Maybe it's just me. I'm not the greatest when it comes down to adjusting and maintaining the depth that the roller digs into the tire.
I've gone thru a stack of tires to prove my inability to maintain tire/roller engagement.
To top it off, I just cannot comprehend how a quick-release shaft can exert the mechanical advantage of enough clamping force between the engine channel and the aluminum rear supports. This is one engagement: Staton-Inc motorized bicycles bike kits and gear drive kits.
Why do the vendors use this concept of engagement?
Well it doesn't work for me reliably. I lose engagement sometimes on a hill or at 20mph. By the time I pull over a a safe work area, the tire has sustained damage. Powdered rubber is on the chainstays and seatstays.
Presently I'm also working on my twin 460 engine/friction drive project. These engines would probably chew up tires even more quickly. I needed solutions for both my commuter "The Dragon Lady" and my 460 project.
"The Dragon Lady" uses twin Staton friction drive assemblies and 1.5" rollers. The 460 project will use BMP engine channel housings, Staton 1.375" front roller/1.25" rear roller. Staton uses aluminum engine channels; BMP uses steel engine channels.
Starting with the BMP kit, I left the left rear engagement in place. Instead of the quick-release axle shaft, I used a 5mm X 20mm bolt, thick engagement washer, lock washer and wing nut. This clamps the left support to the engine housing, but it is not the main engagement. The wing nut is set loose until the right-side engagement is locked in place.
On the right side is the solution which provides bulletproof engagement and precise adjustment. I used the lower mounting bracket from Staton's single-engagement support and discarded the rest: Motorized Bicycles Detail Page
Next I screwed on 14" of 3/8" allthread onto the lower mounting bracket. Then I bolted an L-bracket onto the engine channel. The bracket has a 1/2" hole that the allthread passes through. A flat washer lock washer and 5/16" nut screws on the allthread directly below the L-bracket hole. Another washer and nut screws above the bracket hole.
Exact tire engagement happens by pushing down on the engine channel. Tightening the top nut on the allthread holds the channel in place, then the lower nut is tightened to lock everything into place. The left-side wing nut is then tightened to clamp the support in place.
When the engine needs to be lifted off the tire, simply loosen left-side wingnut and right-side adjusting nut. Raise engine housing off the tire, then tighten both nuts in place.
Friction roller engagement is permanent and will NEVER slip. As the tire wears, adjustment is easily made to both supports.
TIP#1: For testing, I just used the bulletproof engagement on the right side. For symmetrical reasons, it could be installed on both sides.
TIP#2: To make it look better, I slipped nine inches of 3/16" aluminum tubing over the allthread.
TIP#3: The engagement rod could be made of polished stainless steel, but I'm cheap.
I'll ask Hawaii Ed to take and post pictures here of my "mousetrap".
FWIW, I had to devise this because the Dominator pipe on the 460 engine interfered with the dual-engagement assembly. However, this "mousetrap" will work on any friction drive except the Dimension Edge kit.