Having a spare mountain bike kicking around, I decided to single speed it for some offroad fun. Unfortunately, after playing around with different rings/cogs and half-links I wasn't happy with the amount of chain tension I ended up with. It was pretty sloppy and I was concerned about dumping a chain with the slack I had left. So I started looking for a chain tensioner.
After looking at the options, I'd narrowed it down to three: On One Other-doofer, Rennen Rollenlager, and the Soulcraft Convert tensioner. These three had two things in common. First, they are springless. It seemed kind of pointless to use a springloaded tensioner if I was concerned that bouncing around might drop a chain. While that may not be a problem in the real world, I was paranoid enough to avoid it. Second is that all three are/can be used in a push position in that they push the chain upwards rather than pull it down to generate tension. The other-doofer is only to be used in this position, the Rollenlager and Soulcraft can be used in both. I wanted a push type to avoid chainslack if the device was hit from below and to allow as much engagement of the rear cog as possible. I wasn't sure if a pull type tensioner would result in chain skip, but again, I could avoid it with a push type. Here's the three in the line-up:
All three did what I wanted, pushed up with no springs and were robust in construction. The Convert had the added feature of tension release to allow a minimum of effort if the wheel had to be removed as, unlike the other two, it utilizes only the derailleur hanger. At the time I was looking the $88 USD price point for the Soul Craft Convert seemed steep compared to the ~ $25 USD price tag for the Other Doofer and the ~ $50 tag for the Rollenlager, so it went to the back. Unfortunately, at the time I was looking, Rennen's website was down so it looked like they might be out of business. It also appears from another review that it had some foibles (linked below). That left me with the Other Doofer as the most economical choice with no apparent downside. So off went the order.
Less than a week later it was in my hands. Quick shipping from the UK! I installed it, looking forward to getting this bad boy on the road. I was mortified to find that, after installing it, with the tensioner positioned to press as high as possible, no tension was applied to the chain! Suxors. So I emailed the company. Maybe I'd installed it wrong, given no instructions came with it. A quick reply from On One confirmed that I had installed it correctly and confirmed it is intended to push up. They thought that perhaps my derailleur was in an odd location. It's a late eighties Bianchi Grizzly, so it's possible. Looking at the rather shoddy photo below, you'll see a subtle difference in the Other-Doofer I received from the market photo above.
Instead of the L-shape, the attachment end is much broader which might result in a different range of positions although its hard to tell. What can be clearly seen is that the further rearward the derailleur hanger is positioned, the less effective a "push" can be applied to the chain. The derailleur hanger on the Grizzly is positioned far enough behind the dropout to result in this problem with the cog/chainring setup I was planning on using (38:16). So back to the drawing board. I thought that if I increased the chain angle by using a larger rear cog and ring, I might be able to engage the chain.
So on went a 22 tooth SS cog from Misfit psycles and a 44T front ring from a local shop, Cycle Solutions.
You can see here that this worked, but barely! You can also see that as a push tensioner, most of the adjusting space available was useless to me. In fact, with the tensioner positioned as far rearward as possible, it would be pointing straight down. That's quite a chainline! This would work perfectly if the tensioner was intended to be used as a pull tensioner. Looking at the Rollenlager's design, a similar problem might have arisen and, according to another review (referenced below) wide chainstays can also be a problem. The unfortunate thing with my current setup is that I don't have a lot of play room to increase the tension if I need to.
So, while I got this to work, it required me buying a new cog and chainring beyond what I already had on hand, in total costing me more than buying the Convert. So much for saving money. Because the Convert does not use the dropout as a pivot, the derailleur hanger placement probably has less impact on the useful adjustment range. Unfortunately, I couldn't find a detailed review of the Convert to see if there were any quirks with it. The additional anchoring point of the dropout may give the Other doofer and the Rollenlager an edge in stability when boucing off rocks and such.
I'll post some test results after I've beat this thing around a bit, but on the face of it, things have worked out.
First impressions: Robust construction, quick shipping, and email support. Design: Not having a more modern bike for comparison this may be my bike's problem however, I suspect that much of the doofers adjustment range is not useful. A subtle design change to shift the adjusting arc rearward could address this. If you're thinking of using a similar device and your hanger is behind the dropout, I'd skip the other doofer, despite it's nice orange roller. The SoulCraft Convert may be a better option for you.
One One other doofer http://www.on-one-shop.co.uk/acatalog/Tensioners.html
Rennen Rollenlager: http://www.rennendesigngroup.com/Rollenlager_Desc.htm
Soul Craft Convert: http://www.soulcraftbikes.com/convert.asp
A review of the Rollenlager http://www.derailedonline.com/archives/000024.html