New Cube Litening C:68X aero race bike pushes the limits of UCI compliance

Skinny frontal profile helps reduce drag by 30%

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Cube says that the new Litening C:68X has been its most labour-intensive bike development to date, involving 1000 hours of computer modelling and over 100 hours of wind tunnel testing to optimise its aerodynamics.

That’s despite borrowing extensively from the knowledge gained in developing the Aerium C:68 time trial bike.

The objective with the Litening C:68X was to develop the fastest possible bike which still complied with the UCI’s frame dimension regulations. Although the UCI has done away with its 3:1 rule, a bike design still has to fit within defined tube dimensions.

Cube has a diagram showing just how close to those limits its new bike is. The intersections between some frame components touch the very edges of the UCI legal dimensions and it’s had to tweak the radius of the cut-out for the rear wheel on larger frame sizes, for example, to stay within the rules.

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The result, says Cube is a 30% decrease in drag for the new Litening C:68X relative to its 2015 design, meaning a saving of 30 watts. That’s been achieved without excess weight: the frame weight is quoted at 980g for a size 56cm, including the seatpost clamp and the mech hanger.

Low frontal profile and increased integration

Cube concentrated on reducing the Litening C:68X’s frontal area, again while skimming the UCI regs. So the head tube, for example, is waisted. And Cube 3D printed many different bar shapes and wind tunnel tested them.

Like many of the latest crop of bikes, including the just-launched Scott Addict RC and Wilier Zero SLR climber’s bikes, Cube has also enhanced its cockpit integration, with a one-piece bar/stem and internal cable routing. With the round section of external cables generating significant drag, it’s an area where there are still aero benefits that manufacturers are now looking to exploit.

Rear wheel cut-out grazes the limits of UCI-legal sizing

Hidden cables normally pass either in front of the headset bearings or through them. But Cube has passed the cables and brake hoses round the sides of the steerer tube, entering the frame behind it. That results in quite a chunky profile to the stem and Cube has included a stop to prevent the bars from rotating too far and damaging the cables.

So far, all of Cube’s Litening C:68X test bikes have been built up with electronic transmissions, either cabled or wireless, including the SRAM Red eTap AXS-equipped bikes that we tested at the launch. But it says that, as with the Scott Addict, there’s enough room to use mechanical cables to the shifters too.

Cables pass through the bar and stem into the frame

There’s not much point in having an aero cockpit if a bike computer sticks up above it and disrupts the airflow. So Cube has developed its own Garmin mount that positions the computer lower down and out of the airflow. It comes with an adaptor for Wahoo Elemnt computers as well as Garmin units. Plus it’s compatible with K-Edge adapters for Lezyne units and GoPros.

Cube has worked on the Litening C:68X’s seatpost design too. Because of their wider section, aero posts often transmit road buzz and bumps to the saddle. But Cube looked to add compliance, building 20 prototypes to optimise the carbon lay-up while maintaining strength and safety.

Skinny frontal profile reduces wind resistance

Cube has aero tested the Litening C:68X with a range of wheelsets and tyres. There’s clearance for 28mm tyres and some 30mm tyres will fit when paired with some rims.

But it says that it found optimum aerodynamics with narrower front tyres and says that it’s important to preserve the gap between the fork crown and the tyre to keep the aero benefits; when this gap is too narrow, additional turbulence and drag ensue. Running a wider rear tyre doesn’t impact aerodynamics though.

First ride on the Cube Litening C:68X

We were out at the launch of the new Cube Litening C:68X at the brand’s new shop in the Netherlands and took the new aero bike for a 40km spin through the surrounding countryside.

It’s a bike that wants to be ridden fast. Hitting the gas on a flat cycle path on the way back to the shop, we were travelling at over 40kph. This felt like the Litening’s natural environment, with the aero features helping to gather and maintain speed.

Bottom bracket shell design also has a low frontal profile

I liked the wide, flat tops of the aero bars; they’re comfortable to rest your hands on, distributing pressure well. Although the stop on the bar rotation feels disconcerting when you’re stationary, in practice it doesn’t affect manoeuvrability when riding, unless you’re planning to track stand or try some other low speed tricks.

The weather was hot – around 30C – and quite windy, but I didn’t feel any twitchiness when riding in crosswinds. Cube seems to have done a really good job of sorting the Litening C:68X’s handling.

Down tube bottle cage can be mounted in two positions. If you’re only using one bottle, the lower one is more aero

There’s not much up and down near Utrecht, but we found a gently rising and falling road through the forests. Descending, the Litening was fast and assured. Weighing around 7.6kg, the bike is pretty light for an aero machine equipped with the disc brakes that are rapidly taking over on performance bikes, so uphill wasn’t a problem either.

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With long straight roads, there wasn’t much opportunity to test the Litening’s handling. And Dutch road and bike path surfaces could be on a different planet to the UK’s roads. The Litening feels stiff and direct, but to get a comfortable ride in UK conditions, you might need a swap from the 25mm Schwalbe Pro One tyres with inner tubes that we rode to tubeless 28mm tyres, for which there’s clearance and wheelset compatibility.

Model range and pricing

For 2020 Cube will sell the Litening C:68X in four specs and six sizes between 50cm and 60cm. Bikes of different sizes will come with four different cockpit geometries between 90x400mm stem/bar and 120x440mm, although Cube says that it will look to extend the range of bar options dependent on demand. If the supplied bar/stem doesn’t suit you, it says that dealers will be able to swap out for one of the other sizes.

Top of the range, the SLT will come with SRAM Red eTap AXS and DT Swiss ARC 1100 Dicut 62 wheels with ceramic bearings. It’s priced at £7499.

Dutch roads are beautifully paved

The SL comes with Shimano Dura-Ace Di2 and DT Swiss ARC 1400 Dicut 62 wheels for £6499.

The Race spec comes with SRAM Force eTap AXS and Cube’s own Newmen Advanced SLR 38 wheels and is priced at £4499.

Finally, the Pro has Ultegra Di2 with Newmen Evolution SLR 32 wheels and is priced at £3999.

The Litening C:68X will be the bike ridden by Wanty-Groupe Gobert at the Tour de France. The rest of us will have to wait a bit; it’s available to pre-order now with delivery slated for the end of the year.