How to Fix Chainring Wobble? (4 Causes)

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Bike chainring

Chainring wobble happens when the chain and the chainring move in both directions with the frame. That way, the chain catches the sprockets at the wrong angles, causing friction by distributing the riding load over the body of the bike. 

Still, there’s no need to worry, for there’s a way to fix chainring wobble.

Read on for a step-by-step guide on how to fix chainring wobble. This article also lists the main causes of this problem.

Step 1 – Diagnose the problem
Step 2 – Tighten the Bolts of Your Crankarm
Step 3 – Tighten the Bottom Brackets
Step 4 – Fix Bent Sprockets

Step 1: Diagnose the Problem

Recognizing a chainring wobble can be easy in most cases. However, sometimes the problem isn’t obvious or can be mistaken for another.

Generally, when you hear strange sounds or feel abnormal friction while riding your bike, you might think of chainring wobble. Yet, it’s one of many other causes for such noises.

There are four easy methods to make sure it’s a chainring wobble:

  1. Spin the chainring fast: if the wobble is strong, it’ll appear obviously.
  2. Insert a screwdriver into the frame with the head near the suspected sprocket: it’ll show you if your chainring has a little wobble.
  3. Pull the crankarm horizontally: there’s a chainring wobble if there’s any movement in the bottom bracket or the cranks. This wobble would only show under heavy riding load.
  4. Take a test drive: still not sure? Taking a test drive is a bulletproof method to diagnose the problem.

Step 2: Tighten the Bolts of Your Crankarm

Tightening crankarm bolts

A loose crankarm can be one of the main causes of this problem. Therefore, tightening the bolts of your bike’s crankarm is a crucial step.

The way you tighten the bolts depends on the model of your crankarm. While this task is straightforward in most crankarm systems, three systems require special techniques, such as:

Hollowtech II

Hollowtech II is easy to fix. Although having a loose crankarm is rare, restoring it is a no-brainer. Here’s how:

  1. Loosen two side screws only to allow the crankarm to move.
  2. Set the torque of the arm cap that enters the spindle to 2 nM. If you can’t measure the torque, follow a trial-and-error technique until you get rid of any play.
  3. When you’re satisfied with the results, fasten back the screws.

Sram DUB

With a Sram DUB system, you can hardly ever get a loose crankarm. In fact, the bolts get tighter with every ride.

However, if it happens and you need to tighten your crankarm bolts, follow these steps:

  1. Use an 8 mm Allen key to adjust the arm caps torque to 54 nM
  2. Turn the preload adjuster in the + direction until you get rid of any unnecessary movement.
  3. When the preload adjuster gets in contact with the bottom bracket, use a 2 mm Allen wrench to adjust the pinch bolt to completely seal the gap on the preload adjuster.

Square Taber and Octalink

Despite their flaws, systems with octalink spindles and square Taber are simple and easy to maintain. In fact, with this type of crankset, the pedals usually get loose with constant pressure.

Tightening the crankarm in this system is straightforward, but it doesn’t last long. However, there are specific steps to fasten the bolts permanently or at least for some time:

  1. Apply suitable bike grease on the inner side of the bolt to prevent it from biting into the crankarm.
  2. Adjust the crankarm to fit completely into the spindle. 

Step 3: Tighten the Bottom Brackets

If you find that the bolts on your crankarm don’t need tightening, it’s time to move on to the next step. Tightening the bottom brackets depends on your bike.

Bottom Brackets With Adjustable Cup and Cone

This type of bottom bracket is common in old models of mountain bikes. It features an adjustable cup that applies force on the bearings and a lockring to secure it into place.

In this case, you’ll need to tighten both the cup and the lockring, as follows:

  1. Loosen the left side of the lockring.
  2. Untighten the left cup a little. This should enable you to check whether the right cup is tight enough.
  3. Once you adjust the right cup, tighten the left cup back until you can’t feel any play in the spindle.
  4. Hold the cup in place with a wrench to prevent it from moving with the lockring.
  5. Use a suitable lock spanner to tighten the lockring.

Bottom Brackets With Sealed Cartridge

Bottom brackets with sealed cartridges can be a lot easier to adjust. You may need some special equipment, such as an adjustable wrench and a bike bottom bracket removal tool

The process is similar to that performed on adjustable cups and cones. Here’s how:

  1. Untighten the left side.
  2. Fasten the right side.
  3. Tighten the left side again until there’s no play in the spindle.

Threaded Bottom Bracket With No Spindle

This type of bottom bracket is very common. The rule is that when the frame is made of a threaded shell, the crankset is also threaded.

You should perform the same procedure as the other types. However, in this case, you don’t need to tighten the bracket as hard.

Step 4: Fix Bent Sprockets

Bent chainring

Now that you’ve tightened the cranksets and the bottom brackets, does the problem still persist?

If so, your sprockets are most probably bent.

To straighten them, follow these steps:

  1. Remove the chainring from the bike.
  2. Put it against a flat surface to assess the damage.
  3. Use a suitable hammer or pliers to apply pressure on the chainring.

If you follow these steps, you need to be extra cautious because hitting on the wrong spot might bend the teeth or damage the chainring itself.

4 Causes for Chainring Wobble

To fix a chainring wobble, you should know the four main causes of such a problem:

  1. Loose Crankarms

This problem can happen in all crank systems. Yet, it’s a lot more common in Square Taber and Octalink.

Crankarms can go loose due to hitting obstacles on the road. Interestingly, it can also happen for no particular reason.

  1. Loose Crank on Spindle

This can be the most common cause for chainring wobble, especially in the splined cranks of modern bikes.

Cranks may become loose due to two factors:

  • If the wobble happens in one crank, it’s due to low clamping force.
  • If the wobble happens in two cranks, it’s due to decreased axial pull of the crank into the shaft.
  1. Loose or Worn Out Bottom Bracket

The bottom bracket can be either press fit or threaded. It’s the frame via which runs the spindle. It may get loose, causing play in the crank. This issue is more common in new bikes as they’re usually not tightened enough when first assembled.

In addition, chainring wobble may be a result of damaged bottom brackets due to wear. In this case, you might have to replace the bottom bracket instead of repairing it.

  1. Bent Sprockets

One of the common causes for chainring wobble is that your sprockets need straightening. In some cases, the entire chainring may be bent.

That happens due to accidents and hitting hard objects. In addition, it can be a production error, especially in new bikes of cheap brands.

Conclusion

Chainring wobble is a common problem that may happen for several reasons.

Start by adjusting the crankarm. If the problem still persists, try tightening the bottom bracket and checking it for damage.

The last precaution to take is to straighten any bent section of the sprockets or the chainring itself.

No matter what the cause is, there’s always a way to fix a chainring wobble.

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AUTHOR

Paul Tuthill
Growing up in Scotland, Paul developed a love for the outdoors and a desire for adventure from an early age.