Author Topic: Converting a geared bike to single speed?  (Read 2534 times)

Converting a geared bike to single speed?
« on: November 19, 2013, 10:06:46 pm »
At some point in the future, I'd like to get a Surly Straggler, which would replace my hybrid in the heavy-duty-bike-with-many-low-gears category. I've been wondering whether I could then repurpose the hybrid as a single speed town hack bike - however, the sticking point (literally) is likely to be the bottom bracket, which seems to be riveted in. IIRC, it's 122.5mm, which seems on the long side.

The crankset on there is one of the cheapest of the cheap Shimano triples (with non-removable steel rings!). The rear wheel is a cassette hub (10 speed, though it's got a 7 speed cassette and spacer on it). I'd be wanting to use the biggest chainring, which I presume would mean a lot of spacers between the hub and cassette. I'd replace it with a single ring one if it were not for (a) the bottom bracket issue, and (b) cost, which I'd like to keep as low as possible. I think it may end up with a very odd chainline, though.

So - is this likely to be a bad idea from the outset, or could it work...?

Torslanda

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Re: Converting a geared bike to single speed?
« Reply #1 on: November 19, 2013, 10:40:50 pm »
Single speed conversion kits offer a multitude of positions (No! Really, Mrs!*) as the cog and the spacers add up to the width of the cassette, so you can have the cog right against the lockring if you want.

I've never seen a riveted BB, any chance of a pic with the chainset off? (Cor! Look at the taper on that!*)

I can get alloy, single ring [snigger, fnaar, fnaar*] chainsets for £reasonable so if you're in the market give us a shout and I'll see what I can do . . .

* Apologies for the innuendo . . .
VELOMANCER

Well that's the more blunt way of putting it but as usual he's dead right.

Re: Converting a geared bike to single speed?
« Reply #2 on: November 19, 2013, 11:09:50 pm »
I've never seen a riveted BB, any chance of a pic with the chainset off? (Cor! Look at the taper on that!*)

The rivets are underneath the shell, rather than through the middle - it does look like a bodge job. There's a pic here, posted back when I first noticed the weirdness. I think I'll run the frame into the ground and then bin it - I can't see the bottom bracket being replacable, really. That's what's made me think changing the chainset wouldn't work - an alloy single ring one would be great (and save a load of weight!) but I haven't seen any single ring chainsets for a 122.5mm bottom bracket...

I suppose I could get a threadless bottom bracket, but I'm not entirely sure I could get the current one out!

Gattopardo

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Re: Converting a geared bike to single speed?
« Reply #3 on: November 19, 2013, 11:58:33 pm »
Looking at pics you get a square taper bb that doesn't need threads.

http://www.charliethebikemonger.com/yst-threadless-bb-for-damaged-frames-58-p.asp

Torslanda

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Re: Converting a geared bike to single speed?
« Reply #4 on: November 20, 2013, 12:21:43 am »
Truly a bodge of Titanic proportions.

Dr. John sez use it up, wear it out & bin it.
VELOMANCER

Well that's the more blunt way of putting it but as usual he's dead right.

Re: Converting a geared bike to single speed?
« Reply #5 on: November 20, 2013, 12:46:50 am »
They don't look like rivets to me - more like allen head grub screws.

I'd go with iddu's guess in the other thread, that the BB shell thread has stripped and they're being used as lock bolts. I'd guess that if you can undo them and remove the other cup, you'd be able to replace the BB either with a threadless one or by renewing the bodge.

Kim

  • Timelord
Re: Converting a geared bike to single speed?
« Reply #6 on: November 20, 2013, 12:53:26 am »
They don't look like rivets to me - more like allen head grub screws.

IRTA "alien head grub screws"

I think that's my cue for bed.  I anticipate nightmares.
Careful, Kim. Your sarcasm's showing...

Re: Converting a geared bike to single speed?
« Reply #7 on: November 20, 2013, 09:48:27 am »
The traditional bodge is to rip an old cassette apart for spacers and just leave a single sprocket on. I might have some bits in the attic, if you haven't got a spare kicking about. Chainline shouldn't be an issue, as long as you get the sprocket spaced correctly.

I'm with torslanda on the BB/chainset - just leave it on and run it into the ground, unless you want to spend a load of wonga to bodge something else on.

(click to show/hide)


interzen

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Re: Converting a geared bike to single speed?
« Reply #8 on: November 20, 2013, 10:34:22 am »
If you want to replace the rear wheel completely then I've got an unused, unloved fixed wheel in the shed (Goldtec hub on OpenPro, 135mm OLN) - if you can shift the existing sprockets then there's no reason why you couldn't fit an appropriate freewheel.

'Course, getting it to you would be another matter entirely ...

mcshroom

  • Mushroom
Re: Converting a geared bike to single speed?
« Reply #9 on: November 20, 2013, 10:57:25 am »
If you just want a converter kit to try it out I have a spare VeloSolo set and 16/18t 3/32" sprockets in my bit box you are welcome to.

I put a 119mm chainset on a stuck 122.5 bottom bracket on my hack singlespeed last winter and used the middle ring (38x16 - around 64"). The chain was quite a way out from the hub, but I didn't have any problems with it.
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zigzag

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Re: Converting a geared bike to single speed?
« Reply #10 on: November 20, 2013, 11:26:43 am »
judging by the photos, my opinion is that it is not worth to spend any money on this bike. browsing local ads/ebay i can see a lot of bikes for £30-50 which have been used few times then left in the shed. with a bit of tlc (regreasing bearings, retensioning spokes, lubing cables and upgrading brake pads, maybe new tyres) they could be used as runabouts for few years easily.

eta: this for example

Re: Converting a geared bike to single speed?
« Reply #11 on: November 20, 2013, 06:04:34 pm »
Thanks for the comments - looks as though it might work...

judging by the photos, my opinion is that it is not worth to spend any money on this bike.

Oh indeed - it only cost me £20 four years ago anyway, and it was used and abused daily up until recently. It doesn't exactly owe me anything, hence wanting to do it on the cheap! I don't think I'd have to spend anything, since I could destroy the old cassette and use the existing chain (it's not that worn). When it's totally knackered, I'll just replace the frame with something like a Pompino (if On-One ever bring out any colours that aren't horrible) and get a proper chainset.

I put a 119mm chainset on a stuck 122.5 bottom bracket on my hack singlespeed last winter and used the middle ring (38x16 - around 64"). The chain was quite a way out from the hub, but I didn't have any problems with it.

That's the kind of thing I have in mind, though it'd have to be the outer ring (even that's only 42t!) so the chain would be even further from the hub. It might look a bit odd.


Gattopardo

  • Lord of the sith
  • Overseaing the building of the death star
Re: Converting a geared bike to single speed?
« Reply #12 on: November 20, 2013, 09:31:44 pm »
If you want to replace the rear wheel completely then I've got an unused, unloved fixed wheel in the shed (Goldtec hub on OpenPro, 135mm OLN) - if you can shift the existing sprockets then there's no reason why you couldn't fit an appropriate freewheel.

'Course, getting it to you would be another matter entirely ...

700cc or 26"?

Just toying with a frame idea