Suppose you have a geared bike that you want to convert to a SS beater. Is there any functional reasons not to do the conversion the simplest way possible: stripping off the deraileurs and shortening the chain (leaving the crankset and rear cassette alone).

A few questions:
-can you do this with a bike with vertical dropouts?
-is there any reason to leave the body of the front derailleur in place (to keep the chain from jumping off the front chainring). is this even necesarry?
-i'm in the process of the conversion, and when i reconnected the chain, the pedals rotate when you walk the bike. Any reason why this happens?

You can do it, but the chain, chainrings and cassette may be ramped and pinned (designed to shift gears easily) which means you might drop the chain on occasion. All that crap weighs too and looks crappy but thats not really a functional concern.

You can do it to a bike with vertical dropouts if you use a chain tensioner pulley, or if you find a combination of gears that ends up being the right total chain diameter to have a taut chain without a tensioner. Half links can help alot with this.

If you have ramped chainrings it may be a good idea to leave it on, as there is chance of dropping the chain. If you aren't using a tensioner it becomes less necessary

The rear hub is probably cheap and gunked up as hell. The grease has probably hardened keeping the pawls of the freewheel engaged. Some cheap or brand new hubs do this, but its not really a concern while riding. Either that or you have a magic multi speed fixed gear hub.

If the bike has bolted on chainrings you can remove the chainring you aren't using and then shorten the chainring nuts or just buy shorter ones. If the rear hub is threaded you can guy a BMX freewheel and thread that on. If the rear hub is splined, you can buy a spacer kit and put whatever cog you want on it. This all costs money but will be better in the long run.

But in conclusion, if all you are going to do is take off the shifters and derailleurs, theres probably not too much reason to do it in the first place... Just keep it in one gear and be glad the extra gears are there when you're hauling groceries up a mountain.

simplest is maybe, um, just don't shift?

For me, if I was going to leave all that stuff on, I'd probably leave the derailleurs too, unless there was something wrong with them. You can convert a cassette to single speed with some 1 1/8th plastic pipe, and you can convert the cranks with a set of single ring bolts. It's not hard, it dumps some weight, and it looks far better.

I'm with koyman.

i'm about to do this for one of my friends. Just taking off the derailers and shortening the chain

Part of the fun of SS is losing some of the weight. By removing the deraillers, shifters, cables, filing off the various bosses, and the like it is a noticeable difference in weight.

Another advantage is the efficiently offered by a straight chainring-to-cassette drivetrain.

A third (though perhaps more nebulous) advantage is the inability to shift. I find that if I have shifters, regardless of whatever discipline I might have before I get on the bike, I'm going to use them. Take this away and it helps you get into the "one gear" mindset. If there's a hill, better stand up and pedal.

My first bike was a Single Speed running onto the old hub and cassete. It was a beater but still a lot of fun and when I finally got a decent fixed wheelset for it and replaced the rest of the drivetrain it was even better but I was used riding with just one gear so the transition to fixed was not as difficult as it might have been.

I actually still have the wheelset with the old cassette wheels on my bike right now for the winter months so I can go riding in the ice and snow with worrying about messing up my shiny new trackset.

I just did this to my bike, the shifters (brifters, damn them) didn't work, and I got stuck in the highest of high gears last night and couldn't get home. my fiancee came and rescued me. I said F' this, and took all that stuff off. It's going to be fixed/free hopeufully soon.

I'm surfing ebay/webz for cheap wheelsets (yes, I know where to go... I'm just waiting for one ebay auction to end)

If you're doing any sort of long-term solution, or doing any really serious riding other than beating around town, I'd definitely listen to the advice above.

I generally oppose those kind of conversions where the gears are left on, for no other reason than it looks like crap and one big appeal of SSFG (c'mon, admit it guys) is the aesthetic quality of the bikes. Even an old rusty Schwinn frame has a certain elegance to it when it's stripped of all of its unnecessary parts and made into a singlespeed or fixed gear.

But here are the mechanical reasons for a proper conversion:

1. Perfectly straight chainline
2. Solid chain tension.
3. An undished rear wheel which is much stronger than a dished wheel from a geared bike
4. Weight
5. My fixed gear chain stays cleaner than my geared bike (I really don't know why).