CUBE Phenix Rookie

The CUBE Phenix Rookie is aimed at young riders who don't just use their mountain bike for the school run or occasional forest rides. The lightweight C:62 carbon frame, sporty geometry, and cross-country components make the bike a training and racing machine for the next generation. It adopts many technical solutions from full-sized race hardtails and adapts them to smaller frame sizes.

According to the manufacturer, the current CUBE Phenix C:62 Rookie SLX weighs 10.8 kilograms and is available in two sizes. The XS size comes with 27.5-inch wheels, while the S size features 29-inch wheels. This size split is intended to prevent smaller children from riding on oversized wheels, while allowing taller junior riders to take advantage of the rollover characteristics of a 29er.

Such a children's carbon hardtail is particularly suitable for technically confident children who train regularly, ride longer climbs, or would like to participate in their first cross-country races. For leisurely family outings, this consistently sporty design is not strictly necessary. The stiff frame, narrow race tires, and firm setup prioritize efficiency over maximum comfort.

Therefore, in addition to the low weight, parents should also check the seating position, operating forces, and the intended area of use. A lightweight bike is of little help if it is too big or if the child cannot move freely over the bike during descents. With the CUBE Phenix Rookie, a careful test ride is a better indicator of the appropriate size than age on paper.

The CUBE Phenix C:62 Rookie SLX is equipped with an SR Suntour Raidon 32 Air. This air suspension fork offers 100 millimeters of travel, a Boost thru-axle, and a remote lockout. The spring rate can be adjusted to the rider's weight via air pressure. This is more sensible for children than a rigid steel spring, the characteristics of which can only be changed to a limited extent.

However, adjustability does not automatically mean that the fork is internally tuned specifically for very light children. Aside from air pressure, the breakaway torque, damping, and seal friction are decisive. A fork can achieve the correct sag and still respond too sluggishly to small bumps.

In practical testing, the Raidon 32 Air dampened larger impacts but reacted less sensitively to small unevenness. As a result, light young riders may feel more vibrations at the handlebars on roots and hard ground. The statement that this suspension fork is unreservedly tuned specifically for children would therefore be too broad. It is adjustable via air pressure, but its responsiveness should be carefully checked during a test ride.

For the basic setup, the air pressure is first reduced or increased until the fork uses an appropriate amount of its travel under the seated child. This is followed by a test ride over small roots and curbs. If the fork hardly moves despite low pressure, a specialist workshop should check whether the setting, lubrication, and damping are suitable for the low rider weight. Too little pressure is not a good permanent solution, as the fork will then sit low in its travel and bottom out more quickly on stronger impacts.

• The SR Suntour Raidon 32 Air offers 100 millimeters of travel and adjustable air pressure.
• The remote lockout can lock the fork for smooth climbs or sprints.
• The responsiveness to small bumps is rather firm for very light children.
• The correct air pressure must be set using a suitable shock pump.
• A test ride on the usual terrain is more meaningful than a short test on asphalt.

The Magura MT Thirty uses hydraulic disc brakes with 160-millimeter rotors on both the front and rear wheels. Hydraulic brakes require less hand force than many simple mechanical systems. It is still important, however, that the reach is suitable for short fingers. The child should be able to reach the brake lever securely with one or two fingers without having to move their hand far from the grip.

Before the first off-road ride, the levers must be rotated to the correct position and the reach adjusted. If they are positioned too far outward, the wrist will bend. If they are mounted too flat, a natural arm position is missing on steep descents. Proper adjustment allows the child to hold the handlebars firmly while braking in a controlled manner.

The Sram NX Eagle drivetrain offers twelve gears. A single 32-tooth chainring is used at the front, with an 11 to 50-tooth cassette at the back. This 1x drivetrain eliminates the need for a front derailleur and a second gear shifter. This reduces the number of controls and facilitates quick gear changes.

The gear ratio is clearly geared toward athletic riding. For trained young riders, it offers a good speed range. Very light or less strong children may still find the lowest climbing gear difficult on long, steep ramps. In this case, a specialist shop should check whether a smaller compatible chainring makes sense. Chainline, frame clearance, and rear derailleur capacity must be taken into account.

The Newmen wheels and Schwalbe Rocket Ron tires are well-suited for XC use. The tires roll fast and offer good propulsion on firm forest soil. Their narrow, race-oriented design provides less natural damping on rough surfaces than more voluminous trail tires. Instead of setting the tire pressure unnecessarily high, it should be adjusted to the child's weight, the terrain, and their riding style.

Body heights are not binding limits. The BIKE test provides a recommendation starting at 124 centimeters for the model tested. At the same time, the high standover height shows that leg length and riding ability must be taken into account. A child with a long torso and short legs may have difficulty dismounting safely despite having an appropriate overall body height.

Inseam is measured barefoot. The child stands against a wall with their legs slightly apart. A book is pushed horizontally and with gentle pressure up into the crotch. Then, measure from the floor to the top edge of the book. This value serves as a starting point, but does not replace testing on the assembled bike for the Phenix Rookie.

For the standover check, the child stands in front of the saddle over the top tube while wearing shoes. There should be noticeable clearance between the top tube and the body when off-road. In the event of an abrupt dismount, the child must not land on the frame. The more technical the trails being ridden, the more important this safety clearance becomes.

The reach to the handlebars must also be appropriate. The child should be able to reach the grips with their arms slightly bent. If the arms are fully extended, the frame is usually too long or the handlebars are too far away. A significantly hunched back and hunched shoulders also indicate an unfavorable position.

Parents should not buy a bike that is significantly too big so that it lasts for several years. On a kids' mountain bike that is too long, it is harder to shift body weight. This makes tight corners and spontaneous evasive maneuvers difficult. On steep descents, there is also a lack of space to move the body back and down.

1. Measure the child's inseam and height.
2. Start with frame size XS if the child is at the lower end of the size range.
3. Check the standover height with shoes directly on the bicycle.
4. Adjust the saddle so that the knee remains slightly bent when pedaling.
5. Adjust the brake levers and shifters to the size of the child's hands.
6. Perform a test ride that includes tight turns, starting, and controlled dismounting.

If the child is between an XS and an S, the intended use will decide. The smaller bike is usually more agile and allows for more freedom of movement. The larger version rolls more smoothly over bumps and offers more room for further growth. For races and technical trails, a size that is currently easy to control is more sensible than a large growth reserve.