Wednesday, August 13, 2008

When less is more...

A long time ago, I learned that brake spring tension should be just enough so the arms return to open. The feel at the brake lever should be snappy, but not tight. Squeezing a brake lever shouldn't be like squeezing one of those spring loaded hand grippy things that all high school kids used to have. Squeezing that thing gets tiring after a while. Squeezing a brake lever with high spring tension does the same thing after a long ride. "Boy, that downhill sure pumped my arms." No, the high spring tension pumped your arms.

While this doesn't apply to hydraulic disc brakes, it certain does to a lot of the brakes I've been working on recently. I've had lots of v-brakes with the spring tension cranked all the way down and several rollercams with super high spring tension too. Backing off on spring tension produces a brake that instantly feels better. It's so easy to reduce the spring tension that I almost feel guilty about charging labor for this type of brake adjustment - almost.

On the flip-side of less is more, sometimes more is more...better. I've also had several bikes in for tune-ups this week that have, well, weak feeling v-brakes. Everything seems right. Spring tension is good. The cable goes through the housing fairly friction-free. But the brakes feel like poo when squeezing the lever. In a case like this, the first thing I do is check the orientation of the spacers on the brake pads. If the thin spacer is on the inside and the top of the arms are getting close to touching, chances are the arms are over-rotating. A v-brake gets its power as the arms close and become parallel. If the arms close to much with the tops closer than the bottom - icky feeling and lost power. This bike came in with not much brake pad left and the thin washer on the inside. New pads and correct pad orientation and it's like a brand new brake.

The bike above probably has the arms a little too wide at the top, but it's better than too narrow. In this bike's case the reason why the tops are a wee bit wide is because it has "S" bend seat stays. The brake boss is positioned at the narrowest part of the seat stay and the spacing between the bosses is just a little bit too narrow. Sure "S" bend stays look cool, but they tend to position the bosses a little on the narrow side. Exact spacing is also a function of rim width, but most frame designers probably just ball-park the dimension (I do) so brakes will work with a variety of rim widths (hooray for disc brakes !?!).

Anywhoo....lighten up on the spring tension!

(What's playing: The Blasters Border Radio)


bmw brake rotors said...

The first step is to set up your brake levers. Start by loosening the clamp, and then align them so that they match the angle of your arms when you’re riding. Once the angle is set, tighten the clamp. If you have smaller hands and your levers are hard to reach, you can set them closer by tightening the reach adjustment screw on most levers.
Now check your brake arm tension. The brake arms should have good spring tension, which makes them release when you let go of the brake lever. If there isn’t much tension, you may have to increase it on both sides. Undo both bolts one at a time, but don’t remove them completely.

You’ll notice a small piece of metal poking out the backside of the brake. This is the spring, and it slides into one of three holes on your frame or fork. Most brakes work fine in the middle hole. To increase your brake tension, move the spring into the top hole. To decrease the brake tension, move the spring into the bottom hole. Then tighten the mounting bolt. am i right?


blackmountaincycles said...

Well, you're not wrong. There's a little more to it than that. For a complete brake install adjustment, this is a good source.

Anonymous said...

The bit about spring tension is sooo true! I cry a little when I come across a brake caliper with excessive return-spring tension; worse; no return-spring tension adjustment at all-I'm looking at you non-Avid mechanical disk brake makers!