valutazioni - 3, GPA: 4
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Facilità d'uso
Make sure that your hands can reach and squeeze the brake levers comfortably. If your hands fig. 10 are too small to operate the levers comfortably, consult your dealer before riding the bike. The lever reach may be adjustable; or you may need a different brake lever design. Most brakes have some form of quick-release mechanism to allow the brake pads to clear the tire when a wheel is removed or reinstalled. When the brake quick release is in the open position, the brakes are inoperative. Ask your dealer to make sure that you understand the way the brake quick release works on your bike (see figs. 11. 12, 13 & 14) and check each time to make sure both brakes work correctly before you get on the bike. fig. 11 Brakes are designed to control your speed, not just to stop the bike. Maximum braking force for each wheel occurs at the point just before the wheel “locks up” ( stops rotating) and starts to skid. Once the tire skids, you actually lose most of your stopping force and all directional control. You need to practice slowing and stopping smoothly without locking up a wheel. The technique is called progressive brake modulation. Instead of jerking the brake lever to the position where you think you’ll generate appropriate braking force, squeeze the lever, fig. 12 progressively increasing the braking force. If you feel the wheel begin to lock up, release pressure just a little to keep the wheel rotating just short of lockup. It’s important to develop a feel for the amount of brake lever pressure required for each wheel at different speeds and on different surfaces. To better understand this, experiment a little by walking your bike and applying different amounts of pressure to each brake lever, until the wheel locks. When you apply one or both brakes, the bike begins to slow, but your body wants to fig. 13 continue at the speed at which it was going. This causes a transfer of weight to the front wheel (or, under heavy braking, around the front wheel hub, which could send you flying over the handlebars) . A wheel with more weight on it will accept greater brake pressure before lockup; a wheel with less weight will lock up with less brake pressure. So, as you apply brakes and your weight is transferred forward, you need to shift your body toward the rear of the bike, to transfer fig. 14 weight back on to the rear wheel; and at the same time, you need to both decrease rear braking and increase front braking force. This is even more important on descents, because descents shift weight forward. Two keys to effective speed control and safe stopping are controlling wheel lockup and weight transfer. This weight transfer is even more pronounced if your bike has a front suspension fork. Front suspension “dips” under braking, increasing the weight transfer ( see also Section 4.F). Practice braking weight transfer techniques where there is no or other hazards and distractions. Everything changes when you ride on loose surfaces or in wet weather. Tire adhesion is reduced, so the wheels have less cornering and braking traction and can lock up with less brake force. Moisture or dirt on the brake pads reduces their ability to grip. The way to maintain control on loose or wet surfaces is to go more slowly to begin with. WARNING: • Riding with improperly adjusted brakes or worn brake pads is dangerous and can result in serious injury or death. • Applying brakes too hard or too suddenly can lock up a wheel, which could cause you to lose control and fall. Sudden or excessive application of the front brake may pitch the rider over the handlebars, which may result in serious injury or death. • Some bicycle brakes, such as disc brakes (fig. 10) and linear-pull brakes (fig.11) , are extremely powerful. Take extra care in becoming familiar with these brakes and exercise particular care when using them. • Disc brakes can get extremely hot with extended use. Be careful not to touch a disc brake until it has had plenty of time to cool. • See the brake manufacturer’s instructions for installation, operation and care of your disk brake. If you do not have the manufacturer’s instructions, see your dealer or contact the brake manufacturer. D. Shifting Gears Your multi-speed bicycle will have a derailleur drivetrain (see 2. below) , an internal gear hub drivetrain (see 3. below) or, in some special cases, a combination of the two. WARNING: Never shift a derailleur onto the largest or the smallest sprocket if the derailleur is not shifting smoothly. The derailleur may be out of adjustment and the chain could jam, causing you to lose control and fall. 1. How a Derailleur Drivetrain Works a. Parts of the Drivetrain. If your bicycle has a derailleur drivetrain, the gear- fig. 15 changing mechanism will have: (1) a rear cassette or freewheel sprocket cluster (2) a rear derailleur (3) usually a front derailleur (4) one or two shifters fig. 16 (5) one, two or three front sprockets called chainrings b. Shifting Gears. The different types of shifters ...
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