Dumb build or feasible?
 

I'm looking for the down to earth experienced opinions on this idea. Hence 50+. It may be nonsensical but tell me why if it's too off the wall.

I'm scheming on making a psuedo-single speed starting with a CX frameset. The bikeisland/nashbar variety which can be had for 200-300 dollars. Or an aluminum road frame with cf fork if that's too silly, but it's the longer wheelbase with close to road geometry that attracts me.

In my amateurish fashion I only use one crank ring, almost always with 70-85 gear inches, so why not a single-speed crank? No expensive shifting apparatus, lighter weight, would that throw the chain line off? I'd use the same reasoning on the back and go legitimately single speed but, I may prefer or even require some gearing on these hills, and I'd like my wheels to be compatible between bikes. So I thought to just use my current wheels, at least at first, with the 8-speed cassettes. I'll take a junked derailleur and clamp it off at the gear I want with a cable fragment, no shifter. The DR and cassette will cost about a pound but I'll trade that extra weight for flexibility. I figure the whole bike fairly inexpensively will weigh about 18-19 pounds which is featherweight from my perspective, with room to reduce in the wheels and crank.

What have I overlooked? Later on, when I'm thinking "I wish I'd thought of that, before ever starting"?

Nothing dumb about single speeds if that's all you require. Simple is good.
I don't know about Nashbar frames, but a cross frame with horizontal dropouts is a good platform for this.
Surly Crosscheck is a good example. I did some single speed and gearhub builds on these frames when I was a Surly dealer.
Chainline has to be worked out, but it's usually doable. That's where square taper bottom brackets have an advantage over integrated because you can choose a spindle length to suit, although there is some flexibility with integrated cranksets by mounting the ring on the other side of the spider.

Sounds like a workable (if a little odd) approach for what you say you want. Unless you think you might want to change to a normal singlespeed or fixed arrangement at some point (with no derailleur), I don't see any advantage to horizontal dropouts.

Is your intention to be able to change gears if you need/want to? If so, if it was me, would just a well have a shifter to do the shifting. Or you can use spacers on the hub to place the one cog in the proper position to have a proper single speed. You can buy single speed kits that contain these.
The horizontal dropouts enable you to set the chain tension with out a derailer. Or you could use the derrailer as a tension device with vertical dropouts.

I have seen standard bikes built like you describe with a single crank and a cassette in the rear. But they all use a shifter to activate the derailleur. What would be the advantage of not using a shifter with a derailleur? And the complete bikes I have seen are less than 400 bucks.

Ah, that's what I get for skimming a post and then responding. Got single speed stuck in my head and ran with it.
Yes of course, single chainring works just fine on a cassette, and chainline isn't really all that critical. Just get it close to the middle, or to the side you use the most.
I think I'd want a functional shifter on the derailleur though if it's hanging there anyway. Not that big a deal to rig one .
Shedding the front derailleur gets rid of the single most frustrating bike component IMHO.

If I was doing this and wanted to save the expense, weight, clutter...whatever of a brifter or bar end shifter, I would use a downtube shifter for the rear. Cheap, light and simple.

+1 AND.... it would make it infinitely easier to make that rare shift when you wanted it.

Thanks. I was thinking along that line also, or the inexpensive mtb thumb levers that mount on the bars. If you don't care that much about shifting, there's not much point in a high-end setup or so goes my thinking.

I don't have to buy a shifter or decide on one yet, or a rear derailleur since any junk one will do, and can change the gear with a pair of pliers. I realize that with the usual setup I could just put it in a gear and leave it there as a simulated single speed, but I also know that I'll shift if I have it. So, I would never really know. On the other hand, I don't want a SS frame with the narrow rear dropout because the greater likelihood is I'll eventually want the gears after all. And want to be able to trade wheels between bikes.

I didn't know there were cross frames with horizontal dropouts like the Surly that Dan mentioned, so I'm already learning things on this thread. That would be ideal since if I did decide to stick with a single speed I could dispense with the rear DR, remove some cogs and chain and be done.

Our son raced cyclocross on a SS so it is very feasible. However, he saw the error of his way and now rides a custom IF CX with multi-speed drivetrain. His knees are grateful.

I did give him a hard time by telling him:" riding a single speed is like playing a round of golf with just a 9-iron--sometime during the day you might actually have the right tool for the job.":)

Have fun.

And keeping a pair of pliers handy is less complicated and lighter than a downtube shifter?

I think so :) and easier than switching out cogs. I have been a little unclear on my scheme, in that this situation would only be transitional. At some point it would become a single-speed or else fully functional geared.

I agree with this. Using a cassette without a derailleur often leads to a dropped chain. If the cog in the back isnt exactly lined up with the crank you'll dump the chain every few minutes. The cassette cogs are designed to ramp the chain up and down easily with the rear derrailleur to make shifts easier & quicker.

A single-speed cog is free of ramps and this in needed to keep a chain on the cog. Plus, most single speeds are set-up with a near perfect chain-line.

Look into the Pake C'mute frame, it will do what U want: http://www.google.com/products/catal...d=0CCwQ8wIwAQ#

I built a psuedo ss/fixed using an old three speed coaster hub. Laced it up to a 700 wheel and had the shifter mounted on the seatstays. I usually left it in one gear but always liked to have options for the hilly rides. The 3 spd isn't light but I had tons o' fun on the thing. I would try to scrounge around for an old 3 speed rear wheel and give it a try.

But with a thumb shifter there would be the housing to run the cable up to the handlebar. Downtube is cleaner. Just set the RD limit screws so that it won't shift no matter what you do with the lever.

Good point. I'll bet they're sturdier too.

I built an old road frame into an 8-speed with a Shimano Nexus 8 hub. Horizontal dropouts for chain tension, a 48-tooth Sugino single speed crank and a shifter on the end of the bar. Looks just like a single speed but has as wide a range as most road doubles. If I were going to do it again I would look at the new Shimano 11 speed hub. If you want to keep it simple and cheap, the 7-speed and 4-speeds will work too. I'd even use an SA-3 speed like bidaci if I had one for free, but Minneapolis is fairly flat so you don't need a whole lot of gears around here.

Instead of clamping the cable, why not use the limit screws to lock in a gear?

I did something similar. I wasn’t going after a super lightweight ride just the simplistic value of something with a road frame geometry bit of upright posture and the feeling of a single speed setup without the negatives of no gear at all. I started with an old Soma 10 speed used a 26” 3sp wheel and hub in the back and left the 27 up front. I used one side of the stem shifter to operate the 3sp. This is one of my favorite bikes for a recreational family ride now. All made out of old junk laying around.

http://inlinethumb53.webshots.com/49...600x600Q85.jpg

I don't know if the lower limit screw can push it out several gears, but that's definitely worth looking into. Maybe shim it up.

That turned out well. I like to get out sometimes on a comfort bike so that no one recognizes me so that's pretty attractive.

My dumb build scheme is slated to be my main ride so I want to start with the right frame, so that adding decent components in the future won't be nonsensical.

In answer to your original question I would say there is no such thing as a dumb build. If it’s something you will want to ride I say go for it. I have done a lot of different things with bikes in my day that’s for sure. If you start with a frame that you really want the worst that can happen is you can do something more conventional down the road and have something to show for money spent. And best case you will get something really perfect to suit your needs with a single speed.

Like you I have lots of different bikes to suit the mood I’m in to ride and if I have guests that want to borrow a bike I get lots of feedback on some of these clones. On the one I showed the smaller rear wheel relaxed the geometry a little more and along with the upright comfort position it’s a really easy bike to ride. The front chain ring is larger than what would have been common on a 3sp so its gearing is fun. Worked out good but like I posted above if you don’t try you will never know. That bike and my 21sp beach cruiser I built wont set any speed records but they do get used a lot.

Since there's no countervailing consensus other than it might as well have working rear shifting, I'm going to pull the trigger on the scheme. Nashbar CX frame for the sake of frugality and Nashbar Carbon CX fork, some cheap single-speed crankset etc, I figure about $320 in parts it should be a pretty decent bike.

Help me out again please. I'm thinking that the nashbar touring fork is an all-around better choice, but is there a problem with matching the CX frame and a touring fork?

Of course I wound up ordering for a different scheme than what I was contemplating. No cross frame, no single-speed workaround. After the comments here, and thinking about it, making a parts/builds database and generally spending too much time mulling over the possibilities, it just makes sense to me now that if you wanted a single-speed, it's better and cheaper to do it from the start. Same for the cx frame. So I'm building a road bike - thanks for the help.