Building a winter roadie / single-speed / fixie

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Re: Building a winter roadie / single-speed / fixie

Postby ris » 16 Sep 2013 12:12

Bopomofo wrote:Does anybody have any experience or advice on good donor bikes to look for? Interchangeability of cranks over the years? Is it possible to just take the derailleurs off a roadie and shorten the chain (surely this MUST work)?


i would expect chain stretch to eventually be a problem. the horizontal drop-out or tensioner makes it easy to keep the bike running smoothly. i suppose you could just drop it onto the next sprocket down on the cassette every time it starts skipping!

i've emergency-hacked a bike with a sheared rear derailleur into a s/s, but it was for a short period and not a permanent fix.
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Re: Building a winter roadie / single-speed / fixie

Postby JoddyBear » 16 Sep 2013 14:20

dont bother with a flip flop, any bike can be a single speed if you simply have the willpower to not change gear during a ride (which is a damn sight harder than it sounds).

go true fixie, if you have vertical dropouts then you'll need a chain tensioner, if they're horizontal, just pull the wheel back till the chain is taut.

always ask before taking anything from a skip, as anything at your local 'tip' or recycling centre, once in the skip is the property of the local authority, so would still be theft, no matter your perception of ownership.

very tempted to do this myself now. good plan. i wonder if this is WAT free...?
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Re: Building a winter roadie / single-speed / fixie

Postby Ewan » 16 Sep 2013 14:53

JoddyBear wrote:go true fixie, if you have vertical dropouts then you'll need a chain tensioner, if they're horizontal, just pull the wheel back till the chain is taut.


Nope. If you have vertical drop outs then the only kind of chain tensioner that will work is one with an additional jockey wheel where the RD would normally sit. If you are running a fixed drive train then you absolutely can not use this kind chain tensioner, they are for single speed only - every time you eased off the pressure on the peddles the tension in the chain moves from the upper segment of chain to the lower segment. If you do not have appropriate chain tension without a tensioner, then the chain returning from the rear sprocket to the chainring will be slack and likely to jump off. If you are running vertical dropouts your only options are to use a "magic gear" or to buy a White Industries Eccentric hub ($$$$$).
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Re: Building a winter roadie / single-speed / fixie

Postby Bopomofo » 16 Sep 2013 15:11

Ewan wrote:
JoddyBear wrote:go true fixie, if you have vertical dropouts then you'll need a chain tensioner, if they're horizontal, just pull the wheel back till the chain is taut.


Nope. If you have vertical drop outs then the only kind of chain tensioner that will work is one with an additional jockey wheel where the RD would normally sit. If you are running a fixed drive train then you absolutely can not use this kind chain tensioner, they are for single speed only - every time you eased off the pressure on the peddles the tension in the chain moves from the upper segment of chain to the lower segment. If you do not have appropriate chain tension without a tensioner, then the chain returning from the rear sprocket to the chainring will be slack and likely to jump off. If you are running vertical dropouts your only options are to use a "magic gear" or to buy a White Industries Eccentric hub ($$$$$).


That's a damned good point. Thanks for the warning.

What's a magic gear?
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Re: Building a winter roadie / single-speed / fixie

Postby Ewan » 16 Sep 2013 15:25

A "magic gear" is the a specific combination of gear-ratio and chain-stay length that enables you to have exactly the right chain tension on a bike with vertical drop outs. The difficulty is that it can be difficult to calculate and it limits the number of gear ratios you can run (assuming that you might want to run more than one combination). Using a half link can help you find a combination, but make sure you don't use an entire chain of half links because they are rubbish and (unlike normal chains) they DO stretch.

If you have to use vertical drop outs SS, magic gear or Eccentric hub are your only options.

Magic gear calc here:
http://eehouse.org/fixin/formfmu.php
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Re: Building a winter roadie / single-speed / fixie

Postby didds » 30 Sep 2013 08:39

Bopomofo wrote: Is it possible to just take the derailleurs off a roadie and shorten the chain (surely this MUST work)?


Its what I did with an old bike I was given - just adjusted the chain length so it fitted "perfectly" around the chainring and the most "in line" cog. Its certainly the "quickest" way to ride a single speed, though it won't be a fixie. It also relies on drop out positioning for chain tensioning which could be a bit painful.



The problem only comes when you want/need a smaller cog than the straight line provides - I'd imagine the cog each side would be pretty much Ok but you'd probably run the risk of the chain skipping off if you started to move outside those parameters - but by then you can probably justify a "proper"! single speed rear wheel.

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Re: Building a winter roadie / single-speed / fixie

Postby didds » 30 Sep 2013 09:41

as for your local recycling centre... don;t be surprised if you find they can;'t/won;t sell you any bikes they have.

I've asked at our local recycling centre to be flatly refused. Communications with the office merely elicited a one liner that they send the bikes to Africa.

Noble concept though that is, I can't help but think maybe converting the bikes to cash and sending the cash to Africa and also donating the money saved by not having to transport them to Africa (maybe that transportation is free of course) might be a more cost effective way of doing it! Then again... maybe not.

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Re: Building a winter roadie / single-speed / fixie

Postby Kevy427 » 30 Sep 2013 11:15

didds wrote:Noble concept though that is, I can't help but think maybe converting the bikes to cash and sending the cash to Africa and also donating the money saved by not having to transport them to Africa (maybe that transportation is free of course) might be a more cost effective way of doing it! Then again... maybe not.

didds

Good idea. We could then email and say that we have a large sum of cash to be transferred to their bank accounts and all we need is their account details, credit card details and PIN number before we can send it
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Re: Building a winter roadie / single-speed / fixie

Postby Bopomofo » 30 Sep 2013 14:23

Kevy427 wrote:
didds wrote:Noble concept though that is, I can't help but think maybe converting the bikes to cash and sending the cash to Africa and also donating the money saved by not having to transport them to Africa (maybe that transportation is free of course) might be a more cost effective way of doing it! Then again... maybe not.

didds

Good idea. We could then email and say that we have a large sum of cash to be transferred to their bank accounts and all we need is their account details, credit card details and PIN number before we can send it


:lol: :lol: :lol:

I've had a look at the tip in the 'sales' section.. nothing worth even handing a fiver over for. I got an awful old MTB off a colleague... now thinking that it might be nice to stick slicks and drops on it to make a cx bike. Only problem is that I'd need gear levers for drops. Unless I used my now redundant DA bar end shifters and stick them into the ends of the drops... now THAT would be retro. I'd have to run the rear shifter in friction mode, but it might just work...
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