1) Top tube length
For many mountain bikers, this measurement is the most important value of a bike because it allows you to roughly estimate the seating position and therefore the comfort. BIKE measures the top tube in the imaginary horizontal line from the centre of the top edge of the head tube to the centre of the seat tube and not along the actual tube.
2) Seat tube length
The seat tube length roughly corresponds to the frame size. BIKE measures the value from the centre of the bottom bracket axle to the upper edge of the seat tube. We also state this measurement in the test reports in addition to the manufacturer's frame size. Caution: With a very long seat tube, the saddle cannot be lowered as far or you cannot ride as much travel with a dropper post as with a shorter seat tube.
3) Wheelbase
Length makes you run, short wheelbase makes you nervous or agile. Together with the steering angle (and the fork height), the wheelbase has a major influence on the smoothness and manoeuvrability of a bike. On 29-inch bikes and plus-size bikes, the wheelbase is significantly longer than on 27.5-inch MTBs.
4) Chainstay length
Long chainstays ensure good climbing ability because the bike rears up much less on steep ramps. Short chainstays, on the other hand, lead to more playful handling. The bike is also easier to pull onto the rear wheel for a wheelie or to lift the front wheel over obstacles.
5) Protrusion height
We measure the standover height vertically from the ground to the centre of the top tube. This value describes the distance between you and the bike if you have to dismount. A large standover height can lead to painful touchdowns and falls, as you cannot get your feet on the ground immediately when dismounting.
6) Bottom bracket height
The bottom bracket height is easy to measure (from the centre of the bottom bracket axle to the ground), but not as neutral as the BB drop (also called BB offset). The bottom bracket height also depends on the tyre model. A thick, roughly profiled tyre raises the bottom bracket. On a bike with a bottom bracket that is too high (depending on the suspension travel!), you feel somewhat disconnected from the ground, especially in difficult terrain. Fullys naturally need a higher bottom bracket than hardtails because the centre of the bike drops when the suspension is compressed. The more suspension travel, the higher the bike needs to be built. A large BB drop (lowering of the bottom bracket compared to the wheel axles) ensures that the pilot sits or stands "in" the bike.
7) Head tube length
With twentyniners in particular, the head tube must be as short as possible to compensate for the larger wheel diameter. Otherwise the saddle rake will be too low. You then have too little load on the front wheel. BIKE measures the head tube length without the bearing shells.
8) Stem length
Although this is not directly part of the geometry, it has an enormous influence on the riding position and steering behaviour of a bike. In sports use, 70-100 millimetres are standard. The more suspension travel, the shorter the stem. Historical 150 mm dimensions can only be found in museums. The latest trend: long reach and stubby stem (e.g. 30 millimetres).
9) Seat angle
The seat angle influences the riding position and especially the power transfer uphill. If the seat angle is too slack, the rider sits tail-heavy and struggles unnecessarily uphill, or the bike rears up earlier. The seat angle depends heavily on the Bike category down. In recent years, the trend has been towards ever steeper seat tube angles.
10) Steering angle
The steering angle has a decisive influence on the steering behaviour of a bike. The steeper, the more manoeuvrable (negative: less stable), the slacker, the smoother (negative: more sluggish) and more forgiving. For a 27.5-inch all-mountain bike, 66-68 degrees is the right angle. Extremely steep angles cause unsteadiness, very flat angles (64.5 degrees downwards) also take some getting used to due to the tipping steering at low speeds. The steering angle also depends heavily on the Bike category from.
11) Spring travel
BIKE always measures the suspension travel itself in the test laboratory and indicates the measured value on the suspension elements in the test report. The length of the suspension travel characterises the Bike category. BIKE also determines the characteristics of the fork and rear triangle. These are presented graphically in the test report.
Reach
The reach characterises the length of a bike independent of the seat angle. The reach is the distance measured horizontally from the centre of the bottom bracket to the centre of the head tube. A long reach means a stretched position when riding downhill in a standing position, a short reach means a more upright position.
Stack
The stack (vertically measured distance from the centre of the bottom bracket to the centre of the upper edge of the head tube) provides information about the height of the front of a bike - regardless of the tyres or stem. If the stack is too large, not enough pressure can be applied to the front wheel and the front is too high.
A look into the hallowed halls of the test team: Every test bike is dismantled and measured in the BIKE test lab. Numerous test stands provide objective test results and help to explain riding impressions. This video shows which stages a bike goes through in the test lab.
