I was in a shop the other day, looking for bargains. I didn't need anything, but when you see 3-foot-high neon-painted letters spelling out S-A-L-E in front of a bike shop, it's your duty to take a look. I rooted around in the bargain box of mostly awful stuff: leftover Day-Glo jerseys, overstuffed gel saddles, impossibly small or gunboat huge shoes. Nothing useful, so I moved on to ogle the rack of new Euro frames I can't afford.

"Hey! Check out this stem," I heard someone near the bargain box say. A guy was showing his friend a Cinelli X-A, one of the most beautiful stems ever. I'd seen it, too; it was too short for me, but a bargain at $20.

"That's sweet," his friend said. "But it's too short for you."

"Yeah. Maybe there's another one in here." I heard the guy digging through parts, but knew he'd come up empty, just as I had.

I saw them later at the register. The guy was buying the too-short stem. He'd convinced himself that it would work. It was probably nicer than what he had, and 20 bucks is nothing to pay for a piece of forged, polished art like a Cinelli stem. But what he was doing was wrong.

As much as we worship bikes, it's important to remember that the bicycle is secondary to the rider. The bike's supposed to conform to you, not the other way around. You get a lot of freedom when selecting a bike; you pick the frame material the color, the components and what you want the bike for. But when it comes to proper fit, you don't get any freedom at all.  

There's a neat little Campagnolo tool that's used for sizing head tubes, which we call the Passa/Non Passa tool here in the office. (Engineers would call it a go/no-go gauge, which is more correct but less fun.) One side is labeled Passa; the other, Non Passa. After reaming a head tube, you use this tool to see if it's sized correctly for the headset cups. If the Non-Passa side fits into the tube, it's no good. If only the Passa side fits, it's okay. It's black and white; either the thing fits or it doesn't.

How we interface with our bikes depends almost entirely on fit, and it should be treated with the same black-and-white precision of a Passa/Non Passa tool. You can't expect to perform at your best if your bike doesn't fit, any more than you can be expected to complete a daylong hike in boots that are too small.

It's easy to focus on the cost savings when you're basking in the glow of a just-found bargain. But would it be worth 20 bucks to save yourself from a sore back? Compromise anywhere else, but make sure your bike fit is Passa. It's the only way to go!