I am building a frame with the following dimensions:
Wheelbase: 1350mm (53.15")
Ground Trail: 80mm (3.15")
Head angle between 55.8 and 56.2 degrees from horizontal (hard to measure accurately)
Front wheel diameter: 500mm (20")
The styling is somewhere between cruiser and MWB recumbent, inspired mostly by the offerings contained in "Street Machine Choppers" issue #5 (OZ mag). Also, I am aiming for 30 cruising, 45kph top speed (max 28mph). The 20" front wheel has embedded electro-magnetic braking (OK AJ, a "frock" FH205), and the rear wheel is a 26" with 8" diskbrake. It is anticipated that there will be 35/65 weight distribution. The frame is >50% complete with the major, outstanding items being the front forks and headtube/backbone triangulation.
So far, so good.
However, I was reading an old article from "Physics Today April 1970" written by David EH Jones, where he was experimenting with the effects of trail (amongst other things). One of the conclusions reached was that an excessive amount of trail, although extremely stable, became difficult to steer. No absolute measurement was given though, only 0.2 of wheel diameter, therefore 20" x 0.2 = 4" (100mm).
A website dedicated to recumbent design http://bikesmithdesign.com/design/12steps.html
however states that only 6 to 12mm (1/4" to 1/2") should be used!
A third reference is "Motorcycle Handling Chassis Design Manual" by Tony Foale, where between 50 and 100mm is recommended. Note these are heavier and faster machines though.
The result of obviously too much reading is a state of confusion! I'm now thinking that I should reduce my trail to 40mm (thereby increasing the wheelbase to 1390mm). Changing the head angle would be major rework given I've already "goosenecked" it.
So the question is, what trail do you use and/or recommend, and why? For completeness and understanding, you probably would include wheelbase, head angle, front wheel diameter and weight distribution. Road manners and "feel" although subjective are welcome.
Cheers in advance,