Belt noise: causes and diagnosis

Belt noise, whether a squeak, a “zinging” or “ringing” sound or a rhythmic tick, almost always comes from one of five causes. Working through them in the order below finds the cause with the least effort, and avoids changing things that were not the problem.

The five causes

Tension. A belt that is too loose slips and vibrates under load, which makes the typical zinging sound. A belt that is too tight loads the hub bearings and can make bearing noise instead. Both ends of the range are noisy, so “tighten until it stops” is not a valid method.
Alignment. The belt should run straight and centred on both sprockets. On a Booda the most common causes are a rear wheel that is not fully seated in the dropouts, or an axle that is not tightened properly. Noise is the first symptom Gates lists for misalignment, together with early wear and the belt walking off the sprocket.
Dirt. Sand, salt, mud or small stones caught between the belt and a sprocket make a grinding or ticking sound that repeats once per belt revolution.
Contact with another part. A mudguard, a guard, a cable or a piece of clothing rubbing against the belt or a sprocket under load. This is often mistaken for a drivetrain fault.
Wear or damage. Frayed belt edges, damaged or missing teeth, or a sprocket worn to pointed teeth all make noise.

Diagnose in this order

Look and listen. With the bike supported, look for anything rubbing, then turn the cranks slowly and listen. A noise that repeats exactly once per belt revolution points to a single damaged tooth or a trapped stone. A noise that changes with pedalling force points to tension or alignment.
Clean. Rinse with water and a soft brush, as described in Belt care and inspection. This removes cause 3 completely and costs nothing.
Check the tension. Measure it as described in Belt tension, at several crank positions, and adjust in small steps only if it is outside the green range.
Check the alignment. Make sure the rear wheel sits fully in the dropouts and the axle is tight, then turn the cranks 10–15 times and watch the belt. See Belt alignment.
Look for wear and damage. Cracks, fraying, damaged or missing teeth, worn sprocket teeth, bearing play. If you find any of these, no adjustment will make the noise go away. See Belt and sprocket wear.

If the belt passes all five checks, the noise may not come from the belt at all: pedals, the crank, the bottom bracket and mudguards can also creak or tick. Contact us and describe when the noise occurs.

What not to do

No oil or chain spray. It attracts dirt and makes the noise worse over time.
Do not treat silicone spray as the fix. Silicone spray made for Gates belts can quieten a dry squeak (see Belt care and inspection), but it does not correct tension or alignment. If the noise returns, keep diagnosing.
Do not overtighten. Adding tension until the noise stops loads the hub bearings, makes the drive drag and speeds up wear.
Do not change several things at once. Change one thing, then check whether the noise changed. Otherwise you will not know what the cause was.

Rohloff models: “the gears are slipping”

On bikes with a Gates belt and a Rohloff hub, complaints such as “the gears are slipping” or “there is a loud metallic noise” very rarely turn out to be a fault in the hub. The cause is almost always too little belt tension: under load the belt teeth skip over the rear sprocket teeth. That is both the noise and a real hazard, because skipping can damage the carbon cords in the belt. Check the tension before suspecting the hub; see Belt tension and Why a Rohloff Booda has no snubber.

When noise means stop riding

Noise together with any of the following is not a setting problem:

visible cracks in the belt,
a missing or partly broken tooth,
exposed carbon cords,
sprocket teeth ground to a point,
a belt that has skipped over the teeth under load.

My belt drive squeaks. What should I check first?

Never reach for oil: it attracts dirt and damages the belt. Work through the causes in order: look for something rubbing, rinse the belt with water, check the tension, then check that the belt runs straight. If the belt is cracked, has a damaged tooth or has skipped, stop riding and contact us.