Just how light can lightweight road bicycles get?

Weight is important when it comes to cycling. It stands to reason that the heavier the bike, the more you have to drag uphill. But if the recent spate of lightweight racing machines is any indication, we may be approaching the limit of how light we can go.

The history of bicycle weight is a little like a history of the 100 metre dash, in that as the numbers drop, the increments between the improvements get smaller and smaller.

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The first Tour de France was won by Maurice Garin on a La Francaise fixie with wooden wheels. It weighed a back-breaking 18 kilograms. Fast forward to 1968 and Jacques Anquetil won Le Tour on a steel Helyett that tipped the scales at 10.2 kilograms.

Thirty years later Miguel Indurain's Tour winning Pinarello weighed about a kilogram less, and he became the last man to win the Tour de France on a steel-framed bike. In 1997 Jan Ulrich rode a 9.0 kilogram aluminium Pinarello to victory.

Carbon dating

Then came carbon fibre and weights begin to plummet. Carbon fibre has been the frame material of choice for every winning bike in Le Tour since 1999 and led to the Union Cycliste Internationale (UCI) imposing a 6.8-kilogram weight limit after concerns that lighter bikes may break apart beneath the riders.

These days every winning bike in a grand tour will easily come in at 6.8 kilograms (Chris Froome's latest Le Tour victory was on a 6.8 kilogram Pinarello Dogma F8 XLight).

Indeed, mechanics often have to add weights to the inside of the frame to bring it up to the legal limit. That limit is up for review, especially as carbon fibre technology has come a mighty long way in the past 15 years and stories about frames spontaneously deconstructing are thankfully few and far between.

Losing weight

In the meantime, those of us who don't need to meet UCI restrictions are free to go and buy a bike off the shelf that weighs less than Froome rides to victory.

Over the last couple of years, improvements in the carbon fibre, and the advent of super light componentry such as SRAMs Red 22 groupset have seen complete bicycles coming in at below 5.0 kilograms.

But how low can they go? Maybe not much lower.

Unbearable lightness

Almost a year ago, German company AX-Lightness created the lightest production bicycle on the planet. The Vial evo Ultra tips the scales at a ridiculously svelte 4.4kgs fully built, knocking out last year's featherweight; the 4.56 kilogram Merida Scultura 9000 LTD.

And in case you're thinking you haven't seen too many bikes with the AX-Lightness decal on the top tube, that's because the high-end manufacturer is better known for its super lightweight wheels than its complete bikes. Plus, there isn't an Australian distributor, so if you want one you'll need to hop online and fork out close to $20,000 for the privilege.

That money gets you a lot of bike, albeit one that you'll hardly know is beneath you. The frame alone is a ludicrous 600 grams making it the lightest in the world. It is handmade in Germany using aerospace grade carbon fibre and only the bare minimum of resin, to shave off a few extra grams.

Breaking the fourth wall

So will we ever see a production bike weighing in at less than four kilograms? Or is that the equivalent of a sub-9-second 100 metre dash? Possible, but not probable for a long, long time.

Gary Hunt, editor of Bicycling Australia says bikes such as the AX-Lightness and Scultura are already at the extreme boutique end of production bikes. "I think the manufacturers are going to have to come up with some pretty fancy materials to get beneath the 4-kilogram mark," he says.

"Graphine is a possibility; it's one of the lightest materials known to man and yet it is incredibly strong. However, manufacturing a useable product from it at the moment is a stretch. Currently it is being integrated into a few frames, but it is more of a gimmick than of any real value."

Hunt believes the cost of developing such exotic frames is probably not worth it financially. "It's not really feasible from a risk and cost perspective," he says. "Plus lighter bikes do tend to be less stable."

Scroll through the gallery above to see eight of the lightest bikes on the market. 

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