Results 1 to 10 of 10
  1. #1
    Bite Me.
    Reputation: cutthroat's Avatar
    Join Date
    Mar 2004
    Posts
    4,531

    AC Height Effect on HT Angle

    Anybody recall the ratio between AC height and HT angle? If memory serves (getting less likely every day) I thought it was basically 1" of increase or decrease in AC height translates to about 1 degree increase or decrease of HT angle. Is this right? Thnx
    When I see an adult on a bicycle, I do not despair for the future of the human race. ~H.G. Wells

  2. #2
    I dig trails!
    Reputation: Mr.P's Avatar
    Join Date
    Feb 2005
    Posts
    5,533
    Quote Originally Posted by cutthroat
    Anybody recall the ratio between AC height and HT angle? If memory serves (getting less likely every day) I thought it was basically 1" of increase or decrease in AC height translates to about 1 degree increase or decrease of HT angle. Is this right? Thnx
    That is the ratio. It is a rough equation, of course (so plus or minus a degree ).

    Also, more AC also affects all your other geo and angles too. SA & BB height being key.

    P

  3. #3
    mtbr member
    Reputation:
    Join Date
    Oct 2004
    Posts
    6,664
    Quote Originally Posted by cutthroat
    Anybody recall the ratio between AC height and HT angle? If memory serves (getting less likely every day) I thought it was basically 1" of increase or decrease in AC height translates to about 1 degree increase or decrease of HT angle. Is this right? Thnx
    That's a very close rule of thumb.
    Whining is not a strategy.

  4. #4
    Bite Me.
    Reputation: cutthroat's Avatar
    Join Date
    Mar 2004
    Posts
    4,531
    Ok - thanks for the quick replies. Guess my memory isn't totally shot yet. Any idea on the effect on the BB height?
    When I see an adult on a bicycle, I do not despair for the future of the human race. ~H.G. Wells

  5. #5
    No, that's not phonetic
    Reputation: tscheezy's Avatar
    Join Date
    Dec 2003
    Posts
    14,313
    Dusting off my trigonometry, it looks like a 1" change in A-C will produce a 1.27 deg HA change on a bike with a 45" wheelbase, 1.3 deg HA change on a 44" WB bike, and 1.33 deg HA change on a 43" WB bike. Someone check me. I suck at math.
    My video techniques can be found in this thread.

  6. #6
    ~~~~~~~~
    Reputation: airwreck's Avatar
    Join Date
    Dec 2003
    Posts
    5,873
    tscheezy, my actual measurements agree with your math.

  7. #7
    Bite Me.
    Reputation: cutthroat's Avatar
    Join Date
    Mar 2004
    Posts
    4,531
    Quote Originally Posted by tscheezy
    Someone check me. I suck at math.
    Sorry - they made me repeat Algebra II and wouldn't even let me in Trig. If you increase the AC length, don't you also increase the WB? So then what does that do to the HA measurements????
    Too confusing to worry about - the point of the inquiry was just to see what effect the travel adjustment on my fork has on the overall geometry of the Spot. Assuming your #s are correct Tscheezy, it looks like every 15mm of adjustment equals about a .75 degree change - so running the fork at 115mm results in a 69.75 degree front end and conversely, opening it up to 145mm gives you a 68.25 HA. The change in ride feel confirms the change in HA - very Burner-like on the low side and more RFX/6 Pack like on the long end. Best of both worlds - I think I'll keep it.
    When I see an adult on a bicycle, I do not despair for the future of the human race. ~H.G. Wells

  8. #8
    Just another FOC'er
    Reputation: .Danno.'s Avatar
    Join Date
    Jun 2005
    Posts
    2,222

    Geek on

    For a 44" WB bike raising the rear 1" would steepen the HA 1.3 -- (1/44) * (180/PI)

    For the front you've got to factor in that the fork isn't vertical so you get less change per inch of increased fork A-C. That fudge factor would be 0.92 inch/inch for a 67 degree HA -- sin(67)

    So for the front you'd end up with 1.3 * 0.92 or 1.2 degrees/inch

  9. #9
    mtbr member
    Reputation:
    Join Date
    Dec 2005
    Posts
    174
    Quote Originally Posted by .Danno.
    For a 44" WB bike raising the rear 1" would steepen the HA 1.3 -- (1/44) * (180/PI)

    For the front you've got to factor in that the fork isn't vertical so you get less change per inch of increased fork A-C. That fudge factor would be 0.92 inch/inch for a 67 degree HA -- sin(67)

    So for the front you'd end up with 1.3 * 0.92 or 1.2 degrees/inch
    Danno, is your (1/44) * (180/PI) the general formula? wat does PI stand for?? and also the units of measurement used

  10. #10
    No, that's not phonetic
    Reputation: tscheezy's Avatar
    Join Date
    Dec 2003
    Posts
    14,313
    Pi = 3.14... etc. Units are inches and degrees (angle).
    My video techniques can be found in this thread.

Members who have read this thread: 0

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

THE SITE

ABOUT MTBR

VISIT US AT

© Copyright 2019 VerticalScope Inc. All rights reserved.