If you have been biking for a while, you have probably come across the super annoying chainring wobble.
The most common cause behind this is loose bolts.
If the bolts that attach your crankset to the bottom bracket shell are loose, this can cause the chainring to wobble.
Fortunately, fixing it doesn’t always require professional assistance. With a bit of know-how and the right tools, you can get your bike back in top shape.
In this post, I’ll quickly show you how to fix chainring wobble. I’ll also shed some light on what causes chainring wobble and how to spot it.
Diagnosing Chainring Wobble
If you hear strange sounds or feel abnormal friction while riding your bike, you might think it is chainring wobble. But you need to make sure it’s the case.
Also Read: Why Is My Cassette Wobbling?
Here’s how to exactly spot it:
- Spinning the chainring rapidly. If there is a significant wobble, it will be easily noticeable.
- Check if there is any movement in the bottom bracket or the cranks by pulling the crank arm horizontally. Any noticeable movement means wobble.
- When the chainring is spinning, insert a screwdriver into the frame and check for wobbling.
Sometimes, chainring wobble is not visible. If this is the case, you need to take a test drive and feel the wobble while riding.
How To Fix Chainring Wobble
Here is a step-by-step super easy to follow guide on how to fix chainring wobble:
Step 1: Gather Tools and Prepare
Before starting, make sure you have the necessary tools. You need:
- Chainring bolt wrench
- Allen wrenches
- Bottom bracket tool
- Torque wrench (if you can find one)
Find a clean and well-lit workspace where you can comfortably work on your bike.
Also make sure your bike is securely positioned either using a bike stand or by flipping it upside down and resting it on its handlebars and seat.
Also Read: Kickstand On A Road Bike
Step 2: Tighten the Bottom Bracket
Using the appropriate bottom bracket tool, typically a cartridge bottom bracket tool or a socket wrench, engage the tool with the bottom bracket cups.
Turn the tool counterclockwise to tighten the cups. Apply steady pressure and ensure a snug fit, but avoid excessive force to prevent damage.
If your bike features a threaded bottom bracket, make sure both cups are tightened evenly.
For a press-fit bottom bracket, ensure that it is pressed fully into the frame and aligned correctly.
Step 3: Tighten the Crankarm’s Bolts
Start by identifying the bolts that connect the crank arms to the bottom bracket spindle.
Carefully inspect each bolt to ensure they are not stripped or damaged.
Next, position yourself on the non-drive side of the bike. Place the wrench or Allen key into the bolt head and turn it clockwise to tighten the bolt.
Apply firm but controlled force, being careful not to overtighten and risk damaging the threads.
Repeat this process for all crank arm bolts, ensuring they are all tightened.
Also Read: Bike Crank Clicking Under Load
Step 4: Straighten the Bent Sprockets
Start by shifting your chain onto the smallest chainring to get better access to the bent sprocket. Next, using the chainring straightening tool or the wrench, gently apply pressure to the bent area of the chainring.
Apply force in the opposite direction of the bend, gradually straightening it out. Take care not to exert excessive force, as this could cause further damage to the chainring or its teeth.
Once the chainring is relatively straight, rotate the crank slowly and observe for any remaining wobble.
If necessary, repeat the straightening process, making minor adjustments until the chainring spins smoothly without any noticeable wobble.
IMHO bent chainrings are best replaced rather than straightened, as attempting to straighten them can compromise their structural integrity.
What Causes Chainring Wobble
Here are some the main causes of chainring wobble:
Bent Chainrings
Chainrings are the toothed gears attached to the crankset. If they are bent, they are no longer perfectly round.
So when the bent chainring rotates, it causes the chain to be pushed sideways instead of smoothly engaging with the teeth.
This sideways force creates an uneven pulling motion on the chain, leading to chainring wobble.
Loose or Worn Out Bottom Bracket
The bottom bracket holds the crankset and allows it to rotate smoothly.
If the bottom bracket becomes loose or worn out over time, it can create excess movement and play in the crankset.
As a result, when force is applied to the pedals, the crankset can move unevenly, causing the chainrings to wobble during rotation.
Loose Bike Crank Arms
The crank arms are the parts of the crankset that connect to the pedals and transfer the rider’s power to the chainrings.
If the crank arms are not securely tightened onto the bottom bracket spindle, they can move independently from the chainrings.
This independent movement causes the chainrings to wobble as the rider pedals, as the crank arms are not properly aligned and synchronized with the chainrings.
Bad Spindle Fitting Profiling
The spindle is the central shaft of the bottom bracket that connects the crank arms.
Spindle fitting profiling refers to the design and its compatibility.
If the spindle fitting profiling is not well-matched or if there are inconsistencies in its shape or dimensions, it can result in an uneven connection between the crank arms and the spindle.
This uneven connection can cause the chainrings to wobble as the crankset rotates, as the imperfect fit leads to irregular movements and instability in the chainring rotation.
