Bicycles Asked by leftaroundabout on January 30, 2021
It’s really windy today, and the rain tarpaulin makes a good sail for the bike I’m storing on my balcony.
Short of actually mooring the bike to something, I decided to just fasten the tarp a bit tauter and tying down the brake levers to stop the bike rolling back and forth.
With mechanical brakes I would have no concerns about this, but now I’m wondering: are hydraulic brakes also ok with it? After all, they’re not static but kind of “self-adjusting”, and the pistons move out over time as the pads wear down.
Does this cause any problems if the pressure is kept up for not just minutes as it might in a normal descent, but days on end?
@AnAnt remarked that car handbrakes are routinely used in fixed position when the car is parked. I thought about that myself, but I don’t think it’s a really relevant point because a) most parking brakes are apparently not hydraulic, but mechanical or electromechanical and completely separate from the main brakes, and b) the fact that it’s possible to design hydraulic brakes to be pressurised continuously does not imply that all hydraulic brakes are able to do this.
(So, if anything, cars suggest that it’s not a good idea to keep bike brakes locked.)
The self-adjustment is a valid concern. The way that's implemented is through the drag and elasticity of the piston seals. Holding those seals in the extended position for long periods could lead to gradual elastic deformation of the piston seals (reducing their ability to retract). It could also result in the seals gradually creeping back down the piston toward their relaxed state. The latter would cause the pads to drag, but is easily remedied by removing the wheel and forcing the pistons back just as you would do when changing pads. But seal deformation could only be remedied by a caliper rebuild.
We can only speculate here as I don't know of any testing that's been done for this use case. It's certainly outside the scope of the requirements the caliper designers worked to. Doing this for days or even a couple weeks is unlikely to cause any problems, but longer term storage this way (an entire winter) is definitely questionable. A zip tie around a spoke and the chainstay or fork leg will be equally effective and significantly lower risk.
Answered by Kopsis on January 30, 2021
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