Why our Prius "wanders"

Discussion in 'Gen 2 Prius Main Forum' started by artie, Apr 19, 2006.

  1. artie

    artie Member

    Feb 5, 2004
    san diego
    2016 Prius
    This explanation says it more completely than I could, although less
    simply... It doesn't refer directly to mpg, but to power loss which
    causes the reduced mpg.

    Selected excerpts from: Pointed the Right Way

    story by john hagerman


    "When a pair of wheels is set so that their leading edges are pointed
    slightly towards each other, the wheel pair is said to have toe-in.
    If the leading edges point away from each other, the pair is said to
    have toe-out. The amount of toe can be expressed ...as the difference
    between the track widths as measured at the leading and trailing
    edges of the tires or wheels. Toe settings affect three major areas
    of performance: tire wear, straight-line stability and corner entry
    handling characteristics.

    "For minimum tire wear and power loss, the wheels on a given axle of a
    car should point directly ahead when the car is running in a straight
    line. Excessive toe-in or toe-out causes the tires to scrub, since
    they are always turned relative to the direction of travel. ...
    So if minimum tire wear and power loss are achieved with zero toe,
    why have any toe angles at all? The answer is that toe settings have
    a major impact on directional stability. ... With the steering wheel
    centered, toe-in causes the wheels to tend to roll along paths that
    intersect each other. Under this condition, the wheels are at odds
    with each other, and no turn results.
    "The toe setting on a particular car becomes a tradeoff between the
    straight-line stability afforded by toe-in and the quick steering
    response promoted by toe-out. Nobody wants their street car to
    constantly wander over tar strips-the never-ending steering
    corrections required would drive anyone batty. But racers are willing
    to sacrifice a bit of stability on the straightaway for a sharper
    turn-in to the corners. So street cars are generally set up with
    toe-in, while race cars are often set up with toe-out.
    "Remember also that toe will change slightly from a static situation
    to a dynamic one. This is is most noticeable on a front-wheel-drive
    car or independently-suspended rear-drive car. When driving torque is
    applied to the wheels, they pull themselves forward and try to create
    toe-in. This is another reason why many front-drivers are set up with
    toe-out in the front."

    And so it appears that if the toe setting is zero, we get max. power and therefore max. mpg. but that leads to wandering, which is why we wander or at least most of us. apparently by re-setting the toe, we will reduce wander and increase gas consumption.

    I think. :rolleyes:
  2. Begreen

    Begreen Member

    Jan 15, 2006
    Western WA state
    Other Electric Vehicle
    <div class='quotetop'>QUOTE(artie @ Apr 19 2006, 05:51 PM) [snapback]242383[/snapback]</div>
    Thanks for the post. That was educational and helpful.