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Old 11-04-06, 07:18 PM   #1
BROCK SAMPSON
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Gear help

I dunno if this has already been covered but I'm new to gears and I was just wondering if it's possible to have 2 speed front gearings with a fixed rear?
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Old 11-04-06, 07:40 PM   #2
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Go to www.rivbike.com

The Quickbeam uses two chain rings. I used a 12 speed bike with a missing rear derailleur cable for several months. Using only two gears was surprisingly adequate.
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Old 11-04-06, 09:30 PM   #3
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Thanks for the reply, and yeah I find 2 speed to be enough aswell thats why I'm looking into this. Do you know if I could run a 32/22 up the front but with a fixed 13 in the rear? I think this would be best if it works beacause these are basically the only gears I've needed and I wanna lose weight and the hastle of my rears gears.
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Old 11-04-06, 10:16 PM   #4
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Wow. I have seen some cool Rivendales before, but that is really neat.

Besides that bike, not that easy to go fixed w/ 2 in front. It will depend entirely on whether you have enough room in the dropouts to make up the 10t difference. w/ deep horizontal drops, maybe.
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Old 11-05-06, 07:33 AM   #5
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You will, of course, need a rear derailleur to allow the change in required chain length. Just lock it in position under the single cog using the limit screws.
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Old 11-05-06, 08:04 AM   #6
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Quote:
Originally Posted by BROCK SAMPSON
Thanks for the reply, and yeah I find 2 speed to be enough aswell thats why I'm looking into this. Do you know if I could run a 32/22 up the front but with a fixed 13 in the rear? I think this would be best if it works beacause these are basically the only gears I've needed and I wanna lose weight and the hastle of my rears gears.
For a 10 tooth difference on a fixed gear I'm guessing not. The issue is how are you going to take up the chain slack when you're in the 22 tooth chainring?

If you use a derailleur or a chain slack take up device, it will just pivot forward when you try to backpedal. If you had a bike with loooong horizontal drop out slots, it might work but It'd be a PITA to switch gears. For a 10 tooth difference I'm thinking they'll have to be specially designed dropouts, much longer than what you typically see.

If you were to use a flip-flop hub with a 19 cog on the other side, that would accomplish the same thing and might only take dropouts around a couple of inches long.

I used to have a Schwinn Twinn tandem that had an idler pulley to take up the slack in the timing chain. You might be able to weld a slotted piece of metal vertically onto the chainstay and raise or lower the idler pulley as needed to adjust the chainslack. I don't know however if it would be stable enough to handle the stress of backpedaling.
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Old 11-05-06, 11:03 AM   #7
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Quote:
Originally Posted by Retro Grouch
If you use a derailleur or a chain slack take up device, it will just pivot forward when you try to backpedal.
Good point. I forgot this was to be a fixed-gear bike.
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Old 11-05-06, 11:17 AM   #8
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This will do it. A two speed crank assembly.

http://derbyking.com/Detail/?n=145


It's $384 !!!
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Old 11-05-06, 11:20 AM   #9
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S-A hub gears have been used for fixed, but may be hard to find.
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Old 11-05-06, 11:40 AM   #10
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Another alternative is to find an old Bendix coaster brake hub with the 'kick-back' 2-speed. Basicly what you do is slightly back pedal and it shifts into a second gear. A Shimano Nexus 3-speed would fit the bill as well.

http://cgi.ebay.com/BENDIX-YELLOW-BA...QQcmdZViewItem
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Old 11-05-06, 11:53 AM   #11
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Just to be clear, when you say a fixed rear, do you mean just one cog, or do you mean an actual fixed gear cog with no freewheel?

If you're asking about running just a single cog in the rear with 2 speeds up front then, yes, you can do it. If you want to run a fixed gear, then no, you can't/
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Old 11-05-06, 11:59 AM   #12
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Quote:
Originally Posted by HillRider
You will, of course, need a rear derailleur to allow the change in required chain length. Just lock it in position under the single cog using the limit screws.
Not a good idea, on the first downhill you come to, if you stop pedaling, the chain will go tight at the bottom, slack at the top. The chain will then wrap around the fixed cog and rip the derailleur and the frame hanger from the frame. The rear wheel will lock and you will skid to a stop, destoying your tire. Trust me I have seen it happen.
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Old 11-05-06, 12:14 PM   #13
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You'd need one hell of a long dropout to enable you to run chainrings 10 teeth apart with the same chain. It goes without saying that changing between them involves getting off the bike, removing the wheel, moving the chain manually and remounting the wheel.
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Old 11-05-06, 05:57 PM   #14
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Quote:
Originally Posted by LóFarkas
You'd need one hell of a long dropout to enable you to run chainrings 10 teeth apart with the same chain. It goes without saying that changing between them involves getting off the bike, removing the wheel, moving the chain manually and remounting the wheel.

That's a good point. I think the the biggest difference the track ends on my Fuji track bike will accomodate is about two teeth on the rear cog. Maybe three tops.

I guess the best answer is for the OP is that it's possible but not worth the trouble. Change the rear cog instead.
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Old 11-05-06, 07:51 PM   #15
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Quote:
Originally Posted by miamijim
Another alternative is to find an old Bendix coaster brake hub with the 'kick-back' 2-speed. Basicly what you do is slightly back pedal and it shifts into a second gear.
Whoa! Remember he has a fixed gear, so that would be like an automatic transmission upshifting when you want to slow down. Only a vintage fixed hub gear will work.
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Old 11-05-06, 09:24 PM   #16
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Quote:
Originally Posted by Dave Moulton
Not a good idea, on the first downhill you come to, if you stop pedaling, the chain will go tight at the bottom, slack at the top.
Yeah, I realized that as soon as I recalled the OP wanted a fixed gear.
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Old 11-05-06, 09:50 PM   #17
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Sheldon has an article on how to convert a 3-speed Sturmey-Archer AW hub into a 2-speed fixed-gear, which is alot cheaper than buying a rare circa 1950 3-speed fixed-gear Sturmey-Archer ACS hub.
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Old 11-05-06, 10:00 PM   #18
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Quote:
Originally Posted by sivat
Just to be clear, when you say a fixed rear, do you mean just one cog, or do you mean an actual fixed gear cog with no freewheel?

If you're asking about running just a single cog in the rear with 2 speeds up front then, yes, you can do it. If you want to run a fixed gear, then no, you can't/
Yeah I'm planning to just run a single cog on the rear.
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