Clamp on Idler Mounts are great for letting you mount idlers where you really want them, and for tensioning timing chains on tandems. If you have a bike/trike where the chainline has just never been right, or you are changing to a hub gear drivetrain, or need to simply and reliably tension a tandem timing chain, or you just want to try something different, these are the thing for you.
We make a wide range of clamp sizes so we can be sure they will fit perfectly and clamp super strongly. Each of these clamps comes with a vertical slider block that can be adjusted to achieve the perfect fit. The slider block has five 8mm threaded holes for mounting idlers (or racks, or brackets, or whatever else you can dream up).
If you've ever wished your idler was a little bit higher, or a little bit lower, or over here instead of over there, you will appreciate the drivetrain options these mounts bring. For timing chains on tandems, these are a super easy, super sturdy way to get the chain tensioned and keep it that way.
1. Why so many sizes?
Because there are so many different sizes of tubes out there to attach to. It's important the clamp be exactly the right size to ensure the amount of grip needed. We even machine them with the paint thickness taken into account.
2. How do I know which one to get?
First you need to measure the size of the tube you'd like to clamp to. If you don't have a good measuring tool, like a set of calipers, you can download and print our handy dandy Tubing Measurement Tool and find out.
3. Where can I put them?
These clamps are designed to go on any tube of the proper size, as long as the tube is straight or nearly straight where the clamp is. In order to get the clamping strength required, the fit needs to be good. If the tube being clamped to is curving, it's not really possible to make a clamp that will fit accurately enough. It would require some even fancier machining, and it would have to be custom made for each curve shape. So, you need to stick to straight, round tubes. Fortunately, that includes most bikes. The clamps are 1/2 inch (12.7mm) wide, so it's easy to work around obstacles like seat rails and cable stops.
4. Where are the mounting holes relative to the tube?
For the straightest side to side chainline in the low gears, it's necessary on most bikes and trikes to allow the power side idler to go as close inboard as possible. In order to provide enough thread engagement with the idler bolt, the mounting holes are off the tube centerline. The hole closest to the centerline varies with the size, but it's usually approximately just inside the tube profile. The mounts can be flipped up or down, so the idler centerline can be above or below the tube centerline. For two of the most popular tube sizes, we do make an adjustable mount where the idler bolt can go on centerline as well as quite a ways above or below the tube. In order to do this, the closest the idler can come to the tube is pushed out about 3/8 inch (10mm). This is usually more than is desirable on a deraileur chainline, but it can work. This mount is primarily designed for geared hub and tandem timing chain tensioning.
- Mounts are machined from 6061-T6 aluminum and black anodized. Clamping bolts are m5 stainless steel. Idler mounting holes are M8x1.25, threaded 0.6 inches (15mm) deep.
- To most easily experiment with idler positions, put an idler on it's mounting bolt. Holding the bolt in one hand, push the chain up or down with the idler and move the idler around to different places and see the effect on the chainline. When you have identified a promising spot, attach the clamp on idler mount there.
- When tightening the clamping bolts, be sure to tighten them evenly and alternately once they start to take up tension.
- Clamps are made in a variety of sizes for almost every round tube used on bikes and trikes. If you need a size we don't make, let us know. It may be possible to shim it, or perhaps it's time we made a new size.