Regardless of whether you have a single-speed or a multi-gear bike, one of the most irritating problems you're likely to face is a loose or slipping chain. Putting the chain back onto the sprockets when it slips free is straightforward enough.
However, if it keeps happening, you may have a bigger problem on your hands - a loose chain. If your chain can be pulled up or down by more than an inch, then it probably needs more tension.
Fortunately, with a few simple procedures, you may be able to diagnose and fix this problem yourself, without any specialist technical know-how.
Before we take a look at how to tighten a bike chain and the tools you'll need, let's answer a simple question.
What Causes a Loose Chain?
The commonest cause is wear and tear. Over time, even if you service your bicycle frequently, the links of your chain will pull very slightly apart. This is due to the rivets and the cradles in which they sit wearing down, adding extra stretch to the chain. You will probably have to change your chain at least once during the life of your bicycle.
Other common causes of loose chain depend upon what type of bike you have. With a single-speed bike or even a multi-speed with an internal gear hub, there's not a lot that can go wrong. The chain may simply be loose because the rear wheel has slipped forward in its setting, and needs adjustment. The good news is that this is very easy and quick to fix. We'll look at how to do this below.
On a multi-gear bike, gears are changed through a mechanism attached to either or both of the wheel hubs, called a derailleur. Derailleurs are designed to maintain chain tension using a built-in spring mechanism. If chain tension has been lost on a multi-gear bike, the derailleur is probably to blame. You may need to service, adjust, or replace it.
What Will I Need to Fix My Loose Bike Chain?
You may require the following:
- Adjustable bike wrench - to change wheel positioning
- (optional) hex key - to remove a gear changer (on an internal hub bike)
- (optional) de-greaser - to clean the chain
- (optional) chain lube - to lubricate the chain
- (optional) rags to clean off grease and excess lube
- (probably) a reasonably fit friend!
Fixing a Loose Chain on a Single-Speed Bicycle
First, turn the bike upside down and use the pedals to rotate the chain and rear wheel. Check the links of the chain to make sure they are not damaged. Take a look at how much oil the chain contains. If it is too dry or too greasy, consider de-greasing the chain and applying a new coating of bike lube.
Apply a spot of lube to each of the links in turn. Make sure you spin the rear wheel 10-12 times to ensure the chain has run entirely through the mechanism and you have coated every link. Any excess should be wiped off with a rag (spin the rear wheel and let the chain slide through the cloth).
Now, using the wrench, loosen the bolt fixing the rear wheel into its cradle. Pull the wheel back until the chain reaches the correct tension. Ideally, you will not be able to move the chain up or down by more than 3/4 inch. You may need a friend to help to hold the wheel in place while you tighten the bolts. Make sure the nut, bolt, and rear wheel slots are all in good condition. If the nut or bolt looks worn or is slipping, it will need to be replaced.
Make sure the wheel is aligned squarely so that there is the same distance between the wheel and each of the rear forks. Once the wheel is back in place, try to move it forward and back. If it remains rigidly in place despite all your efforts, it is safe and secure in its new position.
If you have an internal hub bike, you may need to detach the gear-shift mechanism from the rear wheel to access the bolt holding the wheel in place. On some bikes, you'll need a hex key to remove and replace this mechanism, or a suitable screwdriver.
Here's a useful video talking you through the process on an internal hub-gear bike.
Hopefully, this will have fixed the problem. If your chain still sags when the rear wheel is set back as far as it will go, then the problem lies with your chain. See below for how to diagnose and fix chain problems.
Things are a little more complex with a multi-speed bike with a derailleur.
Fixing a Loose Chain on a Multi-Gear Bicycle
The derailleur's spring is designed to pull the chain into sufficient tension. The tension loosens slightly when you change gear, allowing the chain to slip free and move onto a smaller or larger sprocket. Some bikes have a derailleur on the rear wheel only, and some bikes (those with many gears) will often have derailleurs on both wheels. Don't forget to check both derailleurs in the latter case.
Here are the steps to follow to ascertain if your derailleur is to blame. Do the following checks with the bicycle sitting normally (wheels down, saddle up). Prop up the bike so that the rear wheel does not touch the ground and can move freely.
As with a single-speed bike, you should only be able to move the top portion of the chain up or down by less than an inch. If you have a loose chain at the top, follow the steps outlined above to move the rear wheel back until the chain is at the correct tension.
If your chain is sagging at the bottom, check that the derailleur is in full tension by pulling it straight and letting go. It should spring back into a right-angle, or L-shape. If it remains down or doesn't jump fully back, you may have a malfunctioning spring. Either the spring mechanism has slipped loose, lost tension, or snapped. Unfortunately, the derailleur spring tension is not usually easy to adjust.
If you have problems with the spring, you may be able to get the derailleur repaired. Unless you are especially skilled, it is not advisable to take the derailleur apart yourself. Leave this to an expert.
To understand a little more about derailleur springs, watch this video.
Alternatively, the mechanism may simply have seized up due to excessive grease and grit. Try using some de-greaser and spray-on lubricant and see if this solves the issue.
If neither derailleur nor wheel position are problematic, but your chain is still slipping or sagging, then the chain itself may be to blame. You can measure your chain to see whether it needs to be replaced using a Chain Wear Tool.
These are metal rulers with prongs at either end. If both prongs can be inserted through the chain at the same time, then the chain is worn and may need to be replaced. Here is a demonstration of one of these tools in action.
This useful video shows you how to diagnose bike chain problems.
If you have bought a secondhand or reconditioned bike the wrong length chain may have been fitted. If the chain is too long, it may be impossible for the derailleurs to hold it in sufficient tension. There is a rather complicated formula to calculate the correct chain size (see FAQ's bellow).
If algebra is not your thing, then take your bike to a repair shop and ask them to assess whether the chain length is appropriate. If your chain is overlong, a repair shop may be able to remove some of the links from the existing chain, or simply replace the chain altogether.
If you decide to replace the chain yourself, here's a video showing you how to size a new chain without resorting to formulas.
Frequently Asked Questions
How often should I change my bike chain?
As a rule of thumb, you should replace your chain every 2000 miles. You can use a Chain Wear Tool, as described above, to assess whether your chain is sufficiently worn to need replacing.
What is the formula to calculate the correct chain length?
L = 2 (C) + (F/4 + R/4 + 1)
Where C is the distance between the front and rear spindles, F is the circumference of the largest front sprocket and R is the circumference of the largest rear sprocket.
For example, if C equals 22 inches, F equals 20 inches and R equals 16 inches, then
L = 2 (22) + (20/4 + 16/4 + 1)
which means that in this case L = 44 + 5 + 4 + 1, so L is equal to 54 inches.
What are the different types of chains?
There are basically two types of chains - single-speed and derailleur chains. The latter are thinner, enabling them to move more easily between different sprockets. Single-speed chains can be thicker and provide greater driving power since they do not need to be shifted laterally while cycling.
There are three main reasons for a loose bike chain:
- Your rear wheel is positioned too far forward
- One or more of the derailleur springs is loose, broken, or jammed
- The chain has "stretched" or has too many links
If you follow the steps above, you'll be able to diagnose what's going wrong. It is relatively straightforward to adjust the rear wheel, or de-grease and re-lubricate the mechanism. Anything more complex might require the assistance of a bicycle repair specialist.
Hopefully, this article has given you a little insight into what can go wrong and what you can do about it.