Drivetrain Tensioners and Belt Drives

Civia Tensioner

Any bike that doesn’t have a derailleur needs a way to tension the chain or belt. The various methods include: horizontal dropouts or rear-facing track-style fork-ends, with or without tensioners; sliding vertical dropouts; spring-loaded derailleur-type tensioners; eccentric bottom brackets; and, eccentric hubs.

Bikes with internal gear hubs and/or hub brakes also require some way to keep the hub from rotating within the dropouts. In most cases, this is accomplished with what is called an anti-rotation washer. An anti-rotation washer is a heavy washer with a slotted opening that matches the flat faces of the axle, and a tab that fits within the dropout opening to prevent rotation. In other cases, the hub is held in place with a reaction arm attached to the frame.

Belt driven bikes are somewhat sensitive to the type of dropout and tensioning device used. On a belt bike, as little as a 1/2 turn on an adjuster can be the difference between being in or out of the recommended belt tension range. And as with belts in other applications, precise pulley alignment is required to keep a belt running on center.

My favorite set-up for belt bikes is the sliding vertical dropout. With this design, the axle stays locked within the vertical dropout slot while the entire dropout itself slides fore-and-aft within the frame. Besides providing the ability to make fine adjustments, once the dropouts are locked in position, no adjustments are required, even after removing the wheel for flat repairs or other maintenance. I’d venture that most belt drive bikes will feature some variant of this design in the future.

My Civia Bryant uses horizontal, rear-facing, track-style fork-ends combined with a pair of tensioners. The right hand tensioner has an anti-rotation plate attached (see the black plate in the photo above). Bryants prior to this year’s model were spec’d with a single tensioner on the drive side and an anti-rotation washer on the non-drive side. This new set-up is cleaner and much easier to use. If you have an older Bryant with the single tensioner and an a/r washer, these new tensioners can be purchased from Quality Bicycle Parts through your local dealer (QBP part number CH5400, retail price $30 pr).

14 Responses to “Drivetrain Tensioners and Belt Drives”

  • Wei says:

    Hi Alan,
    Thanks for pointing the design change in the Bryant out. I am going to order one of those asap. Up till today, I had often wished there was a tensioner on the left hand side as well, just to make my life a bit easier.

  • joe says:

    My next belt bike I’ll pay more attention to the tensioning mechanism. My Raleigh Alley Way uses an eccentric BB. The problem is 2 fold. First I’ve never found a pin tool that matches the size and spacing of the eccentrics adjustment holes. Secondly the cranks and external BB cups make access very awkward. I usually end up having to squeeze in there with a set of needle nose pliers. Not the ideal method for tweaking the belt tension.

  • Don says:

    One often hears about the importance of proper alignment and tension with IGHs, but I never realized just how minute the adjustment can be. Once set, will it stay put so long as the wheel stays put (no flats)? Is there an initial “stretch” period for the belt? Given the cost, I think this would drive me nuts. Somehow tuning a derailleur seems less annoying because the stakes are smaller.

  • Wei says:

    @joe: before the details on the Civia Bryant came out I had hoped it would have a eccentric BB, as I found it a simple and easy way to tension the chain on my SS. However, after hearing your story, the ease of tensioning obviously depends a lot on the design of the system. That is a shame tensioning sounds like a hassle on such a great looking bike.

    @don: in the 12 months of riding my belt drive Bryant with a 8spd Alfine IGH, I’ve probably adjusted the belt tension 2-3 times (mostly after I’ve taken the wheel off for some reason or another). So I can’t comment on whether the belt has stetched. I found myself adjusting tension a few times after the first few rides, but I put that down to all the components “settling in”. From the literature it would seem that the carbon fibres in the belt aren’t supposed to stretch much if at all. Despite the cost of the platform, the lack of chain maintenence, non-greasy trousers, and quietness and easy of cleaning have won me over on the belt drive. Just wish my Brompton was a belt drive as well, somehow the current design will never accommodate that.

  • Alan says:


    Carbon belts actually have zero stretch. Once set, there’s no need to make any adjustments until the belt needs replacing. Gates is claiming twice the life of a chain under normal conditions.

    With a set-up like on my Bryant shown above, if you have a need to remove the wheel, the trick is to loosen the tensioners a specific amount (say one full turn), then tighten them the same amount when reinstalling the wheel. This is a simple procedure that has worked well for me (I used to do this same thing on my motorcycle many moons ago).

    On bikes with sliding vertical dropouts, the wheel drops straight down out of the dropouts and goes back in exactly the same position, so the tensioners aren’t touched when the wheel is removed. The only time the tensioners need to be adjusted is after a belt replacement.


  • Rider says:

    Eccentric bottom bracket is what I have, and I dig it.

    No problems whatsover, and the wheels fit in vertical dropouts. Fenders always fit, never rub, etc., because the wheel doesn’t change location.

    Easier to keep the chainline good and straight, too.

  • Don says:

    @Wei and Alan,

    Thanks. Sounds like it is what it is, and someone will eventually win the dropout war of attrition. The pivot solution on the new Spot Acme looks pretty elegant and seems to address some of the concerns.

  • Joe says:

    @Don, I only messed with my belt tension because the cinch bolts came loose on the BB (and I just can’t leave anything alone). I haven’t touched it since then.

  • Don says:

    @Joe, that’s good to know. Those Alley Ways are darn elegant, as is any EBB that doesn’t squeak. I also can’t leave anything alone, especially if it’s working fine, but then I’m a noob trying to teach myself over time. When people talk about foolproof, I am that fool. If mistakes are the best teachers, I should be a master by now. But it’s like a golf swing: every now and then I get it right in spite of myself, and I’m hooked.

  • Andy says:

    I recently examined the rear dropouts on both the Civia Bryant and the Spot Acme. The Spot dropouts are far superior: Much, much easier to get the wheel in and out, and no belt-retensioning required after changing a tire.

    As a fender user, though, an EBB does sound appealing, for the reasons given above. Does anyone know which EBBs are easy to work on, and which ones are difficult?

  • Alan says:


    There is one trade-off to be aware of (there’s always a trade-off it seems); bikes with sliding dropouts typically have the disc caliper mounted outboard of the seat stay which makes rack mounting a challenge. With a track end set-up like on the Bryant, the disc caliper is inside the rear triangle, which leaves the area open for racks, fender struts, etc. There are special racks made to clear external calipers, but the choices are limited and super tough racks like those from Tubus are not an option.


    PS – I’m hoping to have a Spot Acme for review later this summer. It’ll be interesting to compare it head-to-head with the Civia.

  • Andy says:

    Good points, Alan. I was worried about that on the Spot Acme, but it turns out that the rear caliper is mounted far enough inboard that doesn’t interfere with rear rack mounting. That was a pleasant surprise!

  • Alan says:


    That’s good to know. Thanks for the info!

  • joe says:

    The Spot Acme is at the top of my wish list for next spring. Unless something new hits the market next fall. I’m hoping that an increase in the # of belt drive bikes will reduce the price differential.

    Riding a belt drive bike is like going up a size in underwear, it’s really hard to go back :)

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