How do I know the diameter of my bicycle wheel? This question is most often encountered either during the search for a new iron friend, or when replacing a punctured tube. Usually the parameters of the bicycle become known to the owner at the purchase. Therefore, the question of how to properly measure the diameter of the wheel, more often arises in those who lend a bike for a while.
To begin with, it is worth understanding the terminology.
- Wheel diameter is the gap between the two outermost points on the outside of the tire, passing through the center.
- The rim diameter is the distance between two points on the inner edge of the tire, passing through the center.
These values are sometimes written on the tire of the bicycle, but the markings are not always readable, because over time the rubber rubs off and the inscription disappears.
This article provides methods by which you will learn how to measure the diameter of a bicycle wheel, including a child’s, in inches or centimeters.
Standard bicycle wheel sizes
Wheel and rim sizes have their own classification based on the bike model:
- Children’s, BMX
- Wheel size is 20 inches (508 mm),
- Rim size – 406 mm.
- Wheel size – 24 inches (609 mm),
- Rim size – 507 mm.
- Wheel Size – 26 inches (660 mm),
- Rim size – 559 mm.
- Road, highway
- Wheel size – 28 inches (711 mm),
- Rim size – 622 mm.
- Wheel size – 29 inches (736 mm),
- Rim size – 622 mm.
Inches are more commonly used as a measure because they are easier to calculate.
Wheel sizing systems for bicycles:
- Classic system, in inches or centimeters;
- ISO standard, in millimeters.
The ISO universal value was introduced to streamline measures of measurement. It is the one used in the manufacture of bicycle wheels around the world.
To buy a bicycle for your baby, it is worth knowing his height and age – this will help determine which wheel size is right for him. How to find out:
- Height to 98 cm, 3 years – 12 inches.
- Growth to 98-104 cm, 3-5 years – 14 inches.
- Height 104-110 cm, 4-5 years – 14 or 16 inches.
- Growth 110-116 cm, 5-6 years old – 16 or 18 inches.
- Height 116-128 cm, 6-8 years old – 20 inches.
- Up to 164 cm, ages 8 and up – 24 inches.
From 24 inches begins the range for adults. Separately located BMX (20 inches).
Methods for determining the diameter of the wheel of a bicycle
To find out the diameter, use one of the five methods below.
1.The marking on the tire.
The easiest way. To determine the size and diameter of a bicycle wheel from the tire, examine the markings that contain two numbers separated by a dash.
In the classic version, the two numbers look like this:
- bicycle wheel diameter, inches;
- Tire section width, inches.
For example: 44.4/406.
- profile height, mm;
- Rim diameter, mm.
For example, 20/1.75.
Based on the universal ISO marking, you can calculate the rim diameter:
- 20/1.5 – 2.125. Rim diameter is 406 mm.
- 24/1.5 – 2.125. Rim – 507 mm.
- 26/1 – 2.35. Rim – 559 mm.
- 27/1 – 1.75. Rim – 622 mm.
- 28/1 – 175. Rim – 622 mm.
- 29/1.75 – 2.35. Rim – 622 mm.
2.The designation on the rim.
Also one of the easy ways where you don’t have to measure yourself. Marking is used on the rim (mm), where two numbers with an “x” indicate:
- seating diameter;
- wheel width.
For example, ETRTO 622×19 or ETRTO 622×14.
From the fitment value, the size of the tire itself is determined.
3. measure the radius
To find out what the diameter of the wheels on your bike is, calculate the radius using a regular centimeter tape.
- Position your bicycle straight and perpendicular to the surface.
- Measure the distance from the hub to the ground, that is, from the center to the outer edge of the tire. This value is the radius of the wheel.
- Multiply this value by two to find the diameter.
It’s best to use a wooden or metal ruler to measure, so you get the most accurate values.
This way you can find out what the diameter of a bicycle wheel is in centimeters. To convert the value to inches, divide by 2.54.
For example, the radius is 35.5 cm. So, the diameter is 35.5*2, which is 71 cm. Divide by 2.54 and you get 27.9 in inches. Rounded up to a whole number, you get 28 inches.
4.The ISO system
The International Standards Organization (ISO) has a common way of determining wheel size. This method is used by all manufacturers.
Its fundamental difference is that the radius is measured from the hub to the inner border of the tire. This method eliminates errors due to differences in tread width. Because the tread can sometimes not match the rim. For example, wide tires may be used on rough terrain and narrow tires on highways or freeways.
ISO measurements, contain values (mm):
- tire width;
- rim diameter.
In the designation, the width is spelled out first. For example, 53.3 x700 or 56×550. To determine the size of a bicycle wheel and its diameter in inches, divide the resulting value (mm) by 25.4.
The ISO method is the most accurate way to determine bicycle wheel size.
5.Using the circumference
You can calculate the wheel size through the circumference length. This value can also come in handy when fine-tuning the following bicycle parts:
To find the diameter, divide the circumference by Pi, which is 3.14. To find out the wheel size on a bicycle in inches, divide the resulting value (cm) by 2.54 and round to a whole number.
Finding Wheel Diameters Using the ISO System
Two values are needed for the ISO wheel size designation, let’s define each of them.
- Tire width.
Use a metal tape measure to avoid inaccuracies.
Hold the tape measure firmly against the outside of the tire and measure it (mm).
- The inside diameter of the rim.
- Make sure the bike is upright and perpendicular to the surface.
- Calculate the rim radius. To do this, measure the distance from the hub to the inner edge of the tire (mm).
- Determine the diameter of the rim. To do this, double the value of the radius.
Ways of calculating the circumference of a wheel
You can find the wheel diameter on an adult or child bicycle by measuring the circumference.
There are three methods you can use for this:
- measuring with a cord;
- by drawing a line;
- Using a formula.
Using a lanyard.
You can use a thick string or long rope to do the calculation.
How to measure the size of a bicycle wheel in inches using a shoelace:
- Place the lanyard in the middle of the tread.
- After securing the beginning of the shoelace to the tread, pull the shoelace all the way around the circumference.
- Make a mark on the shoelace at the connection point with the beginning of the measurement.
- Measure the resulting length of the lace (mm) – the length of the circumference.
- Divide it by the number Pi (3.14) to get the diameter (mm).
- Divide by 2.54 to get the size in inches.
For example, the length of the circumference is 2073 mm. Divide this value by 3.14 to get a diameter of 660 mm. Divide by 25.4 and rounded, you get 26 inches.
A fairly simple way to calculate. To make a mark on the tire, take a crayon or paint. Calculation method:
- Put one mark on the tire.
- Ride your bicycle in a straight line until you have 2 marks from one mark on the ground.
- Measure the distance from one mark to the other, indicating the length of the circumference.
- Divide the value by the number Pi (3.14), which will determine the diameter.
- If necessary, convert measurements to inches. To do this, divide the value in cm by 2.54 and the value in mm by 25.4.
For example, the gap from one mark to the other is 1,595 mm. Dividing the circumference by 3.14 (pi), you get a diameter of 508 mm. To convert to inches, divide by 25.4 and rounded, you get 20 inches.
Using the formula
You can find the length of the circle by using the diameter. To do this, you should use a mathematical formula:
L = D * π, where
- L – circumference length of a bicycle wheel;
- D – diameter;
- π is the number of pi, which is equal to 3.14.
For example, the diameter of the wheel is 24 inches. Multiply by Pi (3.14) and you get 75.36 inches, which is the circumference length.
Bicycles are actively entering the life of modern man. They are slowly replacing the usual forms of transport. The main reason for the spread of cycling is to maintain a healthy lifestyle and concern for the environment.
The peak of cycling popularity is in spring and summer. Every year more and more people join this type of transport. Newbies have to get into the intricacies of design and operation.
There are several ways to determine the diameter of the wheel of a bicycle, they are easy to use, even for children.
First, you can read the designation on the tire or rim. Second, calculate through the radius or length of its circumference. Third, you can determine using the ISO system. The method based on the ISO system is considered the most accurate and universal method of sizing. This is why it is used in bicycle manufacturing all over the world.
Knowing the diameter is essential in the following situations:
- choosing a bicycle for a child,
- Changing a punctured inner tube,
- adjusting bike accessories.
Now you will not have any difficulties in the process of calculation.