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Toe question, very theoretical.

Discussion in 'Technical Q&A' started by 24000rpm, Feb 25, 2017.

  1. fatbillybob

    fatbillybob F1 World Champ
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    Aug 10, 2002
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    This thread seems to be kinda all over the place. I think you are trying to learn but don't exactly know what to ask. In general what you want to do is set the car to factory ride height then corner balance the car with how it is to be raced with 1/2 the fuel load of the race. For street it is the number of passengers and 1/2 the fuel level. There is no desired corner weight except all equal which is not possible unless you move weight around the car. So the best you can get is a compromise between left and right turns with a 50/50 cross weight and straight line even braking with equal LF and RF corner weights. So if my choice as a racer to have a 50/50 cross weight and LF/RF unequal by 100lbs or 49.7% cross and equal corner weights LF/RF I would take the later. But then again as a racer you might set up a car to make better right turns if a track has more right turns. See that is clear as mud!

    After that you adjust thrust, rear toe, and camber finally front toe. You adjust caster depending on road crown or desired amount of return to center force vs. ease of turn-in. Then you check all the settings again because each setting can have a small effect on the other. Then you race and tune all of these elements for desired effect on important aspects of the race track like a juicy passing zone. Then if you have adjustable shocks....
     
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  3. DGS

    DGS Four Time F1 World Champ
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    May 27, 2003
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    :p

    I'd guess my neighbors didn't much appreciate my "dialing in" the DMS coil-overs on my Celica GT-Four by running it around the condo circle. ;)

    But after four hours of tweak, test, back on the lift to tweak, test again, etc., I wound up with what may have been the only Celica GT-Four with completely *neutral* handling.

    The factory tunes them with massive understeer for "average" drivers.
    I set mine so I could control over/under steer by how much throttle I applied.

    Which came in handy, as I was cut off in traffic *twice* within a week of setting up the car.
    With the old suspension, either of them would have resulted in a crash.
    With the new set-up, I was able to avoid both of them.
     
  4. Ak Jim

    Ak Jim F1 Veteran
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    Dec 23, 2007
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    Also consider a tire can also make a car pull to the right or left.
     
  5. AEHaas

    AEHaas Formula 3

    May 9, 2003
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    Ali E. Haas
    Very important to check for even tires as above. Make sure pressures and wear are even. Alignment may be perfect and frame perfect but tires can throw it all off.

    Note: pay no attention to the position of the steering wheel at all (more on this later).

    Roads are almost always leaning away from center and castor settings correct for this. It is usually set to keep the car in the correct lane even though the lane is tilted off the road a little. But on a perfectly flat road the car should actually pull slightly to the theoretical middle of the road.

    After all settings are proper the steering wheel may be off center. This is corrected last. It will take somebody who knows what they are doing but actually easy to fix. It is purely cosmetic.

    aehaas
     
  6. AEHaas

    AEHaas Formula 3

    May 9, 2003
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    Ali E. Haas
    Also, like DGS stated, factory settings are for the "average" driver. The first thing I do is change settings for the way "I" drive my big sedan cars as they are rarely set up the way I drive. They are set up for "old folks" drivers not for the truly sporty driver.

    Lastly, if a car dealer wants to "check" your wheel alignment, stop them. If your tires are wearing perfectly well then the alignment is perfect for the way you drive. They can only mess it up by "checking" it. Plus you can save the unnecessary costs involved.

    aehaas
     
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  8. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,312
    Yes, indeed.

    My F355 is setup such that all 4 tires go slick within 100 miles of each other. Brand new tires, never rotated, with or without track events (where tires ARE rotated L<->R 1/2 way through the day) all loose their tread <essentially> simultaneously.
     
  9. 24000rpm

    24000rpm F1 Rookie
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    #32 24000rpm, May 17, 2017
    Last edited: May 17, 2017
    ok. so I had some thoughts yesterday.
    There should be a difference between the following 2 scenarios. Again assuming tires are of the same wear, same PSI, camber is right, complete flat surface, etc.

    Scenario 1. You'll have to hold your steering wheel with force to keep the car straight. And while the car is going straight, the steering wheel is straight. Once your hands are off the steering wheel, the car immediately pulls to the right, together with the steering wheel.

    Scenario 2. If your hands are off the steering wheel, the car will go straight, but the steering wheel is not straight.

    I'd think scenario 1 means that the toe was set correctly but something else is causing the pull?
    I'd think scenario 2 means that the toe was set correctly , just the steering wheel needed to be centered?

    Am I correct?
     
  10. 24000rpm

    24000rpm F1 Rookie
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    ok, suppose I have a perfectly straight, aligned car. Then , I replaced the rear left spring with a 40mm shorter one. Is the car going to pull right, left or nothing will change?
     
  11. andyww

    andyww F1 Rookie

    Feb 7, 2011
    2,775
    London
    Yes but in scenario 2 you should check the toe-adjusted lengths of the track rods are equal before correcting the wheel centering. If one track rod is longer than the other it can cause bump steer and could also cause scenario 1 owing to unequal load on each side (ie the driver sitting on one side) although scenario 1 could be many other factors as already discussed.
     
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  13. fatbillybob

    fatbillybob F1 World Champ
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    It depends
     
  14. 24000rpm

    24000rpm F1 Rookie
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    #36 24000rpm, Jun 4, 2017
    Last edited: Jun 4, 2017
    ok, good. thanks for all of your inputs.

    I have this geometry thing in mind for a while and couldn't sleep occassionally.

    I searched, consulted some local physicist, and wasted a load of scratch papers, and at one point one step short of being reported to the police when I was messing with a cart in a local mall.

    Anyway, now I have some tentative conclusion on 2 of my cars, the modena and the 2002 lincoln town car.

    it seems that there are 2 type of "not going straight".
    #1. you can go straight while holding the steering wheel straight. Whenever your hands are off, you are not going straight.
    #2. you can go straight even when you are not holding the steering wheel, but the steering wheel itself isn't straight.

    Some people call #1 as "drift" and #2 as "pull", claiming these are different things.

    I have concluded that, usually, just usually, the #2(pulling) is caused by front toe problem. basically you just get the steering wheel straight and then adjust the toe accordingly, and you are golden.

    #1 is much more complicated. but one thing for certain : your front toe is correct (at least for each side you are having the same toe out or toe in). The rest can be anything. My town car's problem is probably a combination of rear uneven ride height, which is caused by a leaking LH air spring, and a possble front caster delta LH vs RH. My Modena's problem(drifting to the right) is probably caused by an incorrect toe on the rear.

    I understand there are myriads of factors that can invalidate my aforementioned points, but lets assume that we are dealing with usual situations where tires are inflated, treads are good, no bent suspensions parts, flat surface, etc etc, you name it.

    I'll take my time and do the experiments. I don't have any laser equipment, all I have are threads and pendulums.

    I can take the cars to a alignment shop but guess what, I don't really trust those equipments or the shops. Either they don't calibrate their equipments periodically , or they don't even know the basics, such as ride height. I was totally shocked when some "specialist" told me: i've never adjusted any car's ride height in my 30 years of this profession.
     
  15. fatbillybob

    fatbillybob F1 World Champ
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    Respectfully, I think you need to do more book research before you start experimenting on the car. Based on your posts I don't think you have enough academic understanding on how alignment works and are more likely to make things worse rather than better.

    Here is a start but it is more complicated that that like you alluded to the ride heights and even corner weights.
    Correcting Steering Pull
     
  16. 24000rpm

    24000rpm F1 Rookie
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    thank you for the link. it is ok to make it worst. that's why its an experiment.

    anything that can make me understand more is very very helpful

     
  17. 24000rpm

    24000rpm F1 Rookie
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    i've just read the article. It seems that an uneven ride height won't create a pull

     
  18. spicedriver

    spicedriver Formula 3

    Feb 1, 2011
    2,497
    I would suggest less emphasis on theory, and more on experimentation.

    You can do a crude alignment yourself with some fishing line, and 4 jack stands. Make sure to find the center line of the car first, or else it will be going down the road like a crab.

    IIRC, we setup our road racing cars with toe out, and negative camber on the fronts. Toe in on the rears. This makes the car turn in better.
     
  19. tazandjan

    tazandjan Three Time F1 World Champ
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    It also makes it pretty unstable on the straights. Good for the track, bad for the street.
     
  20. 24000rpm

    24000rpm F1 Rookie
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    #42 24000rpm, Jun 8, 2017
    Last edited by a moderator: Sep 7, 2017
    Thank you for all of your inputs, I read them all, word by word.

    Update : I think preliminary know what happened to my Modena.

    Using 2 parallel strings , I can see the current state of affairs, see picture.

    The 2 dotted lines are imaginary straight lines ( my strings are parallel to them, of course)

    This is assuming the centers of 4 wheels are forming an isosceles quadrilateral(which I didn't check).

    Note that each tire has the same angle to the imaginary straight line.
    Image Unavailable, Please Login
     
  21. 24000rpm

    24000rpm F1 Rookie
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    cue to this discovery is that the rear of the left rear tire is sticking out of the car body just a little bit, compared to the rear of the right rear tire. This prompted me to think that the whole thing is off, even though each tire is parallel to the tire on the opposite side.
     
  22. caferacermike

    caferacermike Rookie

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    Don't forget to rule out mechanical drag. Brakes, wheel bearings, tires - pressure/defects etc
     
  23. 24000rpm

    24000rpm F1 Rookie
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    things have been ruled out

    1. road crown
    2. brake drag
    3. tires wear, inflation, etc.
    4. camber
    5. power steering
    6. ride height


    only thing I didn't look into is the front caster.



     
  24. caferacermike

    caferacermike Rookie

    Jun 5, 2017
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    Caster definitely will cause a car to pull. Generally you can have slightly less caster on the drivers side of the vehicle to compensate for road crown.
     
  25. caferacermike

    caferacermike Rookie

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    If your alignment proves correct, try swapping tires from left to right side to rule out a radial-tire-pull, assuming the vehicle is not equipped with directional tires
     
  26. 24000rpm

    24000rpm F1 Rookie
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    ruled that one out. all 4 new tires

     
  27. 24000rpm

    24000rpm F1 Rookie
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    Update,
    I hope this is the final update.
    I got the car straight now.
    lession learned:
    the rear wheel toes, or the thrust angle, is what kept the car straight or askew.
    the front wheel toes, within a certain limit, HAS NO EFFECT if you keep your hands off steering wheel. It has only effect on if your steering wheel is straight or not while your car is tracking straight.

    it is also counter-intuitive that, if your front toes are skewed to the LEFT, when your hands off steering wheel, while tracking straight, your steering wheel will be off to the right. And vice versa.
     
  28. andyww

    andyww F1 Rookie

    Feb 7, 2011
    2,775
    London
    Not true. If the track rods are adjusted to different lengths, even if the toe is correct, the car will bump steer and also tend to steer under braking dive.
     
    24000rpm likes this.

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