Sitting on the seat, you should be able to touch the ground with your toes, but not your whole foot. If you can stand flat-footed while seated, raise your seat.

While seated, put one foot on a pedal and extend that leg down: Your knee should be slightly bent — at a 10-degree angle. A fully locked knee can cause injury and bending it much more than 10 degrees reduces efficiency.

Straddling your cycle while standing flat-footed, you should have about an inch of clearance between your highly personal bodily property and the frame for a road bike and about two inches for a mountain bike.

When pedaling — seated or standing — your knees should not crowd the handlebars. If you have ever whacked a knee on a gear shifter, you know the reasoning behind this rule.

How far forward you lean to reach your handlebars depends on how aggressively you want to ride. A more-forward lean is more aerodynamic but may be uncomfortable for many recreational cyclists, McDonald said. "Comfort" bikes of recent vintage often leave you nearly vertical. "People should do whatever is comfortable," regarding forward lean, he said.

A super-padded seat may feel great in the shop, but it will require you to work harder because some of your pedaling energy will be transferred to the cushy seat, not the pedals. But the rock-hard seats favored by racers are too severe for most weekenders, so shoot for something in between — like the gel seats that have gained popularity in recent years. Wearing padded bike shorts also helps reduce saddle soreness.

Your bike helmet should fit snugly but should not pinch the skin; the front of the helmet should rest two finger-widths above your eyebrows. "Many people wear their helmets too far back," McDonald said. "Odds are, if you come off the bike you will fall forward." Replace a helmet after just one crash, even if you cannot see obvious damage.

Ensure correct tire pressure and check your brakes before you ride.