MTB Disc Heat?

[KingCrimson]

I've got dinko 6 inch Avid BB5's on my 29er, which gives plenty of spoke leverage acting on the disc, along with a weight of about 200 pounds between the bike and I.

Anyway, riding at Baldy on Saturday on the fireroad, I was practicing rear brake technique, as I don't have many miles (about 40 tops, most of it not involving any hard braking) and the only time I have needed to stop hard was on pavement, and obviously I only used the front brake there. I descended about 1200 feet over 3 miles, riding the rear most of the time. When I hit the pavement at the end of the trail, and prepared myself for the mile long climb to the bottom of the ski lifts (the fire road spits you out way below the lifts) I checked out my brake, which had been blued!

Obviously, I had gotten the sucker pretty damn hot and under the right conditions to oxidize it in such a manner. I have cable brakes so I didn't feel any fade or sponginess, and there was no stink.

Conveniently, the rear rotor doesn't have any light surface rust where I blued it, whereas the front does.

Has anyone had this happen, or at least gotten brakes that hot?

[Fleaman]

My bike's disks get so hot I can smell them when riding. they are hayes 9's but they still seem to work ok. No problems with the heat marks.

Even when going downhill you should still use your front brakes. Your front brake is much more effective than the rear. just watch the trail or road and be prepared to let off the font if you are going to hit a dip or other obstacles.

[KingCrimson]

Well, before the 29er, I had the terminal rear brake technique, but then I jumped into discs and obviously the brakes are so powerful the rear only skids.

So I've gotten very good downhill on the front brakes, I even recovered from a front wheel skid (and pooped myself in the process!)

I hadn't used the rear brakes much at all, so I decided to do a run exclusively on them to get a feel for skids and handling.

Any clue why they don't use discs on road bikes?

Is it because the spokes can't take the leverage? Weight? Or are caliper brakes better when they're clean?

[D.T.]

I checked out my brake, which had been blued!

Obviously, I had gotten the sucker pretty damn hot and under the right conditions to oxidize it in such a manner. I have cable brakes so I didn't feel any fade or sponginess, and there was no stink.

Take some fine sandpaper or emery cloth and remove the blueing. The oxide will decrease the effectiveness of your rear brake and it can gum-up your pads.

obviously the brakes are so powerful the rear only skids.

The rear is skidding because your weight is too far forward. Work on getting your weight back and really feeling what the lever/brake are doing. The brake feel will change once they are broken in.

[KingCrimson]

Ya know, I just found out my saddle was leaned forward, and every time I would brake, I would scoot forwards, even if I resist properly. I've leaned it back to flat, but I haven't ridden yet, it'll probably be the solution.

Thanks

[Derf]

Well, before the 29er, I had the terminal rear brake technique, but then I jumped into discs and obviously the brakes are so powerful the rear only skids.

So I've gotten very good downhill on the front brakes, I even recovered from a front wheel skid (and pooped myself in the process!)

I hadn't used the rear brakes much at all, so I decided to do a run exclusively on them to get a feel for skids and handling.

Any clue why they don't use discs on road bikes?

Is it because the spokes can't take the leverage? Weight? Or are caliper brakes better when they're clean?

In a normal braking situation (on and off road), the front brakes does 70% of the work. I can't confirm this number, but I know it's something like that. I too had some front wheel skid, and yes, it can be scary.

As for road bikes, I think it is a weight issue as disk brakes are heavier than regular brakes. You see them on some touring bikes and some hybrids now too. The UCI banned the use of disk brakes in Cyclocross. I'm in the process of shopping for a new commuting bike (performance hybrid) and I'm thinking about getting one with disk brakes, but I don't know if it is worth the extra weight and money for city riding.

[KingCrimson]

I did some searching on the subject, and there are indeed people who install discs on commuter bikes.

I think something such as a brake doesn't weigh enough to be cause for concern..a 160mm rotor doesn't weigh much at all, and calipers, if for cable discs are also relatively light. Plus, on a commuter, you only need a front disc.

According to Sheldon Brown, 95 percent of your braking force is on the front. Under hard stops, there is so much force in the momentum that the rear tire will lift up (to a controllable extent) and I won't be aware until I come to a complete stop and the rear plunks down.