Cycling: Follow Up On Brake Issue

My Burnt Orange Gary Fisher Cobia

Back in August, I wrote a post about the hydraulic brake system* on my Gary Fisher mountain bike and how the brakes were prone to locking up during summer rides.  In said post, I mentioned that the mechanic with whom I spoke at the Bicycle Sport Shop was of the opinion that the fluid in the lines for my hydraulic brake system was expanding because of the summer heat (which, you will recall, was often in excess of 105 degrees during August 2011).  Considering that the brakes would unlock when placed in the air conditioning of my apartment or another building, I assumed that the mechanic was probably right but that I'd have to wait until after the summer to test things out.  I put the mountain bike into my storage unit and focused on my road bike (roads can be ridden at night, trails cannot).

I've recently pulled my mountain bike out of storage and begun to ride it around central Austin.  Within the past month, I've also taken it onto the Shoal Creek trail and into the Barton Creek Greenbelt.  There have been no issues with the brakes locking up while riding in pleasant temperatures.  It seems logical that the problem with the brakes was caused by the heat.  What interests me now is the temperature at which the brake system becomes subject to failure.


*My mountain bike is a 2010 model Gary Fisher (which is made by Trek) Cobia that has on it the stock ProMax hydraulic brakes and ProMax Hornet brake levers.

Cycling: Hydraulic Brakes + 105 Degree Heat = No Bueno

photo [by WDF's iPhone]: my heat impaired bike on the roof of my heat disliking VW Passat



Right now, as I write this post, I would like to be riding my mountain bike in the Barton Creek Greenbelt.  Unfortunately, it's too hot.  And, when I say "too hot," I don't just mean that I'm staying indoors to avoid a heat related injury.  No, it is apparently too hot for my bike's brakes to function properly.

I have a 2010 model Gary Fisher Cobia equipped with the stock ProMax hydraulic disc brakes and ProMax Hornet brake levers.  Apparently, the rear brake on said bike does not like the heat.  Since June, I have experienced several incidents wherein the rear brake has spontaneously engaged and locked up.

After consulting a couple of bike mechanics and having the brakes bled, I figured the problem would have been solved.  Unfortunately, the problem happened again last Sunday while the gf and I were attempting to ride over to Zilker Park.  I blamed the heat, and had this suspicion confirmed by a mechanic at the Bicycle Sport Shop.  His prognosis was that my bike's hydraulic fluid is heating up and expanding (both from the rotors/disks getting too hot as well as the air temperature cooking the fluid in the lines).  He mentioned that bike owners with varying levels of hydraulic brake systems (including high end systems like Shimano Deore XTR) have been coming into the shop with the same problem I've been experiencing.  He mentioned this right before I asked is buying a better set of hydraulic brakes would solve the problem.   As though the bike wanted to corroborate his story, the brakes began to function normally as the bike sat in the store's air conditioning; however, the rear brakes seized up merely from riding home on my roof rack and being exposed to the heat outside.

This is a fairly annoying problem for a mountain bike braking system to have.  For Summer 2012 I will be in search of a hydraulic system which can stand up to the heat as:

1. Austin can be insanely hot in the summer; and, 
2. You can't ride trails at night to take advantage of relatively cooler temps; and, 
3. Hydraulic disc brakes have excellent stopping power.

If you have a mountain bike with hydraulic disc brakes and they have been misbehaving this summer, it's quite possible that the heat is to blame.  If I find a braking system better suited for summer in Austin, I'll be sure to share on this blog.

On a more retro note: I'm also planning to have my old Trek 8000* refurbished.  It is equipped with some very old school wire pulled cantilever brakes which should be impervious to the heat.   That will be a good set-up to have, as I like for me to be the thing on my bike with the least heat tolerance.  

*Old, as in from 1991.  It has an incredible white-with-black splatter paint job which pegs it as belonging to a very tasteless year.