Fixed Wheel Fundamentals

Fixed wheel, trendy? Who’d have guessed 25 years ago, when the only cyclists riding around with one sprocket minus freewheel were either ancient diehard tourists or, like RCUK’s editor, impecunious types lacking the funds to afford the luxury of gears? Indeed, my first season of competition started on fixed, although that soon changed…

It’s the purity of fixed wheel that gives it that contemporary appeal. Unlike the world of gears, nothing much has changed on the fixed wheel front in a quarter of a century bar better tyres and the option of going for a carbon fork or titanium frame if you really have money to burn. There is, after all, almost no performance advantage to be gained by using flash parts on a machine that, speed-limited as it is by the gear ratio it wears, offers an alternative route to cycling satisfaction.

Let’s start, then, with that gear ratio. It is, after all, the key to the whole affair. Go too high and, while you’ll be king on the flat for perhaps an hour or so, a few standing starts, the odd stiff little climb and an extra 30 minutes or so will leave you praying for two more teeth on the back. Too low and – well, what is too low? 63inches is a practical minimum for general road use, but few fixies carry such an easy gear. Even 66inches or thereabouts is seen as too low judging by the cadence of the average fixer flogging home along the Embankment.

Is 66 inches enough?

This is a shame, for 66inches - 48x19 – or similar - is where it is at. Fast enough for rapid cruising but low enough to get over pretty significant lumps, 66 does what fixed is supposed to do. It helps with the development of that supple pedal stroke beloved of old-time roadies, but challenges on the climbs and standing starts. Low enough to be useable on a fixed tour, it is high enough to give the genuinely fast pedaller a fighting chance on the urban blast.

Where does this leave the double-sided hub? Just right for fitting that occasionally useful bigger gear. Or, to put it another way, you can have a bail-out big sprocket for when your usual 74inches suddenly feels way too high. Double sided is, of course, a form of cheating in that, in an ideal world, a fixed rider should have to choose a gear and stick with it through thick or thin. But, hey; I ride with two sprockets because otherwise the spare thread on my rear hub will get dirty…

Cut yourself some slack

Chain tension is the next consideration, and it is if anything of even greater importance. That’s ‘cos a tight chain will kill the hub bearings very quickly, while a slack chain may jump the rear sprocket at high pedalling speeds. If this happens, the rear wheel will probably lock and you will crash. How tight is right? If the chain feels like the skin of a drum, it is too tight. There should be about 3mm of play – not just movement – at its taut spot. Tighten a chain as much as you like and you will not get rid of some movement up and down if you manipulate with the fingers. This is simply elastic stretch in the plates. Free play can be felt thanks to the sudden change in resistance to further movement.

An easy way to get this right is to pull the wheel back and nip up the track nuts before gently turning the wheel. Tap the chain with your spanner or Allen key to find the point at which it suddenly goes taut and stop the wheel there. This happens because no chain wheel is perfectly concentric. There will be a high spot that will take up chain slack. Some fixed authorities suggest playing around with the chainring to try to get rid of the high spot, but unless the chain has more than about 12mm/1/2 inch of slack at its loosest, there is little need. When the chain goes taut, loosen the right-hand nut and move the wheel until the chain has the right amount of slack. Nip the nut back up. If the wheel is not central between the stays, loosen the left-hand nut and adjust. This has only a small effect on chain slack.

To save time, once you have found the high spot, commit its position, or rather the angle of the crank, to memory and put the crank at the same angle each time you need to adjust the chain slack.

To lock or not to lock

Should you use a lockring? The only time it is absolutely necessary is when you have only one brake on the front wheel. The rear wheel with fixed sprocket then legally constitutes your back brake but only when fitted with a lockring. This brings us to the question of rear brakes. Fixed purists will stoutly maintain that a rear rim brake is unnecessary. In theory, this is true. In practice, a rear brake makes life a lot easier, not least because having two brake levers makes holding the bars when dancing out of the saddle a lot more effective. Fit two and, if you want to enjoy the single brake experience, use only the front…

Chain width is another, but slightly less, contentious issue. The only real drawback to a derailleur chain is that it is designed to shift across sprockets and, if run too slack, will climb off more readily than a 1/8th chain. Otherwise, fit a narrower chain and sprockets. You’ll save a bit of weight and enjoy a smoother transmission.

The same gear achieved with a larger chainring and sprocket will feel smoother and more efficient, but will weigh more. It will also take more effort to accelerate thanks, believe it or not, to the weight of the chain. Smaller is generally better in this respect, although 42t is about the minimum chainring size worth fitting to avoid the ‘soft’, spongy feel associated with tiny chainrings.

Forwards dropouts allow easy wheel removal

Home brew heaven

Building a fixed bike is fun, but if going the home-brewed route, beware of a couple of potential pitfalls. Unless you have long rear dropouts or ends, you will have problems with chain adjustment. There are solutions, but finding a suitable frame in the first place is better. It doesn’t have to have the correct spacing between the dropouts – normally 120mm. Many fixed hubs have enough washers, spacers and locknuts to allow adjusting for with. With the right hub it is perfectly possible to build a wheel to 120mm or 130mm Over Locknut Dimension as required.

The key to a smooth and safe fixed transmission is chain line. The chain must run straight from the chainring to the sprocket without deviating if it is to be safe at high revolutions. Chain line can be checked by measuring the distance of the sprocket teeth from the dropout inner face, subtracting this from half the rear wheel dropout spacing and comparing this to the distance of the chainring from the frame centre line. Find this by measuring the seat tube diameter and adding half to the chainring tooth distance from the side of the seat tube.

Look for a frame with adequate bottom bracket height. Less than 275mm may well cause problems with pedal clearance when cornering, which can be addressed by fitting shorter cranks.

On which subject… conventional wisdom says ride short cranks on fixed because you need to be able to pedal fast. I ride 175mm on mine, just as on my road bikes. This means I get the same training effect, and can transfer the high fixed cadence to my geared machinery. Furthermore, I get a bit more torque on steeper hills at the expense of absolute top speed downhill.

But don’t be swayed; choose your own gear, crank length and cadence and enjoy the ride. Carry a cool spanner so other fixed riders can see it and, whatever you do, keep those fingers out of the transmission. Tight (but not too tight)chain, ride safe!