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Why Does Your Bike Keep Shifting Gears On Its Own?

If you frequently ride a bike, you must maintain it well to ensure it functions properly. This includes keeping the bike clean, ensuring the brakes are adjusted, inflating the tires, keeping its screws tightened, and getting it serviced regularly. However, your bike may start to shift gears on its own. Here’s what you need to know:

A bike shifting gears on its own is referred to as ghost shifting. This occurs when the cables in your bike become loose over time. Additionally, there may be friction within the cables, the derailleur might be bent because of cable tension, limit screws may not be set properly, or the entire chain has broken.

You will need to replace the cable, shifter, hanger, or housing, depending on what is causing ghosting. Keep on reading to learn more about it! 

What Is Ghost Shifting And Why Does It Happen?

This is referred to as a situation during your bike ride when your bike shifts its gears without you shifting them. The sudden change in your gears will decrease your bike’s speed drastically.

Ghost shifting is more noticeable at high speeds. This is because you need to pedal with greater energy than normal at high speeds without changing your gear. However, cable tensions may lead to the derailleur in your bike opening. This results in your chain shifting gears automatically.

If you have bought a new bike, its cables will become loose during the initial few rides. As this is a common occurrence, getting your new bike serviced and adjusted every six months is recommended. This is also important because many local shops provide discounts for tuning up your bike when it is new.

However, if your bike is aged, its cables may stretch as it continues being used. Also, ghost shifting may occur because of a bent derailleur or a derailleur hanger. These two are uncommon because there must have been a crash or toppling over for the derailleur to get bent.

Having discussed why your bike might shift gears on its own, let’s begin detailing how you can fix it! 

Ways To Fix Automatic Gear Shifting/ Ghost Shifting

Once you have experienced ghost shifting, you need to figure out which component of your bike is causing it. If it is being caused because cables are too stretched, then you need to find out which derailleur leads to ghost shifting. For the chain, you may need to shorten it by taking out some links or completely replacing them with the shifter cable.

If the problem lies within the rear derailleur, you must begin by shifting it into the smallest chainring. Then, gradually shift up the bike. If this does not work, more tension is needed in the derailleur. To add more tension, turn the barrel adjuster away from the brake lever. Remember to do this in small twists so that extra tension is not created.

Mostly, half a turn should provide the required tension. If it does not, repeat the process until the derailleur works properly.

The video below highlights ways you can add tension to your shift cables:

If the front derailleur is at fault, the process of fixing the derailleur is very similar to the back derailleur. The only change between the two methods is that the other barrel adjuster needs to be turned to add tension to the front derailleur. It must be done so by screwing in the opposite direction as the rear derailleur.

However, if ghost shifting does not go away following the two procedures, something other than loose cables is the reason. Here, it is advised to take your bike to the local repair shop for a service instead of replacing the faulty components yourself. This is because moving the bike too much without proper experience may damage it even further.

We will now discuss the front and rear derailleur methods in more detail. 

How To Fix A Gear Shift In The Rear Derailleur

As mentioned above, you need to change your chain to the smallest right on your back derailleur if it is the one causing ghost shifting. Then, press the shifter once. If the chain cannot shift to a higher gear, more tension is required.

Following this, twist the right barrel adjuster in your bike. This is found opposite from the brake lever on your brake and is used to pass the brake cable through when it enters the shifter. Twisting it away using half a turn only loosens the adjuster.

In your bike’s rear cassette, shift down to the smallest chainring again and continue pressing the shifter to see if the gears change correctly. If the gear remains unchanged, repeat the above steps while twisting the adjuster away from yourself. 

bike bottom bracket

How To Fix A Gear Shift In The Front Derailleur

The aforementioned process also works if the front derailleur is at fault. Begin by putting your bike in the park and pedal forward manually. Similar to the rear derailleur, the front derailleur also has an adjuster. However, it needs to be screwed in the opposite direction from before to add tension.

If this does not work, visually observe your bike. If too much slack is visible, you need to add more tension, whereas if it appears too tight, then you need to remove some tension. When manually adjusting your cable, you can identify the point where the cable exits the derailleur.

To add more tension, pull the cable outwards. If you need to remove tension, push it further inside to create more slack. Continue repeating this until your bike is no longer ghost-shifting. However, as stated above, to avoid extensive damage to your bike, you must take it to a mechanic at your earliest if you have never repaired it yourself before. 

Final Takeaway

In conclusion, we can see that automatic gear shifting in bikes is referred to as ghost shifting. This may be caused when there is either too much or too little tension in the bike chains, the front or rear derailleurs are at fault, or the derailleurs are bent. If the problem seems too complex, it is advised to use professional help.