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Permalink Reply by Dirke on September 15, 2020 at 4:56am

Elwood, 

Remember, Google is your friend. 

But I remember having this question once, and at the time, found the question answered by Lennard Zinn.  I'll save you the trouble of a link.  FWIW, I've stored 2 bikes vertically with hydros for over 7 years with no problems.  I've bled the brakes several times over that timespan but that's more a reality of use that most manufacturers recommend annual bleeding.  If you have the ceiling height, still better to stagger the front wheel hangers and store them all with handlebars up.

Dear Lennard,
I always wondered about hanging my mountain bikes vertically too but not really worried about the shocks but about the hydraulic brakes and what that might do to the lines. Is it fine?
Paul

Dear Paul,
That’s a good question. If the bike is hanging vertically with the front wheel up, there would be no problem, because any air bubbles would gravitate toward the lever, which would be where you’d want them. But how about with the rear wheel up?

Some systems are designed to have all air evacuated completely from the entire closes system when bled properly, and with such a system, it would be irrelevant if it’s hanging upside down.

More commonly, though, many modern systems do have air above the fluid in the lever’s reservoir, and as long as there is sufficient fluid in the system, there is no problem. If air gets in the system while in use, it rises up to the lever, out through the metering hole in the master cylinder, and up to the reservoir, where it sits above the fluid and causes no problem. With such a system, if you crash arse-over-teakettle, you can find that you have no braking for a while once you get going again, because air from above the fluid in the reservoir passed through the metering hole ahead of the piston and into the brake lines.

The metering hole is ahead of the piston so that fluid can flow down from the reservoir into the master cylinder until the piston is pushed in far enough that it closes off the hole, at which point it can now build pressure through the system and push the pistons in the slave cylinders to force the pads against the rotor. It would seem that hanging the bike upside down (rear wheel up) could conceivably create the geometry such that the air bubble in the reservoir is lined up with the metering hole, in which case air could bubble up into the brake lines.

(For those to whom this is new, air in hydraulic brake lines, whether on your bike or in your car, is a bad thing, because air, unlike liquid, is compressible. So when you pull your brake lever or stomp down on your brake pedal, if there is air in the brake lines, the pressure can simply compress the air, rather than pushing the brake pads, and you won’t be able to stop.)

In practice, I’ve hung a lot of bikes with Shimano and SRAM hydraulic brakes (both of which have reservoirs in the lever that can have air above the liquid) upside down without noticing a loss in braking performance afterward. I would have to guess that normally the angle of the reservoir when upside down is such that the air bubble does not come in contact with the tiny metering hole because of the angle of the lever on the handlebar in three dimensions relative to horizontal. But if air were indeed to travel into the cylinder and into the brake lines, pumping the lever a few times once the bike was again upright should squeeze those bubbles, and, with the help of gravity, move them rapidly up to the master cylinder and up through the metering hole and out into the reservoir, at which point the brake would perform correctly again. I doubt that, in a static situation like hanging a bike, a bubble could make its way all of the way into one of the wheel (slave) cylinders, due to the various bends in the hydraulic tubes.

Air bubbles generally are unimpeded coming back up to the master cylinder under repeated braking unless they get stuck in corners of a slave cylinder.

So, in answer to your question, hanging the bike by the front wheel will most certainly not compromise your hydraulic braking, but hanging it by the rear wheel could, although I suspect that it is unlikely. And in most cases, the problem should clear itself up again soon with some vigorous pumping of the levers.
Lennard

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Permalink Reply by Sharon O on September 16, 2020 at 3:37am

Thanks for this info. I needed that.

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Permalink Reply by ketoguychicago on September 17, 2020 at 12:36pm

Is this for overnight/weekly storage, or for longer term with the 5 bikes? (I'm guessing it's not just for overnight if we're dealing with five of them)   Here's why I bring that up - - -  I'd read that if for longer term, one trick is to unhook/unfasten the brake handle/reservoir from the handlebars, and then elevate that assemble up to the brake rotor level to avoid the whole air thing from happening.  I'm not sure if that's easy to do on your ride or not, but it may be worth a shot.  

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