Geometry Lesson

While I wasn't riding over the winter I was considering buying a new touring bike that could carry panniers and camping stuff, maybe one with straight handlebars that would be easier on my arthritic thumbs. My Cannondale is still a fun road bike, but I've had a few panicky moments trying to brake on a fast downhill on wet pavement wearing thick gloves, when I could barely grip the brake levers. Besides I probably voided the warranty twelve times over during the summer I was travelling between Ferndale and Friday Harbor with a week's worth of luggage on board. But with all the uncertainty caused by the COVID situation, I put that decision aside.

Instead I bought a new Terry saddle for the Cannondale, and switched the old-but-still-good-one over to my old but ever-reliable K2 hybrid, thinking I could take some experimental camping trips on the old bike when the weather gets better. As I began riding more in late March, switching between the two bikes, I started having pain in my right knee, usually a symptom that the seat is too low.* So I experimented with raising the seats by a millimeter or two at a time until the twinges went away. During a rainy spell I rested my knee and treated it with a cold pack, and once I was sure I'd found the sweet spot(s), I marked the seatposts with fingernail polish.

Just this morning, though, as I was looking at the two bikes lined up and leaning against the living room wall, I noticed that the top of the saddle on the Cannondale is actually a good half-inch lower than the one on the K2, though both have been perfectly comfortable to ride. For a moment I thought the seat posts had somehow slipped, and I'd have to start over with trial-and-error raising and lowering to make the two bikes equal and pain-free.

But the seat posts were still at the marks. After puzzling over the geometry for a moment, I looked closer and found that the bottom bracket on the Cannondale is about a half-inch lower than the K2, and the pedal came closer to the ground, making up the difference in the seat height up top.

It's the distance between the pedal and the saddle that matters, not the distance from the saddle to the ground, and standover height is just a rough measure. The current best guide is to sit on the seat and place your heel on the pedal to get a better idea of saddle placement and bike size.

They didn't tell us that at Bicycle Mechanic School.

*If the seat is too high you'll have pain in the tendons at the back of the knee, among other things, I have learned through experience. They didn't teach that at Bicycle Mechanic School, either