# How to Measure the Radius of a Bicycle Wheel

## HOW TO MEASURE BIKE WHEEL AND FRAME DIAMETER?

To date, the popularity of cycling has increased dramatically, this is due to the fact that people began to pay more attention to their health. Many experienced cyclists know everything from “a” to “z” in this business, but beginners sometimes do not even know what their wheel diameter is. Next, we will talk about how to measure the diameter of a bicycle wheel and how to measure the size of the frame.

## WHEEL DIAMETER

Before answering the question of how to measure the diameter of a bicycle wheel, let’s talk a little about the wheels themselves, their dimensions, whether the speed of the bicycle depends on the diameter of the wheels.

A bicycle usually has two wheels. As a rule, bicycles use spoke wheels on steel spokes, there can be from 12 to 42, but as a rule, there are 32 or 36.

Some sports bicycles are fitted with 4-6 pairs of flat carbon fiber spokes. Disc wheels are used, most often for cycling, have the greatest rigidity and aerodynamics.

The wheels, along with the frame, are the most important structural elements of a bicycle, it is the wheels that withstand all the load created by the cyclist. Also, the wheel must withstand all shock loads that occur with uneven roads.

Modern wheels are both very strong and lightweight at the same time. The wheel usually consists of spokes, hub, tube with tire, rim.

The size of the wheel is of great importance, with large wheels you can reach higher speeds, and with small ones, the bike is more compact. The smallest 20 “wheels are used in folding models, 26” wheels are most commonly used for mountain bikes, and the largest 28 “wheels are common for road bikes.

Now, after all, let’s answer the question, how to measure the diameter of a bicycle wheel? And this is easy to do. The size from the highest point of the wheel to the lowest will be the diameter of the bicycle wheel.

## FRAME SIZE

The size of the bike frame is selected not on the basis of the cyclist’s height, but on the length of his legs, so first of all you need to know how to measure the size of the bike frame so as not to become a “victim” of the wrong purchase.

The frame of the bike is the main body to which the bike components attach. A bicycle frame is usually welded from profiles that form two so-called triangles. the front axle and the rear axle.

The bike frame is selected solely on the capabilities of both the material and physical data of the cyclist, as well as on what you are going to do on this bike, just ride in the park or along the slopes of the mountains, or can jump from high slopes and steep jumps.

Still, how do you measure the size of a bike frame? If you decide to buy a sports bike, then you need to stand on a flat floor without shoes and measure the height of your crotch, a tape measure will help you with this, multiply this figure by a factor of 0.665. for sports or road bikes.

And those who buy a bike for aggressive riding on hills and slopes, that is, a mountain bike, then multiply your figure by the coefficient for mountain bikes. this is 0.226, as a rule, mountain values ​​go in inches, the resulting figure must be multiplied by 2.54 and then we get the size in inches.

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## How to measure the diameter of a bicycle wheel?

When you need to replace a punctured tire or purchase a spare tire, it is important to know the diameter of the bicycle wheel. The marking can be viewed on the currently installed bus. It is printed on the side of the tire, and indicates its diameter and width. If the numbers are erased or the inscription is not readable, you can measure the diameter of a bicycle wheel yourself using two simple methods.

## Tire marking

The classical system of standards involves marking the tire in this order: the first number indicates the diameter of the tire, the second indicates the width. The standard units of measure are inches. For example, 29×2.00 says the tire is 29 “(or 73.66 cm) in diameter and 2.00” (or 5.08 cm) wide.

It should be remembered that the marking of bicycle tires according to the international ISO standard has a different form and unit of measurement. millimeters. So, first the value of the wheel width is applied to the rubber, and then the diameter. For example, the inscription 40×700 means that the tire has a width (width) of 40 mm, and its diameter (diameter) is 700 mm.

## Standard measurement method

To determine the diameter, you first need to know the radius of the wheel. Knowing the latter, you can calculate the diameter. According to the mathematical formula, the diameter of a circle is equal to two radii: D = 2 r.

### Wheel diameter

The measurement is carried out as follows: a measuring tape is applied from the ground to the center of the sleeve on the wheel axis. This will be the radius of the wheel. Since the bushing is an order of magnitude wider than the wheel, in order to reduce the error, the measurement should be carried out strictly vertically. The tape must not run along the spokes of the wheel being measured.

Next, the found radius in cm is multiplied by 2. The calculated number is the diameter of the wheel. To convert units (centimeters) to inches, divide the product by 2.54 (1 ″ = 2.54 cm). For example, the found distance is 34.2 cm. Multiply this number by 2, divide by 2.54 and get 26.929.

If the calculation results in a non-whole number, the total is rounded to the accepted standard wheel sizes in inches. In the described case, the wheel diameter will be 27 ″. Bicycles for adults often have wheel sizes ranging from 26 “to 29”.

[attention type = green] Tip! When taking measurements, it is better to use a wooden ruler or a rigid metal tape measure. The elastic tape can stretch and distort the result. [/ Attention]

### Tire width

Measurement, as in the above case, is made with a tape measure. It is placed perpendicularly on the tire and the distance from one edge to the other is measured. The tape should be kept strictly horizontal (that is, across the bike tire) for the result to be as reliable as possible.

The width of a bicycle tire purchased to replace a damaged one may slightly differ from the original one (be slightly wider or slightly narrower). This fact will not affect the ability to install it.

## ISO

The measurements will require the same materials.

• Wheel Diameter The distance from the center of the wheel to the outer edge of the rim is measured. Multiplications are performed in the same way as in the first case. The difference is only in units. According to the international standard, the value of the radius is indicated in millimeters. Therefore, the resulting diameter in cm is converted to mm. 1 cm = 10 mm. For example, D = 50.8 cm, this number is multiplied by 10 and you get 508 mm.
• Wheel width Measurement is carried out in the same way as in the standard method: the tape is placed across the tread pattern. The result obtained leads to the accepted unit of measurement in the ISO system. to millimeters.
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[attention type = yellow] Tip! Their service life will depend on the correct choice of the type of tires. When using the rubber recommended by the manufacturer (or values ​​close to the specified), it will last longer. So narrow tires are suitable for walking on a flat road, and wide. off-road. [/ Attention]

## Wheel circumference

This value is no less important than the previous ones. After replacing an old or damaged bicycle tire with a new one, you need to adjust the exact operation of the instruments (speedometer, odometer, navigator). For this, the size of the circumference of the wheel is entered into the cycling computer.

You can find out this parameter in several ways.

### With an inelastic cord

To do this, pull a thread, cord or cable around the bike tire. Its thickness does not matter, the main thing is that it fits snugly against the rubber. Next, you need to make a mark at the place of its contact with the initial end. Then remove the cord, spread it on the ground and use a ruler (tape measure) to measure the distance from the starting end to the set mark.

### By calculation

The required value can be calculated using the formula, knowing the diameter of the tire. The diameter can be indicated on the tire itself or determined using the previously described method. The circumference of the wheel is equal to the product of its diameter by the number Pi: ​​C = D π. Measurement unit inches.

For example, 20×3.14 = 62.8 “, where 20 is the diameter of the tire in inches, and 3.14 is the pi number (constant).

### By labeling

A mark is applied to the tire. it can be a drop of paint or chalk. After that, you need to drive the bike on a flat and smooth surface, for example, on asphalt. So that the wheel completes one full revolution. After the mark on the tread of the tire touches the road surface, at least 2 tracks will remain on the ground. This is the beginning and end of the path traversed by the wheel. The distance between the spots imprinted on the road section is the wheel circumference. Measurement is made using a metal tape measure.

For more accurate results, the bike with the paint on the tread is rolled in a straight line a little longer. For example, so that not 2, but 4 tracks remain on the ground. Next, the distance between the points is measured in turn (from 1 to 2, from 2 to 3, from 3 to 4) and the arithmetic mean is calculated. The resulting number is the desired value.

When there is no rope or chalk, you can drive the wheel through a puddle or apply a few drops of water to the tire.

## How to measure a bicycle wheel

• measuring the tire in the usual way;
• tire measurement by ISO method;
• calculating the circumference of a bicycle wheel

To purchase a spare bicycle tire, you must first determine the size of the wheel. In fact, measuring a wheel is a common procedure during bicycle maintenance.

There are two ways to measure a bicycle wheel, including tire and rim sizing, and both are easy to perform. Sometimes it is necessary to know the circumference of the wheel, which is also not difficult and can be done in several ways.

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## Measuring the tire in the usual way

Place your bike upright by leaning it against a wall or on a stand. When the bike is set upright, it does not lean on you, and it is easier to measure its wheel. If you are measuring the wheel alone, it is better to use a metal tape measure rather than a plastic one, as this can be done with one hand.

Measure the distance in inches from the ground to the center of the wheel. This will measure the radius of the wheel or half the diameter. Multiply this length by two to calculate the tire diameter. Except for BMX models, most adult bicycle wheels are 26 to 29 inches in diameter.

Measure the distance from one side of the tread to the other. This number is the tread width. It can vary a lot, depending on the destination. Generally, the wider the tread, the higher the flotation, while the narrower tread is used for a smooth and fast ride.

• When buying a new tire, remember that in traditional standard sizes, diameter comes first, then width. For example, a 26 x 1.75 tire will have a 26 “diameter and 1.75” tread width.
• ## Tire measurement using the ISO method

Find out if your tires are measured using ISO instead of the usual method. The ISO system uses millimeters to determine the dimensions of a bicycle wheel. If you do not have a tape measure to measure a wheel in inches, just know that there are 25.4 millimeters in one inch and use a calculator to multiply the width by 25.4.

Make sure the bike is placed against a wall or on a stand. Measure in millimeters from the center of the wheel to the inner edge of the tire. Double this number to calculate the diameter. Most ISO-measured adult bicycle tires are 650 to 700 millimeters in diameter.

Measure the tire width in millimeters. Use the recommendations above for tread measurement. Remember that tires of different widths can be used on the same bike as long as the difference is not too drastic.

• When buying a new ISO-measured tire, remember that width comes first, followed by diameter. For example, a bicycle wheel measuring 53.3 x 700 has a tread 53.3 mm wide and 700 mm in diameter along the inner edge of the tire.
• ## Calculating the circumference of a bicycle wheel

Measure the circumference, or distance, along the outer edge of a bicycle wheel, to more accurately adjust your speedometer, odometer, GPS or bike computer. If you recently purchased a cyclometer or need to adjust an existing one because you have installed tires with a different tread size, you need to determine the wheel circumference.

Calculating the circumference is easy by multiplying the tire diameter by pi. The circumference can be quickly determined if you already know the outer diameter of the tire. Since pi is 3.14, the circumference of a 26 “tire can be obtained by multiplying 26 by 3.14, which equals 81.64”. If you already know the tire diameter and tread width, the circumference can be found on the Internet.

Measuring the circumference with a rope. If you do not know the diameter of the wheel, you can measure the circumference by gently running a thread around the outer edge of the tire. Mark or cut the thread where it reaches the starting point and measure its length to determine the tire circumference.

• Place a dot of paint on the tire tread. Gently roll the bike in a straight line so that the wheel makes two turns and the paint marks are visible twice on the ground. Measure the distance from one spot to another to determine the circumference.