fixed-gear bike?

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fixed-gear bike?

Postby pivoxa15 » Mon Feb 19, 2007 4:39 pm

Where can I buy new or second hand fixed-gear bikes in Melbourne?
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by BNA » Mon Feb 19, 2007 4:47 pm

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Postby europa » Mon Feb 19, 2007 4:47 pm

Do you want a track bike or a road bike? If road, you'd be looking at building it up myself much as I did with my Europa - they're too rare to come across them easily second hand (though I'm sure it happens).

If you're just after a track bike, quite a few bike shops have them or you could try a track club

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Postby cludence » Mon Feb 19, 2007 4:49 pm

I am not sure where you can buy them from down there but if you choose to do it yourself, there are numerous places in Victoria that have secondhand bikes. No doubt one of them would be able to help you. If you go to this link http://bicyclerecycling.com/15.html it has the locations in Victoria. Hope this helps.

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Postby pivoxa15 » Mon Feb 19, 2007 7:19 pm

europa wrote:Do you want a track bike or a road bike? If road, you'd be looking at building it up myself much as I did with my Europa - they're too rare to come across them easily second hand (though I'm sure it happens).

If you're just after a track bike, quite a few bike shops have them or you could try a track club

Richard


A road one. How do you make it so that the wheels stop turning when you stop peddaling? If you have to walk up a hill do you have to lift the bike up so that the back wheel don't touch the ground, otherwise you would be dragging it up without it rolling.
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Postby europa » Mon Feb 19, 2007 8:31 pm

This thread, The Europa Goes Fixie (it's a link, just click on it) tells of how I converted my Europa. I did it the easy way - just took off the old gear cluster and screwed on the new cog. I didn't have to redish the wheel to get a straight chainline (which is fairly important on a fixed gear bike).

On my son's Gitanes, which also got the same treatment, when I screwed on the new cog, it proved to be out of line with the chainring by 5mm. This is fairly normal I'm afraid and to get the rear cog lined up with the chainring I was going to use, I had to shift the spacers on the rear axle around, basically to move the hub of the wheel over that 5mm. Trouble is, that moves the rim of the wheel as well and leaves it offset to the frame by that 5mm. You correct that by 'redishing' the wheel ie, you loosen the spokes on one side of the wheel and tighten them on the other, to pull the rim over until it's in line with the frame again. It sounds worse than it is but is still the hardest part of the job.

Both these bikes have what is called a 'suicide' hub. The cog is screwed onto the standard hub as tight as you can get it (and there are special techniques to do this which I'll talk about later if needed), but it's only that tightness holding it in place. If you apply too much backpressure on the pedals, like you do if trying to skid the wheel, you can spin that cog off with an instantly jammed rear wheel the usual result. If you use brakes to stop you, rather than leg pressure, it's reasonably safe.

The best way to do it involves getting a track hub laced into your wheel. This requires getting the rear wheel rebuilt but it means that you screw on the cog, then screw on a locking ring (which is threaded in the opposite direction) - this prevents the cog from spinning off.

However, for normal road use, a properly tightened 'suicide' hub works and many miles have been done on them.

Now, the cog. I've left this question till now deliberately. The cog you use is a normal track cog. Instead of having a freewheel built into it, the freewheel being that mechanism that allows the cog to spin in one direction but not the other (relative to the wheel), a track cog is a solid piece of metal. It turns with the wheel, it always turns with the wheel. When the wheels are turning, so is the cog and seeing this cog is connected to the chainring via the chain, so are the pedals ... which is where the workout comes from (you can't coast). If you're just walking the bike, the pedals turn with the wheels and you just have to make sure they don't whack you in the ankles.

In many ways, a fixie is no different to a normal bike. The big difference is that when the wheels are turning, so are the pedals. The ride is intense - no gears so you're either spinning like crazy or mashing the pedals and you NEVER get a rest. But they are a blast to ride, a lot of fun. If an overweight old bloke like me can enjoy one, they must be fun :D

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Postby pivoxa15 » Tue Feb 20, 2007 10:30 am

So to brake or make the bike stop you have to apply a reverse pressure to the direction when cycling. Therefore to brake recquires force from the legs as well (unlike a normal bike where the force is applied by the hand). The harder and quicker you apply the reverse force, the faster it will stop. So when going downhill and you need to stop suddenly, it will take quiet a bit of pressure from the legs? Or is this pressure negligible when compared to riding the bike up that hill?
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Postby europa » Tue Feb 20, 2007 10:48 am

If you don't fit brakes, you can only slow the bike by backpressure on the pedals ... or find a solid wall to bump into :shock: It requires a lot of back pressure, far more than you exert in normal riding, even up a hill.

If you are riding on the road, FIT BRAKES and use them.

You don't need to apply any backpressure to the pedals if you don't want to, but you will find yourself slowing down using the pedals after a while - the amount of back pressure you can and do use will depend on the circumstances, your own skill levels and how you feel at the time.

But on the road, in anything pretending to be an emergency, use the brakes. A lot of fit, strong, experienced fixed gear riders go brakeless but you really need to consider that an advanced riding techinique - actually, it's a whole range of techniques, which can be learnt over time with brakes fitted to your bike.

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Postby pivoxa15 » Tue Feb 20, 2007 11:29 am

Your remark about braking and how much force is recquired is interesting. For the people who go brakeless, I imagine the back tyre can get worn out very quickly.
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Postby mikesbytes » Tue Feb 20, 2007 1:26 pm

You can't lock the rear wheel by backwards pedalling.

Please fit brakes for saftey sake.

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Postby europa » Tue Feb 20, 2007 1:34 pm

mikesbytes wrote:You can't lock the rear wheel by backwards pedalling.

Please fit brakes for saftey sake.


Actually, you can, though I'm buggered if know how. You'd have to unload the rear wheel first surely. Big skids are all part of the fixie game, but like I said earlier, consider that an advanced technique - it is NOT something you will achieve by leg muscle alone (and Mike's a track rider, he knows about slowing these things down without brakes - listen to the man).

Yes, brakes are a MUST on the road (have I got that message through yet?). Cripes, I'm looking at upgrading my Europa's brakes from the hysterically inefficient devices we thought were the duck's guts in the eighties to something that actually provides more than a mild retardation - it's only money holding me back.

Actually, dual pivot brakes are really cheap. I can get a pair of quite adequate, dual pivot caliper brakes for a bit under $50. The big question is the reach to my rims - they've been designed for bikes designed for 700c wheels and I'm running an eighties grid with 27" wheels, but I reckon they'll do the trick. And I'd like a set of aero brake levers, you know, the ones where the cables run under the bar tape. Ahh, the old girl will look great eventually :D

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Postby Bnej » Tue Feb 20, 2007 1:59 pm

The same thing that turns the rear wheel faster than your legs provides a reverse mechanical advantage for the wheel to force your legs around. You will not be able to stop yourself down hill by trying to operate the pedals against the wheel, as the bike has a significant mechanical advantage on you.

Essentially you're trying to arm (leg) wrestle against the entire energy it would have taken to get up the hill, but in a fraction of the time. Not going to happen.

The smaller your final gear ratio, the better you should be able to brake by resisting. If you had something like a 20" final ratio, maybe... but I don't ride fixies, and I wouldn't bank on it, and you couldn't get very fast with a 20" gear in any case.
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Postby pivoxa15 » Tue Feb 20, 2007 3:19 pm

Interesting. I have seen people ride fixies without front nor rear brakes in the city. They must be riding very small gear ratios which is probably advisable in general especailly when riding in the city without any brakes.

Just a question about going down hill with a small gear ratio, one would have to peddle very fast, the faster they go. When things get too fast, could one remove their feet from the peddles and dangle them somewhere so that coasting is possible? It wouldn't be very comfortable would it?
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Postby Bnej » Tue Feb 20, 2007 3:26 pm

That would be suicidal.

If you were to take your feet off the pedals on a fixed gear bike going downhill, without brakes, you have lost control of the bike. You won't be able to get your feet back on the pedals and you won't be able to stop without hitting an obstacle.

If you want to coast, don't get a fixed gear bike!
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Postby pivoxa15 » Tue Feb 20, 2007 3:30 pm

Good point Bnej.

So there is the problem of needing to peddle too fast if using a small gear. What do people think about peddling very fast? It's also a feeling of out of control? So when riding fixies with a small gear, gonig down hill is more scary than up hill.

For extra saftey, what about installing back brakes as well as front ones?
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Postby mikesbytes » Tue Feb 20, 2007 3:43 pm

You can get away with just a front brake and its legal as you have a braking method for both wheels. But its no big deal to fit a rear brake, so why not.

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Postby europa » Tue Feb 20, 2007 4:11 pm

Oh no no no no no. You keep in contact with the pedals and spin like crazy :shock: I wear clipless shoes and hook them up to clipless pedals and so far, my max has been about 145 rpm :shock: That was on the flat too.

That's the thing about fixies, you're stuck in one gear. It's a positive and a negative. It's a positive in that you're forced to work at whatever speed you're running at. It's a negative when you have to work at whatever speed you're running at :roll:

Told you it was an intense ride didn't I :twisted:

Seriously, I luvit :D

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Postby pivoxa15 » Tue Feb 20, 2007 4:20 pm

Just a question about gear ratio. How does the system work? Is it this

We count the number of spokes on each gear.

Input:Output where input is the number of teeth on the gear that one peddles and output is the number of teeth on the gear attached to the back wheel and drives it.

Let there be a fixed number of teeth on the peddle gear equaling 8 and than a gear on the rear wheel may have 4 teeth (for going down hill) so the gear ratio is 8:4 = 2:1 = 2

For a gear going uphill one may use a gear with 6 teeth so the ratio is 8:6 = 4:3 = 1.3

This means a high gear imply more force required to peddle on flat ground while a low gear imply less force to peddle on flat ground.

Correct?
Last edited by pivoxa15 on Tue Feb 20, 2007 4:21 pm, edited 1 time in total.
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Postby europa » Tue Feb 20, 2007 4:21 pm

I got caught up with a phone call during my last post, hence it's a bit out of sync :roll:

I can't see why you'd fit only a front brake. If you fit front and rear brake levers, you have both brake levers to rest on, giving you an extra set of hand positions, and if you've got the lever, why not have the brake itself. I have seen fixies with a front brake, no rear brake, but with two sets of levers to provide the balanced hand position - I can't see the point.

If you are running without brakes, you NEED a proper locking ring, a reverse thread locking ring and that means you need to fit a track hub or a purpose built flip flop hub (a track hub with threads on both sides). If you are using brakes, the evidence is that you don't need a locking ring and can get away with a normal hub with a track cog screwed on (no locking ring). If you are riding in traffic, have both brakes and avoid using Volvos as braking devices :shock: , you are fine. If you are on the track, you aren't allowed to run brakes. There is no middle ground in my view. Build the thing with brakes and then, when you are experienced, decide whether you want to save the extra few gramms of weight by removing them ... in the meantime, my fixie will be getting the best brakes I can afford.

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Postby pivoxa15 » Tue Feb 20, 2007 4:25 pm

Bnej wrote:The smaller your final gear ratio, the better you should be able to brake by resisting. If you had something like a 20" final ratio, maybe... but I don't ride fixies, and I wouldn't bank on it, and you couldn't get very fast with a 20" gear in any case.


Why is the smaller the gear ratio, the better ability to brake? Is it because the smaller the gear ratio, the less your speed is likely to be? Ane the less the speed the easier to stop.
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Postby pivoxa15 » Tue Feb 20, 2007 4:26 pm

I am thinking of buying one of these fixie bikes. How much are they? So basically if someone is riding a fixie in the city without any brakes, they are riding a track fixie since they have a ring thing at the back wheel which makes stopping easier?
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Postby europa » Tue Feb 20, 2007 4:46 pm

Price? Whatever you are willing to pay, but considering they are not made by the bike manufacturers, you will be buying something converted by a back yard mechanic. Make sure it's sound.

NB, track bikes are different and for a lot of reasons, don't necessarily translate to the road. Some track bikes can be fitted with brakes but be warned, the steering may lack the stability needed on the road.

Gearing? I run a 42 tooth chainring and a 16 tooth rear cog. I ride in undulating territory. Be prepared to change the rear cog a few times until you get a ratio that suits you.

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Postby Bnej » Tue Feb 20, 2007 5:05 pm

pivoxa15 wrote:Why is the smaller the gear ratio, the better ability to brake? Is it because the smaller the gear ratio, the less your speed is likely to be? Ane the less the speed the easier to stop.


It's the same principle that causes your car to slow down if you put it in a lower gear (engine braking). The gear works in reverse from the wheel to you, so with a lower gear ratio the wheel has a harder time pushing you, and you have an easier time pushing the wheel. In a high ratio, you have a harder time pushing the wheel, but it finds it easy to push you.

That's about as simply as I can put it.

Final gear ratios for bicycles are commonly expressed in gear inches, which is the equivalent sized wheel for the gear at a 1:1 ratio of pedalling (like a penny farthing wheel size)

To get gear inches:

Count teeth on front gear and teeth on back gear, Divide front / back. Then multiply that number by the diameter of the driven wheel.

e.g:

42 teeth front 18 teeth back, 26 inch wheel, 42 / 18 = 2.33, 2.33 * 26 = 60.66 gear inches.
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Postby pivoxa15 » Tue Feb 20, 2007 5:24 pm

Bnej wrote:
pivoxa15 wrote:Why is the smaller the gear ratio, the better ability to brake? Is it because the smaller the gear ratio, the less your speed is likely to be? Ane the less the speed the easier to stop.


It's the same principle that causes your car to slow down if you put it in a lower gear (engine braking). The gear works in reverse from the wheel to you, so with a lower gear ratio the wheel has a harder time pushing you, and you have an easier time pushing the wheel. In a high ratio, you have a harder time pushing the wheel, but it finds it easy to push you.

That's about as simply as I can put it.

Final gear ratios for bicycles are commonly expressed in gear inches, which is the equivalent sized wheel for the gear at a 1:1 ratio of pedalling (like a penny farthing wheel size)

To get gear inches:

Count teeth on front gear and teeth on back gear, Divide front / back. Then multiply that number by the diameter of the driven wheel.

e.g:

42 teeth front 18 teeth back, 26 inch wheel, 42 / 18 = 2.33, 2.33 * 26 = 60.66 gear inches.


So harder pushing a gear ratio also imply harder stopping it once it gets going? That is why it is easier to stop with a lower gear.

Is that how you calculate gears. The principle seems to be exactly the same as how I did it and low and high gears are what I described.
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Postby Bnej » Tue Feb 20, 2007 5:43 pm

pivoxa15 wrote:So harder pushing a gear ratio also imply harder stopping it once it gets going? That is why it is easier to stop with a lower gear.

Yep, exactly.

Is that how you calculate gears. The principle seems to be exactly the same as how I did it and low and high gears are what I described.

Pretty much yeah. But you left out the wheel size, so you only have the transmission ratio not the final ratio.

The reason you multiply by wheel size to get gear inches is because the wheel is also part of the drive train. e.g: 20" wheel BMX vs 26" mountain bike, both with 42 - 18, BMX has a much lower gear ratio, 46.6 gear inches rather than 60.6. So gear inches lets you compare bikes gears when they have different sized wheels.

You can work it out easily in all sorts of measurements here:
http://www.sheldonbrown.com/gears/index.html
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Postby pivoxa15 » Tue Feb 20, 2007 10:39 pm

To be honest, I like the idea of riding a fixie mainly because of its style and elegance attracts me - the simplicity and having no brakes (I'll most likely ride on bike tracks or velodromes and with a high gear) and with handle bars that sticks vertically out in front of the bike, not curved downwards like road bikes nor purely horizontal like MTB.

Are all fixies without a front brake meant to be track/velodrome bikes?

I don't see why someone would want to convert a normal road bike to a fixed gear because you could just force yourself to ride in only one gear on a normal road bike for the whole trip and not coast, couldn't you? The result is the same as riding a fixie?
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