Originally Posted by I_bRAD
Wouldn't the deraileur put too much side force on the chain if it were fixed in place as a tensioner and you're running two different cogs? Never tried it, but seems to me like it would always be trying to pull the chain off. I have used one cog on the back and a MTB triple on the front which worked well. 48X38x28 on the front gives you a pretty large range to work with on the back- regular,easy and 15%grade with a load easy.
I've never used the deraileur as a tensioner so I can't say 100% if it would work with 2 cogs. I've read about them and seen it used. In theory it should work if the chain was a little off. I don't like pull down tensioners though, not enough cog engagment. My mtb has horizontal drops so I manage to do with out a tensioner.
Do you use a tensioner to run the triple crank to one cog?