Description of the Problem: The rear derailleur and the inner part of the chain are coming in contact with the spokes of the rear wheel. In most cases, the issue occurs when the rider is pedaling in the lowest/easiest gear.
Possible Sources Of The Problem
1. Improperly Adjusted Limit Screw
Even the most basic derailleurs have two limit screws labeled as “H” /high/ and “L” /low/
The high screw prevents the derailleur from over-shifting and throwing the chain outside of the cassette.
The low screw limits the inner movement of the derailleur towards the wheel and stops the derailleur from throwing the chain into the spokes.
Ideally, the low screw will have a setting that hard limits the derailleur from reaching the spokes while still allowing it to move the chain onto the largest cog.
In most cases, an improperly adjusted “L” limit screw is the culprit of the aforementioned problem.
2. Bent Derailleur Cage
The derailleur cage connects the pulleys to the body. If the cage is bent inward, the derailleur could get dangerously close to the spokes. In extreme cases, it may even jam the wheel and create an accident.
Ideally, the cage will be straight, and the pulleys will be in line with the chain and the currently used cog.
If this isn’t the case, it will be necessary to re-straighten the derailleur’s cage. It’s often possible to reach sufficient accuracy by eye, especially if the bike isn’t using many gears. (The more cogs there are on a cassette, the more critical it is to have an accurate shifting set-up.)
3. Bent Derailleur Hanger
The derailleur hanger is a small piece of aluminum that connects the derailleur to the frame. The choice of material is strategic. If the bike falls, the hanger would bend without transmitting force to the chainstays (frame).
If the derailleur hanger is bent inward, it will bring the derailleur too close to the spokes and create an opportunity for unwanted contact.
There are two ways to deal with the situation:
a. Replace the unit (Not always possible because derailleur hangers are unique, and it may be hard to find an exact match, especially if the bike is older.)
b. Re-straighten the hanger with the help of a derailleur hanger alignment tool.
The alignment tool could seem pricey, but if you’re working on multiple bicycles, it will pay for itself over the years by reducing the need to buy new hangers.
It’s also worth mentioning that older steel frames come with a hanger that’s part of the frame. If that type of hanger is bent, the only way to replace it is to cut it off and re-weld or re-braze a new one.
While this procedure is doable, it’s pricy and takes a lot of time.
First, the hanger has to be machined and then an experienced metal worker should re-attach it. It will be much simpler to simply re-straighten it with the alignment tool.
Note: On the cheapest derailleurs, the derailleur hanger is part of the derailleur itself.
4. Improperly Installed Rear Derailleur
If the derailleur isn’t properly secured to the hanger, it may come loose and showcase unexpected behavior. Since there’s a great number of derailleurs out there, it’s best to consult the manufacturer on how to install the particular unit.
5. Chain Issues
In some cases, the chain rather than the derailleur will be the culprit. Below are a few possibilities:
- The chain is contaminated and carries lots of debris sticking outside of the chain’s width.
- Some links of the chain are excessively stiff and jump when passing through the cog.
- The chain hasn’t been re-sized properly, and there’s a pin sticking out.
To rule out chain issues, it will be necessary to clean the chain and examine its links.
6. “Soft Wheel”
In rare cases, the problem is the wheel and not the derailleur. If the spokes of the wheel are insufficiently tensioned, the wheel may flex too much. The flex will push out the spokes and create a possibility for contact with the derailleur.
FAQ: What are the dangers of this phenomenon?
This malfunction could result in serious consequences.
Over time the friction between the derailleur and the wheel will weaken the spokes at a single location. Eventually, the spokes will start failing. When that happens, the wheel will get out of true. And if the number of broken spokes is high, the wheel could become seriously deformed. If the bike is relying on rim brakes, the wheel may even get stuck against the brake arms.
If the problem is coming from the derailleur hanger or the derailleur’s cage, the derailleur may get into the spokes. The outcome will include a damaged wheel, derailleur and chain. The accident can also cause a serious physical injury to the rider. For that reason, this issue should be addressed as fast as possible.
Summary: What You Need To Know
- If the derailleur is getting in contact with the spokes, the issue should be addressed immediately because it may result in serious damage to the bike or an injury.
- The most likely sources of the culprit are:
- Improperly adjusted “L” screw of the rear derailleur
- Loose or bent derailleur hanger
- A bent derailleur cage
- Improperly installed derailleur