How to choose the size of bicycle dental disc that suits you?

The core of choosing the right bicycle tooth plate size is to balance the "power efficiency" and "riding comfort" by combining the riding scene, height and leg length (physiological conditions) and riding habits, so as to avoid the difficulty of power exertion or knee injury caused by improper size. Specifically, it can be screened according to three key steps:

Step 1: Determine the "disc size" (tooth number combination) according to the riding scene.

The number of disc teeth directly affects the "tooth ratio" when riding-discs with more teeth are suitable for high-speed cruising, while those with fewer teeth are suitable for climbing, so it is necessary to select the basic combination according to the regular riding conditions first.

Level road/high-speed scenes (such as road commuting, racing)

Priority is given to "large-tooth disc" to ensure that pedaling at high speed is effortless.

Road vehicle: two discs can be selected from 50/34T (compressed disc, taking into account flat road and gentle slope) or 52/36T (standard disc, pure flat road racing); If you often ride the expressway, you can choose 46-50T for a single plate.

Gravel car (both flat road and light off-road): single disc gives priority to 42-44T, which can not only cope with flat road cruising, but also cope with gentle slope through flywheel matching.

Climbing/complex road conditions (such as mountain cross-country and hilly mountain roads)

Choose "small number of teeth disc" to reduce the number of teeth than to make climbing easier and avoid excessive knee force.

Mountain bike: 30-34T is preferred for single disc (32T is common, which is suitable for most mountain road conditions); If you often ride steep slopes (gradient > 15%), you can choose 28-30T；; Three-disc system (such as 44/32/22T) is suitable for extreme steep slopes, but at present, single disc and wide-range flywheel are more mainstream.

Folding bike (mostly short-distance in cities, which may meet the overpass): choose 42-48T for single disc, taking into account the speed of flat road and slight climbing (such as overpass).

Mixed scenes (such as urban commuting, flat roads+a few ramps)

Select "Balanced Tooth Number" to avoid frequent disc switching.

Road/folding bike: Double-disc 50/34T is the most common; 44-46T single disc with 11-34T flywheel can cover most urban road conditions.

Step 2: Determine the "crank length" according to the height and leg length (the core adapts to the physiological conditions).

The length of the crank determines the "arm of force" when pedaling-too long will easily lead to excessive knee flexion and extension (knee injury), and too short will lead to insufficient force, which needs to be matched according to the height or inseam length (the distance from the crotch to the ground).

Fast Matching by Height (General Reference)

Height Range Crank Length (Highway/Mountain/Folding General)

150-165cm 160-165mm (165mm is preferred, short people should avoid being too long).

165-175cm 170mm (the most mainstream size, suitable for most people)

175-185cm 172.5-175mm (for tall people, choose a long crank to exert more force).

> 185cm 175-180mm (avoid excessive knee bending when pedaling)

Accurate matching according to inseam length (more scientific)

If you want to be more accurate, you can measure the length of inseam (standing barefoot with a book in your crotch, measuring the distance from the bottom of the book to the ground) and estimate it according to the formula:

Crank length ≈ inseam length × 0.216 (for example: inseam 75cm, crank ≈75×0.216≈16.2cm=162mm, 165mm or 160mm is preferred, and fine-tuning is required according to riding experience).

Note: if you ride a mountain bike frequently (you need to stand and pedal frequently), you can choose 5mm shorter than the estimated value (if you calculate 170mm, choose 165mm) to avoid your knees pushing against the handlebar when standing; Road vehicles are selected according to the estimated value to ensure the efficiency of road leveling.

Step 3: Set the "BCD value" according to the dental disc interface (to avoid installation incompatibility).

BCD value (the diameter of the center of the screw circle) is the "connection standard" between the tooth plate and the crank, and it must be consistent with the BCD specification of the crank, otherwise it cannot be installed. It is necessary to confirm the BCD of the existing crank before selecting the corresponding tooth plate.

Common BCD values and adaptation scenarios

130BCD: It is suitable for many standard discs of road vehicles (such as 52/36T), and the number of screw holes is mostly 5, which is suitable for discs with large teeth.

110BCD: It is suitable for road car compression disc (such as 50/34T) and folding car tooth disc, with 5-hole design, and is compatible with small and medium-sized numbered discs.

104BCD: Single-disc/double-disc mainstream specifications for mountain bikes (such as 32T single-disc and 36/22T double-disc), 4-hole design, suitable for most mountain cranks.

96BCD/83BCD: It is mostly used for BMX and children's cars, and is suitable for discs with extremely small teeth (such as less than 28T).

Confirmation method

Check the manual of the existing crank, or measure the "distance between the centers of two adjacent screw holes", and then convert it through the formula (for example, 4 holes are 104BCD, and the distance between adjacent screw holes is 73.5 mm); If you buy a new tooth plate, tell the merchant your crank model directly to avoid wrong selection.

Fourth, finally: fine-tune the test ride, taking into account the "habit preference"

If conditions permit, give priority to riding different sizes of dental discs and adjust them according to actual feelings:

If there is pressure on the outside of the knee when pedaling, it may be that the crank is too long and needs to be reduced by 5 mm;

If you feel "stepping on the air" (you need to shift gears when you don't pedal to the end), it may be that the crank is too short and you need to add 5 mm;

If the pedal frequency on the flat road is high (> 100 revolutions per minute) but the speed can't go up, it may be that the number of teeth on the disc is too small, and it is necessary to change the disc with a size of 1-2T;

If the pedaling is heavy (< 60 revolutions per minute) when climbing a hill, it may be that there are too many teeth on the disc, and it is necessary to change the disc 1-2T smaller.