Tuesday, March 08, 2011

Trike Steering Knuckles



Time to set up the front end. Keep in mind that this is the first time I've undertaken this, and I'm no pro. If you know a better way of doing this (short of learning a real cad/cam program), I'd love your input. I propped up the trike frame with a box and set the front tires in place. Shooting for about 1.5" of trail, I took a few pictures to refer to for alignment, and started fabricating the steering knuckles.

I started by cutting some tapered pieces to fit the tapered square of the "bottom brackets" that I'm using as king pins. these came from some 1.25" square tube scraps. I like working with this stuff because it's easy to cut and weld, and it's pretty strong.
Then I clamped the pieces onto the bottom bracket spindle (leaving room at the end to draw them up with the capture bolt, and welded up the joints.
With these parts completed, I used more square tube scraps and a few clamps to adjust the position of the pieces relative to each other in order to get the right angles for my steering and welded it all together. The idea here is to add everything that needs to be added, like brake mounts, and steering arms, then trim away everything extra. Crude but, hopefully, effective.
After drilling axle holes, I installed the wheels and built mounts for the disc brake calipers. Following a test fit on the trike, I added stud for the steering tie rod to connect to, on the wheel side of the trailing arm. To establish a wild stab at ackerman steering, I used a spreadsheet that I downloaded (in the links on the right of this page). The only real guess work was where in blazes to start my measurements from. In theory, one would measure everything from the king pin, but that goes out the window when the king pin is tilted aft and in to obtain center-point (or near to it) steering.

Again, I spent the better part of an afternoon looking at other trikes on the internet. I determined that some of the most respected trikes must be using the point where the tire meets the road as their reference point, so that's what I did. My steering arms will connect just inside and behind the brake rotors. Then I cut off all the extra material on my steering knuckles to lighten them up a little.

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