- DMR Tension Seeker 2
If you're in any way singlespeed averse, look away now. If the mere mention of a bicycle with one gear is likely to make you froth at the mouth and rant about elitism, macho nonsense, excuses for being rubbish and all the rest of it, this isn't for you. If, for whatever reason, you quite fancy a go with just the one gear, keep reading.
It's fairly straightforward to convert your bike to a singlespeed but you're likely to need some sort of chain tensioner. You might get lucky and find a "magic gear" that just fits, or you can use an old derailleur. But it's neater and lighter to use a specific singlespeed tensioner.
DMR's Tension Seeker 2 is, as the observant will probably have noticed, the second version of the company's spring-loaded tensioner. A simple V-brake style spring lives in a carrier with an adjustable angle that bolts into the derailleur hanger, while the jockey wheel is adjustable in and out, runs on cartridge bearings and has nylon side cages as the last line of defence against chain unshipping. Depending on which way round you put the spring, the Tension Seeker can push up or down on the chain. Pushing up is better - more chain wrap around the sprocket, looks neater - but it's more critical on chain length. We used a half-link on the test bike to get as little chain slack as possible and set the Seeker up to push up. Fitting is a little fiddly - you'll probably need a couple of goes to get the spring angle spot on. Pay attention to the instructions and you won't go far wrong. We managed to get the angles a bit wrong the first time and bent the spring, but that's our fault not the tensioner's.
Once in place it works just fine. It was a little noisy at first but seemed to settle down, and in six months of use we haven't lost the chain off the sprocket once. A minor drawback is that you have to unbolt the arm to get the rear wheel out, but the spring stays in place so your adjustments are preserved. It's not hard to do, but you need to be careful not to lose the bolt and spacer in the grass.
Positives: Light, neater than an old mech, works fine
Negatives: Slightly fiddly to fit, slows wheel removal, not as neat as a "proper" singlespeed frame, a little pricey
Verdict: It seems a bit odd to pay the cost of a decent derailleur for something that doesn't even change gear, but the Tension Seeker does its job perfectly well and it's neater than a repurposed mech.