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    1. #21
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      Nov 2002
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      Country Flag: United States
      That looks like semi-trailing arms. You'd still have to relocate at least one of the chassis side pivots, maybe all of them. This one is Figure 17.25 in RCVD. Last I knew for under 2-liter Trans-Am racing, teams running cars equipped as OE with this arrangement simply stiffened everything up (Datsun 510, BMW) just to keep suspension movements small.



      Geometrically, you have just one plane to consider, but since the hub carrier is firmly fixed to the semitrailing arm's plane, when the arm rotates in 3-D about its skewed chassis pivots, so does the wheel (meaning that changes will occur in both toe and camber that you more than likely don't want for either drag or road course performance).

      Norm
      '08 GT coupe, 5M, suspension unstockish (the occasional track toy)
      '19 WRX, Turbo-H4/6M (the family sedan . . . seriously)
      Gone but not forgotten dep't:
      '01 Maxima 20AE 5M, '10 LGT 6M, '95 626, V6/5M; '79 Malibu, V8/4M-5M; '87 Maxima, V6/5M; '72 Pinto, I4/4M; '64 Dodge V8/3A


    2. #22
      Join Date
      May 2002
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      Northern California
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      10,715
      Country Flag: Bosnia Herzegovina
      he's right, your link or arm design would have to be built to the spindle end and not the pumpkin since its just about fixed in place. something in this nature....
      MrQuick ΜΟΛ'ΩΝ ΛΑΒ'Ε

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    3. #23
      Join Date
      Aug 2004
      Posts
      30
      Another view on anti-squat. Same information just stated slightly different.

      Anti-squat is a measure of how much of the wt being transfered during acceleration is supported by the suspension linkages. The rest is supported by the springs.

      Ie if you have 50 percent anti-squat your linkages will support 50 percent of the wt being transfered and 50 percent is being supported by the rear springs.


      The rear suspension inputs a force at the SVIC. anything less than 100 percent the linkages are only able to hold up the that percentage and the springs the rest. When it is over a hundred percent the linkages are able to input enough force to actually over come the wt transfer.

      IE at a 110 percent the suspension inputs 10percent more force than what is being transfered during acceleration resulting in the rearend of the car lift.

      Also keep this in mind. The higher the anti-squat the quicker the force is supplied to the rear tires. This can in some situations cause the car to get upset. Because tires are basically rubber springs (think basketball) the FASTER they are slammed into the ground the more they will rebound. When this happens the tires will lose traction.

      So remember you need to pay attention to the rate of force being applied not just the magnatude.



      Todd

    4. #24
      Join Date
      Apr 2001
      Location
      Central CA USA
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      6,108
      Country Flag: United States
      On a high horsepower road course car the above is very important. High HP cars need a rear suspension that can still absorb a few bumps or dips while accelerating out of a corner. Anti-Squat is great as long as you don't get too much. You don't want to lift the whole car much when you accelerate out of a turn.
      Last edited by David Pozzi; 04-13-2009 at 05:35 PM.
      67 Camaro RS that will be faster than anything Mary owns.

    5. #25
      Join Date
      Sep 2004
      Location
      Santee, CA (San Diego County)
      Posts
      297
      Was wondering on a Leaf spring car how the anti squat % changes with the addition of liftbars or calTracs/slide-A-link. A diagram would be nice showing me the SVSA. I got an idea, but wanted to confirm it. I already know the 3/8 of the leaf thingy to figure the SVSA w/o a traction aid.

      Also is pinion angle related with anti squat? I feel no, but seems the Drag racers talk more about pinion angle for traction than anti squat while we "roadracers" talk about AS. Is one better for straight line? Am I delirious?

      Alcino
      Alcino Manuel Azevedo
      76 Mustang II Cobra II
      Featured in April 2006 Popular Hot Rodding

    6. #26
      Join Date
      Aug 2004
      Posts
      30
      Alcino

      The anti-squat is determined by the theoretical location of force application from the rear suspension. I've never really thought about analysising (I think thats how you spell it haha).

      The way I understand the system to work is that it pivots at the front spring Eye and applies a force to the top of the spring to reduce it's spring wrap during launch.

      If I am correct then your Instance Center would be the front spring eye location. This is because once your suspension is locked (lack of a better term) meaning the spring and cal tracks are reacting with each other that there is no longer any more pivot the force is then applied directly at the mounting point. It then becomes a psuedo ladder bar with a softening characteristic if you will. Because it's movement is determined by the spring.

      If you were using bolt on traction bars then the contact point of the traction bars to the chassis woulc be the instant center (usually the front spring eye). You could change it be changing the location in which the traction bars contact the chassis. Either lower , and/ or lower.

      If

    7. #27
      Join Date
      Sep 2004
      Location
      Santee, CA (San Diego County)
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      297
      Todd,
      If I understand you correctly. Does that mean that the different hole positions on the Cal-Tracs have no effect on anti squat? They must be there to adjust something.

      Alcino
      Alcino Manuel Azevedo
      76 Mustang II Cobra II
      Featured in April 2006 Popular Hot Rodding

    8. #28
      Join Date
      Aug 2004
      Posts
      30
      Alcino

      The additional holes do have a reason. It's to adjust the severity of the initial hit of the launch. The further away the more leverage applied to the spring.

      This system is difficult to decifer because it has a flexible member (the spring). I tell you what now you've got me really interested in this. Give me a few days and let me do a more indepth view of this thing and see what I come up with. I think the answer will still be the same but let me put some pen and paper to it with some numbers.

      Todd

    9. #29
      Join Date
      Apr 2007
      Posts
      77

      4 link anti squat vs Cal trac

      I have been drag racing for 35 years and have national event wins and mutiple records.......never could even come close to some of the knowledge and understanding you guys have of A/S. I am new to this forum and most impressed by the interest and sharing of knowledge you guys do on here.
      Here is one for you....what would a typical 4 link setting in a good suspension drag car like pro stock be in reference to anti squat? This is what I drove for years and I just know what would work and what would not. We would start at a setting of anywhere from 48 to 54 in an imanginary connection point and about 4 to 5 inchs off the ground. Smaller HP cars could work at 36 to 44 in and about the same height. The bottom bar would work with a very small downward angle. Not level but maybe 2 degrees. These cars also have to brake well at 200mph.could not afford any wheel hop. I was curious how much anti squat these cars have. I am not a chassis builder but there is a big difference in the way these cars were built over the years. My first serious 4 link car I built in 1981 and the links were not of equal length. Probably more for package purposes. The intersect point would change more radically going down the track so I dont think that is a good thing in any car. Since then of course 4 links have evolved into equal length bars. If you looked at the car during a launch you would see the car drop as it plants the tire but the body to tire reference should be the same and not move. I was curious as to how much A/s that would represent? My guess would be 100% but how difficult is that to figure out? I am sure ride height c/g has alot to do with this.

      With that being said...you might want to look a new bar called the Max-trac and how the adjustments work with that style of bar...www.smithracecraft.com Those bars are not 4 links but work pretty good. Can an A/S be figured out with this style of traction device?
      Thanks

    10. #30
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      The CG at ride height and wheelbase need to be known, since they both are direct parts of what determines how much load transfers rearward. Perhaps more specifically, the weight and CG height of the chassis and the weight and CG height of the front unsprung weight. I'm pretty sure that A-S increases as the nose rises, at least as long as the rear tire to body reference remains reasonably constant.

      FWIW, I get ~60% A-S using numbers in the middle of the ranges you gave for the bigger-HP cars and an 18" CG height and 120" wheelbase. More like 75% for a similar car with the little motor.

      I'm not at all sure what's happening with the Smithracecraft piece, at least not without seeing how it's installed (does the leaf run between the bolts shown in that front piece that does not have the adjustment holes?).


      Norm
      '08 GT coupe, 5M, suspension unstockish (the occasional track toy)
      '19 WRX, Turbo-H4/6M (the family sedan . . . seriously)
      Gone but not forgotten dep't:
      '01 Maxima 20AE 5M, '10 LGT 6M, '95 626, V6/5M; '79 Malibu, V8/4M-5M; '87 Maxima, V6/5M; '72 Pinto, I4/4M; '64 Dodge V8/3A

    11. #31
      Join Date
      Apr 2007
      Posts
      77

      anti squat

      Hey Norm.....thanks for the reply.....yes the spring runs between the two rollers much like a cal trac. Smith did get permission to apply for a patent so something must be different. The lower piece actually contacts the spring eye which is different than the Cal Trac.......the three holes in the front and the two holes in the rear of course enables you to change the bar angle which does affect how hard the tires are hit. I like the contact much better on the sping eye than the Cal Trac method. I never have backed to back them so dont know of any real difference in performance but being able to adjust the bar at least gives you a chance to learn something if there is even anything to be learned?

      A good four link car in a prostock will maintain the body to tire line as it leaves the starting line with the front wheels off the ground only a couple of inchs through first gear. Of course at that point anycar with the wheels off the ground have all the weight on them and this has to be a big factor in anit-squat I would think. I always thought they had closer to 100 % but I dont really understand this. I just knew what worked. If you had 100% A/S would those cars even be able to brake from 200 mph?

    12. #32
      Join Date
      May 2007
      Location
      Orlando, FL
      Posts
      215
      Hi, guys. Just found this forum (StatCounter told me someone referenced my blog from here.) I see my friend, Norm, is here, so I'm sure this is a good place to post.

      For this discussion, I would only add that the 100% anti-squat line (at Chrysler, we called it the "no squat/no rise line," which I consider to be more descriptive) changes slope...very slightly...as the percentage of rear axle assembly weight (or, with an IRS, the unsprung weight) changes. In other words, it passes through the rear tire patch only if the rear axle assembly weight equals zero. With any finite weight, it passes below at a vertical distance equal to the height of the rear axle assembly cnter of gravity times the ratio of the weight of the rear axle assembly to a value equal to the total weight less the weight of the rear axle assembly. (It takes a lot of words when I'm not there to wave my hands in the air, but I hope that's clear.) This is normally between one and one and a half inches, so its omission...in your calculations or sketch...does not introduce a large error.

      I lied: I'm going to add something else. Any discussion of this sort of thing, and its effect on what the dragracer calls "launch," should include the effects of driveshaft torque on rear tire loading and methods of driveshaft torque cancellation. The maximum tractive effort from a tire pair is achieved when they're equally loaded and this is only possible...with a beam axle car...when some form of asymmetry is present. A static cancellation is effetive, but, since this achieves equal rear tire loading only at a specific level of driveshaft torque, a dynamic method...one which would assure equal tire loading at all levels of driveshaft torque...is to be preferred.

      My blog discusses various forms of dynamic cancellation and provides spreadsheets for specific applications:

      http://home.earthlink.net/~whshope

    13. #33
      Join Date
      Dec 2004
      Posts
      115
      Sorry to dig up and old thread, but I could use some help (yes I know, again )

      By putting in my truck arm suspension info I'm coming up with a A/S number of 13%

      Front point 11.25" off the ground
      Rear point 10" off the ground
      52" arm from front mount to axle centerline
      Using 20" as my ICG

      But playing with it, and putting a 30" ladder bar design in the program I get 185% based on

      UCA Front 10"
      UCA Rear 18"
      Length 30"

      LCA Front 10"
      LCA Rear 10"
      Length 30"


      Now my question is, is the program not figuring A/S correctly due to there not being an upperlink on the truck arm set up?


      If I use my truck arm math and add the upperlink in as:

      52" long
      Front point 11.25
      Rear point 0

      It draws a line front the bottom of the rear tire through the front LCA point and gives me 120%.. Is that figure right?

    14. #34
      Join Date
      Aug 2004
      Posts
      194
      Quote Originally Posted by Norm Peterson
      The anti-squat line for IRS passes through the rear axle rather than the rear contact patch.
      Could you explain why?

      I'm guessing it's because the contact patch on the opposite tire is the other point where force is transferred on a stick axle car. While on an IRS the inner pivots on the transverse links are that point.
      (I can't think of the proper technical terms at the moment, sorry.)

    15. #35
      Join Date
      Aug 2004
      Posts
      194
      Quote Originally Posted by 73-TYPE-LT-LS1
      Sorry to dig up and old thread, but I could use some help (yes I know, again )

      But playing with it, and putting a 30" ladder bar design in the program I get 185% based on

      UCA Front 10"
      UCA Rear 18"
      Length 30"

      LCA Front 10"
      LCA Rear 10"
      Length 30"
      The upper arm might have to be longer
      try
      31.0483494

      or so

    16. #36
      Join Date
      Dec 2004
      Posts
      115
      I'm not too concerned about the A/S with the ladder bar. I more than likely won't go that direction, my issue is more with the A/S being 13% .. I don't think 13% is right. Adding the upper link clued me in to that. I think based on my numbers I put in my A/S would come out to the 120%.. I'm just trying to confirm that.

    17. #37
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      Quote Originally Posted by Beige
      Could you explain why?

      I'm guessing it's because the contact patch on the opposite tire is the other point where force is transferred on a stick axle car. While on an IRS the inner pivots on the transverse links are that point.
      (I can't think of the proper technical terms at the moment, sorry.)
      With a stick axle, the suspension linkage resists the axle torque reaction in addition to the forward thrust, with both taken at axle height. Since axle torque reaction and forward thrust are related via tire radius, it's convenient to consider that only the forward thrust acts at ground level (the moment there being zero).

      With IRS, the suspension linkage cannot resist any amount of axle torque reaction, as the half-shafts cannot transmit any moment across the bearings and there is no connection between the pumpkin and the uprights. So you're left with only the forward thrust at axle height and nothing else to resolve it with to get a force with zero moment at some different elevation.


      Norm
      '08 GT coupe, 5M, suspension unstockish (the occasional track toy)
      '19 WRX, Turbo-H4/6M (the family sedan . . . seriously)
      Gone but not forgotten dep't:
      '01 Maxima 20AE 5M, '10 LGT 6M, '95 626, V6/5M; '79 Malibu, V8/4M-5M; '87 Maxima, V6/5M; '72 Pinto, I4/4M; '64 Dodge V8/3A

    18. #38
      Join Date
      Aug 2004
      Posts
      194
      Quote Originally Posted by 73-TYPE-LT-LS1
      I'm not too concerned about the A/S with the ladder bar. I more than likely won't go that direction, my issue is more with the A/S being 13% .. I don't think 13% is right. Adding the upper link clued me in to that. I think based on my numbers I put in my A/S would come out to the 120%.. I'm just trying to confirm that.
      I rushed my first response and didn't explain any of this, sorry.
      What I was getting at is that the program might not see your ladder bar as a ladder bar.

      Since the front pivots are at the same height, but the upper rear one is 8 inches higher, the upper bar would have to be longer to intersect the front one at the same point, like a ladder bar would.

      That could be throwing off the A/S numbers.

      The same thing could be happening to your truck arm figures when you added a 2nd link.

      Try making the length of the 2nd link
      52.9528092

      and see if the A/S goes back to 13%

    19. #39
      Join Date
      Aug 2004
      Posts
      194
      Quote Originally Posted by Norm Peterson
      With IRS, the suspension linkage cannot resist any amount of axle torque reaction, as the half-shafts cannot transmit any moment across the bearings and there is no connection between the pumpkin and the uprights.

      Norm
      Thanks Norm.
      That makes sense now.

    20. #40
      Join Date
      May 2007
      Location
      Orlando, FL
      Posts
      215
      Quote Originally Posted by Beige
      Could you explain why?

      I'm guessing it's because the contact patch on the opposite tire is the other point where force is transferred on a stick axle car. While on an IRS the inner pivots on the transverse links are that point.
      (I can't think of the proper technical terms at the moment, sorry.)
      While Norm's succinct response was excellent, I'm sure Norm would agree that some readers appreciate pictures and diagrams. So, I just finished adding a short section...on the force and moment balances involved...to the "Getting Started" section on the first page of my site. Hope it will help someone.

      http://home.earthlink.net/~whshope

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