converting to fixed gear

[Vs4b]

I suspect i know the answer but...

Having recently got a new bike my old one is looking unloved and foolishly i sold my fixie last year...

Is it possible to convert it fixed gear, its a Ti Van Nicholas Mistral with vertical dropouts?

if so how would i go about doing it ?

[Chris N]

Magic gear, eccentric hub or eccentric BB. Do not use a tensioner.

[JonB]

Chris N has called it but just to extend the discussion a bit ...

-  the magic gear, I get the idea of this but I regularly have to tighten my chain (sometimes mid-ride on a long audax) by moving the wheel back but surely this isn't possible with a magic gear and so you're stuck with a slack chain which is dangerous or you're constantly changing chains ... am I missing something?
- the eccentric hub seems like the best bet but I have read reports of them slipping under load and the chain going slack
- eccentric BB, don't you need a specific BB shell for this?

Lots of good advice on the Velo Fixie section https://yacf.co.uk/forum/index.php?board=13.0 which is where this thread should probably live.

[rogerzilla]

I had trouble with the ENO hub slipping on an aluminium frame BUT I was using 39 x 14 for chainstay clearance, which gives higher chain tension than 48 x 18 or whatever.  Other people don't always have issues.

If the dropouts aren't perfectly vertical, you have a small amount of adjustment which might be enough to take out wear-related slack with a magic gear.

Amother approach is to use a QR hub (Goldtec, or just a freewheel hub) but cut the axle down to exactly the rear spacing.  This doesn't restrict you to using the dropout slot.  All this is on Sheldon Brown's site.

[Brucey]

I have never found anything with a QR skewer through it to be completely immune to movement in fixed gear use.

In terms of wheel movement the following applies;

chain full link  = 1/2"
chain half-link  = 1/4"
One tooth on chainring or sprocket = 1/8"

to which if you add

Other means  = 1/8"

means you can always keep your chain slack free (even with vertical dropouts) if you have two chainrings 1T apart and a half-link to hand, provided you can somehow get a further 1/8" of hub movement.

Some means of doing this include

-"mix and match chains";   combine lengths of new and slightly (about 0.5%) worn chains to get the correct total length. 

- file the dropouts slightly

- file the axle slightly, where it passes through the dropouts.

A combination of the last two is potentially better than you might expect.  It won't hurt any frame if the vertical rear dropouts are taken from ~10.2mm to 11.2mm (eg by filing a small notch in the back of the slots with a round file).  Once this is done an axle that is 8.0mm wide will move 1/8" within the dropouts; perfect!  Except axles are often 3/8" (9.525"nominal, actually about 9.4mm across the thread tops)  wide.  Here's the clever bit; provided you are prepared to keep track of/adjust the axle 'timing' (which might require that you hold the axle with a spanner whilst tightening the first track nut, and are prepared to have the axle face forwards instead of backwards as the chain wears) you only need have a small flat on one side of the axle.

 How small is small? Well, in a 10.2mm dropout the flat needs to be ~1.3mm deep but in an 11.2mm dropout the flat needs to be only 0.7mm deep to provide enough movement. This is about the same amount required to locally remove the protuberant parts of the thread on a 3/8" axle. A little more removal is required for a nominally 10mm axle.

This won't weaken it significantly.  IME 3/8" and/or 10mm steel axles are almost a consumable in fixed gear bikes anyway, so this means that you can run relatively inexpensive parts and get your fixed gear, er, fix that way.

HTH

cheers

[PhilO]

I use an https://www.sjscycles.co.uk/bottom-brackets/trickstuff-excentriker/  bottom bracket to run a hub gear without a chain tensioner, but I can't speak for whether it would be up to fixed gear use.

Plus a new frame might be cheaper! 

[yoav]

A friend of mine had the same problem. He sent his frame to titanium repair specialist Vernon Barker (http://www.vernonbarkercycles.co.uk/) who replaced the vertical dropouts for track ones.

[rogerzilla]

I've been running the Bob Griffin as a fixie with a QR and haven't had any slippage.  There's a proper hill on the way to work, too.  If a QR will hold in horizontal dropouts on a geared bike it has, if anything, an easier life on fixed with no small chainring up front.  For best results, as usual, choose a QR with enclosed cam and steel teeth to grip the dropout.  The BG has pre-CPSC straight-lever steel Campag QRs.  These were designed to hold onto chromed horizontal road ends in the 1960s.

[andrew_s]

I never hab any problems with an ENO slipping, but that may be because my chain length had it set down and backwards, so chain tension and pothole impacts counteracted each other.

[Brucey]

not everyone pushes as hard on the pedals....  I used to regularly pull derailleur wheels over in slotted dropouts with QRs and I had to make sure I had a fresh RH locknut on my hubs (with sharp serrations) and a really good quality QR if I wanted things to stay put. It was worse than that with fixed gear.

Fixed gears have a special problem in that not only are brutal efforts required at times, but  the top run of the chain and the bottom run of the chain can be tight at the same time. The reason is that when you go over a bump a chain with no slack in it sees an inertial load that is substantial.  In fact the tension load is asymptotic as the chain slack is decreased, i.e. it could become infinite. Yet when riding with a fixed gear there is no doubt that the bike feels nicer to ride when there is very little slack, so that is what folk shoot for.

The other thing that makes QR skewers work not very well is simple physics.  QR skewers are threaded M5. With an external cam skewer you might get 0.5 tonnes load or so (although this will usually reduce as the plastic seating creeps) and with a well-lubricated internal cam skewer you can get ~0.7 tonnes or more. With a security skewer it takes less effort to get a high tension. Depending on the quality of the steel a good skewer might take 1 to 1.2 tonnes before it breaks.

My contrast even a medium strength M10 bolt will take over three tonnes, so unsurprisingly a good track nut can grip about three times better than any QR-like skewer fixing. Which is why track riders, hill climbers, and other folk who don't want their fixed gear wheels to move even when they are pushing out over 1kW use track nuts not skewers.

Typical torque figures for rear track nuts are around 35Nm. IIRC this develops between 1.5 and 2 tonnes of load, something like that. You can go higher than that but the threads tend to strip after a few goes.

My suggestion is that anyone who thinks they might push out a lot of power ought to think about using proper track nuts, not a QR skewer in their fixed gear setup.

cheers

[sojournermike]

That’s interesting Brucey. I’ve seen over 1kW for short bursts and have had trouble with less strong QRs on a Ti frame, even with vertical dropouts. I resolved that by using Shimano QRs and, as you suggest, decent hubs nuts etc. I think the hard Ti dropout also contributed though - the same QR worked fine on an alloy frame with bolt on droupout.

At the moment I’m not making that much power, so probably not as vulnerable to moving wheels:(

Mike

[mike]

I used an ENO hub for ages to convert a Ti road frame into a fixed TT bike with no issues at all - it had allen bolts both sides, not QR.  I'm heavier than average too, so probably putting 'plenty' of watts down!

I'm not using it at the moment, so if you're anywhere near Cambridge and want to try the wheel in your frame, you're very welcome to borrow for a few months.   

[Brucey]

some hubs use M6 bolts that thread into the axle (IIRC the Eno is like this?). These bolts are a fair bit stronger (+ ~1/3) than an M5 threaded skewer.

cheers

[Vs4b]

Mike that's really kind of you, and amazingly i live in peterborough and the kids live in Waterbeach so im in camb often!

If you are happy to lend it then i'd be keen to take you up on the offer

[Chris N]

-  the magic gear, I get the idea of this but I regularly have to tighten my chain (sometimes mid-ride on a long audax) by moving the wheel back but surely this isn't possible with a magic gear and so you're stuck with a slack chain which is dangerous or you're constantly changing chains ... am I missing something?
- the eccentric hub seems like the best bet but I have read reports of them slipping under load and the chain going slack
- eccentric BB, don't you need a specific BB shell for this?

- a bit of slack is no big deal.  Get your chainline right and use good quality SS-specific cogs and rings.  If you have to tighten your chain mid-ride it's more likely to be axle movement than chain wear.
- Don't know.  Had an eccentric hub but the bike got stolen before I got chance to ride it any distance.  Would recommend positioning it like andrew_s suggests.
- Yes.  Eccentrics are available for PF30, BB30 and BS threaded shells.

[mike]

Mike that's really kind of you, and amazingly i live in peterborough and the kids live in Waterbeach so im in camb often!

If you are happy to lend it then i'd be keen to take you up on the offer

have messaged you!