i bought two Sinz chain tensioners(bmx world) and theyre great, although i had to use a half-link chain link for my 47x16 gear ratio. but theyre really nice and you can fine tune them like none other. i also have a huuuuuge Primo one but that looked like i was armor plating my chain stays. the Sinz ones were about 15 for a pair.

surly's look stupid