gains to about -4* camber at 15* steering input and goes to about -5* when bump and body roll is added in. Caster makes a HUGE difference if you put enough in.

      A good rule of thumb is to have enough caster to mask the KPI of your spindle. Say if you have a G body metric spindle that is around 9* of KPI, you need around 9* of caster to keep the camber from going positive with steering input. The amount of dive in braking and resulting camber gain also plays into this, it all has to work together.

      My redneck way of setting this up is to pull the springs, set the car on turn plates and start cycling the suspension and putting steering input into it to see how it reacts with the nekkid eye. Bump the suspension 2" at the wheel and put 10-15* steering into it and put a camber gauge on and set it so the outside front is leaning into the turn. Beautiful thing about caster is, it will also lean the inside front tire into the turn whereas camber will do the opposite. (again, body roll and camber gain come into play as well but you get the point).
      Lance
      1985 Monte Carlo SS Street Car

    4. #24
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      Quote Originally Posted by dontlifttoshift View Post
      Like I said earlier, you made a change, lets see what happens. At the same time, like Lance said, your contact patch is broken. You are giving up all of your camber with body roll and so you are stuck riding on the outside edge......it is 100% a front suspension problem and your roll center is only a very small part of that.

      Are you on crazy stiff shocks?
      Yes we will see. I think getting the roll axis inclination like it used to be will make the car happy again, and I think it will handle better because of the improved camber gain, and thus more camber on the outside front while loaded up.

      Yes the outside front contact patch is not good. That is why the car is understeering, we can all agree on that. Why the contact patch is not good is the topic of debate.

      Two major car attributes changed between the two events pictured: 1. the front RC height and, 2. the camber gain curve. The camber gain curve improved so the only thing left that could cause issues is the front RC height and how it interacts with the rest of the car. To say that the roll center is a small part doesn't make sense to me because it is the only possible negative change from before.

      My opinion on what we are looking at in the two later pictures is excessive jacking forces, due to a number of different things. The first major thing is the RC height. Jacking forces are determined by track width, acceleration, mass, CG height, and RC height. By moving the RC up, you increase geometric weight transfer "jacking" and decrease elastic weight transfer "sprung reaction". Because the springs are compressing less, the camber is not changing much. You can see this in the pictures. The front suspension is barely articulating. Instead the car is pivoting about the outside front tire. The second major thing is roll axis inclination. The rear is rolling about its roll axis much more than in the autox in March. The jacking forces are literally "picking the car up" and unloading the inside front. Thus, the rear is taking much more of the weight from the front. If we give that weight back to the front, from the rear, the jacking is counteracted and the front suspension articulates. From the articulation we gain camber, and the outside front is happy again. There are two ways to "give" weight back to the front, rear sway bar stiffening or rear RC height addition.

      The shocks are Varishocks, the SS model. They are not very stiff IMO, probably somewhere near 0.6-0.7 damping ratio in the lower piston speeds. They are non-adjustable.

      Quote Originally Posted by SSLance View Post
      Agree completely. Your car can only go around a corner as fast as the front tires will let it. My personal theory is not much different than Donny's, get the front as good as you can get it and tune the back to balance it to the front.

      What caster do you have in the car now? And what spindles?
      You can only go around a corner as fast as whatever tire(s) lets go first. That could be any of the 4. In this case, it is my outside front. In other cases it could be inside front, outside rear, or inside rear if you have a FWD car (Ford Focus, Civic, etc.)

      The car has about +6.1° of caster in it. Spindle is a GM short spindle. SAI is about 8.7°.
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    5. #25
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      Sleeper- you are filling your posts with words to fight the very good advice you got: to work on this through caster. Frankly I won't write more, because I am in awe of the politeness shown by others to your passive aggressiveness in this thread.

    6. #26
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      Quote Originally Posted by Sleeper68 View Post
      I appreciate everyone's input. Discussions like this are good and strengthen our understanding of how these complex metal boxes on wheels work.
      Quote Originally Posted by Sleeper68 View Post
      I appreciate the suggestions. Keep em coming. Very interested to see how other set up their rides to match their driving style. Learning as much as I can is always the goal.
      Quote Originally Posted by iadr View Post
      Sleeper- you are filling your posts with words to fight the very good advice you got: to work on this through caster. Frankly I won't write more, because I am in awe of the politeness shown by others to your passive aggressiveness in this thread.
      I am sorry you feel that way. I tried to make it clear that I am open to everyone's ideas. I am always willing to learn from others and enjoys doing so. I also try to show my appreciation when others share their ideas. Even so, that does not mean I agree with those ideas.

      I am not a passive aggressive person. Certainly it has been a goal to make my thoughts known on the subject so that we can can have a discussion.

      It is not my intention for any of my posts to be taken as adversarial or patronizing. I love forums because they are a place where people of common interests can discuss and learn from each other.

      Hopefully this helps to bring some context to my posts.
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    7. #27
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      Quote Originally Posted by Sleeper68 View Post
      My fix for this issue is to raise the rear RC in proportion to the front RC movement to get the roll axis more in parallel with the mass centroid axis as it was before, and to add about -1/2° of camber. That should stiffen the rear up and hopefully migrate the balance away from understeer.

      There is an autox next weekend where I'll test out the change fully. I am doing some street testing this week, but you can only go so far with that.
      So what happened?
      Donny

      Support your local hot rod shop!

    8. #28
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      Quote Originally Posted by dontlifttoshift View Post
      So what happened?
      The rear RC was raised 1" from 12.5" above ground to 13.5" above ground. Kept the rear ARB full stiff. The front got some more camber and I changed the toe.
      Alignment for the event:

      Camber: -2°
      Caster: +6.1°
      Toe: 1/8" out , measured at the rim edges, approx 0.4°

      The car did really well overall. There were only two entries for CAMT so the event guys put me in CAMC. Ended up 3rd, about 0.45s off of 1st place. I have attached the results for CAMC.

      The car would still push on some corner entries but I think it was driver induced to some degree. The car seems very well balanced now. I could get some more rotation when letting off neutral throttle slightly in some corners. Probably not loose enough for autocross, but I think it would do fantastic on a road course. This course favored right hand turns heavily but the car still worked the right hand side tires to a good degree based on tire temps. Unfortunately I was unable to get an infrared temp gun in time for the event. I have one on the way and will have it for the next event to log tire temps.

      I will try to attach a link to a video of my last run (fastest) in the next post. I drove alot better overall too I think this time. Much smoother than last time and tried to shorten distance wherever possible. There is still alot of dead time in there where I need to be accelerating (either positive or negative) usually on corner entry. Definitely could have won the class if I used that dead time better. There is still a bunch of time out there.

      Thanks to all for the suggestions. Certainly open to driving critiques.
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      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    9. #29
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      Good! Keep chasing front grip.

      Are you going to DriveAutoX at NCM? I won't be there but a good friend will be with a LeMans Blue 69 Corvette. Get a ride along or 10.

      I can't offer driving critique, I've never seen you drive. Here are some tips.

      Don't Coast! Your feet (in my case foot, I don't left foot brake) should always be pushing on a pedal to get the most acceleration in either direction.

      Slow in = fast out. First one to the throttle wins.

      Brake. Turn in. Pick up the throttle. Really concentrate on those being three separate things, with seat time, they will blend together seamlessly. This is especially important on a pushy car, lots of people think they are trail braking but they are really just asking too much of the front tires. So they end up grinding tires through the whole corner while the tenths click off and are very late to the throttle then.

      Hit some cones, it's okay. But not with the front, try to run them over with the back tire.
      Donny

      Support your local hot rod shop!

    10. #30
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      Quote Originally Posted by dontlifttoshift View Post
      I can't offer driving critique, I've never seen you drive. Here are some tips.
      Video I mentioned:

      https://youtu.be/Yu5EgJxH_7k

      This may provide some insight

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

    11. #31
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      Amateur analysis forthcoming.

      Settle your hands down. The only time you needed to shuffle was for the rotunda.

      Right off the bat, you were late with the steering input for the chicago box so you threw a bunch of wheel in it and did it harshly. Setting up further left would have given you more room to make that smoother.

      That big right hand sweeper......why U no throttle? Generally late to the throttle every where.

      If you added just 1 mile an hour everywhere, you would have won the class.

      Lance will have more, he watches more video than I do.
      Donny

      Support your local hot rod shop!

    12. #32
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      Car looked good, pretty composed. I agree with Donny it needs to be driven harder. When I say "harder" I mean with more conviction on carrying speed, not necessarily harder on your inputs. Think attacking the course more but doing it in the smoothest way possible.

      I can't tell if it's from the setup (left heavy car) or your steering inputs (harsher to the right) but the front tires don't like to turn right vs turning left. Try to be smoother with your initial steering inputs especially when turning right.

      Entering the rotunda at about 17 seconds, the front was stuck pretty good until you added a bit more steering angle and the fronts protested immediately. This is where more caster would override the spindle KPI and help that outside front contact patch. In fact, as I watch the video back, every time your left hand gets up over the top of the steering wheel, the front tires lose grip.

      Do you have coil overs on the rear? Ever corner balance the car with you in driver's seat?

      Put a camber gauge on that left front in your driveway or garage and turn the steering wheel to the right until your tape on the wheel goes past 3 o'clock (it'll be even more accurate with driver weight in seat) and watch it go to positive camber at that point. Then put more caster in it and try that again. Trust me...you'll like it. And be much faster.
      Lance
      1985 Monte Carlo SS Street Car

    13. #33
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      Quote Originally Posted by dontlifttoshift View Post
      Settle your hands down. The only time you needed to shuffle was for the rotunda.

      Right off the bat, you were late with the steering input for the chicago box so you threw a bunch of wheel in it and did it harshly. Setting up further left would have given you more room to make that smoother.

      That big right hand sweeper......why U no throttle? Generally late to the throttle every where.

      If you added just 1 mile an hour everywhere, you would have won the class.
      Seems like a good assessment to me.

      I agree. Late on turn in in some places, late on the throttle alot. I think the car can handle alot more throttle and using the brakes/accelerator to get the car to turn in better and rotate seemed to work when I managed to do it.

      As far as the Chicago box, not sure how much more left I could get. Definitely late. I think I was being too careful to hit the inside cone with the right rear. Was probably a good 2-3 feet of the cone on the right.

      I didn't use the throttle much on the sweeper because the front tires were talking. I will try adding throttle on turns like that next time and see what happens.
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    14. #34
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      Quote Originally Posted by SSLance View Post
      Car looked good, pretty composed. I agree with Donny it needs to be driven harder. When I say "harder" I mean with more conviction on carrying speed, not necessarily harder on your inputs. Think attacking the course more but doing it in the smoothest way possible.

      I can't tell if it's from the setup (left heavy car) or your steering inputs (harsher to the right) but the front tires don't like to turn right vs turning left. Try to be smoother with your initial steering inputs especially when turning right.

      Entering the rotunda at about 17 seconds, the front was stuck pretty good until you added a bit more steering angle and the fronts protested immediately. This is where more caster would override the spindle KPI and help that outside front contact patch. In fact, as I watch the video back, every time your left hand gets up over the top of the steering wheel, the front tires lose grip.

      Do you have coil overs on the rear? Ever corner balance the car with you in driver's seat?

      Put a camber gauge on that left front in your driveway or garage and turn the steering wheel to the right until your tape on the wheel goes past 3 o'clock (it'll be even more accurate with driver weight in seat) and watch it go to positive camber at that point. Then put more caster in it and try that again. Trust me...you'll like it. And be much faster.
      Absolutely. More speed everywhere, more deliberate and accurate inputs while staying smooth.

      The car does not have any coilovers. The rear is leaf sprung and the front uses traditional coil springs in the stock location.

      I have checked corner weights, albeit before the Watts link and larger wheels. Should be close. Car was heavy on RF and LR by about 60lb compared to the complementary side. Static front weight dist. with me in it was about 56%. Car should be closer to 55% now and should be about 54% soon after I move the battery to the back.

      I really need a carbon hood but man are they expensive. I'm hoping a blemished one comes up for sale soon.

      For some reason, which I have not figured out yet why, the car doesn't really lose camber when you turn the wheel. It actually gains camber on the outside and loses it on the inside, pics attached. I don't think the push from more steering angle is related to the SAI/caster relationship, but it could be. I'll check and see what it does.
      Attached Images Attached Images    
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    15. #35
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      That actually doesn't look too bad. I wonder if it stays like that in dive and roll?

      If the fronts are staying like that mid turn (in dive\roll), the next thing I'd be trying is a way to get the car to release the inside rear between turn in and apex. With a watts maybe lower the rear roll center so the body has a bigger lever to push with or if adjustable sway bar maybe stiffen it up some? My weapon of choice is generally more rear rebound on the shock to accomplish this.

      Actually, scratch that... I'd need to see video of what the rear and front tires are doing while turning each direction before deciding on what changes to make. Seeing that it seems to turn left much better than turn right, a wedge or cross weight adjustment may help more.

      How often do you take a passenger on runs with you? I'm betting on a right turn favoring course like the above, a passenger would net you at least a second if not more off your lap times. I once ran a very similar course on that pad at an optima event and having a passenger bumped me up enough to get my name listed on TV in the autocross results.



      Geez, my car pushed SO bad back then!!
      Lance
      1985 Monte Carlo SS Street Car

    16. #36
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      @sleepeer68

      I read your thread, and I want to suggest a sequence of changes. To start, I have some observations about your car based on the photos, and your depiction it understeers everywhere.

      You don’t need to calculate your roll angle. You have enough information to actually measure it.

      I pasted a copy of the picture that you said is a 1.2G 50MPH corner and measured the roll angle. I did this as follows:
      1. I pasted the picture into PowerPoint. If you don’t have Microsoft Office, you can use Google Slides, construct a triangle, and calculate the angle with high school trigonometry. With PowerPoint, you can do it without any calculations, by:
      1 . draw a horizontal line. You can make the line width as wide as you want and pick a bright color.
      2. I rotated the photo and moved the horizontal line until the contact patches of the inner and outer front tires were on the horizontal line. With a little trial and error, typing in decimal fraction angles, and move the horizontal line until the it is aligned with the contact patches of the inside and outside front tire, you get a picture like I have uploaded. It is a little hard to discern exactly where the outside contact patch is, so I might be a little off, and I recommend you reproduce my analysis on your own computer.

      1. Based on my analysis, while I don’t know the actually cornering force, the measured roll angle (you can see the measurement from PowerPoint to the right of the picture) is (180 degrees - 177.6 degrees) = 2.4 degrees. My conclusion is you are in the right ballpark.
      2. It may be too much of a stretch to judge conclusively that your car understands just from the picture, but since the roll angle is high enough to indicate the lateral force is pretty high, your front steering angle is pretty high, so yes, based on the photo, it looks like it understeers.

      Recommendations:

      1. I would not raise the rear roll center height under any circumstances. Accepting the trade-off of an increase in front roll center height to get a camber gain improvement is one thing, but it is the wrong thing to do to balance the steady-state handling.

      2. I wouldn’t change the spring rates, or geometry at least, yet. Optimizing spring rates in these kinds of cars is harder than it looks, and if you haven’t done anything crazy, there are more important things. Same answer for making further geometry changes. Your geometry isn't way out of whack from what good practice is, I think you are still at the point where you can make dramatic improvements without messing with geometry.

      3. Your alignment specs with this geometry (-1.5 degrees negative camber, ~6 degrees of caster) are not way off. I would leave them until you at least do the following:

      4. I would increase the rear anti-roll bar (ARB) stiffness a bunch, to the point where it clearly oversteers. I would do this with no other changes to start. If I understood your posts, you said slightly increased the spring rate. Whether or not you did, I would not back that off. I would, to repeat what I just wrote, increase the rear ARB stiffness.

      5. If you cannot do (1) right away, try reducing the front tire pressures. Especially for autocrossing, you can get to the low 20 PSI range. This will reduce the ride rate (the tire is also a spring, and reducing the pressure lowers the spring rate of the tire). But you are going to need to to (1).

      6. Regarding locking your inside front tire, you should realize that if the car understeers, it is going to be more prone to inside front lock up because of the lateral and longitudinal load transfer. If you still have problems after increasing the rear ARB stiffness, then there are a few things you can do. First, is to reduce pitch under braking (this might not be enough, but it is easy to do if you have adjustable shocks compared to alternatives.
      a. Increase front damper (shock) compression stiffness. If you happen to have 4-way adjustable shocks, adjust the low-speed compression stiffer.
      b. Increase rear damper rebound (extension) stiffness. Again, if you have 4-way adjustable shocks, adjust the low-speed rebound stiffer.

      7. The front end of the car looks a little high. I can see your headers are kind of low, and I doubt you want to scrape going over speed bumps, but I would lower it. This does three things: First, since with this geometry, the rate of negative camber increase under compression increases the more it is compressed, lowering it will further increase the negative camber on the outside tire for a given roll angle. If you have modeled your geometry, you can confirm this. if you don't think this is correct, please post a curve. Even better, if you do happen to take the front springs out, cycle one of the front assembly with the springs out (so you can move it from full droop to full compression, and plot it. See number 8 (below) regarding ball joints.

      If you lower the car, which will increase the rate of camber change as the outside front suspension compresses, this will reduce the positive camber on the outside front tire. The other two things this does, is lower the CG of the car, and lowers the roll center.

      8. Given you have a way of measuring and adjusting bump steer (I mean measuring it on the car, not just from the model), then I would use a taller upper ball joint, which will increase the negative camber gain. In fact, you can also use a taller lower ball joint, which will have the effect of lowering the car, and further increasing the rate of negative camber gain under compression. As a general rule, if the toe steer (bump steer) goes very slightly positive toe out under compression, then you get a sort of automatic counter-steer, which can make it a little easier to stay at max lateral without so many small steering corrections.

      9.. I am guessing you have aftermarket lower control arms, which have some form of non-rubber bushing. If in the off chance you are using stock lower control arms and bushings, your cornering forces are high enough to compress them to the point where your actual camber on your outside front wheel is more positive than your calculation. The stock arms are probably fine, but you need to replace the bushings, and my strong preference is not urethane. I am focusing on the lower control arm bushings because they see higher load than the upper control arm bushings do, but both are important. Also check for any slop in the ball joints. A number of aftermarket units have enough slop to cause problems. Also, if you do have solid bushings, , it is crucially important if you have solid bushings that they move freely. Even urethane ones can be lubricated with a high-pressure lube, and some have grease fittings.

      10. Beyond the above, there are a set of relatively easy things you can do with spring rate tuning using jounce bumpers, and some other things, but rather than provide more opinions, the first step is to get to a near-neutral balanced car by increasing rear roll stiffness, and then the other things listed.

      I have an observation in general about comments on the thread, and what I see from people that look at Milliken Moment Diagrams, and models with load transfer equations, spring rate calculations and so on. Bill (the now deceased father) and Doug Milliken's book, Race Car Vehicle Dynamics, is a fabulous book, but it has so much information, that it is pretty difficult to appreciate the big picture, and to figure out which changes have the biggest impact, and what to do first. Also, it doesn’t emphasize some crucially important to keep three things in mind, which can screw up the handling: deflection, slop, and stiction. Ball joints and steering linkages have slop, welds in aftermarket parts can crack, solid bushings can bind, and rubber ones can deflect.

      Finally, I am a stranger on this message board, so you might ask, who is this yahoo with all these opinions? Here is an article I wrote that describes how I got my start: https://www.pontiacv8.com/blog/2019/...ry-quackenboss I also built a C4 street prepared Corvette that was national championship competitive, and these days I advise a collegiate Formula SAE team that in the past few years finished first among 80 North American colleges, and finished 6th of 120 global colleges.
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      Quote Originally Posted by SSLance View Post
      If the fronts are staying like that mid turn (in dive\roll), the next thing I'd be trying is a way to get the car to release the inside rear between turn in and apex. With a watts maybe lower the rear roll center so the body has a bigger lever to push with or if adjustable sway bar maybe stiffen it up some? My weapon of choice is generally more rear rebound on the shock to accomplish this.

      How often do you take a passenger on runs with you? I'm betting on a right turn favoring course like the above, a passenger would net you at least a second if not more off your lap times. I once ran a very similar course on that pad at an optima event and having a passenger bumped me up enough to get my name listed on TV in the autocross results.
      Raising the rear RC and stiffening the rear ARB both make the rear stiffer. Unfortunately, my rear bar is at full stiff right now. I never like to be at the edge of the adjustment range but it'll have to be there until I can figure out something else. The car would definitely benefit from more low speed damping force, especially in the rear. Double adjustable varishocks are on the list for upgrades, hopefully soon. I am very happy with my current varishocks, they just don't have quite enough damping force.

      I very often have friends as passengers. I used to be like you and go faster with the better right/left weight distribution, but have found in the last year that I go 3 to 6 tenths faster on average without the extra weight. Very interesting. Some things I guess we'll never understand

      Pretty good driving in the video. Smooth and deliberate. I need to be more like that, although I think it will come. So far I haven't even gone to two events in a row with the same setup in the car. Once I learn the car again I think I'll get to a point where I can trust it more.
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    18. #38
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      Quote Originally Posted by hquackenboss View Post
      I pasted a copy of the picture that you said is a 1.2G 50MPH corner and measured the roll angle.
      Thanks for the reply Harry. The "1.2g 50mph" actually came from Lance in regard to the photos he posted. I am unsure of the cornering load on my car in that picture but I would guess somewhere near 0.9-1.0g based on previous data. The car would do 1.1-1.2g back in March under steady state conditions.

      Quote Originally Posted by hquackenboss View Post
      1. Based on my analysis, while I don’t know the actually cornering force, the measured roll angle (you can see the measurement from PowerPoint to the right of the picture) is (180 degrees - 177.6 degrees) = 2.4 degrees. My conclusion is you are in the right ballpark.
      I agree. The total roll stiffness is pretty close, especially for a streetcar. The balance was the issue in this photo.

      Quote Originally Posted by hquackenboss View Post
      2. It may be too much of a stretch to judge conclusively that your car understands just from the picture, but since the roll angle is high enough to indicate the lateral force is pretty high, your front steering angle is pretty high, so yes, based on the photo, it looks like it understeers.
      The car is absolutely understeering in the photo. That was the main problem at the time.

      Quote Originally Posted by hquackenboss View Post
      Recommendations:

      1. I would not raise the rear roll center height under any circumstances. Accepting the trade-off of an increase in front roll center height to get a camber gain improvement is one thing, but it is the wrong thing to do to balance the steady-state handling.
      For what reason exactly? Moving roll centers are absolutely necessary to make old cars handle because many of them have roll centers under ground.
      My current RC locations are approximately above ground by: 2.5" Front, 13.5" Rear (static).
      The positions when the photo was taken: 2.5" Front, 12.5" Rear (static).
      The positions when the photo in march was taken: 1.3" Front, 12.5" Rear (static).

      Quote Originally Posted by hquackenboss View Post
      2. I wouldn’t change the spring rates, or geometry at least, yet. Optimizing spring rates in these kinds of cars is harder than it looks, and if you haven’t done anything crazy, there are more important things. Same answer for making further geometry changes. Your geometry isn't way out of whack from what good practice is, I think you are still at the point where you can make dramatic improvements without messing with geometry.

      3. Your alignment specs with this geometry (-1.5 degrees negative camber, ~6 degrees of caster) are not way off. I would leave them until you at least do the following:

      4. I would increase the rear anti-roll bar (ARB) stiffness a bunch, to the point where it clearly oversteers. I would do this with no other changes to start. If I understood your posts, you said slightly increased the spring rate. Whether or not you did, I would not back that off. I would, to repeat what I just wrote, increase the rear ARB stiffness.
      How does stiffening the rear bar differ greatly from raising the rear RC?
      I have not changed spring rates in 5 years or so. I do think the car would benefit from a little more rear spring rate however, but it is difficult/expensive to achieve with leaf springs.

      Quote Originally Posted by hquackenboss View Post
      5. If you cannot do (1) right away, try reducing the front tire pressures. Especially for autocrossing, you can get to the low 20 PSI range. This will reduce the ride rate (the tire is also a spring, and reducing the pressure lowers the spring rate of the tire). But you are going to need to to (1).
      At the time this picture was taken, the front left is badly overloaded and the camber wrt to ground is poor. Thus the sidewall is tucking under badly. Lower tire pressure might be a little faster, but it would destroy the tires.

      Tire pressure for the event was: 33psig front , 31psig rear

      It was set this way to preserve the tire outer edge based on how much the tires were rolling over.

      Quote Originally Posted by hquackenboss View Post
      6. Regarding locking your inside front tire, you should realize that if the car understeers, it is going to be more prone to inside front lock up because of the lateral and longitudinal load transfer. If you still have problems after increasing the rear ARB stiffness, then there are a few things you can do. First, is to reduce pitch under braking (this might not be enough, but it is easy to do if you have adjustable shocks compared to alternatives.
      a. Increase front damper (shock) compression stiffness. If you happen to have 4-way adjustable shocks, adjust the low-speed compression stiffer.
      b. Increase rear damper rebound (extension) stiffness. Again, if you have 4-way adjustable shocks, adjust the low-speed rebound stiffer.
      I was able to tune this out mainly through better driving and increased rear braking bias. The shocks I have are non adjustable.

      Quote Originally Posted by hquackenboss View Post
      7. The front end of the car looks a little high. I can see your headers are kind of low, and I doubt you want to scrape going over speed bumps, but I would lower it. This does three things: First, since with this geometry, the rate of negative camber increase under compression increases the more it is compressed, lowering it will further increase the negative camber on the outside tire for a given roll angle. If you have modeled your geometry, you can confirm this. if you don't think this is correct, please post a curve. Even better, if you do happen to take the front springs out, cycle one of the front assembly with the springs out (so you can move it from full droop to full compression, and plot it. See number 8 (below) regarding ball joints.

      If you lower the car, which will increase the rate of camber change as the outside front suspension compresses, this will reduce the positive camber on the outside front tire. The other two things this does, is lower the CG of the car, and lowers the roll center.
      The car is pretty low in the front. I have attached a picture of the static ride height when prepped for competition. If anything, I think the rear needs to be lowered more.

      Quote Originally Posted by hquackenboss View Post
      8. Given you have a way of measuring and adjusting bump steer (I mean measuring it on the car, not just from the model), then I would use a taller upper ball joint, which will increase the negative camber gain. In fact, you can also use a taller lower ball joint, which will have the effect of lowering the car, and further increasing the rate of negative camber gain under compression. As a general rule, if the toe steer (bump steer) goes very slightly positive toe out under compression, then you get a sort of automatic counter-steer, which can make it a little easier to stay at max lateral without so many small steering corrections.
      The car already has a tall upper ball joint (0.9") which, in general, increases camber gain and raises the front roll center. Tall lower ball joint on 1st gen camaros typically aren't great because they very negatively effect the bump steer curve. If the BJ is too tall, you wont be able to get the outer tie rod end low enough to correct the bumpsteer due to wheel clearance issues.

      Quote Originally Posted by hquackenboss View Post
      9. I am guessing you have aftermarket lower control arms, which have some form of non-rubber bushing. If in the off chance you are using stock lower control arms and bushings, your cornering forces are high enough to compress them to the point where your actual camber on your outside front wheel is more positive than your calculation. The stock arms are probably fine, but you need to replace the bushings, and my strong preference is not urethane. I am focusing on the lower control arm bushings because they see higher load than the upper control arm bushings do, but both are important. Also check for any slop in the ball joints. A number of aftermarket units have enough slop to cause problems. Also, if you do have solid bushings, , it is crucially important if you have solid bushings that they move freely. Even urethane ones can be lubricated with a high-pressure lube, and some have grease fittings.
      All front control arms are aftermarket w/ delrin bushings. The inner sleeve that interfaces with the LCA pivot bolt is a steel tube with a wall thickness of about 1/4". The lower control arms actually pivot about this sleeve. The bushing are greasable and are greased every few months. I too agree that urethane is not a great bushing material in many cases. The BJs do not have any humanly perceivable slop and are mode by Howe. The are very good balljoints, probably some of the best you can buy.

      Quote Originally Posted by hquackenboss View Post
      I have an observation in general about comments on the thread, and what I see from people that look at Milliken Moment Diagrams, and models with load transfer equations, spring rate calculations and so on. Bill (the now deceased father) and Doug Milliken's book, Race Car Vehicle Dynamics, is a fabulous book, but it has so much information, that it is pretty difficult to appreciate the big picture, and to figure out which changes have the biggest impact, and what to do first. Also, it doesn’t emphasize some crucially important to keep three things in mind, which can screw up the handling: deflection, slop, and stiction. Ball joints and steering linkages have slop, welds in aftermarket parts can crack, solid bushings can bind, and rubber ones can deflect.
      I agree it can be somewhat "textbookish". I have found Tune to Win by Carroll Smith is better in this regard and gives specific cases for adjustment. In addition the order in which information is presented correlates directly to its importance in the grand scheme of vehicle dynamics.

      Quote Originally Posted by hquackenboss View Post
      Finally, I am a stranger on this message board, so you might ask, who is this yahoo with all these opinions? Here is an article I wrote that describes how I got my start: https://www.pontiacv8.com/blog/2019/...ry-quackenboss I also built a C4 street prepared Corvette that was national championship competitive, and these days I advise a collegiate Formula SAE team that in the past few years finished first among 80 North American colleges, and finished 6th of 120 global colleges.
      I love FSAE. Wish I could have done it in college. Unfortunately, my university did not have a team. Which team do you work with?
      Attached Images Attached Images  
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

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      Quote Originally Posted by hquackenboss View Post

      Finally, I am a stranger on this message board, so you might ask, who is this yahoo with all these opinions? Here is an article I wrote that describes how I got my start: https://www.pontiacv8.com/blog/2019/...ry-quackenboss I also built a C4 street prepared Corvette that was national championship competitive, and these days I advise a collegiate Formula SAE team that in the past few years finished first among 80 North American colleges, and finished 6th of 120 global colleges.
      I just wanted to take a minute to welcome you to the board, Harry. You have an impressive resume and your technical knowledge is helpful to everyone who is following this thread. Please stick around and post more often!
      - Ryan

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      Quote Originally Posted by Sleeper68 View Post
      Pretty good driving in the video. Smooth and deliberate. I need to be more like that, although I think it will come. So far I haven't even gone to two events in a row with the same setup in the car. Once I learn the car again I think I'll get to a point where I can trust it more.
      Thanks... In 2014 I changed the complete suspension setup in my car 3 times during the racing season, and still won a Regional Championship, so I get the different car every time at the track deal.

      Here is a video from the last autocross event I ran back in February just to show the difference between back in 2015 and today in both driver and car ability.



      Many different iterations between then and today but just to show with a bit of time and knowledge, you can adjust the car to work well with your style of racing.
      Lance
      1985 Monte Carlo SS Street Car

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