use glue.

 

?

 

I see alot of bikes on the forum with the so called 'magic ratio',without a tensioner.Does it actually work in the long term.What i am trying to say does the chain slack off quickly or can you run the ratio for a while without it coming off the cogs.Just wondered,thanks.

If your bike doesn't have a way of adjusting the chainstay length (track ends, sliders, EBB) as the chain wears then you must replace the chain when it loosens. A chain might last a day or months. In the long term no chain lasts. A worn chain wears out the cogs and chainring faster than a new chain. So replace the chain often or the other parts too!

I find the KMC chains last longer than others.

 

I have the "magic ratio" on my commuter; an old Diamondback Apex. The chain is not very tight now that it is worn a bit but it never comes off riding. I can force the chain off the chainring by hand, but no the cog (I'm using an Endless cog and a steel Sugino road ring with no ramps). If you use good single speed gears like the Endless cog and a non-ramped chainring you should be fine even when the chain is somewhat loose. Just make sure the chain line is perfect.

 

Maybe the chain doesnt come off due to the bike being a commuter.If the ground is uneven(i.e-mountain biking) perhaps it would?

 

What Polk said. The ideal would be for the chain to be slightly tight when new. I've found that the PC-58 chains I use tend to loosen a bit within the 30-50 miles, then run about the same length until they're nearly worn out. If you have a good chainline and non-ramped SS specific sprockets, your setup should be fairly tolerant of a loose chain anyway.

 

Yes, the chain will loosen with wear. Whether or when this becomes a problem is dependent on a lot of factors. As an example a chain should be replaced if it's "stretched" 1/16th of an inch over one foot of chain. This would equal about a half inch for a 100 link chain. A half inch would be a lot of sag and likely result in a dropped chain. Most magic gear users would have to replace the chain or replace a link with a half link much earlier. A SS chain will typically wear better than a geared bike chain so, theoretically, they should both last about as long. However, your riding conditions, style (do you grind on logs for instance?), maintenance and other factors determine how long a chain will last.

 

I just wondered how long you could get away without using tensioner but as it has been said, what it really comes down to is the life expectancy of the chain.Does checking your chain for wear fit in with the singlespeed mentality

 

A couple of years ago I found that magic gear ration with one singlespeed project, 33:18 fit in a Cannondale Chase. Using a Truvative 33T chainring and a steel DX cog, a new SRAM PC-99 chain would fit REAL snug, but wear in fairly fast to a point where it would fit perfectly and not noticably change tension most of its remaining chain life until the end. I check my chains with a Rohloff chain wear tool. I replace them when they get to a point where the Rohloff tool indicates they are at thye end of their usefull life, and the chain was never loose enough to push off the chainring by hand on that bike. Got lucky I guess. Tried every other close or equivalent gear combo and either too loose or too tight.

I have discovered that the type of chainrings, cogs and chains can contribute to a slight amount of difference with that magic ratio, so nothing is for sure. I ran a Surly Singlator on one bike after that and am currently riding singlespeeds with horizontal drops and chain-tugs, but it is possible on some frames. Your best bet is to get an accurate measurement of the rear axle center to BB center (chainstay length), and type the numbers into a gear calculator. I used to use SingleSpeed gear Calculator, but it's no longer available. Would like to find another good one.

Cheers,

Dave

 

I used to use SingleSpeed gear Calculator, but it's no longer available. Would like to find another good one.

A good program I use is FixMeUp
http://www.peak.org/~fixin/personal/fmu/php/fixmeup.php