Author Topic: Fixed wheel on the cheap  (Read 2764 times)

border-rider

Fixed wheel on the cheap
« on: April 15, 2008, 10:16:58 am »
You will need:

An old back wheel designed for a screw-on freewheel block
Spanners to fit the axle spacers/nuts
A fixed sprocket
A spoke key (optional)

Note: these instructions work for most cup'n'cone hubs. Fancy sealed bearing hubs (like Mavic 501s) may need a different approach that involves reversing the axle.  Specific instructions apply - see www.fixieFAQs.org.uk

The thread on the hub will be the same as the fixed sprocket hub, so it'll just screw on.  The problem is the chainline -  the sprocket ends up way too far inboard.  Spacers wouldn't help because the thread length on the hub isn't enough to be able to space the sprocket out enough - old freewheels actually overhung the thread by a substantial amount.

The solution is to move the spacers on the axle from the drive side to the non-drive side so that the whole wheel moves over in the frame, and the sprocket ends up aligned with the chainring -  but that means that the rim is way offset towards the drive side.

If you aren't fussy about having the rim central in the frame, and don't use a back brake, then that's it, you're done, happy fixing.

I used a bike with this set-up as a London commuter for years.  Just be aware that you can't fit a standard lockring, though if it worried you you could use a BB lockring & Loctite.  I never bothered and never had a problem.



If you do want a back brake, or you want your wheels to track each other, then you'll need that optional spoke key.  The secret here is that all you're trying to do is to change the dishing; you need to loosen off all the drive side spokes and tighten up the non-drive side by the same amount. That way the wheel will stay true.  Work your way round the wheel, starting at the valve hole, and turn all the drive-side nipples exactly a half-turn clockwise (as you look down the spoke from the hub towards the rim) and all the non-drive side ones exactly a half-turn anticlockwise. When you do the non-drive-side ones, the secret is to turn them 3/4 of a turn and then back 1/4 turn to avoid spoke wind-up.  Have a look at how much difference that's made to the dishing and repeat until the rim is centred in the frame.  As you get close, you might need to change the 1/2 turns to 1/4 turns, but remember to turn all the spokes by the same amount on each pass around the rim.


If you have box-section rims - like most modern ones - then the extra sticky-up-ness of the spokes through the non-drive-side nipples won't be an issue - it'll still be below the rim tape.  If you try this on an old solid rim, like the Weinmann 27" , you might need to file the spoke ends down to prevent punctures.


Here's one I did earlier - note the spacers on the non-drive side, the lack of spare thread on the hub and the (reasonable) centred-ness of the rim in the frame.  That bike doesn't have a back brake so I wasn't too concerned about absolute centring.  It took me about 10 minutes.


Re: Fixed wheel on the cheap
« Reply #1 on: April 15, 2008, 11:21:39 am »
I recognise that bike  ;)

border-rider

Re: Fixed wheel on the cheap
« Reply #2 on: April 15, 2008, 11:30:27 am »
Yup  :)

Good wheel, that.  But I'd not run it with a back brake any longer.  It's done an intergalactic mileage, including a full SR2000 series.

Re: Fixed wheel on the cheap
« Reply #3 on: April 15, 2008, 11:58:42 am »
It did another 7.2 miles this morning and is currently in the server room.