Clamping down on stem mismatches

There I was, naively thinking late night working had ended with my University job. That was before bicycles became my profession. And before I'd fully investigated the minutiae of the stem/handlebar interface.

It's a domain where 10ths of a millimetre divide security from danger. The integrity of a bicycle stem is no less critical to the cyclist's safety than the brakes. Try applying the brakes while you and the handlebar are diving for the tarmac. Yet whereas dodgy brake set-up is fairly visible and testable, a 26.4mm handlebar lurking in a 26mm stem clamp may be far from obvious - until the stress points inflicted on the bar suddenly make it an in-your-face problem, as it were.

Cinelli 1A stems in my workshop, waiting for handlebars of 26.4mm diameter. There's a bar for us! 

After re-checking online with Sheldon Brown and Hilary Stone, among others, I knew my Cinelli handlebar was a perfect match for my 26.4mm Cinelli 1A stem. Yet it had felt tight as I threaded it on. Then I had an uneasy sense of light coming through the stem clamp around the handlebar. When I looked closer, sure enough, there was a wafer-thin crescent of light round part of the circumference. It was as if the stem clamp was too small for the handlebar diameter.

Off with the stem again. Out with the Vernier gauge. Everything seemed normal. Re-assemble. Still that sliver of light. Back to the internet, and an hour or so trawling through forums and product descriptions. Had I got the recent re-issue of the Cinelli 1A stem, which has a 26.0mm clamp diameter? No, the Vernier gauge said it must be an original 26.4mm one. Why don't stem and handlebar manufacturers engrave the diameters onto the equipment? It would save many sleepless hours! And why were these wretched bars behaving as if they were 26.7mm diameter?

Out with the laptop. Frantic Googling. Finally something on a forum made the penny drop. Maybe the bars had been distorted? Maybe they weren't circular, but oval in section? Out with the Vernier gauge. Sure enough, they would have done credit to an Easter egg. On one axis the gauge showed 26.0mm. Perpendicular to that axis the reading was 26.5mm. The bars were ovalised to the tune of half a millimeter. Not plain to see, like a slack brake cable or a worn pad, but that half millimeter was more dangerous than either.

The impeccable Cinelli 1A long stem atop the unintentionally ovalised Cinelli bars, destined for the recycling bin.

This is professional bicycle refurbishment. Cytech skills extended with esoteric knowledge, exhaustive information gathering.and obsessive triple-checking. I want my customers to be not just proud to ride classic. I want them safe as well.