The Golden Wrench

A blog about bicycle repair and maintenance by the mechanics at Freewheel Bike.

Monday, July 26, 2010

We Don't Mean to Nag, But...

Cue the creepy, minor-key music: you may be killing your suspension fork with your JRA behavior. Now, I speak (or type, more properly) as one who forsook suspension for several years in favor of a rigid carbon fork on my mountain bike. Incidentally, my wrists declared that decision to be unwise this spring with some spectacular flashes of pain, but those seem to have resolved since I restored my relationship with the old Manitou Skareb I had been using for spider habitat under my workbench.

What never resolves, however, is the subtle effects of riding dusty trails all summer.

Here in Minnesota, it's a lot like training camp for high desert racing. The trails are either closed or dusty, so we spend a lot of time drifting corners that are made of powdered adobe. Although the dust at, say, Theo Wirth is about the consistency of baby powder, each of those little particles of dust looks like a tiny porcupine under a microscope. And to those particles, the anodizing on your fork uppers looks like an axe handle. If you know anything about porcupines, you probably know that their favorite food (after corned beef and goulash) is axe handles, about which they frequently rhapsodize in grunts and squeaks. So then, while you're roosting through powdered terrain at Theo, those clouds of porcupine-shaped dust particles are attracted to your fork uppers by an innate sense of hunger that they can't control.

They begin by chewing away at your upper seals, where oil from the semi-bath reservoir found in all major fork systems gathers dust at an alarming rate, turning it into that brown goop we affectionately call "brown goop." Not only is the brown goop unsightly, it is abrasive: do not brush your teeth with it! After the dust particles breach the upper seals, they mosey or saunter down into the oil ring and the upper bushings where the real fun begins. It's like a microscopic axe handle buffet down there! When they've been at it for a few months, it looks like this:

Axe Handle


Where the Porcupines Hang Out

Oh No, More Porcupines

As you can see, there are lots of nooks and crannies where the porcupines can hide to chew on your fork uppers. Fork manufacturers recommend having the porcupines evicted every forty hours of riding, but if you get it done once a season, you'll save a lot of wear and tear on your equipment. Believe it or not, those upper seals, that foam ring, and even the damping oil itself are all things that wear out and get yicky. Additionally, there are o-rings inside that wear down over time, allowing oil and air to go where they ain't sposta. So it isn't just porcupines chewing axe handles, it's also saber-toothed tree mackerels committing larceny with respect to your o-rings. That's frowned upon by more than one publicly-funded advocacy group!