Difference between revisions of "Head Angle Change With Suspension Travel"

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According to some modeling that I have done, a good rule of thumb is that head angle will change on a hard tail mountain bike approximately 0.05° per mm of travel.
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Wheelbase is the overriding factor for how the geometry changes. Different wheelbase bikes will change at different rates.
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==Formulas==
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Here are the equations:
  
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Bottom bracket height will change approximately 0.372mm with each mm of suspension travel. These again are very rough rules of thumb but make designing frames fairly quick.
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*A12 = Initial Head Angle
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*B12 = Fork Offset
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*C12 = Sagged fork length
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*D12 = Initial Wheelbase
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*E12 = Initail BB Height
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*F12 = Chainstay Length
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*G12 = Wheel Diameter
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*H12 = Fork Compression or extention from sagged
  
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This is good to understand when designing long travel hard tails.
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These formulas are not designed to work with 2 different wheel sizes and do not account for tire deformation or chassis/fork flex.
  
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Otherwise, they are perfect.
  
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==Head Angle Change==
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[[Image:Head-angle-change-formula.gif]]
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or in a more round about way:<br>
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[[Image:Head-angle-change.gif]]
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[[Image:Head-Angle-Change-with-Trav.gif]]
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==Bottom Bracket Height Change==
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[[Image:Bb-height-change-formula.gif]]<br>
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or in a more round about way:<br>
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[[Image:Bb-height-change.gif]]
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[[Image:Bb-Change-with-Trav.gif]]
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==Mechanical Trail Change==
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[[Image:Mechanical-trail-change.gif]]
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[[Image:Mt-change-with-travel.gif]]
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==Wheelbase Change==
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[[Image:Wheelbase-change-with-trave.gif]]
 
[[category:Bicycle]]
 
[[category:Bicycle]]
 
[[category:Frame Building]]
 
[[category:Frame Building]]
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[[Category:Suspension (Bicycle)]]

Latest revision as of 15:51, 19 May 2008

Wheelbase is the overriding factor for how the geometry changes. Different wheelbase bikes will change at different rates.

Formulas

Here are the equations:

  • A12 = Initial Head Angle
  • B12 = Fork Offset
  • C12 = Sagged fork length
  • D12 = Initial Wheelbase
  • E12 = Initail BB Height
  • F12 = Chainstay Length
  • G12 = Wheel Diameter
  • H12 = Fork Compression or extention from sagged

These formulas are not designed to work with 2 different wheel sizes and do not account for tire deformation or chassis/fork flex.

Otherwise, they are perfect.

Head Angle Change

Head-angle-change-formula.gif

or in a more round about way:
Head-angle-change.gif


Head-Angle-Change-with-Trav.gif

Bottom Bracket Height Change

Bb-height-change-formula.gif

or in a more round about way:
Bb-height-change.gif


Bb-Change-with-Trav.gif

Mechanical Trail Change

Mechanical-trail-change.gif


Mt-change-with-travel.gif

Wheelbase Change

Wheelbase-change-with-trave.gif

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