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Discussion Starter · #1 ·
if i can provide a chainstay length is it possible to come up with the "magic" ratio in order to make a bike with a forged vertical dropout a single speed? (with help of half links of course)
 

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here's a calculator

http://eehouse.org/fixin/formfmu.php
I haven't used it, so I can't vouch for it. The basic answer to your question is "yes"; you can calculate (several) "magic gears" that will give you acceptable chain tension.

But I have a question: You said "single speed," which usually refers to freewheeling single-speed (rather than fixed gear). If you really meant SS, you can use a chain tensioner, and not have to worry about being limited to a few magic gears.
 

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Clear Lake, TX
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This is where I would go with the trial and error method, shortening the chain as needed and then perhaps using a half link.
It is so simple and easy, I would never have thought to need a calculator (and I have a somewhat engineering brain!).

As JCavilia said, a chain tensioner works fine for freewheeling SS, but never for a fixed gear. Still, I'd avoid one for aesthetic purposes if possible.
 

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Trial and error

Tig said:
This is where I would go with the trial and error method, shortening the chain as needed and then perhaps using a half link.
It is so simple and easy, I would never have thought to need a calculator (and I have a somewhat engineering brain!).

As JCavilia said, a chain tensioner works fine for freewheeling SS, but never for a fixed gear. Still, I'd avoid one for aesthetic purposes if possible.
The only problem with the trial and error approach is you might have to have a lot of extra parts to try and discard, since some combinations can't really be made to work with true vertical dropouts, even with a half-link. If a shop with an inventory is building the bike, that works, but it's not necessarily practical for an individual. Hence the calculator.
 

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what?

JCavilia said:
The only problem with the trial and error approach is you might have to have a lot of extra parts to try and discard, since some combinations can't really be made to work with true vertical dropouts, even with a half-link. If a shop with an inventory is building the bike, that works, but it's not necessarily practical for an individual. Hence the calculator.
You don't keep every chainring size between 39 and 53, as well as every cog between 13 and 21 around at home?
 

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Clear Lake, TX
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JCavilia said:
The only problem with the trial and error approach is you might have to have a lot of extra parts to try and discard, since some combinations can't really be made to work with true vertical dropouts, even with a half-link. If a shop with an inventory is building the bike, that works, but it's not necessarily practical for an individual. Hence the calculator.
Sorry, as a former shop mechanic, I forgot everyone doesn't do things the same way or have the same resources.

Luckily, that shop still lets me show up and use their tools and parts bin when I bring a bike in. I send them work and customers, so we keep an excellent relationship.
 

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Discussion Starter · #7 ·
f you tig

Tig said:
This is where I would go with the trial and error method, shortening the chain as needed and then perhaps using a half link.
It is so simple and easy, I would never have thought to need a calculator (and I have a somewhat engineering brain!).

As JCavilia said, a chain tensioner works fine for freewheeling SS, but never for a fixed gear. Still, I'd avoid one for aesthetic purposes if possible.

thank you tig for being such a dick! it's because of people likeyou that people are afraid to ask questions about something they don't know anything about. I'm sorry bike riding is only an activity i participate in and not my life. my bad i dont want to buy every chainring and cog possible to see if i can get a magic fit.
 

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whoa

that's a bit of over reaction, isn't it?
russelr said:
thank you tig for being such a dick! it's because of people likeyou that people are afraid to ask questions about something they don't know anything about. I'm sorry bike riding is only an activity i participate in and not my life. my bad i dont want to buy every chainring and cog possible to see if i can get a magic fit.
 

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Clear Lake, TX
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Time to ban "russelr"?

russelr said:
thank you tig for being such a dick! it's because of people likeyou that people are afraid to ask questions about something they don't know anything about. I'm sorry bike riding is only an activity i participate in and not my life. my bad i dont want to buy every chainring and cog possible to see if i can get a magic fit.
You surly must enjoy being banned. Send us a post card.

First, in no way was I being what you clearly are. You've exposed quite a bit about yourself, boy. For the benefit of the rational members here, I'll clarify this for their concern. As for my life, you clearly haven't the slightest clue. I can only hope to one day achieve such accuracy of judgement that you already possess. Dude, lighten the EF up!
/flame

I was simply suggesting what has worked for years. You do NOT need every cog and chainring combo for setting up a useful gear ratio and chain length. Start with a standard 39, 42, or track sized 44 or 46 chainring, for instance. Install a regular wheel that has a 9 or 10 speed set of cogs. From there, simply wrap an uncut chain around the installed chainring and one of the potential cogs for basic measuring purposes. Sure, the chainline will be off, which could affect the chain slack, but this is to get to a starting point only. With that information, you can buy/borrow the desired cog and fine tune the chain length with a half link. Also, the free/unattached cogs from a cluster can be used on the freewheel body by itself for better accuracy.

Wow, I'm such a dick.
:p
 

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Russel, you're way over-reacting. You're new here, and everybody is welcome, but you need to maybe calm down and lighten up and not fly off the handle like that until you get a better feel for the tone of the discussions here. This is a pretty civil place, and that kind of personal attack isn't really appropriate. TIG wasn't being a jerk at all. He mentioned one way to do what you're after, a way that is reasonable and works. When I pointed out that that approach isn't realistic for everyone who doesn't have his resources, he apologized almost immediately and explained why that was his first reaction. Hours later, you post, calling him names.

We really don't do flame wars here. You're welcome to stay around and learn things and talk about your experiences, but don't start attacking people every time a suggestion isn't exactly on point for you.

Edit: I just noticed your other post, in which you ask about spokes for a wheel with an eno eccentric hub. If you're talking about the same bike here, this whole discussion is irrelevant. With that hub, you can get good chain tension with any gear combo -- that's the whole reason for the eccentric mount. You don't need a magic gear.

Re spoke length: links to several calculators are here:
http://www.sheldonbrown.com/wheelbuild.html#length
If you have the Excell spreadsheet program on your computer, Damon Rinard's calculator is worth downloading.
 

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I always wonder if you really need any of these gizmos. Before I figured out that I could tighten the chain easily by hanging the bike from the front wheel and using the weight of the rear wheel for tension (suppose this could work in reverse even better), I simply pulled back the wheel and tightened it where it was. The tighten/loosen walk back method nver really worked for me. The chain was always a bit floppy - I could move it up and down easily with my hand. I admit to being concerned at first and am glad I found a way to make it tighter but I never had an issue in many miles of riding with plenty of fast downhills.

Using the link at a time trial and error method, I'd think you could get a chain with vertical dropouts sufficiently tight.
 

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Discussion Starter · #12 ·
appreciate the forum condescending tone

JCavilia said:
Edit: I just noticed your other post, in which you ask about spokes for a wheel with an eno eccentric hub. If you're talking about the same bike here, this whole discussion is irrelevant. With that hub, you can get good chain tension with any gear combo -- that's the whole reason for the eccentric mount. You don't need a magic gear. .
I was simply exploring different options. ie not getting the eccentric hub hintz why i would need a "magic" ratio for a vertical dropout.
 
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