flip-flop fixie

[Ram]

I am looking to convert my mtb into a fixie with a flip-flop rear hub, and I have a question. How
much difference in rear cogs can you have if your rear dropouts are an inch long? (The dropouts are
almost horizontal.)Will a significant difference in rear cogs be attainable? The other option would
be to put a single-speed freewheel on the other side, but I'd rather have a completely fixed gear
bike with multiple gearing options. Thanks in advance for any advice.

 

[Sheldon Brown]

Someone asked:

> I am looking to convert my mtb into a fixie with a flip-flop rear hub, and I have a question. How
> much difference in rear cogs can you have if your rear dropouts are an inch long? (The dropouts
> are almost horizontal.)Will a significant difference in rear cogs be attainable? The other option
> would be to put a single-speed freewheel on the other side, but I'd rather have a completely fixed
> gear bike with multiple gearing options. Thanks in advance for any advice.

Each tooth added or subtracted moves the axle 1/8 inch.

I've got a lot of information on this sort of thing on my Website at:

http://sheldonbrown.com/fixed

Sheldon "Coasting Is A Pernicious Habit" Brown +-------------------------------------------------+
| I=92ll be appearing with the Sudbury Savoyards | In Gilbert & Sullivan=92s _Patience_ | February
| 21-March 1, Sudbury, Massachusetts | http://sudburysavoyards.org |
+-------------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

 

[Ant]

[email protected] (ram) wrote in message
news:<[email protected]>...
> I am looking to convert my mtb into a fixie with a flip-flop rear hub, and I have a question. How
> much difference in rear cogs can you have if your rear dropouts are an inch long? (The dropouts
> are almost horizontal.)Will a significant difference in rear cogs be attainable? The other option
> would be to put a single-speed freewheel on the other side, but I'd rather have a completely fixed
> gear bike with multiple gearing options. Thanks in advance for any advice.

i have to check news on google, so no doubt ten people have already posted relevant replies, but
my thoguhts:

each additional tooth, at .5" pitch, adds an additional .5" to the necessary chain, distributed over
the top and bottom. perhaps that means that theoretically, you could add teeth to the rear cog for
every 1/4" of dropout travel (apx.)? for a 1" dropout, you woudlnt want to put it at the complete
back or the complete front, so i imagine if you want two different gears, and you use a front
chainring such that your high gear puts the rear axle in the back of the dropout, then you could add
two teeth in the rear and end up with a gear that will still fit in your dropout. maybe three?

my other thoughts are that i'd go for a QR rear hub if you want to switch gears on the go.

fixed is the way to go. even if my other 'advice' isnt valid, this at least is dead on. but it
sounds like you're already sold.

have fun with it.

anthony

 

[David L. Johnso]

On Sun, 16 Feb 2003 23:15:34 -0500, ant wrote:

> each additional tooth, at .5" pitch, adds an additional .5" to the necessary chain, distributed
> over the top and bottom. perhaps that means that theoretically, you could add teeth to the rear
> cog for every 1/4" of dropout travel (apx.)?

No, what you missed was the fact that the chain only wraps around half of the sprocket, so the extra
length of chain from top of sprocket to bottom is only 1/4" for each additional tooth, so 1/8"
difference in position on the dropout.

That allows a fairly substantial difference in gears -- not enough to have an uphill/downhill bike
-- if you want that, keep the gears, but enough to have a twiddling gear and a hammering gear.

> teeth in the rear and end up with a gear that will still fit in your dropout. maybe three?

You could easily do 6
>
> my other thoughts are that i'd go for a QR rear hub if you want to switch gears on the go.
>
Yeah, I agree here. Nice thing to have.

--

David L. Johnson

__o | And what if you track down these men and kill them, what if you _`\(,_ | killed all of us?
From every corner of Europe, hundreds, (_)/ (_) | thousands would rise up to take our places.
Even Nazis can't kill that fast. -- Paul Henreid (Casablanca).

 

[Kinkycowboy]

On Sun, 16 Feb 2003 23:33:31 -0500, "David L. Johnson" <David L. Johnson
<[email protected]>> wrote:

>On Sun, 16 Feb 2003 23:15:34 -0500, ant wrote:
>
>> each additional tooth, at .5" pitch, adds an additional .5" to the necessary chain, distributed
>> over the top and bottom. perhaps that means that theoretically, you could add teeth to the rear
>> cog for every 1/4" of dropout travel (apx.)?
>
>No, what you missed was the fact that the chain only wraps around half of the sprocket, so the
>extra length of chain from top of sprocket to bottom is only 1/4" for each additional tooth, so
>1/8" difference in position on the dropout.
>
>That allows a fairly substantial difference in gears -- not enough to have an uphill/downhill bike
>-- if you want that, keep the gears, but enough to have a twiddling gear and a hammering gear.
>
>> teeth in the rear and end up with a gear that will still fit in your dropout. maybe three?
>
>You could easily do 6

Er, 6 teeth is 3/4", which is a hell of a lot of axle movement in a 1" long slot, allowing for the
thickness of the axle and letting the nut sit fully on the dropout face. For 1" of horizontal
dropout (excluding the half round at the back) the most you can get is 1" less 3/8" axle diameter,
or 5 teeth. Allowing for the chainstay not being the exact right length to accommodate both
extremes, you might lose a tooth at each end in the worst case, cutting you down to only 3 teeth
difference. Still worth having if you go for the small rings and sprockets route, say 42x16 (65")
and 42x13 (79")

>>
>> my other thoughts are that i'd go for a QR rear hub if you want to switch gears on the go.
>>
>Yeah, I agree here. Nice thing to have.

Kinky Cowboy

*Your milage may vary Batteries not included May contain traces of nuts.

 

[David Damerell]

ram <[email protected]> wrote:
>I am looking to convert my mtb into a fixie with a flip-flop rear hub, and I have a question. How
>much difference in rear cogs can you have if your rear dropouts are an inch long? (The dropouts are
>almost horizontal.)Will a significant difference in rear cogs be attainable?

One idea, if you can get the spacing magic right for good chainline, would be to have two front
chainrings as well, with the difference between them being equal to the difference in the rear
sprockets. Then you could use either the big-small or small-big for a very large difference in gears
- giving you a conventional fixed gear, but also a much lower bailout gear if you flip the hub.
--
David Damerell <[email protected]> flcl?

 

[David L. Johnso]

On Mon, 17 Feb 2003 09:23:15 -0500, KinkyCowboy wrote:

> Er, 6 teeth is 3/4", which is a hell of a lot of axle movement in a 1" long slot, allowing for the
> thickness of the axle and letting the nut sit fully on the dropout face.

I guess I was presuming that the 1" allowed for enough bite for the QR. You'd really have to
experiment with ratios to see what works. On my bike, which has track ends, I could get more than
the 6 teeth I suggested, though I don't have much desire to. I have, at the moment, an 18 and a 17
on my wheel, with a 46 chainring.. Except for rare excursions on the track, or when used exclusively
to climb, that's pretty much where it stays.

Another consideration is, if you have a rear brake (belt and suspenders?), you will not be able to
adjust the wheel that far back and forth without messing with the brake.

--

David L. Johnson

__o | To announce that there must be no criticism of the president, or _`\(,_ | that we are to
stand by the president right or wrong, is not (_)/ (_) | only unpatriotic and servile, but is
morally treasonable to the American public. --Theodore Roosevelt

 

[Sheldon Brown]

David Damerell wrote:

> One idea, if you can get the spacing magic right for good chainline, would be to have two front
> chainrings as well, with the difference between them being equal to the difference in the rear
> sprockets. Then you could use either the big-small or small-big for a very large difference in
> gears - giving you a conventional fixed gear, but also a much lower bailout gear if you flip
> the hub.

I've done this. See: http://sheldonbrown.org/hercules.html

52-42 chainrings, 19 fixed on one side and a 20-30 two speed freewheel on t'other.

Sheldon "Works Great" Brown +------------------------------------------+
| To invent, you need a good imagination | and a pile of junk. --Thomas Edison |
+------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

 

[Mark Hickey]

Sheldon Brown <[email protected]> wrote:

>52-42 chainrings, 19 fixed on one side and a 20-30 two speed freewheel on t'other.
>
>Sheldon "Works Great" Brown

REAL MEN don't need so steenken' many gears!

>+------------------------------------------+
>| To invent, you need a good imagination | and a pile of junk. --Thomas Edison |
>+------------------------------------------+

It works the same for a legendary TV show pitting two teams against each other...

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame

 

[Ant]

I wrote:
> > each additional tooth, at .5" pitch, adds an additional .5" to the necessary chain, distributed
> > over the top and bottom. perhaps that means that theoretically, you could add teeth to the rear
> > cog for every 1/4" of dropout travel (apx.)?

A much more knowing person wrote:

> No, what you missed was the fact that the chain only wraps around half of the sprocket, so the
> extra length of chain from top of sprocket to bottom is only 1/4" for each additional tooth, so
> 1/8" difference in position on the dropout.

Whoops. thanks. i think i confused two issues in my head at the same time. Even if you can get 6
teeth difference in for the same dropout, is this practical? Wouldn't you have to add chain? i
definitely resign from the math part of this as ive managed to humiliate myself once in this thread
already, so help me understand..

even with a quick link, adding a bit of chain to go from a a small gear to a big gear (or switching
chains) is a hassle (if it is to be done trailside), especially if this mountain bike is actually to
be ridden off road where dirt makes the quick link a slow link. IMveryHO.

curious, and put in my place,

anthony

 

[Kinkycowboy]

On Mon, 17 Feb 2003 12:19:47 -0500, "David L. Johnson" <David L. Johnson
<[email protected]>> wrote:

>On Mon, 17 Feb 2003 09:23:15 -0500, KinkyCowboy wrote:
>
>> Er, 6 teeth is 3/4", which is a hell of a lot of axle movement in a 1" long slot, allowing for
>> the thickness of the axle and letting the nut sit fully on the dropout face.
>
>I guess I was presuming that the 1" allowed for enough bite for the QR. You'd really have to
>experiment with ratios to see what works. On my bike, which has track ends, I could get more than
>the 6 teeth I suggested, though I don't have much desire to. I have, at the moment, an 18 and a 17
>on my wheel, with a 46 chainring.. Except for rare excursions on the track, or when used
>exclusively to climb, that's pretty much where it stays.
>
>Another consideration is, if you have a rear brake (belt and suspenders?), you will not be able to
>adjust the wheel that far back and forth without messing with the brake.

Yeah, I measured my track frame, currently equipped with 49x18 and the axle right at the front of
the fork end, and could move the axle back exactly 3/4", equivalent to 6 teeth difference in the
sprocket. That suits me fine as it's never going to have a sprocket smaller than 14t in it, and I
can go from 49x15 to 52x15 without lengthening the chain. My road frame with long dropouts has at
most 1/2" of difference between fully forward and fully back even after removing the adjuster
screws. Plenty for what the dropouts were designed for, but realistically only 3 teeth of adjustment
for fixed gear use.

Kinky Cowboy

*Your milage may vary Batteries not included May contain traces of nuts.

 

[Kinkycowboy]

On 17 Feb 2003 16:50:19 +0000 (GMT), David Damerell <[email protected]> wrote:

>ram <[email protected]> wrote:
>>I am looking to convert my mtb into a fixie with a flip-flop rear hub, and I have a question. How
>>much difference in rear cogs can you have if your rear dropouts are an inch long? (The dropouts
>>are almost horizontal.)Will a significant difference in rear cogs be attainable?
>
>One idea, if you can get the spacing magic right for good chainline, would be to have two
>front chainrings as well, with the difference between them being equal to the difference in
>the rear sprockets. Then you could use either the big-small or small-big for a very large
>difference in gears - giving you a conventional fixed gear, but also a much lower bailout gear
>if you flip the hub.

Sheldon Brown has this set up on one of his bikes (albeit with a freewheel on one side of the flip
flop) and a reference to an even more perverted setup using 3 chainrings and 3 fixed sprockets on a
single sided hub to give a very wide range of gears, so anything is not only possible but has almost
certainly been done before.

Kinky Cowboy

*Your milage may vary Batteries not included May contain traces of nuts.

 

[David L. Johnso]

On Tue, 18 Feb 2003 02:12:16 -0500, ant wrote:

> Whoops. thanks. i think i confused two issues in my head at the same time. Even if you can get 6
> teeth difference in for the same dropout, is this practical? Wouldn't you have to add chain?

No, that is what the length of the dropout takes care of.

> i definitely resign from the math part of this as ive managed to humiliate myself once in this
> thread already, so help me understand..
>
> even with a quick link, adding a bit of chain to go from a a small gear to a big gear (or
> switching chains) is a hassle (if it is to be done trailside), especially if this mountain bike is
> actually to be ridden off road where dirt makes the quick link a slow link. IMveryHO.

Well, maybe off-road it would be messy, but you get quite a bit of shift by setting the chain length
so that with the big cog the weel is as far forward as practical, and with the smaller cog it's way
back in the dropout. My claim of 6 teeth was disputed, but it is likely to be possible --- it is
also likely to be more than you really need.

Taking the gear down from a rather challenging one to a twiddly one is great for when you hit the
wall. On the road, for me, that means one tooth. And you'd be surprized how much better you can feel
with that one tooth difference on a fixed gear bike. 3-4 teeth will make a big jump.

--

David L. Johnson

__o | A mathematician is a machine for turning coffee into theorems. _`\(,_ | -- Paul Erdos
(_)/ (_) |

 

[Kinkycowboy]

On 17 Feb 2003 23:12:16 -0800, [email protected] (ant) wrote:

>I wrote:
>> > each additional tooth, at .5" pitch, adds an additional .5" to the necessary chain, distributed
>> > over the top and bottom. perhaps that means that theoretically, you could add teeth to the rear
>> > cog for every 1/4" of dropout travel (apx.)?
>
>A much more knowing person wrote:
>
>> No, what you missed was the fact that the chain only wraps around half of the sprocket, so the
>> extra length of chain from top of sprocket to bottom is only 1/4" for each additional tooth, so
>> 1/8" difference in position on the dropout.
>
>
>Whoops. thanks. i think i confused two issues in my head at the same time. Even if you can get 6
>teeth difference in for the same dropout, is this practical? Wouldn't you have to add chain? i
>definitely resign from the math part of this as ive managed to humiliate myself once in this thread
>already, so help me understand..
>
>even with a quick link, adding a bit of chain to go from a a small gear to a big gear (or switching
>chains) is a hassle (if it is to be done trailside), especially if this mountain bike is actually
>to be ridden off road where dirt makes the quick link a slow link. IMveryHO.
>
>curious, and put in my place,
>
>anthony

All of the argument about how much difference you can have between the two sides of the flip-flop
presupposes that you're not going to start adding or subtracting links from your chain. That being
the case, you need 3/4" of usable axle movement to get 6 teeth difference, always assuming the
chainstay length is exactly right for your small cog option to sit at the back of the dropout with
correct chain tension. If it doesn't, you need to take two links or 1" out of the chain, which
brings your axle forward a full 1/2", thus using up most of your possible adjustment. You can get
around this by a lengthy process of either mathematics or experiment to optimise your chainring
choice. Lets say, for mountain biking, you want your high gear to be 2:1 For example, if 32x16 only
works with the axle halfway along the dropout, thus giving no useful adjustment, 34x17 with two
extra links will move the axle backward 1/8" and give the same gear. 36x18 and two more links gets
you back another 1/8", and so on. Once you've got the axle nearly to the back of the dropout for
your high gear, you should have about 1/2", maybe 5/8", of usable adjustment. Each extra tooth on
the sprocket will use 1/8" of adjustment. I've ignored the fact that the chain runs in converging
lines, slightly over halfway round the chainring and not quite halfway round the sprocket because
these factors make a trivial difference with longish chainstays and low gear ratios. Obviously, this
gets to be more fun on a road bike where your high gear is not a convenient 2:1 ratio and the
combination of short stays and bigger ratios might make a bit of trigonometry necessary for complete
precision, but it wouldn't be rocket science to knock up a quick spreadsheet to calculate the
effective chainstay length for any combination of chainring, sprocket and chain length.

Kinky Cowboy

*Your milage may vary Batteries not included May contain traces of nuts.

 

[Ant]

"David L. Johnson" <David L. Johnson <[email protected]>> wrote in message
news:<[email protected]>...

> No, (followed by an explanation)

Thanks- i see the light.