11 December 2008

bikefix Exclusive Review: Soulcraft The Convert chain tensioner

Single speed mountain biking can be pretty intimidating. The thought of riding a bike, in the dirt, up and down (OK- just up) hills without the multiple gears to which we've become accustomed really doesn't make much sense and the uninitiated often wonder aloud about what they'll be able to ride, how their knees and backs will fare and what's so fun about it all. Given these reservations, it's no surprise that most single speeders' first singlies are conversions. Geared bikes are reborn with single rings and cogs and dérailleurs are replaced with tensioners for a low-cost, low-risk way to give this single speeding thing a go.

Of course, there are plenty of experienced single speeders who chose to run converted setups as well. Often, doing so is a way to keep a sweet (but rarely ridden) vintage (maybe even custom) hardtail in service. Sometimes, as was my case, people can't find a dedicated SS frame that does it for them. With these people in mind, Soulcraft make The Convert. The Convert is, in concept and execution, intended to be a cut above (still very good) tensioners from companies like Surly, DMR, and Performance, which typically use springs to maintain chain tension. Instead, The Convert's urethane roller sits at the end of a stationary arm, which is bolted into the dérailleur hanger. The thought here is that an unsprung tensioner will feel more like a dedicated single speed setup- no bouncing chain, less drivetrain drag created by excessive spring tension.

What makes The Convert clever, though, is its release mechanism. As you can see from the photos here, a stationary tensioner could make removing the rear wheel pretty tough to remove. What Souldcraft have done is installed a rod down the length of The Convert's body. The rod (to which the little black tit below the tensioner is attached) engages a collar which is held in place by the main bolt. If the wheel needs removing, the rod can be pulled, disengaging the tensioner body from the collar and allowing it to swing clear of the quick release, chain and cog. No muss, no fuss. The location of the arm when locked is kept and no extra tools are needed for wheel removal. The Convert can be set up to push up on the chain (for a lower profile and better chain wrap around the cog) or to pull down on the chain, a decision that tends to be made by the particular cog/chainring/frame combination rather than the rider.

The Convert is very nicely made (in Petaluma, CA) of high quality materials. Of course, for $94, it should be. Setup can be a bit fiddly- because rod is a bit smaller than the collar hole engages, it can be difficult to get just the right amount of slack in the chain. Ideally, there will be enough slack to prevent tight spots while pedaling or odd forces on the hub and for the rod to disengage- but not so much that the chain bounces around or rides up on the cog or chainring under torque. The roller can be centered on the cog and chain by adding or removing washers between it and The Convert's arm- it'll take a few tries, but once in the right position, it's not going anywhere. Soulcraft also recommend removing any paint from the dérailleur hanger before installation, to give the collar better purchase.

When I first installed The Convert (about two years ago), it moved. Not a ton, but at least once every ride- and at the worst possible moments. The whole point of the Convert is to keep the chain on the cogs where it belongs, but under extreme chain tension (say, near the top of a very steep climb, with my heart rate closing on 200bpm), the tensioner would move, allowing the chain to ride up on the chainring and slip, resulting in frequent cursing and occasional tears. Not good. I re-read the instructions and even went so far as to lightly sand the nylon bushings to give them a bit more bite. While The Convert certainly does move, I ultimately traced most of my problems to my Scandal's replaceable dérailleur hanger. Even with a bolt-on skewer and firmly fastened mounting bolt, the hanger has enough play to move slightly under pressure. Taking this potential for movement into account and using a big ass Allen wrench to tighten the fastening bolt, I'm able over-tension the chain initially, push the hanger back into its forward position, and be good to go.

Unfortunately, after every four or five rides, The Convert still tends to need re-tightening. While an overly loose chain should (in theory) cause faster drivetrain wear, I haven't noticed any problems. Still, it's no fun to have the chain slip- a problem I never experienced with my relatively inexpensive, sprung DMR Tension Seeker. Soulcraft's choice of a urethane roller is also curious- they claim that it's quieter than a toothed pulley, but I can't help but wonder: if rollers were quieter or more efficient than pulleys, wouldn't Shimano, Campagnolo or anyone be using them in their rear dérailleurs? Toothless rollers were used at some point during the 1970s, but have since been banished to downhill chainguides- not exactly the most noise- or efficiency-sensitive market. Unfortunately, the roller mounting bolt is larger than the hole in a Shimano self-centering pulley, so I haven't been able to experiment myself.

As nicely made as The Convert is, and as much as I like the ideas behind it, the execution could certainly use some work. If they could keep it from slipping, the design and US manufacture might justify the price. Until then, it's a nicely made product that is 2-4 times as expensive as competing products that work just as well (if not better).



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