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Thread: How to do an alignment with a string system?

  1. #41
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    There is no standard for the reference wheel diameter unfortunately. System manufacturers have different wheel diameter reference standards. That is why many manufacturers specify toe dimensions in degrees instead of inches or mm. John Bean uses something around 16" I believe and Hunter uses 28.6" IIRC.


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    Guys,

    I have some questions that if you are able to answer can help me greatly.
    I am using hubstands to do the initial setup so I going to be referencing the end points of a 24" bar mounted to the hub.

    1. being the I am measuring with a laser and not a sting, it may be a bit harder to get a really accurate measurement. to what level of accuracy are these adjustment made to in?
    is +/- 1/8" too coarse?

    I have experience setting camber with a camber gauge, but I haven't never done toe, let alone with a laser.
    how do I ensure I take a good measurement?

    My understanding if that I was to be a perpendicular from my reference points to the laser line or strings.

  3. #43
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    IMO your error is +/-1/2 the thickness of the laser dot. I actually fine strings less accurate because of how they are used and how we would measure from them in real life while in theory they are more accurate than I am saying. Lasers are just dead nuts. And regardless of what you do right or wrong just do it the same repeatable way so that when you make changes the changes are predictable. It is the same reason you always use the same tire gauge and not your friend's so that you can rely on the relative pressure.

  4. #44
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    Quote Originally Posted by fatbillybob View Post
    IMO your error is +/-1/2 the thickness of the laser dot. I actually fine strings less accurate because of how they are used and how we would measure from them in real life while in theory they are more accurate than I am saying. Lasers are just dead nuts. And regardless of what you do right or wrong just do it the same repeatable way so that when you make changes the changes are predictable. It is the same reason you always use the same tire gauge and not your friend's so that you can rely on the relative pressure.
    Hey man, thanks for the feedback.
    Can you elaborate on your response because I am a little confused with the terminology. What does "just dead nuts" mean?
    And also, are strings are accurate, or not?
    when you say strings you mean the actual thread lines?

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    Quote Originally Posted by FoxSTI View Post
    Hey man, thanks for the feedback.
    Can you elaborate on your response because I am a little confused with the terminology. What does "just dead nuts" mean?
    And also, are strings are accurate, or not?
    when you say strings you mean the actual thread lines?
    dead nuts just means accurate. Strings are accurate. They just introduce potential error because they rely on difficult to obtain reference points to set a jig to hold the strings. Or strings require you to make a square box around the car from which to measure from and not hit or accidentally move while you work around the car. Strings made sense before you could buy a a simple craftsmen laser level. Time and tech moves on. Using laser level and "L" rules make for simple reproducible results because the reference points are now stupid simple. Doing something simple like measuring from string to front of wheel vs. rear of wheel to compute toe is worky because you can move the string as you try to measure. That's just the reality of the technique. Everyone has their own way. There is nothing wrong if results are repeatable so if you like strings that's perfect. You like laser that's good too. You can do it way faster just using a shop because they do the work. Some times you chose a technique because of the car. For example I can't work without a lift on my Vette racecar a converted streetcar. But a GT1 tube frame racecar everything is accessible on jackstands and a lift just does not make sense for working on that car.

  6. #46
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    Still not sure how the L ruler would help or how you are doing your alignment, but so far this is what I have come up with.
    Maybe I am totally wrong and not considering some important items.

    I have attempted to find the center of the car (chassis) and from there (center line) offset a parallel laser line at a know distance at both sides.
    Then I take a measurement from the laser line to the center hub. Both measurements should be the same at least at each side of the car. (in my test car all 4 happened to be the same).
    At that point, I imagine I just take measurements to the front and rear of each tire.

    For instance, on the front passenger tire there was a delta of 3/16" (toe out).

    All this testing of the setup was done with the car with the tires on, on my driveway which slopes and is not leveled. Once I level the car and out on hubstands, I should be able to get actual measurements and go from there.


    please confirm this a correct approach. I am interested to learn how I can make it better and how any other tools can help me.
    I have made up a graphical sheet to use as a record working sheet to make sure I use the same setup on the car every time.

    again, not an expert so I am looking for feedback - but this seems a very easy process.

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    Quote Originally Posted by FoxSTI View Post

    I have attempted to find the center of the car (chassis) and from there (center line)

    I look for simple. I look for fool proof. What you are doing works but you have the ability to introduce the 1st error that will carry and magnify itself with every additional measure. Finding chassis centerline is nearly impossible with any degree of accuracy IMO. But if you can truly find it then yes that will be a fine reference point. I can adjust my suspension based on where the wheels are not worrying about the centerline because the distance of centerline to wheel hubs is fixed. So the important thing is just the relationship of the wheels to each other. I would be willing to bet you that if you started with chassis centerline that I could prove to you that your thrust is not zero just because of the difficulty of finding and using chassis centerline.

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    I look for simple. I look for fool proof. What you are doing works... Finding chassis centerline is nearly impossible with any degree of accuracy IMO.
    It all depends on that centerline and making sure the lasers are parallel to it and to known point on the car.
    If you take your time and do it with the proper tools you can find it very accurately. Then as I mentioned you can use your axles to QC. squareness of the setup or rig.

    In essence we just need to be able to lay out a line on each side of the car parallel , not to the wheels but to a constant reference point.

    but you have the ability to introduce the 1st error that will carry and magnify itself with every additional measure
    You can do that in any instance things are not setup up properly. For instance referencing the axle nuts could also throw things off if it happens that one axle is 1/8" longer on one side because the factory goofed off.


    Why don't you share how you keep thing simple and fool proof - would you mind?
    Using laser level and "L" rules make for simple reproducible results because the reference points are now stupid simple
    From reading several responses it seems like these setup ups are kind of a hidden art and not many want to share how they do it. I don't mind if the next guys knows how I do my alignment, all I care is about driving a better line on the course than him. No alignment can do that for you.

    Anyway have a happy 4th folks (for those of us in the USA)
    This is starting to sound like one those mine is better than yours.

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    it is hard to put it down on paper. Takes 10 mins to show it. Like some people try and use laser level and ruler to get a flat floor. Some carry around long poles and strap levels on poles. Some use a bucket of water, aquarium tube and a ruler. There are many ways. Think about it and tell me which way introduces the least potential error and is the fastest and most convenient? Do the math on being 1/2 degree off with your laser beam over a 9ft wheel base is almost 1". That will totally jack your flat floor. With water all you have to do is read a ruler and your margin of error is 1/2 of the smallest division on that ruler. I have tried them all and pick my poison. I did not invent any of them so I'm not married to a technique. They all work. Ultimately you have to do what works for you. Everything has pluses and minuses.

  10. #50
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    water level wins every-time for leveling unless you have a "total station".
    The whole idea here for anyone who is interested in down their own alignment:

    1- provide a leveled surface under the car
    2- establish equidistant parallel lines (laser or strings) to the cars longitudinal axis on both side of the side - one one each side.
    3- take measurements from those lines to point on the wheels or wheel stands.

    Its very simple in principal. How you level your floor and how you establish those lines along side the car is where the "magic" comes into to plan and its up to the person doing the alignment to figure out.
    For me it seems that if I am find the center of my chassis, that is a good reference, and if I can confirm and QC it with then hubs, then I am good.

  11. #51
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    Today I decided to play w me wife's car. I laid a line along the center of the car, then offset a line to leach side 36".
    I took measurement to the wheel hubcap on the rear and front axle. (I know this was just a test.

    Here is what I found. Measurements where the same on both sides of the car. However the fronts where 2.25" to the string (laser) and the rear measurement was 2.75"
    So there was a consistent 1/2" different between the front and the rear.

    So here is my question. I thought that axles lengths were the same front and rear on cars. But apparently they are not - Or I screwed up laying out my lines.. (?)
    Or my lasers are walking by the time they reach the front wheels?

    If I had set the outside laser lines equidistant to all 4 hubcaps /axles, the lasers would be a smaller distance apart along the back wheels compared to the front.
    Last edited by FoxSTI; 07-04-2017 at 09:04 PM.

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