Hydraulic brakes better for long descents?
April 21, 2011 9:52 AM   Subscribe

I am looking for a cross-country bike for use in a mountain-y watershed area. I am not a skilled or graceful descender, and there is going to be a lot of descending. Bike shop guy, who I have known for a while and trust, says hydraulic discs are the way to go because of how they handle heat. Is this really a factor I should account for?

He said that the fluid will act as something of a heat sink, while cables will not. Would that buy me more/better heavy-handed braking on miles of downhill?

I have not done any serious off-road riding since the mid 1990s, so I need clues.
posted by everichon to Sports, Hobbies, & Recreation (13 answers total) 1 user marked this as a favorite
As I understand it, and please correct me if I'm wrong:

Hydraulic discs can FAIL under high heat. If you ride your brakes down a steep hill, you can boil the brake fluid.
Mechanical disc brakes won't suffer from that.

...but my informal survey says that almost everyone rides hydraulics, they're very good, and it really doesn't sound like you'll be doing the kind of riding that can cause that. They're fantastically strong, responsive brakes, and you'll be able to stop on a dime... once you remember how to do that without flying over your handle bars. ;)
posted by Stagger Lee at 10:06 AM on April 21, 2011

This is not necessarily the case, and I have seen several people go over the handle bars when their disks lock or fail for a variety of reasons. The hydraulic fluid is not involved in heat dissipation, nor are the cables. I personally can't stand disk brakes of any type, so I might not be the best person to ask.

Do you have the mechanical ability to fix a hydraulic system in the middle of nowhere using a few tools? If not, you could be carrying your bike several miles when/if it breaks. It sounds like you are dealing with somewhat of a salesman here and if hydraulic brakes have any advantage, it is in the price markup at the bike shop.
posted by I_am_jesus at 10:08 AM on April 21, 2011

Yea, the fluid actuates the brake calipers, nothing more. It has nothing to do with heat disapation. Disc breaks can overheat and warp/break the rotors on a sustained downhill, but the solution is simply to not ride the brake lever all the way down, let off a bit a let the brake cool. It's fun to go fast anyway. Also, other types of brakes using the rim surface can degrade the rim strength or even cause a rim break over time, so there's no such thing as a perfect downhill brake. Downhill is hard on bikes, all types of brakes will eventually fail if overworked or not maintained.
posted by T.D. Strange at 10:26 AM on April 21, 2011

I agree with Stagger Lee. In theory, hydraulics are prone to fail under high heat; in practice, I don't think that happens. The whole "heat-sink" hypothesis is ill-informed hand-waving.

I like disc brakes. I think hydraulics are probably a needless complication. There have been some very bad mechanical, ie cable-actuated, disc brakes out there (coughHayesCough), but Avid BB7s are just fine.
posted by adamrice at 10:48 AM on April 21, 2011

I'm racing a race this year, with 100's of miles between any sort of mechanical help available. I'm running disc brakes.

Just pump the brakes instead of holding them continuously and you won't overheat them. The fluid will cool off fairly quickly (I was told almost instantaneously). If you somehow break one brake, well that's why you've got two and that should get you home.
posted by alex_skazat at 10:51 AM on April 21, 2011 [2 favorites]

Response by poster: Ok, this is good. I am sold on discs in general, that's a non-issue. The heat dissipation assertion was just plausible enough to make me wonder. Thanks, all!
posted by everichon at 10:55 AM on April 21, 2011

It sounds like it's settled, but your bike shop guy is wrong. If you've ever heard of "brake fade" in cars, where the brake pedal becomes spongy under hard use, that's caused by heat buildup and bubbling in the brake fluid, and heat dissipation should not (as others have already said) be done by the fluid at all.

You actually want heat to be kept as far away from the brake fluid as possible.
posted by Dipsomaniac at 11:54 AM on April 21, 2011

Response by poster: It's not settled, in that I have not purchased a bike yet, but now I know that the heat dissipation thing is not a criterion by which to evaluate bikes.

I don't think hydro vs. mech is going to be a deal breaker or maker for me, but mech sounds a little less complicated.
posted by everichon at 12:20 PM on April 21, 2011

I love my Avid BB7's. I chose cable-actuated discs because I think it's perverse to have to deal with hydraulic fluids on a bicycle. Such religious issues aside, I've always loved the feel, modulation, and power of my cable disc brakes. On the few occasions I've tried hydraulics, they felt unpleasantly light-switchy (i.e., on/off).

Which is not to say that you should ride what I like. Rather, I think you should be sure to ride both kinds and see what you like. The two types feel a lot different.
posted by richyoung at 3:23 PM on April 21, 2011

Best answer: I've been riding hydraulic disc brakes in the mountains since they were introduced.

Disc brakes operate more efficiently than rim brakes, therefore you use them less, therefore there is less chance of over heating. I've never seen anybody overheat a disc brake. Sometimes the power fades a bit with heat up but that's all. Take a break, look at the view, smoke a bowl or something while they cool off.

Also, I've never seen any catastrophe or wipe-out that necessitated trail maintenance... hydro discs are very reliable.

Lastly, front or full suspension, discs will make the suspension on your bike more effective. No data here other than hundreds of miles ridden on discs and rim brakes, but I suspect that removing the braking mechanism from the close proximity to the suspension that you get with rim brakes makes those systems work more independently.
posted by No Shmoobles at 5:19 PM on April 21, 2011 [1 favorite]

Hydraulic disc-brakes are the cat's particulars. Nothing else gives you that level of control. I wouldn't ride with anything else, off-road. Haven't had any on-trail disc-brake failure after the first couple of years, when there were cable quality and routing issues we needed to learn. The sport has had that dialed in really well since about the second year though, and pretty much everyone I've ridden with for the last 15 years run hydros. Sure, we need to bleed them every 6 months or so, but it's really not a big deal.
posted by PareidoliaticBoy at 6:07 PM on April 21, 2011

Pretty much all medium to high end downhill and freeride bikes use hydraulic disc brakes. Mechanical disc brakes (the Avid BB7) are found on XC bikes. Your bike shop guy is correct.
posted by thewalrus at 6:53 PM on April 21, 2011

Response by poster: Followup: went with a Felt Q620. Hydraulic brakes.
posted by everichon at 11:03 AM on April 28, 2011

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