Hello. I don't know much about riding but hoping to connect with fixed gear enthusiasts for advice and potential help on a short film I'm working on.
Robert Ruiz de Castilla
Steering stabilizers as used on Dutchbikes are really for parking, not steering but the concept is good. Look at how the Dutch do it then rig something up, probably you want two springs and you'll want to spend time balancing them.
You want to search for the flattest possible pavement. Side to side flat, as in a road with no crown. Tricolor is spot on w/ suggesting downhill. And flames.
Headset should be left free so the caster built into the frame can accommodate the little bumps and ripples that are going to be there in the best pavement you can find. If I'm wrong about that this is one of the easiest things you'll fix as you go. Pair of headwrenches, ten degrees of adjustment from loose to locked. Try a little loose and a little stiff before you try locked.
I'm thinking this could be a good application for a lowtrail bike. Lowtrail doesn't much lean around corners, you turn the 'bars like it was a steering wheel to make the things turn. They tend to just go straight unless you haul on the 'bars. Easiest way to get a lowtrail bike is to graft a long rake fork into an old racing bike with a steep head angle. Stupidly steep heads were common from late 70s into the early 80s.
You'll want heavy wheels. Heavy but good. Straight, round, centred. Could be worthwhile to add weight to the valvestem and get them roughly balanced. Something like Schwinn steel rims and those monstrously overbuilt Schwalbe tank tires. Lowest air pressure that gives the tires their correct shape. You want a straight frame and fork too.
The swing weight of the handlebars will try to steer the bike. Use a short stem and the smallest lightest handlebar that looks right in your viewfinder. No brake cables messing up. Pedals swinging around will steer the bike too, so light pedals or even minimalist pedals like Crank Brothers or Speedplay. Or just the pedal spindle from a broken pedal.
We used to do this as kids, having contests for whose bike would go the furthest. The launch is important. Luck and chance circumstances make a big difference. Sometimes the bikes would go 200 yards and same bike next trip would just fall over. 200 yards is a good long tracking shot. And it wouldn't hurt to have some smart 10 and 12 year old kids around who enjoy playing with bikes.
Just thought I'd add our launches were always by hand and then the downhill took over. Much shallower downslope past the first streetcorner. Faster launches just made the bikes fly out of control quicker.