Brompton beater: The world's lightest folding bicycle weighs under 6kg

The world's lightest folding bicycle has been built by a talented engineer who wanted to take his mind off his health problems. And what a job he's done.

It's no overstatement to describe Derek Cranage as a guru where folding bicycles are concerned. Not content with modifying a Brompton so that it weighs only 7.1kg, Derek has built his own aluminium, carbon fibre and titanium tribute to the iconic British folder which tips the scales at a featherlight 5.9kg. For reference, Brompton's range-topping S1E-X is a claimed 9.3 kg.

The world's lightest folding bicycle

Carbon fibre is 40 per cent lighter than aluminium and many times stronger, but due to the main frame hinge assembly and its mounting, which had to be in aluminium (a one off in carbon fibre would have been prohibitively expensive), Derek plumped for a bespoke frame in aircraft spec aluminium paired with a carbon rear frame and forks. Every single item in the bike's construction is bespoke or trimmed to the last fraction of a gram.

For example, Derek made his own headset expansion nut that he bonded into the forks tube. This came out at under half the weight of the lightest one he could find for carbon forks. Forgoing a standard Brompton rubber for the rear suspension, Derek opted for a lightweight titanium version that he fitted with a titanium bolt and carbon fibre washers.

A standard seat tube clamp proved too heavy so a titanium bolt with an aluminium quick release does the job of keeping the seat stem in place.

The frame weight when painted (powered coated) and complete with the carbon fibre down tubes and their fixing bolts with all the folding hinge assembly comes out at 1.20kg – over 42 per cent lighter than the Brompton.

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Derek has form when it comes to beating Brompton at their own game. When we covered news of the Tern Elektron and eagerly awaited Brompton electric folding bicycles, he wrote to us about two bikes he had recently built.

To my mind, Tern have lost out; both ours fold considerably smaller than the Elektron.

One is a highly modified Brompton, which folds in the same way as the standard version but is 1 cm wider. It has v brakes and an eight-speed hub gear. It weighs 14.9 kg and the battery takes it 25 miles with an output about twice that of the Tern Elektron.

The second bike is another eight-speed hub gear with v brakes, the same electric drive and battery as our Brompton, and a folded size of 73 x 56 x 34 cm; a bit larger than the Brompton, but considerably smaller than the Tern. It weighs a more at 17.3 kg, but considering the eight-speed hub gear, it is light.

Both bikes have the motor in the front wheel, the battery goes in a Brompton bag at the front, and with a small amount of pedalling will go 25 miles.

Watch this space. We're confident we haven't heard the last from Derek and that not content with building the world's lightest folding bicycle (with 16" wheels), he's already working on another hyper-light tribute to Brompton.

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