Standards: Types of bicycle carriages. Geometry of a bicycle (bike) Distance from pedals to ground
H1 - frame height - distance between the center of the carriage and top part seat tube.
L - bicycle base - the distance between the centers of the wheel hubs.
P - rudder height - the distance between the rudder axis and the ground level.
D is the outer diameter of the wheel.
H - saddle height - the distance between the top of the saddle and the ground level.
α is the angle of inclination of the steering column.
B - stability arm - a parameter determined by the angle of the steering column and the bend of the fork stays.
h - ground clearance bicycle - the distance between the center of the pedal axis and the ground level.
L1 - connecting rod length - the distance between the center of the carriage and the center of the pedal axis.
Also read on this topic:
Brakes:
— front brake;
— rear brake;
— brake pads;
- brake cable...
Aluminum alloys. The most common material today for the production of bicycle frames. Aluminum is not used in its pure form. There are a large number of different alloys containing different percentage silicon, magnesium, zinc and copper...
From the threads obtained in this way, fabric is woven with various patterns of the fabric. The fabric is used in the production of large bicycle parts. To obtain maximum strength, carbon fabric is laid in several layers with different directions...
The diamond frame is the classic, most commonly found frame, mainly on men's road, road and mountain bikes. Open frame - The top tube is close to the bottom tube and sometimes has a bend closer to the seat tube. Found on women's and children's bicycles...
I found a great article about the influence of various parameters of the geometry of a bicycle frame on its behavior.
The geometry of a bicycle frame affects its behavior in a significant way. In this article we will tell you how to find out what the frame of your bicycle is.
A bicycle is a wonderful thing. Take two wheels along with a bunch of cables, stick it to a frame and you have a real masterpiece of plumbing fixtures. Now stick some kind of seat - the narrower the better - and add a pipe in front to hold on with your hands. Mount a bunch of gears, connecting rods, stompers and a chain and off you go... don't forget to pump up the tires. So we have a personal means of transportation. Great, brakes are also useful for braking, and switches are also useful for convenience. But really, all there is to a bike is: a few pipes, a few cables, a few gears and a chain, and some rubber and plastic. It's great that this works at all.
But, if a simple bicycle is an impressive manifestation of the art of engineering, then a mountain bike is a real miracle! Let's take a closer look at this. Any old bike drives, stops and sometimes turns - this became known a century ago. Mountain biking is different in that all this can be done on any surface, something that people previously could not imagine. Also part of this capability is achieved through modern manufacturing and materials - a lot depends on the characteristics of the frame, because the design of the frame affects where all the other components of the bike will be stuck, the relationship of the handlebar to the saddle, the saddle to the bottom bracket, the handlebar to the angle of the front wheel, the bottom bracket to the ground and so on.
And it all comes down to frame geometry - a deceptively simple set of angles and lengths that dictate how all the different parts mountain bike will work as a whole. Fortunately, the frame geometry is complex complex rules that lend themselves to some scientific principles and a little bit of designer luck. To know this means to remember the last classes of mathematics: sines and cosines. This can be a headache, so to save you from it, below is a complete guide on this issue.
Mountain bike designers are facing a thorny set of problems that YOU are giving them?! To be more specific, it is your weight and where your center of gravity is. Any bicycle with a cyclist on board is a heavy and unstable structure. Everything is fine as long as you are rolling on a flat asphalt surface and your weight is fairly evenly distributed between the two wheels and everything is easy to control. Try to go off-road and the rules change. Instead of an even distribution of weight, the situation changes indirectly - then 100% of the weight falls on rear wheel, and a moment later 100% - already in the front. As the surface changes, the experienced cyclist shifts his weight to control the bike and pedal comfortably. But a novice biker will not be able to cope with a 45-degree change in terrain even on a double-suspension bike with bad tires. However, for bicycle designers, the task remains the same - you need to make a bicycle so that anyone can say - this is a work of art!
A valid question
If all this is not enough, shock absorbers can also help deal with the problems. Now not only does the cyclist move the center of gravity, but the shock absorbers also work on this issue. When the front, rear, or both shock absorbers are engaged, the efficiency of the frame geometry also changes. Shock absorber design must take into account how the bike will perform in different situations, taking into account any combination of rider weight and shock absorber response. And all this is at the core of the requirements of the frame geometry of any bike - to make the pedaling position ergonomic, to achieve comfortable movement, steering and braking.
Add all these factors together and you begin to see that the logic behind a mountain bike is very complex. To take a closer look at the importance of bike geometry, read below ANATOMY OF A MOUNTAIN BIKE.
ANATOMY OF A MOUNTAIN BIKE
Bicycle concepts:
— Stability shows how much effort a cyclist needs to put in to maintain a straight ride. More stability is mostly good for all-day freeride and downhill racing machines, while technical sections of the trail want a bike that can be easily moved to the side.
— Rapidity— how quickly the bike reacts to the cyclist’s maneuvers. Almost similar to stability, but not quite the same - it's ideal to have a stable bike that is also fast in tight and twisty conditions.
— Gap— the distance between the carriage and the soil surface (rocks, roots, hummocks and other obstacles). Increasing the clearance usually reduces the bike's stability and vice versa - a more stable bike should have a lower bottom bracket.
— Clutch— how easily the rear wheel grips the surface. Depends on the rider's weight distribution and frame design factors such as seat tube angle (seat angle), chainstay downtube length and wheel spacing (base).
TOP TUBE LENGTH- the distance between the centers of the steering column and the seatpost, an imaginary line running parallel to the ground. Frames of different sizes differ in both length and width.
BASE— the distance between the front and rear wheel eccentrics. A longer wheelbase means less maneuverability and greater stability, and a shorter wheelbase means a faster and more nimble bike.
Base length effect:
STICK LENGTH- measured from the center of the steering wheel to the center of the steering column. Stem length can have a significant impact on how your bike responds to steering input, and other factors include top tube length and steering angle. Basically, a shorter stem is better for more maneuverability, while a longer stem makes turns more difficult and unpredictable.
Stem Length Effect:
CARRIAGE HEIGHT— the distance between the ground and the center of the carriage (CLEARANCE). A lower carriage gives greater stability - it is easier to brake - but there is a greater risk of the pedal catching earthen obstacles. A taller carriage gives more clearance, better turning, but less stability.
Carriage height effect:
STAY LENGTH- distance between carriage and axle rear hub. There is little variation between bikes in the length of the chainstay - the length is usually as short as possible. A shorter rear stay gives greater rear wheel traction and less slippage.
Down tube length effect:
SEAT ANGLE- the angle between the seat tube and a line parallel to the ground. A lower number is a lazy angle - the rider's weight moves to the rear wheel and traction is increased, but speed force is reduced. A steeper angle moves the rider's weight forward, forcing the suspension fork to work and providing better landing for fast and aggressive pedaling.
Seat angle effect:
STEERING ANGLE- the angle between the steering column and a line parallel to the ground. A lower figure - a lazy angle - gives the bike a slower, more relaxed feel. A higher number—a steeper angle—means faster response to maneuvers. However, steering response also depends on other factors such as fork length, clearance and offset (see below) and stem length.
Effect of steering angle:
FORK CLEARANCE- the distance between the center of the front wheel hub and an imaginary line drawn through the steering column. Clearance is a characteristic of the fork, not the frame, but when combined with head angle and stem length, it affects the bike's response to handlebar turns. A shorter gap makes the bike more controllable, a longer gap makes the bike more stable.
FORK CARE- Almost the same as the fork gap. It is measured from the point of contact of the front wheel to the point of contact with the ground of an imaginary line drawn through the steering column. Like clearance, fork offset affects how the bike handles when turning. The difference is that while the clearance is constant, the clearance becomes shorter as the front fork is dampened.
Effect of gap length and fork care:
The geometry of the bike - the angles and dimensions - determines a lot about how the bike behaves. Stability, controllability, cross-country ability (in a good sense), acceleration dynamics, effective braking, going down and up a mountain, taking sharp turns and the ability to engage in extreme extreme sports depend on it. In ancient times, the geometry of a bicycle was strictly and unambiguously determined by the geometry of the frame. This is no longer the case. Suspensions appeared, front and rear. This means that the geometry of the bike and the behavior of the bike depend on the characteristics of the suspension (travel, stiffness, damping), and on their settings. In order not to delve into the wilds, but simply take a look at the dense forest, with the casual gaze of an expert, let’s consider the main points.
1. Bike geometry and seat tube angle
It largely determines the biker’s position and the ease of pedaling - if the tube sticks out vertically and the carriage is located exactly under the saddle, then it’s uncomfortable to pedal, there’s nowhere to put your hips. It also determines the weight distribution of the bike, that is, the distribution of the load on the front and rear wheels. The smaller the angle of inclination (it is measured from the horizontal) and the higher the biker, the greater the load on the rear wheel and, naturally, less on the front. On a steep climb, if the biker is sitting in the saddle, the front wheel can become completely unloaded and lose contact with the road. And the biker risks tipping over on his back. And on steep descents, everything is exactly the opposite. The front wheel is loaded, and the further back the biker is moved, the more stable the bike is and the less likely it is to fall over the handlebars. It is believed that the seat tube angle of 73° (plus or minus 1°...2°) ensures a correct, comfortable fit and load distribution. This angle is precisely adjusted for the ideal biker with a 32" (813mm) thigh length. To further adjust this angle and adjust the bike to the actual dimensions of the rider (height, length of arms and legs, ...), you can replace the straight seatpost with a curved one (Thomson). And, even easier, you can move the saddle forward or backward. When the saddle is correctly installed, the leg in the lower position is almost completely straightened.
2. Carriage height
Determines the bike's clearance - the gap between the pedal and the road when the crank is lowered vertically. Too low ground clearance does not allow you to tilt the bike too much; when cornering at high speed, you can catch the pedal on a rock, bump, or root, accelerating out of the bend. Or the stars of the system hit a bump. Therefore, bikes for different riding styles have different heights of the carriage above the ground - for DH and freeride the carriage is raised higher, up to 34...36cm. As a specific material, there is table No. 1, which was kindly provided by Alexey Madzhuga and where, using the example of KONA bicycles, it is shown how sizes change depending on the purpose of the bike and riding style.
Note. Due to obvious progress in the design and operation of suspension forks and rear shock absorbers and the creation of “stable platforms”, shock absorber travel has increased by last years and, quite possibly, will increase even more.
In addition, the higher the carriage is located, the higher the saddle must be raised and the greater the height of the bicycle becomes and the higher the center of gravity of the bike + biker system is located. Which undoubtedly affects stability and controllability. On a tall bike it is easier to maintain balance, and when entering a turn, the angle of inclination required to compensate for the force of gravity, the centrifugal force arising from movement in a circle (radius) will be LESS than that of a low bike. What follows from the most elementary geometry. Consequently, it is easier to ride on a tall bike on narrow forest singletracks and easier to “steer” it into sharp turns. That is, once again, to corner at a given speed and along a given radius, a tall bike must be tilted sideways at a smaller angle than a low one. But when braking and descending, the picture turns out to be the opposite. On steep climbs, descents and when braking sharply with the front brake, a tall bike has a greater chance of losing its balance - tipping back or flipping over the handlebars. To reduce this harmful effect, increase the bicycle base - the distance between the wheel axles. At the same time, they get greater softness and smoothness of the ride, the bike bounces less on potholes, roots and bumps. But a long-wheelbase bike has greater directional stability and fits worse into sharp turns, which again follows from simple geometry. To improve handling and maneuverability, you have to “play” with the angle of the steering tube and reduce the Trail (roll-out of the front wheel).
3. Head tube angle (measured from horizontal)
Let us only note the following. The larger this angle, the closer to the vertical the fork stays are, the faster the bike accelerates and the better the fork handles small bumps and bumps on the road. And, conversely, if the angle is smaller, and the fork stays are located more hollowly (sharperly) to the surface, the worse the dynamics and controllability, but the fork swallows large potholes and bumps more easily and they have less effect on the movement of the bike. In cross-country, the steering angle is usually 71...69 degrees, and the wheelbase length is 100...107 cm, then in DH it is 64...65 degrees and 110...117 cm. See table No. 1. A small angle of inclination of the front fork in combination with a large length of stays, which is typical for bicycle choppers, leads to a deterioration in maneuverability - efficiency (sharpness) of control: an increase in the minimum turning radius and the need to turn the steering wheel at a larger angle.
4. Geometry of the bike and the front fork and Trail (front wheel rollout)
A little experiment. If you place the right bicycle vertically on both wheels, holding it by the frame and tilt it to the side, then the steering wheel itself will turn in the same direction. The reason for this behavior lies in the design of the front fork and steering column. They determine the relative position of two important points. Points A are the places of contact of the front wheel with the road and points B are the intersection of the steering column axis with the same road. The relative position of these points determines not only the direction in which the steering wheel will turn when the bicycle is tilted, but also its directional stability, controllability, control rigor, stability on turns, and much more. All bicycles can be divided into two types: BA and AB. Type AB - in which the point of contact of the front wheel with the road is located in front of point B (Fig. No. 2a). Type BA - Point A lies behind point B (Fig. No. 2b).
When a bicycle of type AB is tilted in one direction, its handlebars will turn in the other direction and for a very clear reason - the point of application of the friction force A lies in front of the axis of rotation of wheel B. The bicycle, when turning “without hands”, will fold in half like a screen and with fall to the ground with a roar. The steering wheel and front wheel of a BA-type bicycle react to tilt in a completely different way - they will turn towards the tilt of the bike themselves, and without any hands. And when correct sizes and corners, the bicycle will strive to return to a vertical position just as if its handlebars were turned by hand - you just need to help the handlebars a little, point it in the right direction, and everything will be OK! For this reason, AB type bicycles cannot be found in stores.
Now about the shape of the front fork.
The options shown in Fig. No. 3, a) and b), give us too much distance between points B and A, which leads to “over-stability” of the bicycle. The greater the distance between these points, the greater the moment of force that turns the front wheel and, of course, the handlebars towards the tilt of the bicycle. The result is clear, directional and vertical stability is very good, and controllability is “below the baseboard”. Therefore, to reduce the distance between these points, the fork on bicycles is bent forward, Fig. No. 3, c). But, even if the fork is straight, then its inclination is changed relative to the axis of the steering column, or the cocks in which the front wheel is attached are shifted forward. Fig. No. 4.
The distance between the axis of the steering column and the axis of the front wheel hub is called differently, Rake and Fork Offset, but here you can encounter run-out, displacement or offset of the fork. The fork offset R is usually in the range from 30 to 50mm. Knowing the offset of the fork, the angle of inclination of the steering column axis and the actual diameter (taking into account the thickness and deformation of the tire) of the wheel, you can easily calculate the distance between points A and B. This distance is called Trail or rollout (runout) of the front wheel, sometimes it can be found in catalogs . So, knowing the Trail, the stability (handling) coefficient (Ku) is calculated, which is equal to: Trail (T), divided by the sum consisting of the length of the bicycle base (G) plus Trail (T), the result of the division is multiplied by 100%. Now the formula: Ku = (T/)100% (1), everything is very simple. U modern bicycles Ku lies in the range from 5% to 7.5% and a value close to the stability limit is usually selected, for a very clear reason - such a bicycle is easier to control.
5. The geometry of the bike changes when the shock absorbers work.
At the moment of braking, when the bike “nods” when the suspension fork is compressed, the base decreases, but the Trail decreases even more, and, consequently, the Ku decreases. It turns out that when braking, the bike becomes more controllable, but also less stable. The same thing happens when pedaling while standing, when the biker brings his body closer to the handlebars and when descending from a slope, especially if the front wheel is intensively braked.
If you now load the trunk with a heavy load (a pretty girl) or reduce the travel of the rear suspension (install a shorter shock absorber) on a dual-suspension system, then the situation will change directly to the opposite. Trail will increase, Ku will increase, the bike will become more stable, but it will be more difficult to control. This is probably familiar to many cycling tourists. With a well-loaded trunk, the bike rushes like a tank, especially if you accelerate well. But it’s not easy to turn or drive along a winding path at low speed. Nowadays, many extreme bikes have long rear dropouts, which allow you to move the rear axle over a wide range or install a smaller diameter wheel, not 26, but 24 inches. Not surprisingly, this changes the stability and controllability of the bike. The first trail bikes have already appeared, the geometry of which can be changed directly on the go within a wide range. For example, the new product of the season, the BIONICON EDISON bike. With the help of an industrial valve, which is used in pneumatic automation devices and pneumatic lines, the frame geometry can be changed by 6 degrees! The head tube angle is 67.5°…73.5°. The seat tube angle is 71°…77°. Fork travel is 69mm...147mm, rear suspension travel is 142mm with a wheelbase of 1056mm. On the same bike you can now both ride in cross-country style and effectively descend from steep slope.
6. Upgrade
Replacing the suspension fork and rear shock with longer or shorter ones will affect the stability and handling of the bike. This should definitely be taken into account.
7. Top tube length
Top tube length is defined as the distance from the axis of the head tube to the axis of the seatpost. This distance, together with the length of the stem, largely determines the rider's riding position. And, in addition, it also affects the weight distribution of the bike. The long pipe helps to unload the front wheel, which can cause slippage when cornering. A shorter one can cause your knees to touch the steering wheel when pedaling in a “dancer” manner. XC enthusiasts choose a long tube and long stem (100...130mm) for a low, stretched stance. This makes cornering and difficult sections difficult, but the main struggle usually occurs on the climbs. For downhill and freeride riding they combine a slightly shortened top tube with a short stem. Therefore, on a slope, the raider moves far back and ensures correct distribution of the load between the wheels. In addition, the additional load on the front wheel when the raider moves slightly forward helps with technical sections.
8. Tilt of the top tube
First of all, it sets the standover height - the safe distance from the biker’s vital organs to the top tube of the frame. This is very important in extreme sports. In addition, the construction height of the frame decreases and, as a result, its rigidity and strength increases, which plays a role in jumping disciplines and hard freeride. Recently, lowered top tubes have been used in road and cross bikes. This makes it possible to reduce the number of frame sizes produced and their weight.
9. Chainstay Length
It is determined by a line parallel to the ground, from the axis of the carriage to the axis of the rear hub. The length of the chainstays affects the weight distribution and dynamics of the bike. And it doesn’t matter whether the biker is sitting in the saddle or standing on the pedals, this is the difference between the influence of the length of the stays on the weight distribution and the inclination of the seat tube. After all, when the biker gets up from the saddle, the inclination of the seat tube no longer affects the distribution of the load between the wheels. Short chainstays load the rear wheel and increase its traction, and also make the rear triangle more compact, tucked and rigid. The bike climbs mountains easier, goes faster, turns and accelerates. Recreational bikes and touring bikes usually have a larger wheelbase and a stretched rear triangle. This worsens the dynamics and requires more energy to climb the mountain. But this has to be done in order to place a large and voluminous bicycle backpack (pants) on the trunk and not touch it with your heels when rotating the pedals.
And a few more words about what bike geometry is suitable for different riding styles.
The sharper the bike is “tailored” for downhill and hard freeride, the longer the stroke of its shock absorbers, the sharper the angle of the steering tube, the longer the wheelbase and the higher the bottom bracket. The dirt bike has a shortened seat tube, low standover (the distance from the ground to the middle of the seat tube) and a short stem. This is useful for the safety and comfort of the raider when performing jumps and tricks and for greater frame strength.
06.11.2005 Yuri Razin. Bike geometry.
PS. I express my gratitude to Alexey Majuga for valuable advice and recommendations on the geometry features of modern bikes
© “Federation of Travelers” – Bicycle geometry
This clearance is determined solely by the frame design. A well-designed frame requires the installation of tires of a certain width (depending on the purpose of the frame) and, of course, implies some distance from the fender to avoid friction.
Historically, all track bikes have been built with minimal clearances, as this uses the smoothest, narrowest possible slick tires. In the 1980s, road bikes began to adopt the basic design principles of track bikes, and as a result, most "race" bikes subsequently ended up with unreasonably low clearance. The reason for this was simply a blind desire for stylization. At one time, when this design disease reached its peak, the bicycle industry as a whole began to acquire a morbid tendency to produce rather strange bicycles and parts. On a bicycle with minimal clearance, you can install a clamp brake with only the shortest levers. Because of this, many brake system manufacturers switched entirely to producing short-lever brakes, and normal brake systems simply disappeared from sale. Manufacturers of frames and forks, in turn, picked up the trend and continued to produce products with minimal clearance.
One person who worked at Rivendell, Grant Petersen, noticed an unhealthy trend and was able to influence the return of brake systems with longer levers.
It is impossible to repair a frame with minimal clearance. Somehow you can try to solve the problem only by installing wheels of a smaller diameter.
Turning pedal distance
At the moment when a cyclist enters a turn and leans to the side, there is a high probability of the pedal catching on the road surface. This gap depends on several parameters:
- Carriage height
- Crank length
- Pedal length
The combination of all these values determines how much lean can be made in a turn without eliminating the possibility of pedaling.
This distance is especially important for fixed-wheel drive bicycles, since such systems do not have free play and the pedals are constantly spinning. In addition, when the pedal hits the ground in a fixed position, the rear wheel instantly jumps up, which can lead to a fall.
Distance from toe
There is another important gap on a bicycle - from the toe of the cyclist's foot to the front wheel or fender.
Many parameters of the bike’s behavior depend on the geometry of the bicycle (bike) - on the dimensions and angles. It all depends on handling, stability, acceleration dynamics, cross-country ability (in a positive sense), braking efficiency, climbing and descending a mountain, the ability to engage in extreme driving and take sharp turns. Since ancient times, the geometry of a bicycle has been uniquely and rigidly determined by the geometry of the frame.
Today, this is no longer true. Suspensions appeared, rear and front. And, therefore, the geometry and behavior of the bicycle largely depend on the characteristics of the suspension (damping, stiffness, travel) and their settings. In order not to go deeper into the wilds, but just to take a casual glance at this dense forest with the casual gaze of an expert, let’s move on to considering the main points.
WHAT SHOULD BE THE INCLINES AND ANGLES OF THE BIKE, CHOOSE THE CORRECT GEOMETRY OF THE BIKE
For the most part, it sets the cyclist’s position and determines the comfort of pedaling. If the tube is located vertically and the carriage is located directly under the saddle, then pedaling is inconvenient, there is nowhere to put the hips. Another parameter determined by the inclination of the seat tube is the weight distribution of the bike, in simpler terms, the distribution of the load between the rear and front wheels. The smaller the angle of inclination (it is measured from the horizon line) and the higher the cyclist’s position, the less load falls on the front wheel and the greater the load on the rear wheel.
On a steep uphill climb, while the cyclist is sitting in the saddle, the load on the front wheel of the bike can disappear completely and there will be a loss of contact with the road. And the cyclist, at this time, risks falling on his back. On steep descents, the process occurs in reverse. The front wheel is loaded, and the more the cyclist is shifted back, the more stable the bike is, and thus reduces the likelihood of falling over the handlebars.
It is generally accepted that if the angle at which the seat tube is tilted is 73° (with an error of 1°...2°), the cyclist is provided with a correct, comfortable fit and his weight is correctly distributed. This statement is valid for an ideal cyclist whose thigh length is 813mm (32 inches). To make an additional adjustment to this angle and adjust the bike to the actual dimensions of the cyclist (length of legs and arms, height...), you can replace the straight seatpost with a curved one (Thomson). Or you can move the saddle back or forward, which is even easier. If the saddle is installed correctly, in the lowest position of the pedal the leg should be almost completely straightened.
WHAT SHOULD BE THE HEIGHT OF THE GREAT CARRIAGE?
This parameter determines the bike's clearance - the distance between the road and the pedal at the moment when it is in its lowest position. If the ground clearance is too low, this will not allow you to tilt the bike much, then during high-speed cornering there is a high probability that you will catch the pedal on a root, bump, or stone while accelerating when exiting the bend.
For this reason, bicycles designed for different ways skating, the height of the carriage above the ground varies. For example, for freeride and DH the carriage is raised much higher than in road bikes (approximately 34...36 cm). How clear example, Table No. 1 is provided (which for this article was kindly provided by Majuga Alexey) in which, using the example of KONA bikes, the change in geometric dimensions is demonstrated depending on the riding style and purpose of the bike.
Note: Due to the fact that there has been clear progress in the design and operation of rear shock absorbers, suspension forks, as well as the creation of stable platforms, shock absorber travel has increased significantly in recent years and there is a high probability that, over time, it will increase even more.
In addition, if the carriage is located high, the saddle also needs to be raised higher; accordingly, the height of the bicycle increases and the center of gravity of the mobile “bicycle + cyclist” system rises. There is no doubt that this affects handling and stability. On a tall bicycle it is easier to maintain balance, and when making a turn, the angle of inclination, which is designed to compensate with the help of gravity, occurs when circular motion(radius) centrifugal force will be smaller than that of a bicycle with a low bottom bracket.
This follows from a school geometry course. Accordingly, a high-riding bike makes it much easier to ride on forest singletracks and easier to navigate sharp turns. This means, once again, to negotiate a bend at a given speed and along a fixed radius, a low bike needs to be tilted sideways by more than a high angle. However, when descending and braking, everything looks completely opposite. During steep ascents, descents and when braking instantly using the front brake, on a high-riding bicycle, the likelihood of losing balance, falling backwards or somersaulting over the handlebars is much greater. To minimize this unpleasant effect, they try to increase the wheelbase of the bike - the length from the axis of the front wheel to the axis of the rear.
At the same time, greater smoothness and softness of the ride is achieved, the bike bounces less on bumps, potholes and roots. But a bicycle with a large wheelbase has greater directional stability and takes sharp turns worse, which, again, can be understood thanks to a school geometry course. To improve maneuverability and controllability, you have to “twist” the angle of the steering tube and make the Trail (front wheel offset) smaller.
HOW WILL THE BIKE GEOMETRY CHANGE WHEN REPLACING THE FORK
It is worth noting the following point. The greater the value of this angle, the closer to the vertical plane the fork stays are, the higher the acceleration speed of the bicycle, and the better the fork handles all kinds of small irregularities and bumps on the road. And, accordingly, if the angle decreases, the fork stays will become flatter relative to the surface (sharper), as a result, controllability and dynamics deteriorate, but at the same time, the fork begins to tolerate large bumps and potholes more easily, and they, in to a lesser extent, affect the movement of the bicycle.
For cross-country bikes, the steering angle is most often from 71 to 69 degrees, and the distance between the wheel axles is from 100 to 107 cm, and in DH the angle is approximately 64...65 degrees, and the wheelbase length is 110...117 cm (See. Table No. 1). The low inclination of the front fork paired with long stays, which is quite often used in bicycle choppers, leads to a significant deterioration in the maneuverability of the bicycle, the sharpness (efficiency) of control, an increase in the minimum possible radius of turn and forces the steering wheel to be turned to a higher angle.
TRAIL (FRONT WHEEL REMOVEMENT) AND BICYCLE FRONT FORK PARAMETERS
A little experiment. If you place a bicycle of the correct configuration vertically on two wheels, take it by the frame and tilt it to the side, then the steering wheel itself should turn in the same direction. The reason for this phenomenon lies in the geometry of the steering column and front fork. It is these details that determine the location of a pair of important points between each other. Points A are the points of contact between the road and the front wheel, and points B are the points of intersection of the axis passing through the steering column and the road. The relative position of these points determines not only the direction of rotation of the steering wheel when the bicycle is tilted, but also its controllability, directional stability, stability during turns, control rigor and much more. Bikes can be divided into two types: AB and BA. An AB-type bicycle is one in which the point of contact of the front wheel and the road is located in front of point B (Figure No. 2a). A BA-type bicycle is one in which point A is behind point B (Figure No. 2b).
If you tilt an AB-type bicycle in one direction, the handlebars will turn in the opposite direction and, for a very clear reason, point A, at which the friction force is applied, will be closer than the axis of the head tube (point B). A bicycle, if turned without hands, will fold in half like a book and fall to the ground with a thud. The front wheel and handlebars of a BA-type bicycle react completely differently to the tilt of the bike - they will tilt towards the tilt of the bike themselves and without the help of their hands.
And with balanced angles and dimensions, the bike will return to an upright position exactly as if the handlebars were turned by hand; the handlebars just need a little help, adjusted in the right direction, and everything will turn out just fine! For this reason, AB-type bikes cannot be found in stores.
NOW A LITTLE ABOUT THE GEOMETRY OF THE FRONT FORK.
The designs that are shown in Figure 3, a) and b), will give us an excessively large distance from point A to point B, which causes the effect of over-stability of the bike. The longer the distance from one of these points to the other, the higher the moment of force that turns the front wheel and, naturally, the steering wheel in the same direction in which the bicycle is tilted. The result is clear, vertical and directional stability are quite good, but handling is worse than ever. For this reason, in order to reduce the distance between these points, the fork on bikes is bent forward, Figure No. 3, c).
However, even if the bicycle is equipped with a straight fork, its inclination changes relative to the axis passing through the steering column, or the cocks to which the front wheel is mounted are moved forward. Figure No. 4. The distance from the axis passing through the front wheel hub to the axis of the steering column has different names, Fork Offset, and Rake, and here sometimes you can come across run-out, offset or offset of the fork. The value of the fork offset R, most often, falls within the range of 30 to 50 millimeters.
If the fork offset, the angle of the axle passing through the steering column, and the actual diameter (taking into account the thickness and deformation of the tire) of the wheel are known, then you can easily calculate the distance between points B and A. This distance is called Trail or rollout (coast). front wheel, it happens that it can be found in catalogs. As a result, with a known Trail, you can calculate the controllability (stability) coefficient (Ku), which is equal to: Trail (T), divided by the sum of the same Trail and the length of the bicycle wheelbase (G), the result of the operations performed multiplied by 100%. Let's look at the formula: Ku=(T/)*100%(1), there is nothing complicated. For modern bicycle models, Ku is within 5 ... 7.5%, and the value closest to the stability limit is usually selected. The reason for this is quite simple - a bicycle of this design is easier to control.
HOW DOES THE GEOMETRY OF A BICYCLE CHANGE DURING THE OPERATION OF SHOCK ABSORBERS
At the moment when braking occurs and the bike nods while the suspension fork is compressed, the wheelbase decreases, but at the same time, the Trail decreases even more, and therefore the Ku becomes smaller. It turns out that during braking, the bikes' controllability becomes greater, but stability decreases. The same situation is observed when pedaling while standing, at the moment when the cyclist brings his body closer to the steering wheel and during descent from a hill, especially if intensive braking is carried out with the front wheel.
Now, if you load the trunk with a heavy load ( beautiful girl) or make less travel of the rear shock absorber (install a shorter shock absorber) on a dual-suspension system, then the position will change to the exact opposite. The trail will become larger, the Q will increase, the bike will be more stable, but it will become more difficult to control. This is no doubt familiar to most bike tourists. With a tightly loaded trunk, the bike rides confidently, like a tank, especially if the acceleration is good. But making a turn or driving along a winding path at low speed is, oh, so difficult.
Today, many bikes designed for extreme sports are equipped with long rear stay dropouts, making it possible to move the rear axle within a wide range or install a wheel with a smaller diameter instead of 26 - 24 inches. No one will be surprised by the fact that during this the handling and stability of the bicycle changes.
The first trail bikes are already on sale, the geometry of which changes directly while riding, and within a wide range. For example, the new product of the season, the BIONICON EDISON bicycle. Using an industrial valve used in pneumatic lines and pneumatic automation devices, you can change the frame geometry by 6 degrees! The head tube angle is from 67.5° to 73.5°. Seat tube inclination from 71° to 77°. Move front shock absorber from 69 to 147 mm, rear shock absorber travel 142 mm, taking into account the wheelbase of 1056 mm. Now, on one bike you can both impressively slide down a steep slope and ride in cross-country style.
Tuning a bike or how to improve the ride quality of a bike Replacing the rear shock absorber and front suspension fork with shorter or longer ones affects the handling and stability of the bike. This must be taken into account.
Top tube length is the distance from the seatpost centerline to the head tube centerline. This distance, together with the length of the stem, for the most part determines the rider’s position. In addition, the size of the top tube significantly affects the weight distribution of the bike. A long pipe allows you to unload the front wheel, which can cause slippage during turns. A shorter top tube can cause your knees to catch on the handlebars when pedaling like a dancer. People who prefer to ride XC style usually choose a longer tube with a long stem (100 to 130mm) to achieve a low, stretched riding position.
This makes it difficult to take sharp turns and overcome difficult sections, however, the main struggle, most often, occurs during climbs. For freeride and downhill riding, a combination of a slightly shorter top tube and a short stem is used. Thanks to this, on a slope the cyclist transfers his weight far back, thereby ensuring correct distribution of the load on each wheel. In addition, the additional loading of the front wheel, when the cyclist moves slightly forward, will help overcome technically difficult areas.
BIKE TOP TUBE TILT ANGLE
First of all, it determines the height of the standover - the distance from the top tube bicycle frame to the vital organs of the cyclist. This parameter is very important for extreme species sports
In addition, the construction height of the bicycle frame becomes smaller, as a result of which its strength and rigidity are even greater, which is important for jumping disciplines and hard freeride. Recently it has become fashionable to use a lowered top tube in motocross and road bikes. This makes it possible to reduce the size of the frames produced and their weight.
LENGTH OF BIKE STAYS
The length of the chainstays is determined along a line parallel to the horizon, from the axis of the rear hub to the axis of the carriage, the length of which affects the dynamics of the bicycle and its weight distribution. Moreover, it doesn’t matter whether the cyclist is in a sitting or standing position, this is the difference between the influence of the length of the chainstays on weight distribution and the influence exerted by the inclination of the seat tube. Because when the cyclist gets out of the saddle, the angle of the seat tube no longer affects the distribution of weight between the wheels.
Short stays increase the load on the rear wheel and help increase its grip on the road, and, at the same time, make the rear triangle more compact, rigid and tucked. The bike rides uphill easier, corners faster and accelerates faster. For touring and recreational bikes, the base is most often increased and the rear triangle is stretched. This makes the dynamics worse and forces you to apply more energy to climb the mountain. But these sacrifices have to be made in order to place a voluminous and heavy bicycle backpack on the trunk and not cling to it with your heels while pedaling.
And a few more words about the differences in the geometry of bicycles in accordance with different styles skating.
The more a bike is designed for downhill and hard freeride, the longer the shock absorbers will travel, the sharper the head tube angle, the higher the bottom bracket position and the longer the wheelbase. The dirt bike is distinguished by a shortened seat tube, low standover (the distance from the center of the seat tube to the ground) and a short stem. This ensures the safety and comfort of the cyclist during tricks and jumps, and higher strength of the bicycle frame.
