[Rabie]

A while back I converted my vertical-dropout ht frame to singlespeed with a Rennen tensioner. I seem to be having a problem, though, getting regular tension on the chain. For every revolution of the cranks, the chain will have good tension for half the revolution, and then slacken up for the other half. I've tried swapping out every part of the drivetrain (cranks, chainrings, bb, cog, wheel, chain), and it's always the same problem. If I get it tight enough in the slack half, it binds when I turn the cranks, but if I let off some tension to keep it from binding, the chain will drop during the slack half of the crank-turn. Frustrating. I don't have much experience with singlespeeds, so any help would be most appreciated.

 

[V-Dub GTI]

check the hub. My geared bike was doing the same thing and i had to re-greese the hub because it was sticking.

 

[jrfor0]

the reason why you are getting a tight spot and a loose spot is due to the chainring. the chainring is not perfectly round. there is no way to make a chainring perfectly round. every chainring is very slightly out of round no matter where it is made or who makes it. you just need to find the perfect balance of chain tension. what also helps to stop the chain from jumping off the cog or ring is running a perfect chainline, even if it means spacing the crap out of the cranks.

 

[BikeGeek]

Try this:
http://sheldonbrown.com/singlespeed.html#tension
Might not fix it entirely, but it works to get you close to even tension.

 

[BikeMike]

Are you runing a ss-specific chainring of good quality? As stated above, your problem is likely a non-concentric chainring. I know reputable bmx chainrings are usually kept pretty round, and I would assume the same would be true of single speed specific mtb rings.

 

[Rabie]

I've tried a few different rings --a couple Salsa single rings and an old truvativ with ramps/pins. They all have the same problem. Loosening and tweaking them may have helped a little, but not as much as I'd have liked. I guess I'll look into a higher quality ring. Thanks all.

 

[BurlyShirley]

Sounds like one of your crank arms is longer than the other.

 

[Yess]

Yes, that's the problem with "chain tensioners" that fix the axle or fix a load on the chain.

The only real chain tensioners are the ones that use a spring and can apply a constant load throughout the tight/loose spots. Checkout these two videos and you'll understand what I'm trying to explain.

Single Speed riders will be impressed!

(Vertical dropout)

(Horizontal dropout)

Check us out at www.yesspro.com

 

[BikeGeek]

The only real chain tensioners are the ones that use a spring and can apply a constant load throughout the tight/loose spots.

I've hated every spring tensioner I've ever used, but I'm sure there have been improvements since I threw my last one away 5 years ago. I've been riding SS for quite a while now and with good chainline, I have yet to see a ring give tight/loose changes drastic enough to cause problems with a fixed tensioner (à la Soulcraft, Rennen, etc.) after a little tuning like I mention above.

Single Speed riders will be impressed!

Want to impress me? Check this out!

 

[Yess]

I've hated every spring tensioner I've ever used, but I'm sure there have been improvements since I threw my last one away 5 years ago. I've been riding SS for quite a while now and with good chainline, I have yet to see a ring give tight/loose changes drastic enough to cause problems with a fixed tensioner (à la Soulcraft, Rennen, etc.) after a little tuning like I mention above.

I think it's difficult to convince people who already have an opinion over a product they have never tried. I think what's fair is if you see someone with our tensioner to try it out. If not, I still appreciate your criticism.

IMO re: fixed tensioners is that yes, it helps solve the problem just like chain tuggers, but it won't give a perfectly smooth ride. It's important to some people (not all) to have a consistent pedal. If you're going to shell out more money, you should have a perfect tension.

 

[peter6061]

That YESS tensioner looks pretty nice. I'd love to try one out, but most of my bikes have gone to EBBs. What's the price for the Vertical model? Maybe I need to lose the Surly or DMR off my CX or jump bikes.

 

[KevinR86]

It could be the Bottom Bracket spindle. I recently had this problem on my bmx bike. I took off the crank arms, and spun my spindle. The chain ring side was bent, causing the sprocket to move towards, and away from the rear wheel with each revolution of the cranks, thus causing my chain to tighten and slack w/ each crank revolution. I replaced the spindle with a straight one, and the problem was solved.

 

[-dustin]

Different bearing manufacturers have different tolerances and actual sizes for their bearings. If your hub is a loose ball setup and has been overhauled, there is always a chance that 1 or 2 of the bearings in the hub, while labelled as the same size, might be different. Those smaller bearings will cause the hub to sort of wiggle around when turning on the axle.

The only reason I mention this is because the first hub overhaul I did at the shop involved me using 2 different packages of 1/4" bearings from 2 manufacturers in the freehub. The bearing sizes weren't immediately discernable, but after busting out a measuring tool, it was rather obvious.