Cube Acid 240 Hybrid Rookie SLX

If you are buying for a child who will ride with the family, and you want the 24-inch bike with the more considered controls and suspension, the SLX 400X is the one that fits that brief. It is the current UK Acid 240 Hybrid Rookie SLX, aimed at supervised outings that run longer than a lap of the park, on gravel paths and moderate unpaved routes.

The riding it is for

Bosch pedal assistance is what helps a child cover more ground with adults on a longer outing. Cube's category 2Y class for the 400X covers paved routes, moderate unpaved roads and gravel paths, with drops limited to 15 cm. Jumps and demanding trails sit outside that class, so the rides to plan are family routes where the surface can turn loose and everyone is still rolling together.

The motor Cube fits is the Bosch Performance Line SX at 55Nm, with assistance up to 20km/h. Cube also describes up to 60Nm. Bosch says that figure needs an optional software setting the bike maker can limit, so 55Nm is the output to expect as supplied. Gearing is Shimano Cues 1×11 with an 11-50T cassette, which means a proper low gear for a climb and something taller when the path flattens. The fork is a Suntour Raidon34 2CR Air with 80mm of travel. You can set the air pressure for the child on the bike, and that adjustability is the point of this fork on gravel and moderate paths.

Who it fits, and where they may ride

The frame comes in one 24-inch size. Cube's height recommendation is 124 to 141cm, and that's a small child. It has to be read beside UK electrically assisted pedal cycle rules, which require the rider to be at least 14. Assistance that cuts out at 20km/h leaves that age rule in place, so a child inside the height band is not cleared for public roads or cycle paths on fit alone.

Cube claims 18.2 kg for the bicycle. The maximum rider weight is 50 kg, including clothing and kit worn on the body, and system weight is a separate cap of 80 kg. At that claimed weight, lifting the bike into a car or up the steps is an adult's job, even when the child can turn the pedals with the motor helping.

Small hands are looked after in the cockpit. Cube fits a 590mm kids' handlebar, grips of 19mm diameter, and Magura MT Thirty hydraulic brakes with lever adjustment highlighted for smaller hands. A handlebar-operated dropper is part of the build, so the saddle can be lowered from the bar and raised again for pedalling. Those contact points, next to the weight and the rider limit, are how you judge whether this particular child can manage the bike.

Charging, and a little extra kit

The battery is a Bosch CompactTube 400, 400Wh, fixed inside the frame. The down tube has no access hatch, so you charge the bike where it lives, with the Bosch 2A charger that comes with it. Cube publishes no distance and no riding time, so treat 400Wh as capacity and plan the loop from the rides you already do. If you later want more watt-hours, the Bosch PowerMore 250Wh range extender is compatible and bought separately.

Mounting points on the frame let you add Cube's compatible SIC 2.0 youth carrier and 24-inch mudguards. Any carrier still has to stay within the 10 kg carrier limit and the 80 kg system limit. Cube's table specifies no trailer load for this build.

Telling this SLX from an older one

A heading that says 2026 or 2027 can still be the same SLX 400X. The current bike is the one with the Bosch Performance Line SX, the integrated CompactTube 400 battery, and Cube's handlebar-operated dropper. The 2024 SLX 400 is the earlier generation: a 40Nm Bosch Active Generation 3 Youth Edition drive, an external PowerPack 400, Shimano Deore 10-speed gearing and an SR Suntour XCR LO Air JR fork. Motor and battery are the clean split between those two bikes. If a 400X offer describes a different seatpost, Cube's fitted dropper is the specification to hold that description against.

Once you have the 400X, the useful jobs are simple. Set the fork air for that rider, leave the dropper so they can move the saddle themselves, and keep a socket where the bike lives. That's how you set it up for the longer family loop, on the gravel and moderate paths its category 2Y class describes.