Problems in general
The squeaking of wheel brakes is an old story and was already omnipresent with rim brakes. The problem was not eliminated with the introduction of disc brake technology in the bicycle industry. There are various reasons why disc brakes also squeal:
- The pads are new and not braked in
- The brake pads/disc are damp or wet
- The brake linings (pads) are glazed (grind the linings on a flat grinding plate)
- The brake pads are worn or old
- The brake disk is oily (e.g. after oiling the chain or a leaking brake caliper)
- Contamination on the windshield and/or pads
- The brake disc and/or caliper setting is incorrect
- The brake piston retraction is not working correctly
Specific Stromer
The rear brake in particular often makes squeaking noises on the Stromer. The front brake can also squeal. In addition to the reasons mentioned above, they may be amplified by design „peculiarities“ on Stromer.
At the rear, the brake disk is mounted directly on the left-hand flange of the hub motor. This acts as a resonance amplifier (drum effect). A solid, hollow rigid fork is installed at the front, which also serves as a resonance body.
There are also differences depending on whether braking occurs in wet or dry conditions. „Wet“ is always louder! The brake pad (sinter/organic = resin) also influences the soundscape.
A problem solution is usually not 100%% sustainable. As two power traders confirmed to me, the whimpering or squeaking cannot be permanently eliminated. Sooner or later it returns, no matter what you do. Rebuilding the system for another product also does not solve the problem, is correspondingly expensive, and Stromer fundamentally prohibits modifications to the braking system.
Solution approaches
1. Properly break in/bed in brakes
Before looking for other causes for the squealing, make sure that the brakes are braked in and, in the case of resin pads, that they are also burned in.
See BREMSEN - 'Brake in/burn in brakes'
Resonance damper disc for the rear wheel
Stromer offers a resonance damper disk for the rear wheel. It is mounted between the brake disk and the motor flange.
Practical experience: Works!
3. Use resin (organic) coatings
One way of reducing noise is to install organic (resin) surfaces. Noise reduction can be achieved at least in dry weather.
In the wet, resin pads squeal even more than the original sintered pads, at least until they are braked dry. They usually have a slightly softer pressure point, but then brake just as well as the sintered pads.
Resin linings, like sinter linings, need to be bedded in but also cured. This is done by braking on a downhill slope and heating the linings to over 200 °C. The solvents then gas off, achieving optimal braking performance and minimizing noise. This step is not necessary for sinter linings.
See BREMSEN - 'Brake in/burn in brakes'
Practical experience: I've been using SwissStop brake pads on my ST3 for the past 10,000 km or so. Together with the Motor01 spacer, the combination is silent in dry conditions. In wet conditions, they also squeak.
4. Brake Silencer
From SwissStop there is the Disc Brake Silencer, a spray that diffuses into the brake pad to reduce noise.
Practical experience: A noise reduction occurs with the original Stromer TRP pads. However, the effect does not last very long and the silencer must be reapplied.
Copper paste
S-Ped riders also report that applying copper paste to the back of the brake pads helps.
Practical experience: None. The sluggish consistency of the paste allows for vibration damping.
6. Balancing weights as vibration dampers
The following solution is a somewhat unconventional approach.
Practical experience: None
My experience with the ST3
I use the resonance damping disc at the rear according to Solution 2. and I ride organic pads from SwissStop (Disc 15E). For the front, I use resin pads from TopBrake (BD01-E+). I have bedded in the pads properly, precisely centered the brake calipers, and checked the piston retraction. With these measures, I usually ride without squealing in dry conditions. In high humidity, a short whimpering can sometimes be heard. In rainy weather, the pads always squeal.
Alternatives to the original pads
See BREMSEN - 'Spare parts....'
Topic: Braking in general and “braking correctly”
Books could be written on the subject of brakes. Just like with batteries or chains, there are many different opinions. An overview of brake pads, their advantages and disadvantages, or suitability, is provided, among others, by the website flowzone.ch or velonerd.cc.
Braking also needs to be learned, not just because of the pads, but to avoid accidents. How to brake properly is in the Article by Sheldon Brown described.