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How to measure toe yourself (with pictures)

Discussion in 'Model S: Driving Dynamics' started by zwede, Jul 5, 2014.

  1. zwede

    zwede 2013 P85+

    Joined:
    Jan 17, 2014
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    501
    Location:
    Plano, TX
    #1 zwede, Jul 5, 2014
    Last edited: Jul 11, 2014
    The question of rear toe comes up on a regular basis and how one might measure it. As many of us have found out, having incorrect rear toe will quickly destroy tires. This is especially true with the 21" wheels as their shorter sidewall is less able to compensate for incorrect alignment.

    First a quick recap of what toe is:

    WhatIsToe_zpsf7fdc67a.jpeg

    What we want in the rear is a slight toe-in. This is so that when the torque of the motor propels the car forward, suspension bushings deflect and the wheels point straight.

    The current spec for the Model S is as follows.


    MinMax
    Total rear toe-in (degrees)0.250.45

    Note:
    This spec differs slightly from the one in the owner's manual. I received this in response to an email I sent to Tesla ownership 07/11/14 asking for the latest spec.

    Measuring this on your own is fairly simple. All that is needed are 2x jack stands, some string, and calipers.

    Place one jack in front of the car and one behind and run the string between them. Place the stands so the string is 45 mm from the rear center cap and 64 mm from the front.

    Here I'm setting the rear distance to 45 mm.

    Toe_1_zpseaef5628.jpg

    Placing the string like this makes it run exactly parallel to the car. The 45 mm / 64 mm setting works on all factory wheels. 19" as well as 21", including the staggered P85+.

    Next I measure the distance from the rear rim lip to the string. Note that I'm measuring from the rim, not the tire.

    Toe_2_zps5356896e.jpg

    I ended up with a measurement of 9.2 mm.

    Finally I measure the front lip to the string.

    Toe_3_zpsea5d9083.jpg

    And this was 10.2 mm.

    So what do my measurements mean?

    My front distance is greater than the rear. I have toe-in.

    The difference is 1 mm. Turns out each mm of difference corresponds to ~0.1 degrees with 21" wheels, and ~0.11 degrees with 19". You can do the trig, or just use my numbers. :)

    So on the right rear wheel I have 0.10 degrees toe-in. On the left I have 2 mm, or 0.20 degrees.

    My total rear toe is thus 0.30 degrees toe-in. With the spec being 0.25-0.45, my rear toe is in spec.

    Don't worry about small differences side-to-side. They are not harmful. If the difference is too large the car will go down the road sideways, but 0.1 degree is nothing to worry about.

    So that's how easy it is to check your toe. You can measure the front wheels the same way. Make sure the wheels are pointed straight. In the front the spec is:

    Air suspension: 0.10 toe-in to 0.30 degrees toe-out.
    Coil suspension: 0.24 toe-n to 0.16 degrees toe-out.

    Yes, it is OK to have slight toe-out in the front. The drag of the wheels deflects the suspension bushings differently than in the rear, so a slight static toe-out is not a problem.
     
  2. drees

    drees Active Member

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    San Diego
    For measuring other cars, what's the easiest way to make sure the strings are parallel to the car?

    For the Model S, 45 mm / 64 mm I assume is relative - you just need to make sure that the rear is 19 mm greater than the front...
     
  3. zwede

    zwede 2013 P85+

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    If you know the track width of the car and the rims are the same rear and front you can use the difference between front/rear track. If the rims are different you may end up running string on both sides and then measure the distance between the strings until you get them equal. Of course you also need to make sure the car is right in between the strings.

    Correct.
     
  4. tezco

    tezco Sig P85

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    Colorado
    Thanks for the tutorial. I'm have to give it a try.
     
  5. redi

    redi 2013 P85+ with HumanPilot Technology

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    Aug 31, 2013
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    Location:
    DFW, TX
    While you can only get a total toe measurement, toe plates seem to work and you can read the tapes down to about 1/64". Takes about 3 minutes to get a check. There are cheaper and more expensive models, the more expensive have arms to touch only the wheel rim. The plus part is that it does literally take about 3 minutes to check.

    Deluxe Toe-In Plates (pair)
     

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