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    1. #61
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      Quote Originally Posted by jetmech442 View Post
      I've been quietly following this thread for a while and appreciate the excellent mix of technical and hands-on discussion. Your first statement has me scratching my head, not because I have a different opinion, just want to understand it. On the dunning-Kruger map, I'm at the peak of Mt. Stupid in terms of the contact patch, and how even and uneven loading can affect traction, as well as how friction is non-linear with load(I know enough to get most of it wrong lol). Any thoughts you guys could share might help me on my descent from that glorious mountain lol.
      I'm no psychologist, but based on the fact you have the understanding that your knowledge of a particular subject could be better, I imagine you are not overestimating your ability. That being said, I think we can all learn something from each other. The best explanations I have gotten regarding tire dynamics at a basic level came from the book Tune to Win by Carroll Smith. You should read it; the entire thing. KYLE.ENGINEERS on YouTube also has a few videos on general tire frictional coefficient effects as a function of normal force and "slip" angle. Obviously this neglects the added variable of dynamic camber angle. He also worked for Mercedes F1 for a couple of years.

      Since we are but lowly consumers, and do not own race teams, we are generally relegated to our own tire testing to obtain good tire data. Different tires like different dynamic camber angles for different loading situations (slip angle and normal force). I am switching to a new tire this year, RT660 from the BFG Rival S 1.5, so I will be performing my own tire testing to see what the Falkens like. Like iadr said, the tire likes what the tire likes. The best set of loading conditions for your car are what net the greatest average cornering forces on the same day, with the same conditions, on the same surface. Now, this ALSO neglects other considerations such as longitudinal tire forces (acceleration and braking) and any combo of the former on transverse or "cornering" forces. It has been my experience that more negative dynamic camber angle improves transverse but hurts longitudinal tire characteristics. Since most of us have solid rear axles, we can mainly concern ourselves with the front end in terms of alignments settings. I will be going to a test and tune next week before my first event to get a feel for the 660s on the surface I normally run on throughout the year. I will report back with my findings. SO far my experience with the 660 is it is less forgiving than the rivals, but is far better at communicating its status. Additionally, the 660s respond much better at lower temperatures and they heat up faster, good for a single driver like me. I imagine this will translate to a shorter tire life, but my rivals lasted about 2 seasons so I am ok with that.

      Quote Originally Posted by iadr View Post
      It's a particularly/typically ugly application of academe against the human intellect, and should be left in the corrupt sewers it came from.
      Yes.

      Quote Originally Posted by iadr View Post
      So in action, whatever keeps the tread surface making generally the most effective contact with the road, is good.
      I agree.

      Quote Originally Posted by iadr View Post
      Empirical discovery shows there is actual bonding taking place, some say molecular or materials bonding. That means every millimeter squared of contact patch is better.
      I would expand this to say that the every bit of additional contact patch with a significant pressure acting over its area matters. Distortion of the contact patch and its associated pressure gradient against the road or "pneumatic trail" is very important and is the ultimate output of all tire loading inputs. The resultant tire force is dependent entirely on the contact area, its pressure gradient with the resultant force acting at the contact patch center of pressure, the dynamic frictional coefficient at that time, and the force of the car acting on the tire. All of the input factors that lead to the resultant tire force and pneumatic trail are complexly tied together, and again, are generally characterized empirically as iadr said, especially in our case. One can educate himself on general trends for radial tires, but getting hard numbers from models is virtually impossible for laymen such as myself. It should also be noted that a tire will give you back whatever force to command of it up until it starts to "slip". I do not mean slip angle, what I mean by that is the tire will create a frictional force equal that of its portion of the force the car exerts on it to keep the car on a prescribed arc until its available frictional coefficient starts to fall off. Most tires follow curves similar to the one I have attached. Tires described as "peaky" usually have a friction peak that is taller but narrower and thus are harder to drive at the limit but are theoretically faster. This is represented by the blue line. Tires described as "forgiving" usually have a friction peak that is lower but wider and thus are easier to drive at the limit. This would be represented by the green or red line. The picture is not the best example, but you get the idea.

      The center of pressure of the contact patch is generally behind the unloaded tire center if positive castor is present. This trailing effect is what generates self-alignment torque, which is what you feel in the wheel with your hand and is the torque that straightens the tires when you take your hands off the steering wheel. It is also the torque that falls away as the tire starts to become unloaded and starts slipping. This phenomenon is the basis of "feel" in the wheel and is one way experienced drivers stay on the limit of adhesion of the tires.

      Suffice to say, the best way to educate oneself on tire dynamics, in my opinion, is to read books devoted to the subject. Specifically those books written by experienced race team members, drivers, or engineers such a Carroll Smith.
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      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    2. #62
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      Good post Sleeper68.

      @jetmech442 - Here's a good short explanation of tire dynamics with some nice, simple figures that are worth a thousand words: http://racingcardynamics.com/racing-...lateral-force/. It's no substitute for a whole book/chapter on the subject, but it's a good high level summary to get started.

      One key point that really helped me when I started learning about tires is that the rate of grip increase trails off as vertical load increases. It's not linear like they taught us in basic physics. This validates the "common sense" rule of thumb that, all other things equal, a car with a lower center of gravity, wider track width, or lower weight will be faster.
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      - Ryan

    3. #63
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      Quote Originally Posted by stab6902 View Post
      Good post Sleeper68.
      Thank you Ryan.

      Quote Originally Posted by stab6902 View Post
      @jetmech442 - Here's a good short explanation of tire dynamics with some nice, simple figures that are worth a thousand words: http://racingcardynamics.com/racing-...lateral-force/. It's no substitute for a whole book/chapter on the subject, but it's a good high level summary to get started.
      Just read through this. Exceptional primer to tires. I am going to explore this publication in its entirety now. Thank you for sharing.

      Quote Originally Posted by stab6902 View Post
      One key point that really helped me when I started learning about tires is that the rate of grip increase trails off as vertical load increases. It's not linear like they taught us in basic physics. This validates the "common sense" rule of thumb that, all other things equal, a car with a lower center of gravity, wider track width, or lower weight will be faster.
      Yes, and this is the exact reason why more weight transfer over a pair of tires hurts their tractive capacity. This is also why the generalized, and in my experience, underexplained statement "softer suspensions have more mechanical grip" is true; although is misleading to some degree. A softer end of the car will transfer less weight and thus have more mechanical grip, at the expense of the other end of the car. The end of the statement is the part that is often not explained.

      To expand: A pair of tires have the most tractive capacity (aka potential for grip) when they are equally loaded. As weight is transferred from one tire to the other, the total capacity of the pair is reduced. Since wider track, lower center of gravity (CG), and less weight reduce WEIGHT TRANSFER, the pair (or set of 4) tires have more tractive capacity and thus the car has the ability to be faster through any given corner. This is why aerodynamic downforce is known as free weight since it increases tire load, does not really affect weight transfer, and does not have to be accelerated.

      So to relate all of this to the original discussion: The Magic Number, which Milliken covers and calls Total Lateral Weight Transfer Distribution, is the ratio of roll stiffness (aka roll gradient in °/g) of the front to the rear. The roll couple is the moment exerted on the sprung mass while cornering and is what loads the outside suspension, unloads the inside suspension, and makes the car roll. The car as a whole has a roll couple but one can break it down into front and rear. The Magic Number and split between the front and rear roll couple is the greatest influencer of a car's propensity to understeer or oversteer (aka the car's balance).

      I was having a lot of issues with balance, namely excessive understeer. After reading a lot to understand the mechanism by which anti-roll bars (aka sway bars) worked and how they changed a car's balance I came upon the magic number. What I learned was that, all else being equal, a car will transfer more weight on the front and less on the rear if the front roll stiffness is increased. More front weight transfer = more likely to understeer. One can increase weight transfer of one end of the car by increasing roll rate (sway bars or ride springs), lowering the CG (lowering the car), or by raising the roll center.
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    4. #64
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      Quote Originally Posted by iadr View Post
      First off, Dunning-Kruger is a "gate keeping"/Credentialist bit of gaslighting. It is best un-wound by observing the ferocity with which the elite try to undercut your perceptions: ie "What are you going to believe, me or your lying eyes?" Think it was just co-incidence that it came out at the time of internet adoption? It was in fact a direct response, as in: "Can't have the plebe's thinking their newfound, newly shared perceptions of the way the world is run have validity, can we?" It's a particularly/typically ugly application of academe against the human intellect, and should be left in the corrupt sewers it came from.
      I took a while to respond to this. My first reaction to this aggressive take was to dismiss it as another woke/partisan/conservative/liberal(choose your insult) freakout. But I figured it was a strong reaction to have on a forum amongst car guys talking about tires..so I gave it time tried to read up. You have to go a ways down on google to find an article by Johnathan Jerry who shows that the effect can be seen in large scale random generated scenarios and thus the effect might not be part of the human psychi afterall, and I agree with that now. I don't think any literature should be used to dismiss someones opinion outright, but I do still find the graph a useful reflection of where I might evaluate my knowledge on a subject. Heat transfer and thermal radiation...I've got a solid, successful career and feel confident I can speak and teach it...tire camber curves, I still feel like I am sliding down Mt stoopid.

      So thanks iadr for alerting me that the D-K effect is not fully accepted by the science community( in fact it seems more studies are being done to try and eliminate it's regression to the mean issue). I think we, as a country, need to get back to presenting differing views in a way that doesn't alienate the other side immediately and force them to dig in.

      Speaking of camber curves and traction...


      Quote Originally Posted by Sleeper68 View Post
      The best explanations I have gotten regarding tire dynamics at a basic level came from the book Tune to Win by Carroll Smith. You should read it; the entire thing. KYLE.ENGINEERS on YouTube also has a few videos on general tire frictional coefficient effects as a function of normal force and "slip" angle.

      Big Fan of Kyle Engineers! He got me started on tire basics, as well as the book "How to build a high performance miata". I see "tune to win" on amazon, I scoop that up at your suggestion.

      As with all your posts Ryan, I need to read them some more when the house (and my mind) is quite to fully absorb what your saying. Your posts are always clear and you choose words carefully, and sometimes I miss the nuance. I appreciate the effort you guys put into the posts.

      Quote Originally Posted by stab6902 View Post
      Good post Sleeper68.

      @jetmech442 - Here's a good short explanation of tire dynamics with some nice, simple figures that are worth a thousand words: http://racingcardynamics.com/racing-...lateral-force/. It's no substitute for a whole book/chapter on the subject, but it's a good high level summary to get started.

      One key point that really helped me when I started learning about tires is that the rate of grip increase trails off as vertical load increases. It's not linear like they taught us in basic physics. This validates the "common sense" rule of thumb that, all other things equal, a car with a lower center of gravity, wider track width, or lower weight will be faster.
      I'm on board with this concept. I read an article that explained the traction curve becomes more non-linear the closer you get to the tires load index.

      So for a Hankook RS4, a 225/40R19 has a load index of 1279 lbs. a tire with more width, but a 235/35R19(slightly more width, but slightly less sidewall) has a lower index by ~70 lbs. In general, the slightly narrower tire would "fall off" less quickly than the 235 as more lateral load is transferred to it. But perhaps the 235 has slightly more traction due to its width so the fall off is a wash. Open to thoughts/criticism of this train of thought....

      Thanks again for everyones response to me just jumping in and asking a question. Discussions like these are what continues to make this forum so great.

      1969 442 6.0L LQ9 T56
      Fab9 w/ custom 3 Link conversion
      FAYS2 Watts link
      Thanks to Mark at SC&C for his honesty and passion for the sport, and Ron Sutton for the wealth of knowledge that has helped shape so many of the cars on this site.

    5. #65
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      Nov 2014
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      This post is provide an update as to how the car and myself have been performing since the last post.

      List of events since last post:

      HSSC 03 OCT 2021, BFG Rival S 1.5, Setup 5: https://youtu.be/L6FEjmYwQUY Very cold. Tires were about out of life here.

      TRSCCA OctoberFAST Day 1 31 OCT 2021, Wet, RT660, Setup 6: https://youtu.be/Iv36rB08GYQ Falkens worked great. Alot of turn-in understeer but it was wet.

      TRSCCA OctoberFAST Day 2 01 NOV 2021, Dry, RT660, Setup 6: https://youtu.be/H83PK4gJ9JI Love how fast the RT660s heat up. Great for a one driver car.

      ETRSCCA Points #1 06 MAR 2022 BRISTOL, Setup 7: https://youtu.be/P1UkFrvwsqs First event post-spindle failure. First time and bristol (high speed courses) with the new tires.

      ETRSCCA POINTS #2 03 APR 2022 SMOKIES STADIUM: https://youtu.be/ahyv41IntUs Starting to learn how the car drives with the new Falkens. They are more precise and provide far more feedback than the BFGs.

      ETRSCCA POINTS #3 15 MAY 2022 BRISTOL: https://youtu.be/h5ZU228ThRs

      ETRSCCA POINTS #4 29 MAY 2022 SMOKIES STADIUM: https://youtu.be/G0QG2SxoYRw

      ETRSCCA POINTS #5 12 JUN 2022 BRISTOL: https://youtu.be/zXOY9T7Akzc The falkens can certainly get greasy when it is super hot outside, especially in the rear when applying power at the end of the run. Setup 7 is definitely working the outside rear tire more than before based on temps. Could also be driving improvement.

      ETRSCCA POINTS #6 10 JUL 2022 SMOKIES STADIUM: https://youtu.be/gWhB4XF6apg

      ETRSCCA POINTS #8B 24 JUL 2022 BRISTOL: https://youtu.be/ERG2jg3YfOk

      ETRSCCA POINTS #9 21 AUG 2022 BRISTOL: https://youtu.be/gnW6uy7s5L8

      ETRSCCA POINTS #10 09 OCT BRISTOL: https://youtu.be/sAUohwkN96A

      As you can see from these videos, the car understeers far less and generally rotates better; however, it still understeers in steady state cornering. I think the balance (TLLTD) is still off, but I think there is another contributing factor. More on that later.

      Thanks to contributions from members here at pro-touring.com and some driver improvements, I have been able to win the 2021 and 2022 ETRSCCA points championship for CAMT. I want to take this opportunity to thank everyone who has contributed to this thread. Public discourse, in my opinion, is very good for improving all of our understanding of vehicle dynamics.

      My next area of focus for the car is fixing the steering geometry and the excessive steering arm flex the car has. The steering arms are made by Chassisworks of 7075-T73 Aluminum https://www.cachassisworks.com/p-295...-aluminum.aspx. The fact the steering arm is aluminum and because of the very low position of the outer tie rod end (approx 0.2" from the wheel inner lip), the steering arm flexes. This excessive flex (approx 0.2" of movement of the outer tie rod before the wheel moves when car is static on the ground) makes the car very hard to place while racing on the limit.

      So, my plan currently is to use a higher inner tie rod pivot to allow the outer tie rod to move up. Currently, I want to use the ridetech TruTurn centerlink/draglink instead of modifying a factory one or making my own. This will reduce the cantilever distance to the outer tie rod from the spindle. Additionally, I will need new steering arms to accommodate this so I will be making my own steering arms from steel with very similar Ackermann geometry to the Chassisworks units. The combination of the fact that steel is stiffer than the aluminum and the reduced cantilever should make for a much stiffer steering system.

      Now, back to why I think the car is understeering in steady state: It could be the balance is still biased to understeer due to weight transfer, and shock settings are improving turn-in and transient balance; hiding the steady state balance issue. There could be another issue though, one related to the known steering arm flex. It COULD be that once the car is cornering hard and virtually steady, the steering arms (especially the outside steering arm) are flexing so much that the dynamic toe has changed to be very toe-ed in. Maybe this is part of the steady state understeer issue? Maybe I should return the inner upper control arm pivot point to the OEM holes and maintain the 0.5" tall or 0.9" tall UBJ?

      What do our fine members at pro-touring.com think?

      I think we all will agree that the steering arm flex should be reduced as much as possible.



      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.

      SETUP 6: Switched from BFG Rival S 1.5 to Falken RT660 tires (same size 275/35R18). Reduced toe out to zero. -2.1° camber , +6.7° castor , 0" total toe out. This change occurred just before an event at NCM Racetrack in Bowling Green, KY in OCT of 2021.

      SETUP 7: Post-spindle failure. -2.25° Camber, +6.75° Castor, 0" total toe.
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    6. #66
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      Apr 2007
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      193
      A concern is that arm:
      https://www.cachassisworks.com/p-295...-aluminum.aspx
      being made of aluminum, that type of .2in flex 100% guarantees eventual breakage. It's a matter of time- that said, could be a long time, but at .2inch I don't think it would take long at all. Even 0.040" under much greater (ie active) load would worry me if I were the manufacturer.

      Now rather than condemn a product, I'm going to go the other way. Are you absolutely sure the arm itself is flexing? It's not within the wheel bearing or even tire carcass?
      Where is it flexing? You believe it's bending off the solidly mounted rear spindle bolt? (this is rear steer, right?) That's the only way I could see possible- I see it as solidly mounted, then a cantilever off the rear bolt. You're saying you document that at standstill? Makes no sense. If it were that much of a wet noodle, the first hard corner or hard corner with a bump in it, and it would be gone.

      It just doesn't make sense to me- the size of that, & that the equivalent parts made by Stielow and DSS and others with access to modelling are if anything less beefy- that it would flex problematically. If it were a drag race part meant to guide pizza cutters over a few dozen miles of runs, adapted over to protouring, OK. But that is specifically made for Protouring.

      I'm not naive- faulty products make it out there, occasionally even at OEM level (pad knock back and wheel bearing issues the last few years), but no offence, just my gut here, I'm suspicious this is as much of one as you currently think it to be.



      *sorry if anyone was trying to write a reply. As I thought about it, I edited my posted several times.


    7. #67
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      Quote Originally Posted by iadr View Post
      A concern is that arm:
      https://www.cachassisworks.com/p-295...-aluminum.aspx
      being made of aluminum, that type of .2in flex 100% guarantees eventual breakage. It's a matter of time- that said, could be a long time, but at .2inch I don't think it would take long at all. Even 0.040" under much greater (ie active) load would worry me if I were the manufacturer.
      I agree, this is another reason I am changing to steel steering arms for this geometry. Aluminum has a finite fatigue life, regardless of loading condition. This being a fully-reversed load, it is virtually worst-case. Steel CAN have an infinite fatigue life if the stress is kept low enough and stress risers are properly addressed.

      Quote Originally Posted by iadr View Post
      Now rather than condemn a product, I'm going to go the other way. Are you absolutely sure the arm itself is flexing? It's not within the wheel bearing or even tire carcass?
      I am not absolutely sure. Other sources of compliance may exist, certainly. The fact I could watch the distance between the tie rod and the wheel change while moving the steering wheel with the car static, told me alot of this compliance in the steering system was coming from the steering arms. Wheel bearing play could cause this, but I precisely set wheel bearing preload with a bearing spacer and torque wrench. Also, wheel bearings are replaced every season, so I doubt much of the compliance comes from the bearing. This, is in no way, a dig at Chassisworks. I love their products and I do believe they put alot of thought and time into their products. It is, however, my belief that the majority of the compliance is coming from the steering arms.

      Quote Originally Posted by iadr View Post
      Where is it flexing? You believe it's bending off the solidly mounted rear spindle bolt? (this is rear steer, right?) That's the only way I could see possible- I see it as solidly mounted, then a cantilever off the rear bolt. You're saying you document that at standstill? Makes no sense. If it were that much of a wet noodle, the first hard corner or hard corner with a bump in it, and it would be gone.
      Yes, it appears the steering arm is bending, in two different axes. One axis is the steering axis, but the other, more significant, axis is a horizontal (more or less) line at the rear spindle mounting bolt. One important note: most users of this arm will see less flex than I do because they use it as intended: with a factory tie rod end. I have lowered my outer tie rod end about 0.75" from the factory position to correct bumpsteer, further increasing the cantilever on the arm. 1st gen F and X bodies are rear-steer, yes.

      I need to apologize, as I was not clear about where and how the ~0.2" flex was measured.

      1. Displacement of the zerk fitting of the outer tie rod end was measured with a dial indicator. No indicator was placed on the wheel.
      2. The car was sitting at ride height on concrete floors.
      3. ~0.2" (I don't remember the exact number) is the TOTAL displacement displacement of the zerk fitting on the outer tie rod end of one side of the car when turning the wheel both left and right up until visual indication of wheel movement was detected.

      This was not a robust test method, nor are these displacement values representative of what may others would experience. The main reason for this is because my outer tie rod end is quite a bit lower than the factory steering geometry, which is what these arms were designed for. So low, in fact, that the wheel has contacted the tie rod when I had my bumpsteer virtually corrected. I had to move the tie rod end up 0.05" to prevent rubbing under hard road loads.

      I plan to re-measure this displacement when the car is static with the current setup. I will amend my test method by placing an indicator on both the wheel rim and the tie rod end. Rod end displacement will be recorded in both directions when wheel displacement is 0.010" from straight ahead. The 0.2" number will likely shrink following this procedure. I will also repeat the test 3 or more times to ensure repeatability. Then, the new setup (steel arms with les vertical cantilever and trutrack draglink) will be tested in the same manner and flex difference can be directly compared. If further sources of steering compliance exist after this, they will be identified and reduced as much as possible.

      Regardless of the fact this test was not super scientific, I can tell you the steering system flex is significant. How I know this is, when driving down the highway, one can oscillate the steering wheel violently about 30° both left and right from center with hardly no effect to straight ahead motion. This tells me something, or many things, is/are flexing. You can watch the whole steering system move with the steering wheel with the car static on the ground up until the steering arm. The tie rod moves, but the wheel won't (up to a point obviously).

      Maybe I can take a video to show you guys what I am seeing. It is very possible I'm missing something.

      Quote Originally Posted by iadr View Post
      It just doesn't make sense to me- the size of that, & that the equivalent parts made by Stielow and DSS and others with access to modelling are if anything less beefy- that it would flex problematically. If it were a drag race part meant to guide pizza cutters over a few dozen miles of runs, adapted over to protouring, OK. But that is specifically made for Protouring.
      I have been unable to find any comparable products from DSE or Stielow. If you have found some I would love to take a look at them and possibly procure them. The only steering arms I see on DSE's site for 67-69 camaro comes on their hydroformed subframe assembly. They appear to be made from steel forgings. Pics attached.
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      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    8. #68
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      Apr 2007
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      193
      I like how you examine things. Kudo's- it's often said and certainly true of me, that one doesn't understand something until one explains it to someone. I can see you working through this.

      I will keep it short through because I'm procrastinating putting a family members car back together after an overheat (she didn't know or listen to my rushed explanation that no heat in a Canada winter means your antifreeze is low, and that "failure to react" set off a series of cascading failures). Got to get in the garage.

      The Stielow reference was to his using a fabricated arm on a Corvette spindle on one, & maybe two of his builds- I have a soft cover book by him and a ghost writer somewhere with multiple pics of that... that I made distinct note of as I was figuring out a front end plan for a largely still born project. He's smart and I've always regarded him as being able to "run it by" the right people and maybe more significantly, their computers when he needed to. That said some of his cars were almost pure SEMA type builds and not run in anger more than a few hours.

      I also distinctly remember seeing what appeared to be steel *tube* (!) steering arms on a highly regarded Pro-touring car- some time ago, or maybe at a/the "other" site. I don't have a link, though I'm pretty sure have photos saved on my hard drive.

      I've also seen off road buggies built with fabricated spindles and steering arms, and those guys are, obviously hard on their stuff when it comes to instantaneous G-forces, even if the tires seem cushiony and the ground less grippy, they still have huge leverage back from road surface to tie rods, with the 35-40" tires, not to mention the impacts. They were using welded steel plate, maybe 3/8, but more likely 5/16 or even 1/4 making a hollow, lengthy box-fabrication containing/joining 3 steel blocks- 2 mount-point blocks & a tapered "block" for the tie rod to go in. (Not recommending this, just saying...).
      Circle track has examples, too. IDK, but I could believe those are only equal to street strength, but you don't hear of breakages much at all outside of contact.

      I've followed self built cars of multiple genres- "locost" lotus7 replicas being one, and gt40's/supercar replicas being another. Lots of fabricated spindles/steering arms. That said you never know if what you see done is actually effective (safe). The few accidents I can recall were from over driving and straight up loss of control, and a locost where he tacked it together to do a motion test then forget to pull it apart and do full welds. The original Factory5 '34 Ford car had a public development failure its rocker front suspension. More I think because the rocker itself by definition has exactly double the suspension forces acting on its pivot.

      That said, the Chassisworks piece looks beefy. I mean, yes, you can see cut paths were a factor in design but not in a bad way. But in thinking about it, the relatively few OEM bolt ons I can think of seeing/touching have all been always steel and always forged.

      I'm staying subscribed to this thread and I am curious about seeing resolution and understanding.

    9. #69
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      Aug 2022
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      Quote Originally Posted by Sleeper68 View Post
      Maybe I can take a video to show you guys what I am seeing. It is very possible I'm missing something.
      I mean, as a mechanical engineer, you could just break out your old beam calcs and find out that there is absolutely no way that arm is flexing 0.2" without breaking. It'd have to be significantly thinner to withstand that kind of deflection. And that's a single turn - no chance it'd survive even low cycle fatigue.

      By measuring to the tie rod, you're including that rod end joint in your slop. Seems far more likely to have a bad tie rod end than a steering arm flexing that much. Either that or the steering arm isn't actually tight against the spindle, but that would likely be catastrophic and very obvious.

      Video would be good.

    10. #70
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      Nov 2014
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      Quote Originally Posted by Olds.PhD View Post
      I mean, as a mechanical engineer, you could just break out your old beam calcs and find out that there is absolutely no way that arm is flexing 0.2" without breaking. It'd have to be significantly thinner to withstand that kind of deflection. And that's a single turn - no chance it'd survive even low cycle fatigue.
      Olds,

      I understand your point. As stated previously, 0.2" refers to the total displacement (both loading directions, 0.1" from center) of the zerk fitting on the bottom of the outer tie rod end. This means that the zerk fitting moved about 0.1" from the unloaded position in both directions. This also means that the steering arm itself did not move the entirety of this distance. I did not measure steering arm deflection at any point. Additionally, as mentioned previously, this test procedure was not very robust and the likelihood for error is high. A test will be performed soon with a more robust procedure. I agree 0.2" steering arm movement does not pass the smell test. The reality is the steering arm does not move that much, the zerk fitting at the bottom (end) of the cantilever moves half that much (maybe). The steering arm furthest point probably moves more like 0.040-0.050". Regardless, this will be fleshed out with a proper test soon.

      Quote Originally Posted by Olds.PhD View Post
      By measuring to the tie rod, you're including that rod end joint in your slop. Seems far more likely to have a bad tie rod end than a steering arm flexing that much. Either that or the steering arm isn't actually tight against the spindle, but that would likely be catastrophic and very obvious.

      Video would be good.
      The likelihood that there is any slop in the outer tie rod end is very low, in my opinion. The reason I believe this is because the outer tie rod end is made by Howe and has a user set pre-load or lash. I set the rod end up with some preload (as recommended by Howe). There certainly will be some flex of the rod end stud, however. It is approximately 5/8" in diameter and is made from alloy steel. The bolts attaching the steering arm to the spindle are 1/2-20 grade 8 and all are tight.

      I have attached a few pictures of the modified steering arm including the outer tie rod end and the wheel for reference. You will be able to see that the rod end is very low near the wheel. Deflection at the bottom zerk fitting will be about double of the deflection of the steering arm lowest point.
      Attached Images Attached Images    
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    11. #71
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      Nov 2014
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      East Tennessee
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      There is a new development in the understeer saga. While underneath the car checking fasteners, I found that my rear sway bar was cracked. Pictures attached below. I am uncertain when this happened. The car has not really been driven since the last SCCA event on 09 October 2022 (video: https://youtu.be/sAUohwkN96A). I think crack started to significantly open up during the run in this video. You can see that car yaw fairly well early in the run, but at 0:43 I start a higher speed right hand sweeper. In the previous 4 runs, I was able to stay off the cone wall to the left by about 2 feet, but on my fifth run (shown in the video) I push out and hit a cone in the wall. SoloStorm data shows cornering G's to be comparable, as well as corner entry speed. Max corner accelerations for run 4 and 5 were 1.05 and 1.00 g respectively. Corner entry speeds for run 4 and 5 were 54.1 and 53.3 mph respectively.

      The car was able to make counter centrifugal force, but it wasn't able to maintain the correct arc at the same speed. My current hypothesis is that the rear bar failed just before, or going into this turn on run 5, causing me to push out and tag a cone in the wall. The ARB (anti-roll bar) is made by Hellwig. They are sending me a replacement bar for free under warranty. I have had both the front and rear bar for about 7-1/2 years.

      If this hypothesis is correct, I believe it would support the argument that the car needs the rear stiffness it has (or maybe more) since losing the rear bar would impart more weight transfer on the front and thus reduce the front end's tractive capacity.

      What do our fine pro-touring.com members think?

      Thanks again to all who have contributed to this discussion.
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      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    12. #72
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      Nov 2014
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      The broken sway bar has been fixed and some other issues have come up. Two events have been completed so far this year with not the best results. Setups below:

      SETUP 7: Post-spindle failure. -2.25° Camber, +6.75° Castor, 0" total toe.

      SETUP 7.5: Broken/cracked rear sway bar. -2.25° Camber?, +6.75° Castor?, 0" total toe?.

      SETUP 8: Replace broken rear sway bar. -1.5° Camber, +6.50° Castor, 0" total toe. This setup snuck up on me. The the change in camber happened gradually overtime and seemed to result from loose upper ball joints. This prompted an evaluation of all Howe adjustable rod ends and ball joint on the car. I found that all four (both upper ball joints and both outer tie rod ends) were slightly loose to the point of lash. This was addressed and corrected in SETUP 9. It is unclear how long they ball joints had been loose. The car pushed at 2023 Event #1 with this setup and was difficult to place on the racing line. Tires were fairly cold at that even due to semi-wet and dusty course, low ambient temps, and low solar angle.

      SETUP 9: -2.5° Camber, +6.8° Castor, 0" total toe. A different toe measurement method was used (toe bars on camber caster gauge, straight edge on opposite wheel, tape measure). This method is far easier to prepare but I fear it is far less accurate. Previous toe measurement and adjustment had been facilitated with a set of parallel strings attached to jack stands that had been aligned to the center longitudinal axis of the car. Toe was measured by taking the difference between front and rear distances to the wheel lip from the string on each side using a machinist scale. I am switching back to the old method but I am going to streamline it by making two tubes with notches at equal distances to locate the string eyes.

      Event #1: Car pushed, my driving was sloppy, tires were cold, track was wet in places and very dirty/graveled. I had it in me to win but I hit a cone in a wet section on my fastest raw run.

      https://youtu.be/370CngHJhpY

      Event #2: Loose ball joints fixed, camber changed to -2.5°, car was far looser than before. The surface was cold, I was sloppy and not used to this setup, and mine lines were wide in places which killed me on a slow course like this one. I think there is room to improve the car's balance with with a rear shock or rear sway bar adjustment. Toe could be compromised and not actually 0". Need to re-check with the original, validated toe measurement method.

      https://youtu.be/pOWlzmbBzkc
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

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