Forum Discussion

Harvard's avatar
Harvard
Explorer
Jul 09, 2013

Frame Angle vs Front End Caster

It is my belief that raising the rear end by 1 degree (frame angle) will reduce the front end caster by 1 degree.

The problem is interperting this Ford Frame Angle link.

If we have a "specified caster" of +4.5 degrees, a "frame angle" of 0.0 degrees and we measure a caster of +4.5 degrees then we are on spec.

Now, if we were to raise the rear end to give us a "frame angle" of +1.0 degrees would we not have a "measured caster" of +3.5 degrees?

So, the logic used in this link tells us "correctly" to get back to the "specified caster" we add the "frame angle" to the "measured caster" and we get back to specification. BUT, then it goes on to say the "changed required = NONE" :h

What the heck? We started out with +4.5 degrees of caster, raised the rear end, and ended up with +3.5 degrees and that is "good to go"??? Where have I gone wrong?
  • K_Charles's avatar
    K_Charles
    Explorer
    Jul 09, 2013
    Your link says

    Caster Specification: 4.5º
    Measured caster angle: 3.5º (out of spec?)
    Frame angle: 1.0º (up in rear)
    Corrected caster: 4.5º (3.5 + 1.0)
    Change required: NONE


    spec should be 4.5 but measured "out of spec" at 3.5
    If you correct it with the frame angle then there is no change required.
    In that example thay took the frame angle into account when they set the caster.
  • BruceMc's avatar
    BruceMc
    Explorer III
    Jul 09, 2013
    I considered frame angle when I took mine in to be aligned. Lots of folks here say to load the MH as you would for normal travel - I took the opposite approach, and made sure it was as empty in the rear as possible, and the air bags and rear tires were inflated to their maximums. Then once it was aligned with that frame angle, any loading would add positive camber.
    For some reason, Four Winds decided the far aft end and across the back was the best place for a water tank....
  • j-d's avatar
    j-d
    Explorer II
    Jul 09, 2013
    So maybe the "raise the rear to shift weight to the front and improve handling" really has more to do with increasing the CASTER than shifting the WEIGHT...

    What is the reference benchmark for measuring Caster? I guess I'm simple, but it seems to me that Caster is a number of degrees from Vertical, Plumb if you prefer.
  • Harvard's avatar
    Harvard
    Explorer
    Jul 10, 2013
    j-d wrote:
    So maybe the "raise the rear to shift weight to the front and improve handling" really has more to do with increasing the CASTER than shifting the WEIGHT...

    What is the reference benchmark for measuring Caster? I guess I'm simple, but it seems to me that Caster is a number of degrees from Vertical, Plumb if you prefer.


    Caster is the number of degrees between PLUMB/VERTICAL (the wheel axel to the contact patch) and a line drawn through the center of the upper ball joint, the wheel axel and lower ball joint. So when you lift the rear end you are rotating the line through the upper and lower ball joint counter clock wise (looking at it on the drivers side) which REDUCES the +caster. And, that we do not want to do. IMO


    ON EDIT:


    Here is a picture, the red horizontal line represents the "Frame Angle" of 0.0 degrees. The almost vertical red line represents the +caster angle from the vertical line, the "plumb" line.

    If we raise the rear end we have a + "frame angle" shown by the near horizontal green line. The +caster angle has been reduced as shown by the nearly vertical green line.

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