Even on my high racer I set the lights off because my wheels aluminum sets them off if I get it right over the line in the road that shows where they have buried the wire in the asphalt. Incidentally the bottom bracket on that baby is about 3 feet off the ground. So the aluminum rims are the only thing that it can be sensing unless it is the rear dropouts but those are pretty high too.

Incidentally I found a 21 pound 105 equiped road bike with rack eyelets ideal for my 18 mile (one way) commute and then my 24 mile commute when I moved. The cool benefit was I got to train for centuries and stuff every time I commuted because it was the same bike I used for both puposes. I logged about 13000 commuting miles that way without a problem over the last few years. I eventually switched to a bent as my back just wouldn't let me put out enough power on a traditional road bike due to an old injury that only acted up when I was pushing hard.