I've read articles explaining "Camber thrust" theory but never seen any real world evidence of the effects of camber on a bike in a similar way that Bill Milliken did with his MX1 "Camber Car". Often wondered how to do that but couldn't think of an easy way until the 2WS Demo Bike construction was almost done. Replacing the 2WS Demo Bike forks with 30 degree cambered forks, but with only one wheel steering, was fairly easy.
The cambered tire contact patches had to go in precisely the same place relative to the steering axis and with identical ride height. The constant radius (26mm) of the Maxxis Hookworm tread profile was very helpful with getting the geometry right in the jig and for maintaining contact patch symmetry.
So why bother? Every single explanation I've read (Or watched on YouTube) was analogous hot air, markerboards, cone shaped objects, inappropriate tires, etc... NO tests with camber on bike tires. The science of single track vehicle dynamics shouldn't depend on tenets of faith and devotion.
A 3D bike tire surface interacting with a stationary 2D road surface does . . . what? Bike tire diameter differential at the contact patch is fixed for any given tire, yet it will track with no otherwise different input over an infinite variety of corner radii and lean angles. And if it rolls straight because of equal diameter on either side of the contact patch, it shouldn't go straight gracefully when bike tires are cambered.
Not all single track vehicles have tires yet steer and handle the same - single track vehicles have been ridden with large round sawblades and ice skate blades - NO camber thrust there. The most basic single track vehicle is a simple disc with a sharp edge - roll it across a hard surface and watch roll along gracefully until it turns gracefully in decreasing circles as it slows until, fully depleted of grace, it falls down - NO camber thrust involved, is there?
Yes, it really messes with your head at first when you look down and see the front wheel in action - that must do something different, right? What is different: Tire scrub (Which was expected) and lateral displacement on bump (Not expected but easily figured out). Rolling resistance increased even more with right turns. Rolling resistance decreased a lot with left turns. As it rolls, the tire's leading surface moves to the left before it makes contact: Step shaped bumps would move each end of the bike over to the right. Wave shaped bumps would move each end of the bike in a right/left motion.
Otherwise, completely normal. The steering and handling was exactly the same. NO tendency to veer, dart, shimmy, weave, careen, squirm, yaw, crab, etc... Braking either/both wheels and acceleration was normal. It tracked effortlessly and predictably, turning either direction or straight ahead.
Ergo: NO camber thrust.
While this is obviously not an SAE level technical publication or doctorate level dissertation, the methods and results are clearly reproducible. As always, it is very satisfying to roll something finished out of the shop, test something unproven, and have an awful lot of fun doing it.
PS: Inquisitive of moto-heresy? Bike and associated components are for sale - email me if you're interested...
