Bicycle Science

How your bike is set up has an enormous effect on how you ride. The position of the saddle [seat] and handlebars help to determine the type of performance the rider can expect.

Three parts of the rider's body are in contact with the bicycle: the hands, the feet, and the seat. First, consider the seat tilt.

Bicycle saddles can be extremely uncomfortable. The tendency is to angle the saddle forward in an effort to make it more comfortable. This position makes the rider slide forward off the saddle, and causes the rider to have to put too much weight on the hands. A saddle that is mostly level is the best choice. Choose one that is comfortable for you.



How high should the saddle be? The general ideal is to have the saddle high enough that the rider's extended heel should just touch the pedal at the bottom of the pedal's rotation. Since most people pedal with the ball of their feet, this position gives just enough flex in the leg.

The type of riding you plan to do will determine how far forward the seat should be. If you are racing, your body will be leaned forward to make the most of a lower, more aerodynamic profile. In this position, the saddle will need to be farther back. If you are touring, however, and maintaining a more vertical profile, you will not want your saddle to be more forward.

When the objective is speed, and the seat is farther back and the rider's body is leaning forward, the handlebars need to be further forward and down about 2-3" below the saddle range. It the rider is upright and taking in the scenery, the handlebars should be about level with the saddle and farther back.

Proper adjustment of your bicycle will increase your comfort and help you better enjoy your bicycling experience.

Bicycle frames can be made from a wide variety of materials. While most are made from steel, aluminum alloys, titanium, wood, bamboo, and carbon fiber are all possibilities for frame construction.

The specific material or combination of materials depends largely on the intended use of the bicycle. Bicycle designers consider the need for stiffness, as in track bicycles. Light or heavy weight materials are considerations for various racing bikes. Also, the fatigue limit of a material is important in the construction of mountain bikes, which must be able to hold up under heavy abuse.

Steel is the most common bicycle frame material. It is strong and easily formed. It is also inexpensive. The disadvantage of steel is that it is fairly heavy.

Aluminum alloys are lighter than steel, but they are not as strong. Because aluminum is more flexible, aluminum frames are often made of larger tubing to increase stiffness.

Titanium is the most expensive metal used for bicycle frames. It is very strong in relation to its weight, and is very corrosion resistant, but not as easily formed. Titanium and aluminum frames are usually assembled using Tungsten Inert Gas [TIG] welding.



Carbon fiber is not a metal, so frames are either made as a single piece, or are made in parts that are glued together. Carbon fiber is lightweight, corrosion resistant, and strong. It is also very expensive. Carbon fiber frames can be made in different shape profiles to improve aerodynamics.

Bamboo and wood frames are usually made for their beauty and unique visual characteristics, not for performance reasons.

Round tubing is used in some type s of bicycle frames, but it is not always the best choice. Rectangular tubing has excellent strength vertically when the long side is vertical.

What design makes the best bicycle frame? That really depends on what kind of riding you will be doing on your bicycle. The frame of a mountain bike has to be much sturdier than that of a road racer. Let's look at some basics of frame design.

In the diamond frame, the frame consists of a front triangle, and paired rear triangles. In the step-through frame, the top tube is lowered. This style was often called a girls' bike.

What are the advantages of each design?

A diamond frame is stiffer and stronger than a step-through frame. Because the diamond shape consists of triangle shapes, it is very resistant to flexing. Look at the trusses used on the roofs of houses. They are built as triangles. Any time you want to make something stiffer, a triangle is a good way to go.

A diamond frame is also lighter in weight. Because the top bar is shorter than on a step-through frame, the frame will be lighter. Also, because the step-through frame is not as stable, the frame needs to be made out of heavier material.



A step-through frame has many advantages of its own, though. With a step-through frame, a rider can wear a skirt without it having to be stretched awkwardly up over the top tube.

A step-through frame is good for people with limited mobility, as it is easier to get on and off a bicycle with a step-through frame. It is also good for delivery bicycles, as the rider makes frequent stops and must be able to get on and off quickly and easily.

If you are like most people, you have a 10 speed bicycle, but no idea what that means or how it works. A 10 speed actually refers to the number of gear ratios the bike can make.

Some mountain bikes contain as many as 27 gear ratios. It takes 3 different sized sprockets in the front and 9 different sized sprockets in back to produce all those gear ratios.

The point of all the different gear ratios is to keep a constant cadence. The cadence is the speed in which the rider cranks the pedals. It is easier on the rider to keep a constant pace whether traveling uphill or down. Different gear ratios make that possible.

On a fixed gear bike, one turn of the pedals all the way around would turn the rear wheel all the way around once as well. That is a 1:1 gear ratio.



Suppose you want to know how far a 20 inch wheel will travel in one complete revolution. In order to find that out, you would take the diameter [the distance across the tire from one side to the other] of the tire and multiply it by pi, which is 3.14. [OK, it's 3.14159265... so I'm rounding it to 3.14] So a 20 tire would travel 20 x 3.14 = 62.8 inches.

Now suppose you are pedaling at a cadence of 50 RPMs [revolutions per minute]. That means you will travel 3140 inches [261 2/3 feet] in one minute. That's not quite 3 mph [miles per hour], which is basically a leisurely walking speed. That's not very fast.

Now, take a gear ratio of 6:1. That same 20 inch wheel would turn 6 times for every once the pedals went around. At the same 50 RPM cadence, it would cover 1570 feet per minute or about 17 3/4 mph. That's what makes gears so useful.

In the early days of cycling, the first bicycles had no brake systems. Much like the fixed gear bicycles of today, the rider would need to reverse the force of the pedals to slow down. In an emergency, the only other recourse was to jump off the bicycle, which was especially dangerous with the high bicycles of the late 1800's. Track bicycles today are still manufactured without brakes.

With the development of the safety bicycle came the spoon brake. A spoon brake consists of a pad, usually of layers of leather, that depresses into the front tire with pressure from a rod operated lever or by the rider pressing it into the tire with his foot. Spoon brakes are still frequently found in developing countries. Their main disadvantage is that they cause excessive wear to the front tire.

Rim brakes are the most commonly used bicycle brakes today. There are a wide variety of styles, but they all work on the same principle.



Rim brakes have friction pads that contact the bicycle wheels' rims only. The pads are usually made of leather or rubber. The friction of the pads against the metal rims cause the bicycle to slow down.

Rim brakes should be checked often for excessive wear to the pads. Because they do not contact the tire, they do not wear the tire down the way spoon brakes do. However, they can cause wear to the rims themselves, especially in wet and muddy conditions, which also reduce their ability to perform.

Another, less common type of bicycle brake is the disc brake. Disc brakes have a metal disc attached at the hub with pads attached to calipers on the frame that squeeze the disc and cause the wheel to slow by use of friction. They work much the same way as rim brakes.

The main advantage of disc brakes is that they are farther from the ground, and therefore do not come into contact with dirt and water as readily as rim brakes do. Disc brakes work well in wet or muddy conditions. They are most commonly found on mountain bikes.

Have you ever seen a car race where the cars travel closely, one behind another? They are using a technique called drafting.

Drafting occurs when many competitors align themselves closely to
reduce the fluid resistance of the group. Everyone in the group except the lead rider benefits from the effect of being in the slipstream.

The slipstream is an area of reduced pressure that occurs behind an object as it moves through a fluid medium, such as air or water. As an object moves through the medium, it forces the particles of the medium apart. They flow around the object and reform behind it. If something is in the slipstream, however, the particles continue along the sides of that object before reforming.

In large races, such as the Tour de France, the winner is aided by the members of his team, who race ahead of the competitor part of the time, allowing the rider to expend less effort by traveling in their slipstream during portions of the race.

In such cooperative efforts, the lead cyclist will have the energy reserves needed to break away near the finish. While we think of the one competitor as the winner, they would not have won without the assistance of their team members.



When cyclists ride in a single file line, it is called a paceline. This type of cooperative behavior is also seen in nature. Lobsters migrate in close,
single file formations called lobster trains.

Cooperative behavior is also seen similarly in geese. You may have
observed geese flying in a "V" formation. In this pattern, geese not at the tip of the "V" benefit from lift created by the lead goose. Geese take turns in the lead position as they fly.

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