Setting the Right Chainstay Length for a Single Speed Conversion

Converting a geared bike into a single speed machine has become a popular project in workshops from Sydney's Inner West to Melbourne's Brunswick. The appeal is straightforward — fewer moving parts, lighter overall weight, and a drivetrain that does not need constant cleaning after a wet commute along the Yarra or a dusty loop around Wellington in Hobart. Yet the conversion itself rests on a single measurement that many home mechanics underestimate: the chainstay length of the frame.

Once that figure is sorted out, the rest of the build tends to follow. Chain line, sprocket pairing, frame spacing, and the type of dropout all sit downstream of how long those stays actually are. Understanding this measurement from the start saves both frustration and the cost of buying parts twice.

What the Chainstay Length Actually Means

The chainstay runs from the bottom bracket shell out to the rear axle, on both sides of the bike. In practical terms, it is one half of the rear triangle and determines how much room is available for a rear sprocket, the chain itself, and any mudguard or rack that the rider wants to install. On most production road, gravel, and mountain frames, this measurement sits between roughly 405 mm and 475 mm, with frames in the medium size range typically landing around 430 mm to 450 mm.

Shorter chainstays tend to make the rear end feel responsive and quick when accelerating, which is why track bikes and fixed gear conversions often run numbers closer to the 405-410 mm mark. Longer chainstays trade some of that agility for stability under load, useful when the bike is loaded with panniers for a long weekend through the Macedon Ranges or carrying groceries down a busy route in Adelaide. When deciding on a single speed setup, riders need to know this baseline before any cutting, spacing, or tensioner decisions are made.

Measuring an Existing Frame the Right Way

Measuring is a simple job, but the technique matters. Drop the rear axle out of the dropouts and lay a straight metal rule from the centre of the bottom bracket to the centre of the rear axle slot. Some Australian workshops use a pre-made axle gauge for this — it slots into both dropouts and gives a reliable reference point. The reading should be taken on both sides of the frame because a slightly bent chainstay will produce two different numbers and signal a frame that needs straightening before the conversion proceeds.

There is also the spacing to record. Older road frames built in the 1980s and early 1990s in the local market often came with 126 mm rear hubs, while modern road and gravel frames run 130 mm, and mountain bikes typically sit at 135 mm. The chainstay measurement stays the same, but the distance between the two dropouts shifts. A singlespeed conversion will need this rear spacing altered to match the chosen hub standard, which leads directly to the next step in the build.

Adjusting Spacing and Choosing Track Ends

Most single speed hubs built for the Australian aftermarket come in either 120 mm fixed/fixed or 130 mm freewheel spacing. If the frame is currently set up for 130 mm and the chosen hub matches, the geometry can be left alone. If the frame is older and measures 126 mm, the dropouts need to be cold-set outward by 4 mm. Local bike shops in suburbs like Fitzroy, Newtown, or Fortitude Valley usually have the press tools for this and can handle it for a modest fee, or coach an experienced owner through the process at home with a wooden dowel and patient hands.

Track ends — the forward-facing, horizontal tubes that replace standard vertical dropouts — are another consideration. They make chain tension adjustment far easier because the axle slides back and forth in a slot. For anyone building a dedicated single speed or fixed gear commuter through the streets of Perth or along the Brisbane Valley Rail Trail, fitting track ends is often worth the effort. They also pair well with chain tensioners for those who want to keep vertical dropouts intact and still run a wider range of sprocket sizes.

Chain Tension and the Sprocket Question

The chain needs to sit at a consistent tension, neither overly loose nor under excessive load. With track ends fitted, this is achieved by sliding the rear axle backwards until the chain has about 10-15 mm of vertical play in the middle of the run. Without track ends, the tension comes from where the axle sits in the vertical dropouts, and the chainring and sprocket combination has to be chosen so the chain length matches the wheel position closely. This is where ratios and tooth counts come into play.

A common setup around Australia pairs a 44-tooth chainring with a 16 or 18-tooth rear sprocket for casual commuting on flatter routes, while hillier streets in suburbs like Sydney's Eastern Beaches or Brisbane's inner slopes push riders toward lower gearing, often a 42/16 or even a 38/16. The chainstay length itself does not change the gearing, but it does dictate how much room the chain has to flex and whether a half-link chain can be used to fine-tune length when the chosen sprockets produce an awkward gap.

Chainstay ranges commonly seen in workshop conversions:

Tools worth having before starting the project:

Adapting the Build to Australian Roads

Australia throws a few local challenges at single speed riders that change the way a conversion should be approached. Heat is the first, with summer temperatures in regional New South Wales and inland Queensland regularly pushing above thirty-five degrees. Heat expands the chain, which is why the recommended 10-15 mm of vertical play becomes the minimum allowance during the warmer months. Leaving a touch more slack avoids snapped chains on a climb through the Blue Mountains or during a fast descent along the Great Ocean Road.

Mixed terrain is another factor. Many rides around Adelaide's Hills, the Dandenong Ranges, or Launceston's back roads include short, steep pinches that feel very different on a single speed than they do on a geared bike. The frame choice matters here — a steel touring frame with slightly longer chainstays tends to cope with rougher roads better than an aluminium race frame with very short stays, simply because there is more room to mount wider tyres and extra clearance for mud. Riders often pick their frame first, then work out the chainstay length around it, rather than trying to squeeze an unfavourable frame into the wrong riding style.

Grab a tape measure, pull the existing wheels out, and start logging the frame numbers this weekend. A clear set of measurements taken before any parts are ordered makes the rest of the conversion far smoother and turns a complicated upgrade into a satisfying afternoon in the shed, with a bike that finally rides exactly the way it should.