Polar challenge: How do you cycle to the South Pole?

Leather seat Made of tough organic leather, as a plastic seat would shatter like glass in the sub-zero temperatures Seamless frame Made of seamless aluminium aircraft tubing, heat-treated to withstand harsh environments Simple brakes Simple, mechanical brakes, as the fluid in hydraulic brakes would freeze Fat wheels Fat, tubeless, rubber tyres designed to bulge over the rim to provide maximum stability and traction

An expedition is attempting to be the first to use a bike to reach the South Pole. It will mean tackling some of the most extreme conditions on the planet. So how can a bike manage it?

Snowdrifts, blizzards, rutted ice, altitude sickness, frostbite and snow blindness. They're hardly the odd speed bump, tree root or wayward pedestrian a cyclist usually faces on a bike ride, but this isn't an average journey.

Blue Peter presenter Helen Skelton is hoping to become the first person to use a bike to reach the South Pole. She is attempting to travel 500 miles (805km) across Antarctica and will cycle for large parts of it, as well as snowkiting and walking. She hopes to complete the trek for Sport Relief in 20 days.

At this time of year, the average temperature in Antarctica is -25C, but can drop to -50C. Severe coastal winds come from cold air flowing down off the interior ice sheet. Wind speeds can reach up to 125mph (201km/h) and average about 80mph.

Continue reading the main story The challenge Trek starts at 83 degrees south

Will cover 500 miles (805km) to reach South Pole

Will be travelling for up to 14 hours a day

Will cover anything from eight to 40 miles (13 to 64km) a day

Will have to climb to altitudes of 3,000m (9,840ft)

Will burn up to 10,000 calories a day

In addition, she will be dragging 12.9st (82kg) of equipment and supplies behind her on a sledge.

It's no average ride and she is not using your average bike. The specially-built Hanebrink "ice bike" took designers in Los Angeles three months to finish. Dan Hanebrink and Kane Fortune have been building all-terrain hybrid bikes that can be used in all environments for many years.

They previously worked on one for explorer and polar guide Doug Stoup. He wanted an alternative to skis that could take him and his equipment across the icy terrain. He biked for 200 miles in Antarctica's Heritage range.

With the help of Stoup's first-hand experience of cycling in snow, they have fine-tuned the design for Skelton. Even so, the challenge is a first for everyone involved.

"The bike has never been tested in conditions quite as extreme as Helen is doing," says Fortune, 29.

It is designed to be as minimalist as possible, to make it aerodynamic and very low maintenance. In total, it weighs about 40lb (20kg), a lot of that weight being the fat, tubeless tyres. A standard mountain bike averages 25 to 30lb.

"It will be huge if she makes it," says Stoup, who is currently in Chile preparing to go to Antarctica for Ice Axe Expeditions. "It would be the first bike expedition to the South Pole. I get calls every day from adventurers wishing to bike to the pole, but no one has ever attempted it.

Continue reading the main story “ Start Quote Like Captain Scott, Helen is attempting something that has never been tried before” End Quote Explorer Sir Ranulph Fiennes

"When I cycled in Antarctica, I was hit with an atypical storm that grounded me for five days. I experienced 100mph winds - it was epic. I still biked 200 miles and know Helen will be successful."

The presenter, who last year completed a 2,000-mile kayak trip along the Amazon for Sport Relief, has already been hit by bad weather and the start of her challenge has been delayed. She was finally able to start today.

"People keep saying a bike shouldn't be able able to make it to the South Pole, but that makes me even more determined," she says, speaking from Antarctica.

"The biking is going to be really tough. What I like about this challenge is that 90% of people know what it's like to ride a bike, so will be able to relate in some way to what I'm doing."

So how has Skelton's bike been designed to cycle on snow?

Wheels

The wheels are key to the challenge, says Fortune. The hand-made wheels and wheel hubs with sealed bearings weigh only 1lb each. The tubeless rubber tyres measuring 50cm (20in) high and 20cm wide weigh almost 8lb each. Thin steel belts are woven inside to make them as durable as possible.

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The tyres are designed to bulge over the rim to provide maximum stability and traction. They also allow a high degree of "flotation". This keeps as much of the wheel above the snow and ice as possible, so the bike hardly sinks in and only leaves a light impression. The wide surface area of the tyre does this by distributing the rider's weight over the width of the tyre.

"They're a lot like the tyres for golf carts," says Fortune. "They are designed to leave the smallest impression as possible, so the grass on the green isn't damaged."

Skelton will be able to adjust the air pressure in the tyres depending on the weather. This is vital as there are many types of snow and ice conditions. Set at a low pressure, on firmer snow she will need more air pressure.

She also won't be taking a puncture repair kit with her as it is extremely unlikely the tyres will puncture due to the steel belts woven inside.

Frame

The frame also needs to be as light and aerodynamic as possible, as well as durable.

Continue reading the main story Tips for cycling in snow Let some air out of your tyres, you'll get more grip

Relax the hands and arms, and keep your weight back

Make directional changes progressively and with your whole mass on the bike

Brake early and as much as possible in a straight line Source: The Guardian

It is made from seamless aluminium aircraft tubing, which is heat treated to withstand the harshest environments.

Skelton visited the designers in LA to test out the bike in a wind tunnel. This allowed them to make aerodynamic adjustments to suit various riding positions in harsh Antarctic winds. Such fine-tuned adjustments could be the difference between Helen making it or not.

The back wheel is set back slightly further than a usual bike, so it has a lower centre of gravity. This will allow better climbing ability and it also makes it more stable.

"To the untrained eye the bike looks quite different from your average one," says Fortune. "It looks like Batman's bike."

The frame is very similar to the one used by Stoup. He helped the designers make adjustments and also trained with Skelton.

"The bike is designed specifically to cycle in soft snow or sand," says Stoup. "We trained together in the desert this past summer. It helps because the temperatures are so cold the snow has little moisture and has a sand-like consistency."

Brakes

The rear-only disc brake is set to give as little drag as possible while providing maximum braking power.

Stoup managed 200 miles on his bike

Those used on the bike are simple mechanical ones, not hydraulic ones. This is because the fluid in them would freeze in such low temperatures. Designers also tried to make the bike as maintenance-free as possible.

The brakes probably won't be needed much anyway. To add to all the other challenges, the journey is uphill all the way, says Stoup.

While tailor-made for the South Pole attempt, the technology involved can be used in other extreme conditions.

"The US Army use similar bikes in the Middle East," says Fortune.

Seat and extra

The saddle is made of extra-tough organic leather and copper rivets. "A plastic seat would shatter like glass in Antarctica's sub-zero weather," says Fortune.

Pedals allow Helen full 360-degree power

The metal cage pedals are designed with power straps specially set to fit Skelton's snow boots. This will allow her to pedal with full 360-degree power as if she was in standard cycling shoes and pedals.

Skelton's handlebar is equipped with adjustable clip on handle bars, as seen on triathlon bikes. This will allow her to adjust her positioning for warmth, comfort and aerodynamics during long hours and harsh conditions.

The hand-made 6.9in suspension fork is also adjustable for different conditions. It spent nights in a meat locker while being built to test freezing conditions during the design process.

"When it comes to gears, the 21-speed bike is similar to a standard mountain bike," says Fortune.