jonwvara 

I'm getting ready to build a winter singlespeed with fenders and studded tires--something I can ride on bad frozen roads and hose off and spray with WD40 from time to time without getting obsessive about dirt and salt. Because I have some monster climbs to deal with, I want to use double chainrings and two cogs in back that I can shift manually. Based on parts I've got on hand, I'm thinking of something like a 47 and 36 on the front and a 21 and 32 on back. I know, that makes for a very low bottom gear and a not-very-high high gear. Show some compassion and don't make a big deal about it.
I know I could quite easily do that with a spacers and cogs on a cassette hub--have done it in the past, in fact--but Sheldon talks about doing the same thing with a freewheel:

https://sheldonbrown.org/hercules.html

All of my bikes have freewheels, but I've never had one apart. Generally speaking, how hard would this be to do? I know how to get the cogs off with two chainwhips, but I'm not sure what happens after that. Are the spacers the same thickness as the cogs (I'm talking 5-speed here)? Do you just take off the cogs you don't want, replace them with the same number of spacers, and screw everything back together? Though not entirely clueless in other areas, I am as a babe in the woods on this subject.

stien

IMO if you're not even going to use a derailleur and are looking at this whole thing as sacrificial, just leave all 5 speeds on the FW, no?

You're also going to do have some pretty big movement of the rear wheel to get onto that 32. Might even be too much depending on your dropout. I nominate still using crappy friction parts.

jonwvara 

Well, I might or might not find a 5-speed freewheel with a 21 and a 30 tooth cog. And if I have to take the freewheel apart to customize it anyway, why would I want to carry around three cogs that I won't be using? I don't care about the weight, but it seems pointless.
As I said, I've never done this before. Are you saying that the 36-32 combination and the 47-21 will position the wheel differently in the dropout even though the total tooth count is the same? I didn't think that would be a problem.

Iowegian

Most or all of the freewheels I've had apart have different size ID's for the various cogs. The smallest cog attachment varies but it's usually just threaded onto the body to hold the rest of the cogs. You'll need to use the smallest cog that came with the freewheel or maybe a BB lockring or the smallest cog with the teeth ground off to hold it all together. The spacers are also different sizes to fit over the stepped-size freewheel body so it will take a few donor freewheels to make one 2 speed.

Zaphod Beeblebrox 

How about a new 3 speed?

https://cgi.ebay.com/ws/eBayISAPI.dll...=STRK:MEWAX:IT

Jon, your reasoning about the tooth count is correct.

David Newton

That 3 speed freewheel is something I'd be interested in, but look at the tooth form, something's not right.

jonwvara 

Why didn't I buy that big box of cogs and spacers at the Park Pedals going out of business sale a few years ago? I mean, what was I thinking?

Not to mention all that other stuff, too. Sigh.

jonwvara 

I love that--especially if you look at the little specifications chart, where it identifies the "material" as "iron." That's a C & V item for sure. None of this sissy new "steel" stuff--give me good old iron any day.

surreal

this wouldn't be a winter singlespeed; it'd be some sort of homegrown dingle-speed. between the headache of setting this up, manually changing gears for "monster hills", and still having to clean/maintain everything else on the bike, i think you'd be better off with a cheap 1x5 set-up. Or, pick a gear you can live with, and run singlespeed.

i know you didn't want a hassle, and i feel bad, so this post is written with all due respect. But, sometimes we gotta try to help folks out. If i posted a question about "which toothpaste makes for the best chainlube? Show some compassion and don't make a big deal about it", i hope someone would mention that toothpaste makes for poor chainlube.

just my $.16. (inflation)

-rob

clasher

Sounds like a headache, why don't you want to go the cassette route? You can get a perfect chainline pretty easily.

jonwvara 

Boy, have you got my number! You're very likely right about it not being worth it. I'd say that two out of three gearing projects like this that I've tried in the past haven't worked out for one reason or another. A couple of years back, I spent a fair amount of time tinkering with a three-cog cassette meant to approximate the gearing you'd get with a Sturmey-Archer AW. I ultimately did get it to work, but it was basically an interesting (to me) novelty. I eventually made it back into a singlespeed.
Funnily enough, Sheldon Brown--who, as I noted in my original post, had a two-cog freewheel setup--more or less called me an idiot for the three-speed project. I'd emailed him to ask him something about the project--I forget what now--and he responded that it was a waste of time, and that the amount of weight I'd save by geting rid of four cogs and a front derailleur would be insignificant. Ouch.
Regardless of how this works out in a practical sense, it promises to be sort of entertaining and will give me an excuse to take apart and reassemble some freewheels.
As far as changing gears goes, my situation is that I can handle most of the riding I do in high gear. I would need to switch for one hill I ride over often that climbs just under a thousand feet in the course of two miles, with some very steep sections. I'd also change at the end of every ride to come up the 3/4 mile steep dirt road that leads to my house--a climb that I always have to make when I'm at my most tired. It's not as if I'd be getting off the bike and changing gears at every little rise in the road. If I get tired of messing with it, it will be easy enough to make it into a singlespeed--which, as you correctly point out, is likely to be more practical anyway.