I have a mate who has gone "Darkside" on his Suzuki Boulevard 109 Cruiser. Simple experience has shown that 26 psi works best. Higher than 26 and the tyre wall does not flex enough, and the flat contact area profile tries to lift the bike as it turns, which strongly resists the turn. Less than 26psi and side wall flex is excessive and the tyre looses too much shape across the flat contact patch. I have followed him closely through some twisties to watch his rear tyre, and could see that in the turns the side wall would flex, and about 75% of the "flat" contact patch of the tyre remained in contact with the road.
Cost caving was huge, as the Boulevard rear is over $600, and a Commodore size radial cost him $120.
