Bicycle Helmet
In choosing a helmet, only those that meet helmet safety standards of either the American National Standards Institute (ANSI) or the Snell Memorial Foundation should be worn. Proper fit is crucial to guaranteeing proper function of the helmet. The following are suggestions:1
- The helmet should touch the head at the forehead, back, sides, and crown.
- The helmet must cover the forehead.
- Pick a size that seems appropriate. If there is a space between the helmet and your head add pads to fill the gap; if there is still a gap, pick the next size down.
- Adjust the strap with the helmet covering the forehead over the eyebrows. The strap should connect just below and in front of the ear with no slack apparent. The chin strap should feel tight when opening your mouth.
- Attempt to pull the helmet off from the front and back.
- If the helmet tips off, add padding, if the helmet still tips off, get the next size down.
Type of Bicycle and Frame Size
The recommended size of a bike frame is a reflection of the type of riding. Racing bikes and mountain bikes are used on different surfaces, and ridden differently. The following are some general recommendations:2
- With a racing bicycle, there should be a 1-2 inch clearance between the frame (top tube) and the crotch. With the proper saddle height established (see below), 4-5 inches of seat post should be showing. If the frame is too short, the seat will ride above a marked extension line on the post; this will cause the seat to be unstable.
- With a mountain bike, there should be 3 to 6 inches clearance between the top tube and the crotch.
Seat (Saddle) Height
There are several formulas recommended. The result of each formula does not necessarily result in the same seat height. Consider one of the following:
- 100 percent of the greater trochanter height or 106-109 percent of the pubic symphysis height (measured from the ground while standing barefoot) or multiply inseam (while wearing bicycle shoes) by 1.09.
- With the heel on the pedal in the six o'clock position (bicycle stationary), raise or lower the seat so that the leg is almost straight (2-5 degrees flexion).
- With the ball of the foot on the pedal in the six o clock position, the knee should be flexed between 25-30 degrees.
Changes in seat height should not exceed more than .25 inches at a time. The seat should tilt into slight extension or be level. Some women prefer a slight tilt forward to take pressure off of the perianal area.
Fore and Aft Seat Position
It is recommended to adjust the forward and backward position of the seat until a perpendicular line can be drawn between the front of the patella and the ground with the pedals cranks horizontal to the ground (pedals in the three and nine o'clock position). This is referred to as the neutral knee position.
Upper Body Position
There are various adjustments that affect upper body position and the amount of weight distributed onto the hands.
- The handlebar stem should be adjusted so that the handlebars (top bar) on a racing bike are 1 to 2 inches below the top of the seat for a short cyclist; for a taller cyclist, this may increase to as much as 3 to 4 inches.
- The "reach" is the distance between the front of the seat and the front bar off of which the handlebars extend. A proper length is when the cyclist can touch the tip of the elbow to the seat and touch the front bar with outstretched fingers
- Seated on the bike, looking forward, and bent forward with hands on drops (lower part of handlebars), a plumbline should be able to drop from the tip of the nose through the center of the stem
- While riding, elbows and knee should be separated by 1-2 inches at their closest position.
- Handlebars should be level or angled down toward the rear hub with a racing bike.
- The width of the bars should be the same as shoulder width (AC joint to AC joint).
- The width of mountain bikes bars vary from 21 to 24 inches. The shorter bars are more efficient for quick turning and allow less risky navigation through paths with trees or boulders.
- With clip-ons or aerobars, the cyclist should (over several weeks) gradually bring the arm rest pads in until eventually the forearms are almost touching. Ride with a straight back, eliminating the hump often seen. The rider may need to lower the chin between the arm gap (interestingly this position does not seem to affect breathing).
Next month a discussion of overuse injuries and bicycle adjustments that may help prevent recurrence will be presented.
References
- Ellis TH, Streight D, Mellion MB. Bicycle safety equipment. Clin Sports Med. 1994;13:75-98.
- Burke EN. Proper fit of the bicycle. Clin Sports Med. 1994:13;1-14.
Thomas Souza, DC, DACBSP
San Jose, California