Cruiser handlebar rotating because clamp not strong enough

Question

My new cruiser handlebars rotate no matter how much I tighten the clamp on my electric bike.

The bike is a Lectric XPremium: https://lectricebikes.com/products/xpremium-black

Here is the handlebar: https://www.westpointcycles.com/product/electra-cafe-cruiser-handlebar-159195-1.htm

Replaced my straight handlebars with a cruiser style because leaning forward was causing circulation problems in my shoulders. They're both 22.2 mm in diameter (measured with Mitutoyo calipers). I'm 5'10" tall (1.78 m).

I can get by if I don't lean too heavily on the handlebars, but since I'm on an electric bike, the higher speeds mean bigger bumps. Plus, the extension on the cruiser handlebar shape creates a lever arm that didn't exist with the original straight bars. Thus, the clamp isn't strong enough to keep it in place with this new and significant rotational force.

I had a bike technician look at it, and he suggested finding a shim. The only shims I could find are meant to adapt the between different handlebar diameters, like 22.2 mm to 25.4 mm, but not to the same size, i.e., 22.2 mm to 22.2 mm.

Other fixes I've tried for my posture problems before buying the cruiser handlebar was to raise the height of the original straight handlebar, lowering the seat,

What kind of product should I be looking for?

Answer 1

Try some combination of these and potentially all four:

• Very thoroughly lubricate the stem bolt threads and shoulders with grease, then torque them properly.
• Roughen up or remove the paint on the bar at the clamping surface.
• Clean the clamping interface and then put carbon prep (aka fiber grip, etc.) on it.
• Have a shop knurl the bar.

An assessment should be made whether the bar's outside diameter being a little too small or large is part of the problem or able to be improved upon. For too large you'd look for limited contact as the stem is being tightened (for example look for light gaps from the side at the center of the faceplate and 180 degrees away), and non-continuous marks in the paint where the stem contacts. For too small, you're looking for visible gaps at the opposite orientation from above (contact at the center of the faceplate and mast but not the sides), or for the faceplate being able to bottom out or almost bottom out (no gap/slit), or for evidence of only a limited contact area with the faceplate and stem in the wear pattern. If it's too small, a knurling tool can fix that by expanding the clamp diameter in addition to roughening it to make it more twist-resistant. If too large, start by taking off all the paint from the clamp area. Note that the game here isn't necessarily only looking for gross issues, it's figuring out what direction you would tune things if you had to, since bars that generate lots of leverage like this can need all the help they can get.

A shim is mostly not applicable unless one of the parts is way undersized or oversized to the point of being defective, for example if the bar is nominally 22.2 but comes in at 22.0. However, the catch is that taking this measurement from a bar is easy but from a stem is impractical or impossible. (Conceptually there are various ways of doing it, but they involve finicky measurements and/or fixturing, and threaten to rely too much on the parts having ideally formed geometry). That being the case, if you see any signs that the stem clamp is oversize, you can try shimming it with something like an aluminum can, which have a wall thickness of essentially 0.1mm (in the US at least). A wall thickness of 0.1mm results in an increased OD of 0.2mm, and it can be tricky improvising workable shim material that's much thinner. (Though you can buy all you want from industrial suppliers). What you don't want to do is force it if the shim results in things not fitting right, which can damage the stem/faceplate. Knurling it is the far superior option because then the fit can be dialed exactly as needed at the same time that the surface grip is optimized. Serious mechanics will solve this type of problem with knurling long before shimming.

Answer 2

The problem is that the diameter of your handlebars is too small for the headstock.

Your options are:

• get the correct sized handlebars
• get a headstock that fits your current bars
• you can buy shims, as you've found out
• you can make your own shims. I use pieces from tin cans

I'd ask the vendor why they sell bikes configured in such a dangerous configuration and why their techs can't amend it or offer useful advice.