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New S14 bumpsteer graphs

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  • #31
    They'll just be streched in the y axis. The longer the arms are the more travel you get until things go to ****. :P

    You should be able to increase all the arms to increase track. The angle of the traction rod will change however if you have sphericals all round then you should have enough misalignment to accomodate.

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    • #32
      Actually, with longer arms you have less of an angle change at all points.

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      • #33
        I was talking specifically about the traction rod being pulled to the side. I don't know if the angle on it would be too great?

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        • #34
          I was wondering if i am on the right track or not!?

          I was thinking i should be able to dial out the bumpsteer in the rear of my hicas subframed s13 by moving the lock bar up or down and or having adjustable length tierod ends in the rear!?

          Then I should be able to run the "traction rod" at what ever length would promote the best squat/ anti squat or camber change etc!

          Thoughts people??

          Thanks

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          • #35
            I'm getting decent car related library, so I "hit the books" last night. I highly reccomend both of these books. You'll get a bunch more out of them for th 20-30 bucks you'd spend, then on a couple magazines.

            Toe changes really come down to changes in stability. From "How to make your car handle" by Fred Puhn:

            "Toe-in causes stability and initial understeer in a turn. Toe-out causes instability and initial oversteer. Usually you want just enough toe-in to keep the wheels from going into toe-out at speed. On most cars this is about 1/8 inch..."

            Toe changes on factory cars are mostly caused by bushing deflection. On a rear wheel drive vehicle (things are very different with FWD) the driving forces forces tend to cause toe-in @ the rear, and toe-out @ the front wheels. This is why most cars factory settings are something like 1/8" toe-in @ the front, and zero toe at the rear. The 1/8" in the front is meant to cancel out any natural toe out caused by the driving forces (braking and rolling resistence). The rear requires no such precautions and can be set to zero toe because power-on causes the aformentioned natural toe-in.

            The above applies to both the front and the rear. But I suspect the less compliance that your suspension has the less you have to preempt the toe out tendency in front with dialed-in static toe-in, and the more likely you are going to be able to run zero toe in the rear.

            In "Tuning to Win" by Carroll Smith he describes what "stable" mean and the ideal set-up:

            "Understeer... is basically a stable condition... If the car is not stable we will not be able to brake really hard. In corner entry [we want] light understeer... In the mid-phase of the corner [we want] very light understeer... In the corner exit phase [we want] we want to the car to gently change over to slight power oversteer... [which requires a set-up of] natural neutral steer or very slight understeer."

            Basically, toe-out is always bad (excluding FWD). But in the rear you don't need any static toe-in either.

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            • #36
              It looks to me like 12.25, 8.5 gives the least change in toe for the longest distance. Extra toe under compression would promote stability/traction as I see it. Toe out with droop won't hurt as much and may help steer the direction you want to go. I am looking for a minimum of 2 inchs of compression travel, 2.5 would be better if I can get it.

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              • #37
                I attended this year's SCCA National Convention and Dan Brinks gave a great car setup seminar. Dan is a crew chief for Pratt and Miller on the ALMS Corvette project and has decades of experience in everything from club to IMSA to ALMS and ACO.

                He mentioned that the pro race prep will do toe and bump sweep measurements as part of the pre-race prep at the shop.

                They determine what aliment and ride height setups they might run for a track and then to a full geometry check and record the toe and bump sweeps so they know exactly what the car is doing for their predefined weekend setup.

                An amateur could do the same with some decent alignment tools and a level setup area in the home garage.
                The Nerd shall inherit the podium for knowledge is power.

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                • #38
                  Limit of travel?

                  Originally posted by logr View Post
                  It looks to me like 12.25, 8.5 gives the least change in toe for the longest distance.
                  It's also the only one that never toes out!

                  What is the first thing that hits and stops/limits bump travel?

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                  • #39
                    Shock.

                    The UCA length will have to change to adj camber so putting the traction to 8.5 and setting camber where you want it is probably the best I can do. imo

                    I still wonder what lowering the toe rod mount at the spindle would do. That would be fairly easy and I'm thinking it could put the toe rod in a level position when the rest of the arms are not and therefore change toe the least. Just a thought.
                    Last edited by logr; 02-20-2010, 08:06 AM.

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                    • #40
                      Originally posted by logr View Post
                      Shock.

                      The UCA length will have to change to adj camber so putting the traction to 8.5 and setting camber where you want it is probably the best I can do. imo

                      I still wonder what lowering the toe rod mount at the spindle would do. That would be fairly easy and I'm thinking it could put the toe rod in a level position when the rest of the arms are not and therefore change toe the least. Just a thought.
                      That s what I was getting at earlier! That way or moving the hicas lock bar etc! If that fixes the toe problem would we be able to tune anything else eg squat/ camber change etc with the traction rod??

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                      • #41
                        Don't forget that you can project/estimate setting that aren't there. That's why I took so much data.

                        Take these examples:
                        -A 12.50/8.75" setup would likely be vertical through 0 height and toe-in under compression based on how the plots keep moving right under compression as the traction arm gets longer.

                        -A 12.00/8.25 setup would likely be vertical through 0 heignt and toe-in under compression based on how the plots (the 2 pink ones) keep moving right under compression as the ruca gets shorter.

                        -The 12.25/8.50 plot is vertical through 0 height and toes in under compression.

                        Noticing the trend here? The stock arm lengths are 12.00/8.25. When making adjustments to the ruca, adding the same length to traction arm should keep the bumpsteer graph the same.

                        I was wondering if this is why SPC only sells the ruca and traction arm together. Probably.
                        She's built like a Steakhouse, but she handles like a Bistro.

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                        • #42
                          Originally posted by Epstein View Post
                          Don't forget that you can project/estimate setting that aren't there. That's why I took so much data.

                          Take these examples:
                          -A 12.50/8.75" setup would likely be vertical through 0 height and toe-in under compression based on how the plots keep moving right under compression as the traction arm gets longer.

                          -A 12.00/8.25 setup would likely be vertical through 0 heignt and toe-in under compression based on how the plots (the 2 pink ones) keep moving right under compression as the ruca gets shorter.

                          -The 12.25/8.50 plot is vertical through 0 height and toes in under compression.

                          Noticing the trend here? The stock arm lengths are 12.00/8.25. When making adjustments to the ruca, adding the same length to traction arm should keep the bumpsteer graph the same.

                          I was wondering if this is why SPC only sells the ruca and traction arm together. Probably.
                          props for the time taken to measure this out.
                          i was wondering if you referenced the eccentric camber adjuster at subframe as i think this can have an effect on the measurements; IMO

                          so in practice, i was thinking is to set your camber,traction & toe arms to the exact calculated lengths & adjust your toe & camber via the eccentrics in that way you get the calculated kinematic effect, right????

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                          • #43
                            good concept cheeky,

                            in that way an alignment would be much more OEMish in the approach, rather than trying to get to the ruca to adjust it for camber
                            I am SKULLWORKS

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                            • #44
                              i dont know how i missed this thread EPSTEIN YOURE SICK!!! i was just about to setup my own toe gauge, this will help me get started THANK YOU

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                              • #45
                                epstein - what were your eccentric bolt positions? full in, full out, or dead center?

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