ironhanglider wrote:Use a 'Ghost Chainring'.
I used one as a chain tensioner with great success on a previous tandem, I have also seen some discussion of using them as a chain tensioner of 'fixies'.
If the chain does lengthen, then you can just use a bigger ring (or two).
A yes. A friend has done this to tension his tandem timing chain. I think that even by repositioning the chain-ring you should be able to slightly vary the tension.