Steering rack mods

Discussion in 'Corner Carver Racing Tech Discussion' started by Dreadknought, Feb 27, 2018.

  1. Norm Peterson

    Norm Peterson corner barstool sitter

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    Toe in is more to eliminate twitchiness. Tramlining is a different phenomenon.

    At -1.7° you could even run minimal toe in without sacrificing much peak lateral grip.

    Zero toe on the machine could end up either 'in' or 'out' in operation depending on bushing compliances (how much and where).


    Norm
     
  2. buster

    buster Junior Member

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    Ok will do. Ive been meaning to do it for a while. Ive just changed a shit load of suspension ( well all of it apart from roll bars) so it's bound to need doing.
    It was just as twitchy before I swapped out the suspension though.
     
  3. Dreadknought

    Dreadknought HOON MONSTER

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    Good refresher on the toe settings. It had been a minute since thought about it. As far as my particular needs, I'm currently running a 275 square set up and will be moving to a 305 or 315 square. I'm on MM caster camber plates running approx -1.5 camber and maxed out castor. Something like -7 to 8 degrees. May have the (neg) part backward. A while back I found a shop in the Dallas Texas area that rebuilds ford steering racks for performance applications, but I have not been able to find them recently.

    I'll have my old rack rebuilt, and see about their opinion as to the scale of the torsion bar mod and potentially a quicker ratio.
     
  4. SoundGuyDave

    SoundGuyDave This Space For Rent

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    To add to what Kerry said, IN GENERAL toe-in helps with stability, but toe-out helps with turn-in... The drag guys usually go zero toe strictly to minimize rolling resistance. I run factory toe-in on my daily driver, but the race car? 1/8" toe-out with -2.75* camber. Turns in nicely, with only a hint of instability at braking threshold.
     
  5. 01yellerCobra

    01yellerCobra forum member

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    Good to know. I always thought the toe in was to help take up the slack of the bushings when the car started moving forward. So essentially when the car is moving it's at zero toe. Made me wonder if set ups running parts with less deflection (poly bushings, bump steer kit, etc) would be better off running less toe.
     
    Last edited: Mar 9, 2018
  6. Sky Render

    Sky Render Stig's Retarded Cousin

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    I run zero toe on my dual-purpose car for a compromise between response and stability.
     
  7. Norm Peterson

    Norm Peterson corner barstool sitter

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    You could run less because of the poly bushings, but I don't think the bumpsteer kit would be any reason (if anything, the greater distance between the pivot ball and the steering arm would suggest that a tiny bit more deflection would exist, for which you'd set a tiny bit more toe-in).


    Norm
     
  8. Pentalab

    Pentalab forum member

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    Norm, what is your toe + camber set at ?
     
  9. kerrynzl

    kerrynzl forum member

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    Scrub Radius and Backspacing is the best way to control any slack in any bushings. A wheel with a small scrub radius and a lot of back spacing will have drag on the inside [and want to toe-in]

    When you increase the overall wheel diameter the scrub radius will get smaller and sometimes become negative scrub radius. This sometimes requires more negative offset to counteract increased drag on the inside.
     
  10. Norm Peterson

    Norm Peterson corner barstool sitter

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    -1.9°-ish camber, small amount of toe-in (don't remember the exact value any more).

    Camber is not too much for my street driving, not quite enough for the track time. Definitely not enough to ride the inside curb through T10 at NJMP/Thunderbolt (a 55-ish mph 180° left) because the curb's height takes a degree or more out of what the right front tire actually runs at through there.


    Norm
     
  11. Sky Render

    Sky Render Stig's Retarded Cousin

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    Scrub radius changes with tire width and wheel offset/backspacing, not wheel diameter.

    http://www.motoiq.com/MagazineArtic...ur-Caster-King-Pin-Inclination-and-Scrub.aspx
     
  12. Norm Peterson

    Norm Peterson corner barstool sitter

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    I suspect that 'tire diameter' was intended, else "overall" is redundant.


    Norm
     
  13. kerrynzl

    kerrynzl forum member

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    Correct!
    Whenever we do calculations we always refer to the overall measurement of the wheels [being a tyre and rim combo]

    Scrub radius is the major cause of "death wobble" on old Ford Hotrods. The first thing they do is put smaller diameter and wider wheels on the car.[with the same percentage offset]

    By doing that they increase the scrub radius [all it takes is one bump to start the death wobble]
     
    Norm Peterson likes this.
  14. Norm Peterson

    Norm Peterson corner barstool sitter

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    ↑↑↑ so what you're telling me is that "bigs 'n' littles" on hotrods wasn't just for appearance sake. Never knew that.


    Norm
     
  15. kerrynzl

    kerrynzl forum member

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    No..... What I'm really saying is some people should never touch cars [with tools] 90% of their improvements are usually a step backwards.

    On the subject of "death wobble" ,the standard knee-jerk fix is to add more +caster.
    But because these Rat-mobiles are lightweight ,the caster will try to lift the vehicle instead of self aligning the steering.
    This causes the cross-leaf shackles to try and correct the height difference by shifting the axle sideways [making it worse]
    Then to aggravate the situation, a lot of hotrodders will split the "A" frame wishbone and use them as parallel 2-links
    During death wobble these links will parallelogram themselves because there is no lateral control.
     
  16. syberspace

    syberspace Junior Member

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    You might consider the FR500S rack. Kohr Motorsports is selling them for $450. Supposed to give better feedback due to less assist and different ratio. I just ordered one.
     
  17. Speedboosted

    Speedboosted Found missing cylinders

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    One place I read that the ratio is different, but another place I read listed them as the same ratio. I guess I need to email Dean directly and ask.