3 Methods to Change the Length for a New Bicycle Chain

This article explains how to change a new bicycle chain with a gearshift to the perfect length

What Tools are available?

Chains for bicycles with a gear selector switch must have a certain length. To long or to short chains can cause problems in shifting speeds and driving. However, the foot of the rear derailleur should be long enough to pull up a weakened chain as it moves between different gear combinations. All of this relates to the theme of “overall performance” and is discussed below.

 

Three ways by which you can choose the desired chain length

This article describes three ways you can select the desired chain length. All three options can do this, but you do not have to apply all three methods, but only one that suits you and your situation.
The first method is “USING THE ALREADY EXISTING CHAIN.” It implies that the bicycle chain is already installed.
The second method is called “THE BIGGEST STAR – THE LARGEST RING OF THE CHAIN” and does not require an old chain.
The last method is the “MATHEMATICAL CALCULATION” of the chain length.

Switch Capacity: The term “switch capacity” refers to its ability to lift the foot when switching speeds. Some bicycles have star combinations where the switch cannot lift the chain foot. In this case, the gearbox on the bike exceeds the capacity of the switch. If the capacity of the switch does not match the size of the bicycle transmission, the circuit does not pass the test as “too long” or “too short”. You can not choose the length of the string that meets both parameters. In this case, it is better to leave the chain longer than the shorter one. Both methods and the method described below using an existing circuit and the mathematical calculation method determine the safe length of the circuit when the capacity of the switch is interrupted. Perhaps, in this case, it is worth avoiding those high-speed combinations that cause cycling problems.

Method 1 “USING THE ALREADY EXISTING CHAIN.”

Method 1 "USING THE ALREADY EXISTING CHAIN."

Before removing the old chain, check the length of the required chain. Cut off a new chain whose length is the same as the old one. Switch the speed of the bicycle so that the chain is the smallest front sprocket and the smallest rear. Check up a part of a circuit between the bottom switch and the smallest asterisk carefully. At this point, the chain should not sag. Also, make sure that the lower part of the chain does not touch the pulley. It is considered normal if a slight slack occurs at this point in the chain, but should not bend too much. Heavy sagging is an indication that the chain is too long.

If the chain is too long, locate the rivet that contacts the sprocket and mark the sprocket at this point. Count two rivets towards the switch, lift this link and move it to the mark on the asterisk. The necklace is much shorter now. Check the slack again. Repeat the process by counting the two rivets and moving the chain to the mark. Reduce the number of links by 2, 4, 6, etc. Repeat until no visible sagging is visible.

To determine if the chain is too short, slide it to the largest front sprocket and the second largest sprocket. The chain should stretch in this position. Carefully check the S-shaped part of the chain as it passes the pulley. Turn the largest sprocket slowly and carefully. If the chain is very tight, it is too short. If the chain moves but there is no double bend, it is too short when the chain passes the pulleys. The new chain must be added two links opposite the old chain.
Warning: Do not try to extend the old chain and add new links.

Test passed?

If the chain length passes one of the tests listed above but does not pass the other, then most likely the possibility of the switch does not match the transmission. Determine the length of the chain so that it leads through a large sprocket to the largest rear part. After that, the entire responsibility for the switching combinations when switching is the owner of the bicycle.

If you want to install a new chain and the old one has the correct length, you can measure the new chain along the length of the old one before installation. First, remove the old chain and place it on a flat surface with the rollers upright. Align the chain. Put a new chain next to the old one in the same way. Make sure the ends of both chains are the same (either both chains should have rivets at one end or both chains without rivets). The new chain will be displayed shorter. Therefore, move the links of the old chain to match the new chain. Match the rivets on the new chain to the rivets on the old one. Add or remove links, if necessary, according to the results of the tests described above, and cut the chain off at this point.

Method 2 “THE BIGGEST STAR – THE LARGEST RING OF THE CHAIN”

An alternative method of measuring the length of a new chain is to use the largest sprockets of a bicycle. This is the easiest way to measure a circuit without passing it through a switch. Remove the chain and cut it off after determining the length. Then pass the circuit through the switch and connect.

First Step: Remove the old chain.
Step 2: Place the derailleur on the largest star and the rear on the smallest.
Step 3: Pull the chain through the derailleur. In this case, it does not have to be pulled through the back. Simply wrap it around the largest front sprocket and the largest rear sprocket.
Step 4: Pull on the chain and pay attention to the next rivet where the two links connect. Note: Only connect the chain by crossing the inner and outer plates.
Step 5: From the next rivet, count two links (one inch) and lengthen them. Cut the chain at this point.
Step 6: Remove the chain from the bicycle, pull it through both switches and connect the ends.

Pay attention to the main link: If there is a main link in the chain, it is necessary to count on one side of the chain. Measure the chain and cut off the additional links.

Method 3 “MATHEMATICAL CALCULATION”

Method 3 "MATHEMATICAL CALCULATION"

Bicycle chains consist of inner and outer plates. The only way to connect them is to connect the outer plate to the inner one so that the chains can be connected when there are whole links. For example, the chains of some high-speed wheels 51, 52, 53 inches long. The chain cannot be cut to a length of 52 – 2/ 8″, 53 – 1/ 8″ or even 52 – 4/ 8″.

It is possible to determine and cut off the length of a chain with an industrial track equation before you mount it on a bicycle. Start by counting the teeth on the largest front and rear sprocket. The next step is to measure the distance between the center of the crankshaft and the rear axle. This is the length of the string, a multiple of 1/8 “, and will be converted to decimal form, as shown in the following table.

Convert to a decimal fraction of multiples of 1/8 “:

1/8 “= 0.125”
2/8 “= 0.25”
3/8 “= 0.375”
4/8 “= 0.5”
5/8 “= 0.625”
6/8 “= 0.75”
7/8 “= 0.875”
For most bicycles, you can use the relatively simple chain length equation. For bikes with a larger difference in the size of stars and a short chain, you can use a more complex equation. I will describe it later in the article.

Simple Equation: L = 2 (C) + (F / 4 + R / 4 + 1)

 

Example:

Bicycle mounted front sprockets 42-32-22. To calculate, you need an asterisk 42. The largest installed rear sprocket has 32 cloves. The distance between the center of the crank bolt to the rear axle is 16 – 3/8 “, which is equal to 16.375 in. 

MATHEMATICAL CALCULATION

Strict Equation

An example of bicycles for which the exact equation must be used are road bikes with large front sprockets (possibly 55 cloves) and small rear sprockets (11 cloves). If the bicycle has a very short distance between the center of the crank bolt and the rear axle (15 inches or less), then again a strict equation is required. Since the sprockets have different sizes at the front and rear, the chain must diverge and form a triangle. The length of the chain of the resulting triangle can be added due to the hypotenuse. This also applies in very exceptional cases.

Chain Lengt = 1 + 0.25 x (F+R) + 2 x √ C² + (0.0796 x [F – R])²

The equation for calculating the length of a bicycle chain
As an example of applying a strict equation, it is assumed that the chain length of a bicycle at a speed of 15 inches, the front sprocket of 58 teeth, and the rear sprocket is 11 inches. The length need not be increased by 1 inch. This duty should be added only on bikes with switching speeds.

After we have calculated the length of the road bicycle chain with a shortened equation, we get the answer 47.25 inches. This result is rounded to 47 inches. Using a strict equation, we get the result of 48.17 inches, rounded to 48 inches. Also in the above example, no duty was added to the circuit since there is no speed selector. When calculating according to the simplified equation, the chain is one inch shorter. However, this is not a typical situation. When the sprocket is reduced to 55 teeth, even in the example of a single stage bicycle, two equations usually show the same result.

Read also: HOW TO CHOOSE THE RIGHT TYPES OF LUBRICANTS AND OILS FOR BICYCLE CHAINS

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