Steering Trail Calculators
Online tools to help you design your recumbent bicycle steering geometry
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By Warren Beauchamp
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High
Speed trail Actual Trail
Notes Disclaimer What's trail, and why do I need it?
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Optimal
High Speed Trail Calculator
This calculator finds the
"optimal high speed trail" for a specific design. Note that in
many cases this may be more trail than is practical for general use. A trail value
greater than 5 inches will generate excessive fork flop. The trail calculator
should be used as a design aid to give you a good idea of how changes in your
bikes geometry effect the need for additional trail. This equation is still
being developed. Calculator updated 9/11/06 to provide more realistic trail values.
Personally I feel that the numbers generated with the "Jet Fighter" K5 value are the best for me. YMMV.
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Actual Trail
Calculator (English or Metric)
This tool allows you to calculate the actual trail of a bike, given the wheel size, the fork's offset, and the head tube angle.
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Notes:
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cg = Center of gravity, generally your belly-button is at the bike's cg.
Kx = radius of gyration for a specific seat back angle.
- 35 @ 90°, .345 @ 80°, .335 @ 70°, .32 @
60°, .30 @ 50°, .275 @ 40°, .24 @ 30°, .20 @ 20°The equation with which this page calculates is:
T = K5 B/M (1/Kx2 + 1/h2)
K5 = steering feel, the calculator here uses values of 0.5, 1.0, 1.2, and 1.5
B = horizontal distance of the cg from rear axle
M = mass
Kx = radius of gyration
h = cg height fom ground
2 means squared.
All units in meters and kg.
Bikes that are ridden by more than one person should be designed for a 160 pound rider.
The trail equation is only one design value and can seldom be used alone.
Bill Patterson notes that he does recommend K5 values under 1.2, but that for high performance
vehicles that do not need to be ridden by the general public, it can go lower (as it does in the
"Normal Fast" and "Jet Fighter" settings on this calculator).
Thanks to all the work that Bill Patterson put into creating the equation behind
this page. This equation is just a small part of a book on bike handling that is available
for:
$48 plus $2.50 s.h in North America. Shipping is
$6.50 elsewhere.
From:
Bill Patterson
3058 Lancaster
Santa Maria CA 93455
Also see the following links for more information on Bill
Patterson and his Single Track Vehicle design course at Cal Poly.
Single Track Vehicle Design and
1998 class
photos
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What's trail, and why do I need it?
Trail is the distance between the bottom end
of a line drawn through your headtube to the ground, and the point where your tire
contacts the ground. In general to make the bike handle well, it's a good idea to have
some positive trail. This means the line through the head tube ends up in front of your
tire patch. Too much trail and you get excessive fork flop, not enough, and the bike is
too twitchy. |
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Note that trail is not the only thing that effects a bike's
handling. The head tube angle, wheelbase and well, pretty much every other aspect of the
bike effects how it handles. Your job is to make a series of compromises to get the bike
that does what you want it to. These tools are designed to help you do that.
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Disclaimers:
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- The equations used in the
"optimal high speed trail" calculator are still being refined.
- By using these tools, you agree to
release all parties involved in the creation, translation, and
publishing of this information of any responsibility for anything bad that may happen.
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