Trail is the horizontal distance between the steering axis and the contact patch of the front tyre.
Fork offset, or fork rake, is the distance between the front axle and the steering axis – the imaginary line running straight through the midpoint of the steerer tube.
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Calculators
http://yojimg.net/bike/web_tools/trailcalc.php
Head angle:
Fork offset:
Bead seat diameter:
Tire width:
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Jones LWB
Head angle: 67.5°
Fork offset: 76mm
Bead seat diameter: 622 (700C)
Tire width: 71.12
Trail: 78
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Soma Groove
Head angle: 71.5
Fork offset:
Bead seat diameter: 559
Tire width: 53.34
Trail:
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Rawland Ravn
Head angle: 73
Fork offset: 69
Bead seat diameter: 559
Tire width: 58.42
Trail: 32 (Rawland says 30)
Higher trail means greater stability and lazier, slower steering. Shorter offset or a slacker head angle results in more trail (slower steering); longer offset or a steeper head angle reduces trail, quickening the steering response. Finally, into the mix comes wheel size. Bigger wheels imply more trail, as the axle is higher and so the gap between the steering axis and contact patch increases proportionally. However, 29ers use steeper head angles and increased offset to compensate for this.
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Jan Heine and the iBobbers, advocating trail around 45 mm for general-purpose riding, especially if a handlebar bag is to be used (and I plan to use one sometimes), and especially with 650b wheels (which I'm not planning to use at this point).
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However, it isn't a matter of either Americans or Oliver being right.
The thing few people understand is that two factors play a role: More
trail increases stability, especially at high speeds (to the point
where it is difficult to change line in mid-turn), yet it also
increases wheel flop (which persists into moderate speeds). So you
have two counteracting phenomena, which is why so different bikes can
handle similarly.
When you add a front bag, you increase wheel flop, and you really
need a low-trail geometry.
https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry
GOOD DESCRIPTION: https://www.cyclingabout.com/understanding-bicycle-frame-geometry/