Single speed cyclocross

[stewlewis]

If you bust your hanger a shortened chain would get you home.

A modern version of the DCD. Specialized Dangler or :

http://www.jensonusa.com/DMN-Chain-Tensioner-Chinstay-Mount

 

[bm0p700f]

I have missed something here, are your vertical dropouts the forward facing type or the modern type? If they are you can get away with a Q/R but it does need to be good as mentioed. I would go for magic gearing, I have have on one of my MTB bikes and it is perfect. My other MTB SS uses a road mech as a chain tensioner, need to ditch that.

Single speeding is a good idea so do it but with out a tensioner. Every tooth you add or take away from the front or rear cog adds or takes away 1/4" from the total chain length (see that magic gear website for the maths behind it). Knowing this it is easy to find the magic gear. All you need is your existing cassette and chain set, wrap the chain arround and the take teeth off or add until you have a ratio you can deal with that allows your chain to join up.

 

[Dead Rats]

but what if the chain is too long / short - magic gear is not always possible?

 

[bm0p700f]

2) My question about chain tensioners had to do with what happens
when you get stuck with a broken derailleur and a bike with vertical
drop outs. This happened to me recently - one of the reasons I want to get rid of the bike with vertical d/os and go single speed. I tried to shorten the chain but could not get the correct tension. I was probably doing something wrong.

You use a chain tool and shorten the chain and hope y

ou can single speed it.

but what if the chain is too long / short - magic gear is not always possible?

Given every tooth you add/take away from a cog adds/takes away 1/4" of chain length you can magic gear any* bike with vertical dropouts. You should be able to set the gear ratio so you have no more than 1/4" of extra chain. This is sufficient to ensure the chain is not too tight. Well at least that's what I do and it works for me of my off road machines.

*I have yet to find one that you can't*

 

[Dead Rats]

but does it dictate what ratios you can run?

 

[Woz]

RE: Magic Gear

This
http://eehouse.org/fixin/formfmu.php has been posted, but in my experience it gives you a good indication at best where to start finding a Magic Gear. If you don't have the published chain stay length from the bike manufactuer, then trying to measure it accuratly with a ruler will give you a starting ball park figure. When you've plugged in the info, then try these practicle tips to finalise your Magic Gear:

- put your wanted chain-ring on.
- get your wanted chain ready.
- set up the spacers closest to the hub to give you a reasonable chain line.
- play with old sprockets from a cassette first by simply seeing
if the chain will more or less join. Old 6/7 speed Uniglide road corn-cob cassettes are perfet for trying and perfectly rideable in SS mode.
- if it looks alright, put the remaining spacers on, tighten it all up.
- break the chain to right length and fit it.
- Pop the wheel back in.

If the chain is a fraction too slack, a new SS cog of the same teeth will tighten it up nicely. They have a slightly larger diameter, along with taller teeth.

If the chain is too tight - the wheel won't even engage or marked locking points when you turn the cranks, file a bit from the hub axel - and I mean a bit - so the rear wheel can move forward slightly. See Saint Sheldon: http://www.sheldonbrown.com/singlespeed.html

OR if you are not keen on filling, get your chain back on a normal bike, do a few 100 miles, then try again with the added chain stretch. Riding with no oil will speed up the process...

DON'T file the frame unless you are really settled on that Magic Gear on that bike.

Bear in mind that what is seemingly a very tight new chain will actually loosen very quick after a few rides in SS mode. Putting new chains on first that seem perfect with a magic gear can quickly lead to a disappointing sloppy chain after a few rides.

If the above doesn't work, then try a chain tensioner. I've had no success really faffing with half-links - but that's just me.

I've even heard people having custom chain stay lengths with vertical drop-outs using the above principals since there's no faffing with EBB or fiddling with sliding drop-outs when using disk brakes. Looking back, I've now done 5 SS conversions all with magic gears and pretty much on the ratio I want with the above procedure.

 

[Woz]

Follow-up: Just take a chain breaker and a few links of chain with you when riding. IMHO the chances of a broken chain with SS is far lower than a geared bike since you are always having a close on perfect chain line.

 

[pigman]

And remember a new chain will stretch ever so slightly after a couple of rides. So what starts out as a bit tight will prob end up ok. And I found that out with 1/8" stuff, so 3/32 might stretch more?