Rear Wheel Alignment Question

Discussion in 'The Garage' started by Yossarian™, Sep 13, 2017.

  1. Yossarian™

    Yossarian™ Deputy Cultural Attaché

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    Let's assume for a moment that everything else in the bike is straight and in alignment. No twisted forks, tweaked frame or swingarm, etc. Only the rear wheel is out of alignment -- it does not "point" straight ahead and through the centerline of the front wheel.

    So -- which way does the bike want to naturally turn?

    Scenario: bike wants to turn left with hands removed from bars. Forget road crown issues, rear end of rider in the seat position, etc.

    My findings seem to indicate that if the rear wheel alignment is toward the right; that is, the front of the rear wheel "points" to the right of centerline, then the bike will tend to turn left when hands are removed from the bars.

    I'm wondering if that is correct.

    TIA,

    Y
    #1
  2. trailer Rails

    trailer Rails Washes hands before going to the bathroom

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    Sounds right. An easy way to check alignment is measure from the swingarm pivot to the rear axle.
    #2
  3. Project84

    Project84 I can haz adventure?

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    Testing this on a bicycle would take less than 10 seconds (if I were home), but I do believe your account of the situation is correct.
    #3
  4. foxtrapper

    foxtrapper Long timer

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    Fundamentally, you're right. If the rear is canted to the right, the bike will scribe an arc to the left, radius of the arc being the distance to the intersection of the two axle lines.

    In riding, you the rider will compensate by turning the handlebar to get the wheel axles aligned, and perform any slight leaning necessary.

    All bikes are slightly misaligned this way. Some quite minutely, others rather signficantly. Back in the day of crude chain tensioners by sliding the rear wheel in the swing arm and eyeballing alignment, things were often appreciably off and many bike crabbed a bit going forward.
    #4
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  5. lnewqban

    lnewqban Ninjetter

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    The front tire will steer right in order to become parallel with the rear tire.
    The chassis will point to the left a little and the bike will crab along the road.
    #5
  6. markk53

    markk53 jack of all trades...

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    Kinda like that ratty old pick up truck I was following yesterday...:D
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  7. dddd

    dddd Been here awhile

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    I think the front trail will turn the front right and bike will fall left due to counter steer. But if bike CG is moved right a bit to avoid falling, then the whole thing not turn but crab straight in line of wheels.
    #7
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  8. ohgood

    ohgood Just givver tha berries !!!

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    depends

    are you riding a wheelie ?
    are you riding the bike and trying to go straight?
    is the bike just ghost riding through a parking lot ?
    what's really fun is a twisty road. all your inputs give fucked up responses from the bike.

    best thing is to align it and enjoy.
    #8
  9. MrPulldown

    MrPulldown Long timer

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    Rear wheel steering.

    I dealt with this issue on my bike as the stock rear wheel had a cush drive. This pushed the centerline of the rim to the right of centerline of the swingarm. When mounting the rear wheel I would center the tire in the swingarm and actually have the wheel point to the left of center. I can't remember exactly anymore but I think it made the bike want to steer right. But it felt funny.

    I used a long 2x4 to figure out that my rear wheel was out of alignment and that the rim was not dished properly. Next I purchased the motion pro chain alignment tool. And it too confirmed and agreed with the 2x4. Now when ever I mount a rear wheel on a new or someone elses bike I pull out the chain alignment tool and check. Though chain alignment is not necessarily the same as wheel alignment it generally is.
    [​IMG]
    #9
  10. Yossarian™

    Yossarian™ Deputy Cultural Attaché

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    My theory has a data point in its favor. I aligned the rear wheel (using string method, dial caliper, and chain alignment tool all independently.) Bike now tracks straight with hands off bars.

    For the record, I only turned in the right hand chain adjuster 5 flats of the nut (5/6 of a complete turn) and that made the difference. Small amounts, but big differences.
    #10
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  11. DonM

    DonM Do-dah Do-dah

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    Good info!
    #11