chain tension?

[dmw010]

My setup is 32x18 with a Rennen Rollenlager tensioner on my old hardtail frame. I'm using the tensioner in push up mode, and taking up as much chain slack as possible for maximum wrap around the cog. I noticed when lubing the chain that as I rotate the cranks, there is one spot in the rotation where it "sticks" slightly, always in the same place relative to the crankarms. I took the chain off and spun the cranks -- no sticking, so I figure it's not the bottom bracket bearings. I'm thinking that maybe the chainring or the cog are not absolutely perfectly round, so if the chain is overtensioned it's possible to hit a point in the rotation where the chain is just a hair too tight. I think I'll try backing off the tensioner slightly and see if it smooths out.

Any other ideas? It's not noticeable while pedalling, but I'd like to know the cause.

[bdee]

Maybe a stiff link? If not run it so there's a little more slack and go from there. Also, is the ring or cog ramped ?

[dmw010]

Belated thanks for the input, bdee. Looks like my theory of too much tension was it, I backed off the chain tensioner slightly and everything smoothed out. No ramps, by the way.

[minkhiller]

Sounds like I should look into the tensioner that you have. I have the singulator and am not real happy with it. How would you rate your tensioner, adjustability, effectiveness, bearings?

[dmw010]

I give the Rollenlager tensioner a general thumbs-up, although I've only done limited trail riding with it so far. I saw it mentioned favorably in the MTBR newsgroups last year, then found out it was designed by a couple of guys in Lynn, MA. Figured I'd give the local guys some business. The design seems pretty bombproof.

The Rollenlager is a rock-solid chunk of aluminum. The only moving part is the roller, which runs on very smooth sealed cartridge bearings. The unit attaches to the frame very rigidly with both the quick release skewer and a bolt into the derailleur hanger. You can use it in either push-up or push-down mode (I use push-up for more chainwrap around the cog). Adjustments are made at the bolt into the derailleur hanger; the bolt goes through a curved slot in the Rollenlager that lets you slide the whole unit up and down when the bolt is loosened. I guess you can say it is infinitely adjustable within this arc. This thing is not springloaded, the tension is set purely by adjusting the position at the bolt. Only downside -- you better bring a wrench with you in case you need to change a flat or adjust the tension on the trail. No biggie for me, I already carry a 6" adjustable in my pack.

You can check it out at http://www.rennendesigngroup.com/.

[minkhiller]

Thanks for the info.