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Old 05-21-09, 10:42 PM   #1
The Big Wheel
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Convert 7 speed to single speed

How do I convert a 7speed bike into a one speed bike? And how do I go about installing the right gear? Say I want to make it a single speed but I want it to have gear #5.
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Old 05-21-09, 10:50 PM   #2
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What is the make/model/year?
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Old 05-21-09, 10:54 PM   #3
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if you have a freehub, you can use this.
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Old 05-21-09, 11:05 PM   #4
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It's a 700C Men's Mongoose Paver Commuter bike. I plan to use it in the winter time only and I've read that single speeds are better for winter riding. The description says it has a SRAM/Shimano 7-speed shift system.

http://www.kaboodle.com/reviews/700c...-commuter-bike
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Old 05-21-09, 11:27 PM   #5
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Well, one of the requirements for a singlespeed conversion is to have a frame with horizontal or semi-horizontal dropouts. The Paver frame has vertical dropouts, which cannot be modified for proper singlespeed operation.

To explain, in a multi-speed bike with a rear derailleur, the chain is kept tensioned by the action of the rear derailleur. On all bikes, it is absolutely necessary that the chain be kept tensioned properly, that is, that the chain not be allowed to be slack. A slack chain on a singlespeed bike means that the chain will fall off by itself, which is very bad. Now, to tension the chain without the use of a rear derailleur, you must have a frame with dropouts that are not vertical, so that you can set chain tension by adjusting the position of the rear wheel within the dropouts. In other words, on a frame with horizontal or semi-horizontal dropouts, you can choose the wheelbase of the bike to tension to chain.

There are alternatives that do not apply in your case - the first is to have a special frame with an eccentric bottom bracket and appropriately oversized bottom bracket shell. The Paver frame cannot be modified for this. Another option is to have a wheel with an eccentric rear hub - such a wheel would cost over $200.

Now, there are other options. One is a phantom chainring, which is a bad idea. The other is a magic gearing combination, which is difficult to achieve and has many downsides, including the need for complex, obscure and magical computations and the need for spare parts and tools that may be expensive.

The last option, and in my humble opinion the only viable and affordable (as in free) option for a singlespeed conversion in your case, is to set the rear derailleur limit screws so that the rear derailleur will be frozen in a gear of your choice, disabling the shifter in the process.

Such a configuration would not gain all the advantages of a proper singlespeed. However, your chain will stay a lot cleaner if it does not shift from gear to gear.

If you want the singlespeed experience with that bike, my recommendation would simply be to select a gear and never touch your shifter again. Eventually, your rear derailleur and control cable will rust in place and you'll have achieved a free singlespeed conversion without performing any work. Your chain will stay cleaner and you won't have to worry about the upkeep of your deralleur and shifter.
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Old 05-23-09, 02:08 AM   #6
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Quote:
Originally Posted by hernick View Post
Well, one of the requirements for a singlespeed conversion is to have a frame with horizontal or semi-horizontal dropouts. The Paver frame has vertical dropouts, which cannot be modified for proper singlespeed operation.

To explain, in a multi-speed bike with a rear derailleur, the chain is kept tensioned by the action of the rear derailleur. On all bikes, it is absolutely necessary that the chain be kept tensioned properly, that is, that the chain not be allowed to be slack. A slack chain on a singlespeed bike means that the chain will fall off by itself, which is very bad. Now, to tension the chain without the use of a rear derailleur, you must have a frame with dropouts that are not vertical, so that you can set chain tension by adjusting the position of the rear wheel within the dropouts. In other words, on a frame with horizontal or semi-horizontal dropouts, you can choose the wheelbase of the bike to tension to chain.

There are alternatives that do not apply in your case - the first is to have a special frame with an eccentric bottom bracket and appropriately oversized bottom bracket shell. The Paver frame cannot be modified for this. Another option is to have a wheel with an eccentric rear hub - such a wheel would cost over $200.

Now, there are other options. One is a phantom chainring, which is a bad idea. The other is a magic gearing combination, which is difficult to achieve and has many downsides, including the need for complex, obscure and magical computations and the need for spare parts and tools that may be expensive.

The last option, and in my humble opinion the only viable and affordable (as in free) option for a singlespeed conversion in your case, is to set the rear derailleur limit screws so that the rear derailleur will be frozen in a gear of your choice, disabling the shifter in the process.

Such a configuration would not gain all the advantages of a proper singlespeed. However, your chain will stay a lot cleaner if it does not shift from gear to gear.

If you want the singlespeed experience with that bike, my recommendation would simply be to select a gear and never touch your shifter again. Eventually, your rear derailleur and control cable will rust in place and you'll have achieved a free singlespeed conversion without performing any work. Your chain will stay cleaner and you won't have to worry about the upkeep of your deralleur and shifter.
ha! I love that! "you want a one-speed bike you ask?" don't shift!
seriously, you could get yourself a chain tensioner, which is sort of like a half a derailer (or you could use the tension pulley on your existing derailer) to keep your chain from going slack. if you go all out and procure a singlespeed wheel, you might have to add spacers to the axle for it to fit into the bike's dropouts, not to mention getting a new bottom bracket to get the right chainline. you can adjust the chainline by moving your chainring's position on the spider.
good luck
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Old 05-23-09, 02:19 AM   #7
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I know a lot of people who ride derailer equipped bikes through the winter and when it gets really cold and thinsg freeze solid they often get to enjoy the single speed experience.

To take that Paver from a 7 speed to a one speed you need an ss kit and a chain tensioner which you can buy, or you can use the existing rear derailer and lock it into position.

A rear derailer is also as fine a chain tensioner as one can get.

If you don't live in a frozen hell then the 7 speed should be fine.
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Old 05-23-09, 09:12 AM   #8
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You can also try to find the "Magic Gear". It took me about 10 minutes, but maybe I was just lucky.

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Old 05-23-09, 12:10 PM   #9
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The use of a half link on the chain can also aid in fining the "magic gear".
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Old 05-23-09, 12:21 PM   #10
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Quote:
Originally Posted by hernick View Post
Well, one of the requirements for a singlespeed conversion is to have a frame with horizontal or semi-horizontal dropouts. The Paver frame has vertical dropouts, which cannot be modified for proper singlespeed operation.

To explain, in a multi-speed bike with a rear derailleur, the chain is kept tensioned by the action of the rear derailleur. On all bikes, it is absolutely necessary that the chain be kept tensioned properly, that is, that the chain not be allowed to be slack. A slack chain on a singlespeed bike means that the chain will fall off by itself, which is very bad. Now, to tension the chain without the use of a rear derailleur, you must have a frame with dropouts that are not vertical, so that you can set chain tension by adjusting the position of the rear wheel within the dropouts. In other words, on a frame with horizontal or semi-horizontal dropouts, you can choose the wheelbase of the bike to tension to chain.

There are alternatives that do not apply in your case - the first is to have a special frame with an eccentric bottom bracket and appropriately oversized bottom bracket shell. The Paver frame cannot be modified for this. Another option is to have a wheel with an eccentric rear hub - such a wheel would cost over $200.

Now, there are other options. One is a phantom chainring, which is a bad idea. The other is a magic gearing combination, which is difficult to achieve and has many downsides, including the need for complex, obscure and magical computations and the need for spare parts and tools that may be expensive.

The last option, and in my humble opinion the only viable and affordable (as in free) option for a singlespeed conversion in your case, is to set the rear derailleur limit screws so that the rear derailleur will be frozen in a gear of your choice, disabling the shifter in the process.

Such a configuration would not gain all the advantages of a proper singlespeed. However, your chain will stay a lot cleaner if it does not shift from gear to gear.

If you want the singlespeed experience with that bike, my recommendation would simply be to select a gear and never touch your shifter again. Eventually, your rear derailleur and control cable will rust in place and you'll have achieved a free singlespeed conversion without performing any work. Your chain will stay cleaner and you won't have to worry about the upkeep of your deralleur and shifter.
I have a 1999 Trek 6000 with vertical drops which I am able to run several different ratios on without the use of a tensioner.

Once you find a magic gear, the computations involved in finding other compatible gears is not really all that difficult (each additional tooth requires an additional 1/8" of chain). If a "magic gear" is not possible, a chain tensioner is inexpensive and effective.

I'm pretty sure the OP's bike uses a cassette type hub, so chain line should not be an issue. All that is needed is a spacer kit.
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Old 05-24-09, 01:03 AM   #11
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Originally Posted by tFUnK View Post
if you have a freehub, you can use this.
This is the Forte conversion kit on a 7-spd freehub wheel I had lying around. The kit comes with three cogs to choose from, and various spacers to make a straight chainline. I'm using the 16T cog, with my inner 40T chainring. If you have vertical dropouts, you use the included tensioner.


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Old 05-24-09, 06:06 AM   #12
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If you have not yet bought the 7-speed bike, (that's what I get from your posts), buy a factory-built singlespeed, instead.
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Old 05-24-09, 07:41 AM   #13
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A new 7 speed bike will have a freewheel.

Tom Deakins' article on sheldonbrown.com applies although you may not be able to redish a 7 speed wheel enough, and the dropouts will be vertical so you'll need a chain tensioner (which only works with ss, not fixed.)
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