Bicycle crank length how to choose

Open

Such carriages are a carriage shaft with a set of bearings pressed by cups and screwed into the carriage tube of the bicycle frame.

Their main drawback, however paradoxical it may sound, is their openness. Dirt, moisture, and other road debris can quickly clog the carriage, so it must be handled and cleaned frequently. However, it can serve faithfully for a neat owner for many years, it is enough only once to choose the right carriage for a bicycle.

ISIS Drive

This is a spline standard that is supported by such well-known manufacturers as Race Face, FSA, Truvativ, Chris King, Bontrager, Stronglight. This standard is not inferior in reliability to the OctaLink standard, but due to the different number of slots, they are completely incompatible.

Closed

Or, as they are also called, cartridge. They are a non-separable, one-piece housing with bearings and a carriage shaft, which is screwed into the carriage tube of the bicycle frame.

This design avoids the ingress of moisture, dirt or sand and completely eliminates misalignment of the bearings. But closed carriages have one significant drawback. the carriage will order a long life immediately after water or dirt gets inside the cartridge. The reason is the inability to disassemble the cartridge (you have not forgotten that this is a one-piece part?).

To choose a bottom bracket for a bicycle, you need to know its size.

With the length of the axis, things are a little more complicated. If there are only two standard diameters, then the axle length standards are several times larger. The mountain bike provides the following standards. 110 mm, 113 mm, 118.5 mm, 122.5 mm and 128 mm. Take the Truvativ Overdrive DH, for example, which is exclusively available in 128mm lengths.

From all this, we can conclude. choose the length of the carriage axis, focusing on the length of the carriage tube of your bike frame, the type of system and the number of stars on it.

And the last thing left to figure out before choosing a bottom bracket and a system for a bicycle is what types of connection between the bottom bracket and the connecting rods are.

On Soviet bicycles and Russian-made bicycles, the connection of the carriage shaft with the connecting rods using a blade (key) is used. But let’s say right away. this design is unreliable and tends to loosen up if the key was not screwed in properly before the first trip. But, despite this, she also has an advantage: it lies in the rather easy removal of the connecting rods without special pullers.

Imported bicycles are mostly squared. The ends of the shaft in such carriages are in the form of a cone with a square section, on which the connecting rods sit. Such a connection is quite rigid and does not loosen over time, since the load is not on the key, but directly on the shaft.

Advanced mountain and road bikes have gone further. They use the so-called spline connection today. There are 2 standards:

Bicycle crank length how to choose

bicycle, crank, length, choose

Finding Your Ideal Crank Length

Shimano OctaLink

This is the Shimano standard, which is a closed bottom bracket with spline and round shaft. It is not difficult to guess that only systems made by Shimano will fit such carriages. Thanks to the splined connection, it has become possible to produce a carriage with a large hollow shaft. This results in a reduction in weight and an increase in shaft stiffness when compared to a square connection.

Should You Ride A Shorter Crank? | Choosing Your Bike Crank Length

How to choose the right bottom bracket and crankset for your bike

Eh, I’ll pump it!. and the cyclist flew along the track or down the hill. Wind, speed, adrenaline Do you crave these sensations? Then be smart about choosing a bicycle carriage, because it is she who is directly responsible for the torque transmitted from it to the wheels. But before that, we will teach you how to choose the right bottom bracket and connecting rods for your bike.

How To Choose The Correct Crank Length – The Most Important Bike Adjustment You’ve Never Made?

An experienced cyclist knows what a bottom bracket and cranks are and what they are for. We explain to beginners: the bottom bracket is a bearing unit that provides rotation relative to the bicycle frame of cranks with pedals and leading sprockets. The point of life of the bottom bracket is to transmit torque with minimal losses from the pedals to the wheel.

It is located at the bottom of the frame behind the front wheel. This arrangement leads to the fact that the carriage assembly is constantly thrown by dirt and water, therefore, reliable protection of the carriage bearings is a guarantee of its long and happy life.

To choose a carriage for a bicycle, first you need to figure out what they are. All carriages can be divided into two groups:

Let’s summarize. What connecting rods and carriage to choose for a bicycle?

It is rather difficult to advise something specific in this case. Bogies and squared systems are still supported and are available in both cheap and very expensive versions.

Important note. ISIS is more suitable for aggressive use than other types, and the square wins in terms of pricing.

Bicycle crank length

I think that anyone who, himself assembled a bicycle or changed the body kit, faced such a question. There are several methods (slightly different from each other) 1) We measure the distance from the crotch to the floor. (See the picture where a naked man waves his hand to you) The data obtained in millimeters multiply by 0.216 and we get the recommended length of the connecting rods. L = X (mm) 0.216

So my distance X is exactly 80cm = 800mm, respectively, I need to use the connecting rods 172.8 mm.

2) We look at the foreign table. Where in the left column is the length of X, in the right column is the length of the connecting rods. According to this table, I got 165mm

3) Foreign Internet calculator. (by link) http://www.machinehead-software.co.uk/bike/cranks/cyc.received 165mm

4) Domestic table. (for a classic road bike) Here the length of the cranks is calculated from the length of the upper tube of the frame. For a mountain, cross-country bike (MTB), the length of the cranks can be chosen 2.5-5 mm longer. (as they write on the Internet). With the length of mine frame 56cm. we get 170-172mm.

Based on your riding style. and averaging the data from all sources, I choose 170mm.—— The main thing to be guided by when choosing the length of the connecting rods is height (leg length). The longer the legs, the longer the cranks. It will be inconvenient to twist long cranks with short legs, as well as vice versa.

Connecting rods are from 145 (for children) 160 and up to 180mm, with a step of 5 and sometimes 2.5mm High revs (high cadence) are more convenient to hold on the cranks shorter, the power one. on long ones (because the lever is larger). Longer connecting rods (175, 177.5 and 180 mm) also cause the saddle to lower and move forward a little. They are easier to hit the ground when overcoming obstacles and on a bend, they somewhat limit the permissible tilt of the bike, and the cadence is slightly reduced due to the possibility of using higher gears. The longer the cranks, the easier they are to turn in the same gear, but the longer the distance will be. pass the foot, the muscles will work harder and fatigue faster. The length of the crank determines the diameter of the circle that the pedals describe. The larger the circle, the more you will have to bend your knees and tighten your thigh muscles while rotating the cranks. Your thigh muscles cannot develop the same force throughout the range of motion.

Also, the length of the cranks depends on the riding style.

In road racing, shorter cranks are generally used due to cadence (cadence) requirements. Downhill DH also uses shorter cranks to reduce the likelihood of crank contact with obstacles.

For XC and BMX, cranks are usually longer than road bikes.

The standard size of the crank, which is installed on bicycles at the time of sale. 175 mm.

In general, when making a choice, remember: The length of the crank determines the range of motion, affects the position of the saddle, the height of the hip and the angle of flexion of the knee at the highest point. On the other hand, it determines the cadence, maximum torque (low thrust), speed and throttle response of the bike.

The length of the connecting rod determines the range of motion, affects the position of the saddle, the height of the hip and the angle of flexion of the knee at the highest point. On the other hand, it determines the cadence, maximum torque (low thrust), speed and throttle response of the bike.

Unfortunately, bipedal walking and running have evolved for many hundreds of thousands of years, and the pedal-powered bicycle did not appear until 1821. Therefore, the biomechanics of the adult human is optimized for walking, not pedaling. The research results showed that the optimal stride length when walking at a speed of 4.5 km / h is 0.7 m, the frequency is 105 steps per minute, and the long-term developed power is 150 W (Beletsky Yu. V. Two-legged walking. M., Science, 1984). Curiously, the optimal step when walking is approximately equal to the pedaling step. four times the length of the crank. If we take the two most common crank sizes (170 mm and 175 mm), then the pedaling step for them will be, respectively,

0.68 m and 0.7 m. This coincidence is not accidental. Nature, on the one hand, and bike designers, on the other, came to the same result. By the way, with a power of 150 W and a speed of 105 rpm on a horizontal smooth highway, the bike can be accelerated to a speed of 24 km / h. Another conclusion follows from this. Having spent the same energy, during the same time a cyclist will travel 24 km instead of 4.5 km traveled by a pedestrian. Thus, cycling is 24: 4.5 = 5.3 times more efficient than walking. But this is theoretical. In practice, the efficiency is only 2-4 times higher due to various losses we did not take into account.

READ  How to insert a pin into a bicycle chain

Longer connecting rods (175, 177.5 and 180 mm) also cause the saddle to lower and move forward a little. They are easier to hit the ground when overcoming obstacles and on a bend, they somewhat limit the permissible tilt of the bike, and the cadence is slightly reduced due to the possibility of using higher gears. With shorter connecting rods (165-172.5 mm), everything, respectively, is the opposite.

So how do you choose connecting rods? There are two recipes.

First recipe. A very rough estimate of the crank length for a classic road bike.

For mountain bikes, cross-country bikes, you can choose 2.5-5mm longer crank lengths.

Second recipe. A simple principle: the shorter the leg, the shorter the crank should be. It is considered that the length of the crank should be 18.5% of the distance from the top of the tibia to the ground.

None of these recipes take into account the actual size of the legs, the ratio between the length of the thigh and lower leg or differences in metabolic rate, the number of fast and slow fibers in the muscles, the tendency to sprint or stayer physical activity. The only reliable, albeit costly, way is to try different crank lengths to find the one that suits you best. But meticulously accurate crankset selection is essential for athletes and bike travelers doing 8

12 hours in the saddle many days a year. Those who like to ride for their pleasure can happily and for many years twist those cranks that are in stock, if only the purchased bike fits them in size.

Crank length is measured as the distance from the center of the pedal axis to the center of the system axis (carriage). The length of the connecting rod is standardized and can be from 160 mm. up to 190 mm. with a step of 5 mm. or 2.5 mm. in the middle of the range, and is selected for the anthropometric data of the cyclist and the riding style.

A rough estimate of the required crank length for a road bike. From this size, you can start trying different options. If your leg is relatively short, then you need a shorter crank.

If you want a classic road frame in the following sizes:

For a mountain bike, the length of the connecting rods is taken 2.5-5 mm more than for a road bike.

The length of the connecting rod determines the diameter of the circle that the pedals describe. The larger the circle, the more you will have to bend your knees and tighten your thigh muscles while rotating the cranks. Your thigh muscles cannot develop the same amount of force throughout the range of motion. This is very easy to show. If you squat with your knees fully bent and stand up, say five inches, it will take much more effort than it takes to squat five inches from a standing position and then straighten again. When you squat, your muscles cannot deliver the same power as if your knees were only slightly bent to lower you five inches. So if you have to choose between a crank length that forces you to fully bend and extend your knees, and a crank that forces your knees to bend only within, say, 20 degrees, choose a shorter crank. This crank will allow your muscles to work in a more efficient range of motion.

So how long should the connecting rods be? Yes, that’s a good question. I wish I knew a good answer, but I don’t know. It is probably clear that a 5’2 “biker will not want to ride with the same length of cranks as a 6’7” biker, unless of course they have managed to grow legs the same length (which is highly unlikely). Several studies have been performed to determine the optimal leg / crank ratio. I doubt there is an optimal ratio that applies to all people. One author in a major publication just a few years ago argued that, after a significant amount of testing with many different cyclists, it was established that the length of the crank should be 18.5% of the distance from the top of the tibia to the floor. You will find the top of the shin bone very easily. It is 5-6 inches below the bump of your pelvis and moves back when you raise your knee. After reading this, I instantly changed the standard 170mm road bike cranks to 175mm. Recoil and stamina increased immediately. I started using this formula when choosing connecting rods for clients. So far, no complaints have been received. But this, of course, does not mean that my clients will not be as, or even more satisfied with some other length of the connecting rods. And I have to admit that I have never used cranks longer than 175mm long enough to conclude that they are even better for me.

The measurement of the apex of the tibia does not take into account differences in the legs themselves. Differences in the proportions between calf and thigh length should affect the optimal crank length. A biker with longer thighs and shorter calves will put in a longer crank to flex the knee to the same angle as a biker with short thighs and long calves. One of two cyclists with the same proportions may prefer to pedal faster. A shorter connecting rod can help here. Or maybe even two bikers with identical skeletal proportions will find out in practice that they need different crank lengths to get the most bang for their buck, simply because of differences in musculature.

The length of the connecting rod determines the diameter of the circle that the pedals describe. The larger the circle, the more you will have to bend your knees and tighten your thigh muscles while rotating the cranks. Your thigh muscles cannot develop the same amount of force throughout the range of motion. This is very easy to show. If you squat with your knees fully bent and stand up, say five inches, it will take much more effort than it takes to squat five inches from a standing position and then straighten up again. When you squat, your muscles cannot deliver the same power as if your knees were only slightly bent to lower you five inches.

Types of connecting rods

One-piece. monolithic construction combining the shaft and two connecting rods. In fact, it is a thick metal bar bent in different directions at right angles. This kind of crankset was used on the first bicycles. Currently seen on BMX and kids bikes.

Two-piece. this is not only the combined one-piece right connecting rod and drive sprockets, but also the carriage shaft tightly welded to them. In this case, only the left lever is a separate piece, which is fixed to the free end of the shaft.

Until recently, this method of assembling cranks in a bicycle was considered obsolete, until in 2004 the Shimano factories revived the two-piece design, improving it with a cartridge bottom bracket with large-diameter bearings. Other bicycle parts makers support the renaissance of the two-piece crankset.

Three-piece. the most popular design today, it is possible to replace the drive sprockets separately from the right arm. Everything is understood in it: the cranks for the pedals and the treadmills themselves, separately the carriage shaft and the front sprockets one by one.

What materials are used for connecting rods

Depending on the stated requirements of the bike, manufacturers make the connecting rods aluminum, steel, titanium or carbon. To achieve these goals, manufacturers also improve the shape of these parts. Thus, the complex shape of the part, hollow inside, with a groove on the outside, allows to reduce weight. In addition to making the bike lighter, the lightweight design makes it easier to spin and achieve faster acceleration. At the same time, the hollow parts are strong and rigid.

So, steel connecting rods are both solid and hollow. Solid parts are used for road bikes, but tubular ones are often designed for mountain bikes and BMX sportbikes to lighten models.

Aluminum parts are hot or cold forged. This enhances the robust properties of the material and minimizes breakage. Aluminum connecting rods can be hollowed out to reduce weight.

Titanium and carbon are less common in connecting rods, usually for sports bikes. It can be a homogeneous carbon piece with either aluminum or titanium inserts. The complexity of the technology affects the cost of the bike upwards.

Rotary system RS4X

As a standard, the cranks on the bike are fixed along one straight mowing line. In this case, the rider’s leg is excessively bent at the knee at the top dead center. It’s no surprise that knee joints get stressed from time to time.

In addition, it has been noticed that when pedaling, a situation occurs in which the cyclist cannot transfer his entire force to the rear wheel. A dead zone occurs when the cranks are horizontal to the ground. Naturally, because of this, the efficiency decreases.

The RS4X rotary system radically solves these problems. When shifting from a straight line, the upper dead center is underestimated and a failure of the moment of force is excluded during the entire cycle of pedaling, which provides an increase in the efficiency.

Experience has shown that the new setup provides an actual 16% power increase on a track bike. Due to the absence of a sharp drop in the load, the risk of pain in the knee joint, as well as stretching of the tendons, decreases.

Connecting rod dimensions

Depending on the size of the frames, the connecting rods are produced in different lengths. Longer pedaling levers are more comfortable for taller cyclists, while smaller cyclists require shorter ones. Too long levers on a low frame can cause inconvenience when driving off-road, even in the city they can hit the rail at a level crossing or curb.

Short levers are difficult to spin, but then they are easier to maintain high speed. This can be explained by such indicators as cadence. the number of pedal revolutions per unit of time. The cadence increases if you have to pedal with short levers, and in the case of long levers, everything happens exactly the opposite.

The length of the connecting rods can vary from 150 to 185 mm. For an adult bike, you need to choose levers between 165 and 185 mm. On a children’s and teenage bike, cranks with a length of 150 to 177.5 mm will be comfortable.

The final point when choosing the length is set by each cyclist himself, taking into account his preferences in riding style. Shortened cranks are preferred by track riders. On mountain bikes, a reduced cadence is preferred for extra pick up when going downhill. Downhill fans in particular use levers as long as possible.

Elliptical Crankset Bicycle Cranks

The experiment with non-standard asterisks began at the end of the 19th century. Even then they knew about the existence of a problem dead zone.

READ  Women'S Bicycle Saddle How To Choose

For the first time, the mass production of oval stars under the Biopace brand was opened by Shimano in 1983. Then in the world of cycling there was a lot of controversy about the need for innovation, but over time they disappeared, since professional cyclists did not like the novelty. The term Biopace has stuck, and this is how they call cases of uneven pedaling. There are currently two Osymetric and Q-rings in production specifically for racing bikes.

Oval sprockets make it easier to overcome horizontal pedals. The gear ratio at this point is increased to match the reduced pedal effort. As a result, the pedals rotate more smoothly. However, miracles do not happen, and when climbing a hill you have to sweat, because nothing comes of anything.

How to remove cranks from a bicycle. in a useful video:

Custom rotor system RS4X

Consider the latest design, the RS4X Rotary Crankset. The fundamental difference from standard levers is the location with an angle offset by several degrees (standard fastening is along one straight mowing line). With standard fastening, the cyclist’s leg is strongly bent at the knee at the top point and this negatively affects the knee joints, does not allow the cyclist to use his strength in full.

The rotor system allows you to increase efficiency by lowering the top dead center and eliminating the failure of the moment of force. According to research, the power increases by 16%. This bike crankset is quite expensive (around € 400), but is good because it relieves stress on the biker’s knee joints and tendons.

Taking into account the peculiarities of the connecting rods of different systems, size, material, you can choose the most suitable option for your bike and the purchase will meet all your expectations.

Many people argue about which bike frame is better. steel or aluminum. In order to understand which frame will satisfy the needs of the cyclist, we will understand in detail what material will meet the stated requirements.

How to choose a wheel motor for an e-bike. What factors to pay attention to when choosing. Advantages and disadvantages of varieties of motor-wheel motors.

Whether to use disc or rim brakes on a bicycle is a common question that worries many cyclists. To deal with it, it is necessary to study the positive and negative aspects of each type of brake system.

How to choose the right crank length?

The question of choosing the length of the connecting rods comes down to the type of bike and bike fit

How to find the length of the cranks on the bike? When triathletes buy a bike, they focus almost exclusively on the frame for size. The idea is clear. the taller the athlete, the larger the frame. And yet, the length of the cranks is almost as important as the size of the frame.

The length of the connecting rod is measured by the distance from the pedal axis to the center of the carriage. Most bikes come with cranks ranging from 170-175mm, but the range can stretch from 140 to 190mm.

Why connecting rod length matters?

On a bicycle, the athlete has three points of contact: the saddle, handlebars and pedals. With a saddle, it is more or less clear, a suitable saddle is comfortable, all other options cause discomfort. From this we can argue that the height of the saddle affects the position of the athlete on the bike, and therefore its comfort and power. Keep in mind that saddle position has a profound effect on comfort and pedaling efficiency, although this is often overlooked by many. Girls or smaller athletes will know that position and handlebar width are critical in terms of comfort, handling and the ability to quickly reach the brakes. Our third point of contact with bicycles is a little more complicated.

The connecting rod is the radius of rotation of the pedal relative to the carriage. A shorter connecting rod makes a smaller circle, which means that the range of motion of the legs is less. This range of motion will affect all key joints in the legs: hip, knee, ankle. When you pedal, there is always an optimal range of motion for these joints. In particular, maintaining the angle of the hip as much as possible “open” results in more power, usually better aerodynamics and, important for triathletes, better running after cycling.

In the image above, we show the green color in which corners the working body parts would be if the crank length were shorter. Red is the real state of affairs. There are no angles to simplify the diagram. Here are some observations regarding riders with long (and possibly longer than necessary) cranks:

Of course, the mowing line in this image only conditionally shows general principles, you should not measure the angles thoroughly. It just shows how changing the length of the crank can have a significant impact on how a person sits on a bike, even if they have the right frame size.

Second, remember the squat in the gym. If you squat down deep, can you lift a lot? Muscle strength is often limited by the individual characteristics of the range of our joints. Keeping your hips open and your knees less bent tends to be easier to lift.

Third, longer leverage means that the extreme positions of the leg are deeper and higher. This often results in the need for more hip control. Often to riders who are powerful “crush” hips, they are told to lower the saddle in order to push even harder from above, forgetting that in the lower position of the pedal, their legs do not work at all! A long connecting rod will only worsen the situation, and lowering the saddle will make it even worse.

As with all talk of bikefitting, choosing the right crank length is based on the individual. Flexibility, biomechanics and sporting experience / shape influence any decision to change the length of the crank. However, consider two cyclists of different heights: one is 180 cm, the other is 160 cm.If each of them has the same crank length (take an average length of 172.5 mm), their feet are raised 34.5 cm (top and the bottom of the pedal travel). For the first rider, this is 19% of his height. For the second rider, this is 21.5%. And the length of the legs will only increase the difference.

What length of connecting rods should I choose?

There are limited guidelines on how to choose the optimal connecting rod length. There is a general recommendation. for a 180 cm athlete, the optimal length is 172.5 mm. University of Utah’s Jim Martin suggests that the optimal length should be about 20% of your inseam or 41% of your shin length. It is also worth paying attention to the ratio of the length of the connecting rod to the height of the saddle from the carriage. This ratio is likely rider-specific, but can help normalize differences between athletes. As of today, there is no standard answer. With a triathlon, the answer becomes even more difficult as a bicycle. it is simply a means of getting to the running stage faster and with minimal effort. Generally, if you are short, a shorter crank would probably be fine.

Does shorter crank lengths mean loss of leverage??

“Give me a long enough lever and a fulcrum and I’ll turn the world”. Archimedes

The power generated from a bike depends on how fast you pedal and how much effort we put in. We know from the school course that a longer lever allows more force to be applied. With a shorter pedal arm (crank arm), the athlete will need to increase the cadence slightly to generate the same power. However, the force change is minimal with extremely short levers. Thus, the ability to crank a larger gear with longer cranks has little difference in pedaling efficiency.

The type of bike matters?

Considering the position on a TT bike, where you lower yourself forward, curl your back, and reduce the angle between the raised knee and your back, opening up that angle as much as possible, you have many benefits. Hence, you are more likely to notice an increase in aerodynamics and power when riding with shorter cranks. On a road bike, due to a more relaxed and / or upright stance, the difference will still exist, but it will be less noticeable. Perhaps this is not the upgrade that will lead to a dramatic increase in power or speed, but if you are small, then the selection of the length of the connecting rods should be taken into account more carefully.

Rotary system RS4X

As a standard, the cranks on the bike are fixed along one straight mowing line. In this case, the rider’s leg is excessively bent at the knee at the top dead center. It’s no surprise that knee joints get stressed from time to time.

In addition, it has been noticed that when pedaling, a situation occurs in which the cyclist cannot transfer his entire force to the rear wheel. A dead zone occurs when the cranks are horizontal to the ground. Naturally, because of this, the efficiency decreases.

The RS4X rotary system radically solves these problems. When shifting from a straight line, the upper dead center is underestimated and a failure of the moment of force is excluded during the entire cycle of pedaling, which provides an increase in the efficiency.

Experience has shown that the new setup provides an actual 16% power increase on a track bike. Due to the absence of a sharp drop in the load, the risk of pain in the knee joint, as well as stretching of the tendons, decreases.

Connecting rod material

Pedal levers can be made from different materials:

  • steel,
  • aluminum,
  • titanium,
  • carbon.

What tricks do the manufacturers of connecting rods go to in order to reduce weight: they make them with a complex intricate shape, make a groove on the outside, and leave a void inside. Lighter cranks, in addition to reducing the overall weight of the bike, are even easier to spin. The less mass you need to unwind, the faster you can accelerate.

Although cranks are some of the most stressed parts on a bicycle, they can be made hollow. As with the bike frame, the hollow pedal arm retains its strength and rigidity with much less weight. The presence of a void inside the part does not significantly affect the strength indicators.

Steel connecting rods can be solid and tubular. For domestic bicycles and road bikes, they are made in one piece. Very often, lightweight hollow pedal levers are installed on mountain bikes and BMX sports bikes.

All durable, low-breakage aluminum parts are hot or cold forged. Bicycle cranks are pressed against a metal insert, and then removed, after which a finished part with a shaped groove is obtained. Hollow aluminum arms are only made using the Hollowtech cold forging method, pioneered by Shimano. Such products are used together with a hollow carriage shaft, fixed on its 8 spline ends with an increased diameter.

READ  How to adjust the bicycle rear wheel bearing

For rare sports bicycles, cranks are made of titanium or carbon. Carbon fiber products can be either homogeneous or with an aluminum or titanium base inside. It is clear that the more complex the manufacturing technology, the more expensive the finished product.

Mounting methods on the carriage shaft

A wedge-shaped pin is a familiar detail on old bicycles, now it is found only on children’s two-wheelers.

The square end of the shaft is a traditional method of fastening, in which both connecting rods are fixed on square planes beveled with an inconspicuous wedge. Tightening on the wedge occurs with a screw or nut that is screwed into the ends of the shaft. The joints are always covered with a plastic boot.

Hexagonal shaft end. also made with a bevel to wedge the connecting rod.

The splined connection is the OctaLink standard: the carriage shaft is made with a through hole in the axis, but has an increased diameter; the ends of the shaft are round with eight protrusions; the connecting rods are attracted by a large hollow hex bolt by 10; from the outside, the connection is closed with a boot. A traditional puller for disassembling this connection cannot be used, because it will have nothing to rest against.

Q. factor

On a bicycle, to improve pedaling efficiency, you need to take into account the distance between the planes in which the ends of the cranks rotate, that is, the Q-factor. It was checked on the stand that with a correctly selected Q-factor, a person develops 4% more power than with legs set with a slope.

It is so arranged by nature that the knee joints of a person cannot bear long-term loads if the legs are not close to each other. The most leg pressure can be applied when the applied force vector is exactly 90 degrees to the surface.

With the advent of off-road bikes, the stays of the rear triangle of the frame had to be pushed apart to fit the wide tire. With the decrease in free clearance, it was necessary to make the crank arm for the pedal bent, otherwise it would hit the frame. Therefore, on all mountain bikes, the Q-factor is overestimated.

From nature or for other reasons, people’s legs are different: bent at the knees or straight, narrowed at the pelvis or curved to the sides. For example, women have wider pelvic bones from birth than men. It is impossible to take into account the anatomical uniqueness of each in the mass production of bicycles, and for professional athletes it is quite possible to select the Q-factor individually.

Connecting rod dimensions

Depending on the size of the frames, the connecting rods are produced in different lengths. Longer pedaling levers are more comfortable for taller cyclists, while smaller cyclists require shorter ones. Too long levers on a low frame can cause inconvenience when driving off-road, even in the city they can hit the rail at a level crossing or curb.

Short levers are difficult to spin, but then they are easier to maintain high speed. This can be explained by such indicators as cadence. the number of pedal revolutions per unit of time. The cadence increases if you have to pedal with short levers, and in the case of long levers, everything happens exactly the opposite.

The length of the connecting rods can vary from 150 to 185 mm. For an adult bike, you need to choose levers between 165 and 185 mm. On a children’s and teenage bike, cranks with a length of 150 to 177.5 mm will be comfortable.

The final point when choosing the length is set by each cyclist himself, taking into account his preferences in riding style. Shortened cranks are preferred by track riders. On mountain bikes, a reduced cadence is preferred for extra pick up when going downhill. Downhill fans in particular use levers as long as possible.

Types of connecting rods

One-piece. monolithic construction combining the shaft and two connecting rods. In fact, it is a thick metal bar bent in different directions at right angles. This kind of crankset was used on the first bicycles. Currently seen on BMX and kids bikes.

Two-piece. this is not only the combined one-piece right connecting rod and drive sprockets, but also the carriage shaft tightly welded to them. In this case, only the left lever is a separate piece, which is fixed to the free end of the shaft.

Until recently, this method of assembling cranks in a bicycle was considered obsolete, until in 2004 the Shimano factories revived the two-piece design, improving it with a cartridge bottom bracket with large-diameter bearings. Other bicycle parts makers support the renaissance of the two-piece crankset.

Three-piece. the most popular design today, it is possible to replace the drive sprockets separately from the right arm. Everything is understood in it: the cranks for the pedals and the treadmills themselves, separately the carriage shaft and the front sprockets one by one.

What are the bike cranks and how are they attached?

The connecting rod in a bicycle is an integral part of the mechanism with the power of which the reciprocating motion is converted into rotation of the rear wheel. The connecting rod cannot work separately, it must be akin to sprockets, a carriage and a bicycle frame. Most often, one sprocket or sprocket cassette is inseparably connected to the right arm. This is done in inexpensive two-wheelers. Maybe in a different way. On expensive bicycles, the front sprockets can be unscrewed from the crankset for replacement when the teeth become too worn.

Most cyclists do not have the opportunity to replace only the sprockets worn out to the limit on their vehicles, they have to remove everything at once. Then you need to buy the cranks for the bike along with the chainrings. Although the connecting rods themselves rarely lose their performance, only in the event of an accident they bend, break, wear out the seats on them.

When buying pedal levers, you should be aware that there are several different types of carriages, which have different methods of fastening to the ends of the shaft. There is nothing difficult about this. you just need to take a sample with you. Also, if necessary, it is easy to find a carriage assembly with connecting rods on sale.

Length of legs using table

Foreign experts have developed a table where the leg length range is indicated in the right column, and the required connecting rod size in the left column.

Bike type and riding style

The basic rule is that long cranks are used for mountain biking, shorter ones for road biking. This is explained by the following reasons.

When driving on the highway, the cadence (already mentioned cadence) is of prime importance. Increasing cadence increases torque and helps prevent blind spots during pedaling. Therefore, short levers are preferred by athletes who are involved in track racing. In addition, such connecting rods cling less to the ground on bends, which also contributes to an increase in the speed parameters of the bike.

Mountain cycling requires a different. power riding style. A large number of revolutions are not required here; the effort that must be applied during the ride (for example, to climb a mountain) comes to the fore. As a consequence, this type of cycling uses long cranks: the longer the lever is, the less effort is required to crank the pedals. Therefore, for BMX bikes (i.e. those used in motocross), as well as XC and other mountain bikes, the size of this part should be larger than for road bikes.

At the same time, in DH (downhill), smaller cranks are preferable, which will not touch the uneven terrain.

When driving in the city, overly long cranks can be uncomfortable, as they are more likely to cling to the slightest obstacles. This will cause serious inconvenience when crossing, for example, rails or curbs.

Length of legs using formula

The most popular way of calculating. In accordance with it, you need to determine the distance from the groin to the bottom of the foot in millimeters. The measurement is carried out barefoot and in an upright position. Then the resulting value is multiplied by 0.216. The final figure will be the required length of the connecting rod.

There is another formula according to which the length of the specified part should be 18.5% of the distance between the top of the tibia (knee joint) and the ground.

What affects

The connecting rod is the part of the bicycle transmission that converts the movements performed by the athlete during the pedaling process into the rotation of the rear wheel. This part forms a single unit with the frame, sprockets and the bottom bracket of the bike. In inexpensive models, the connecting rod and the main sprocket make up a monolithic structure, for variants with a higher price, it is possible to purchase this part separately.

The length of the connecting rods ranges from 145 to 180 mm, the pitch is 5 (less often 2.5) mm. Parts with a length of 165 mm or more are intended for adult bicycles, shorter ones for children. This parameter is defined as the distance between the center points of the carriage and pedal axes.

As a rule, manufacturers install 170-175 mm cranks on bicycles by default.

The size of the part can be found on the inside of the part.

  • the position of the athlete in the saddle;
  • the angle of flexion of the knee joint when pedaling;
  • cadence;
  • the effort required to pedal;
  • bike speed and start speed.

By frame size

This method is mostly suitable for classic road bikes. Guided by this method, it is necessary to measure the length of the upper frame tube and correlate it with the connecting rod length, which is indicated in the right column of the corresponding table.

Cadence

Cadence, or cadence, is a unit of measure that characterizes the number of revolutions of the pedals that an athlete makes in one minute (rpm).

The cadence is directly related to the length of the connecting rod. Using a short lever makes it easier to maintain high speed. In this regard, the cadence increases in proportion to the decrease in the length of the lever: when using short connecting rods, the indicator increases, while using long ones, it decreases. Thus, the more speed you need to develop, the smaller the size of the part you need to use.

In addition to the speed of movement, cadence also affects the load on the muscles and the cardiovascular system, as well as the health of the knee joints. Therefore, it is necessary to choose the right length of the connecting rod so that the cadence is optimal for you.