Since your bike has two brakes, one for each hand, if you want to stop as safely as possible, you need to pay attention to how you use each of them.

Conventional wisdom says to use both brakes at the same time. This is probably good advice for beginners, who have not yet learned to use their brakes skilfully, but if you don't graduate past this stage, you will never be able to stop as short safely as a cyclist who has learned to use the front brake by itself.

The fastest that you can stop any bike of normal wheelbase is to apply the front brake so hard that the rear wheel is just about to lift off the ground. In this situation, the rear wheel cannot contribute to stopping power, since it has no traction.

The rear brake is O.K. for situations where traction is poor, or for when your front tire blows, but for stopping on dry pavement, the front brake alone provides the maximum stopping power, both in theory and in practice.

If you take the time to learn to use the front brake correctly, you will be a safer cyclist.

Many cyclists shy away from using the front brake, due to fear of flying over the handlebars. This does happen, but mainly to people who have not learned to modulate the front brake.

The cyclist who relies on the rear brake for general stopping can get by until an emergency arises, and, in a panic, he or she grabs the unfamiliar front brake as well as the rear, for extra stopping power. This can cause the classic "over the bars" crash.

Jobst Brandt has a quite plausible theory that the typical "over-the-bars" crash is caused, not so much by braking too hard, but by braking hard without using the rider's arms to brace against the deceleration: The bike stops, the rider keeps going until the rider's thighs bump into the handlebars, and the bike, which is no longer supporting the weight of the rider, flips.

This cannot happen when you are using only the rear brake, because as soon as the rear wheel starts to lift, the rear wheel skids, limiting its braking force. Unfortunately, though, it takes twice as long to stop with the rear brake alone as with the front brake alone, so reliance on the rear brake is unsafe for cyclists who ever go fast. It is important to use your arms to brace yourself securely during hard braking, to prevent this. Indeed, good technique involves moving back on your saddle as far as you can comfortably go, to keep the center of gravity as far back as possible. This applies whether you are using the front, rear or both brakes. Using both brakes together can cause "fishtailing." If the rear wheel skids while braking force is also being applied to the front, the rear of the bike will tend to swing past the front, since the front is applying a greater decelerating force than the rear. Once the rear tire starts to skid, it can move sideways as easily as forward.

If you don't believe me, perhaps John Forester can convince you...see his Entry in the rec.bicycles FAQ on Front Brake Usage (Subject: 9.17). (Unfortunately, the maintainer of that site has a habit of breaking links, so you may need to go to the rec.bicycles FAQ index to find the article.) Or read John Allen's advice.

Skidding the rear wheel also wears the rear tire very quickly. A single rear-brake-only stop from 50 km/h (30 mph) with a locked rear wheel can wear the tread of a road tire right down to the fabric!

Maximum braking occurs when the front brake is applied so hard that the rear wheel is just about to lift off. At that point, the slightest amount of rear brake will cause the rear wheel to skid.

If you ride a conventional bike, the best way to master the use of your front brake is to practice in a parking lot or other safe space, applying both brakes at once, but putting most of the effort into the front brake. Keep pedalling as you brake, so that your legs will tell you immediately when the rear wheel starts to skid. Squeeze, don't grab, the brake levers, so you can sense when this happens. Practice harder and harder stops, so that you will learn the feel of stopping fast, on the edge of rear-wheel lift-off.

Test the brakes in this way whenever you are about to ride an unfamiliar bike. Some brakes are more sensitive than others, and you need to know the "feel" of the brakes.

Once you are comfortable with the front brake, also practice releasing the brakes to recover control, until this is an automatic, reflex action. At a very low speed, apply the brakes hard enough that the rear wheel skids, or just begins to lift. When it does, immediately release the brakes. Wear your helmet.

Some cyclists like to ride a fixed-gear bicycle, that is, a bicycle that does not permit coasting. When you brake hard with the front brake on a fixed gear, the drive train gives you excellent feedback about the traction at the rear wheel. (This is one of the reasons that fixed gears are favoured for winter riding.)

If you ride a fixed gear with only a front brake, your legs will tell you exactly when you are at the maximum brake capacity of the front brake. Once your fixed gear has taught you this, you will be able to stop any bicycle better, using the front brake alone.

If you find the fixed-gear concept intriguing, I have a major article on Fixed Gears for Road Use on this site, and also a page of Fixed-Gear Testimonials from happy converts.

Skilled cyclists use the front brake alone probably 95% of the time, but there are instances when the rear brake is preferred:

• Slippery surfaces. On good, dry pavement, unless leaning in a turn, it is impossible to skid the front wheel by braking. On slippery surfaces, however, it is possible. A front wheel skid almost always leads to a fall, so if there is a high risk of skidding, you're better off controlling your speed with the rear brake.
• Bumpy surfaces. On rough surfaces, your wheels may actually bounce up into the air. If there is a chance of this, don't use the front brake. If you ride into a bump while applying the front brake, the bicycle will have a harder time mounting the bump. If you apply the front brake while the wheel is airborne, it will stop, and coming down on a stopped front wheel is a Very Bad Thing.
• Front flat. If you have tire blowout or a sudden flat on the front wheel, you should use the rear brake alone to bring yourself to a safe stop. Braking a wheel that has a deflated tire can cause the tire to come off the rim, and is likely to cause a crash.
• Broken cable...or other failure of the front brake.

Generally I advise against using both brakes at the same time. There are exceptions, however:

• If the front brake is not sufficiently powerful to lift the rear wheel, the rear brake can help, but the best thing to do is to repair the front brake. Typical rim brakes lose a great deal of their effectiveness when the rims are wet, so using them both together can reduce stopping distances.
• If the front brake grabs or chatters so you can not modulate it smoothly, you must only use it lightly. Again, repair is in order.
• On long, straight mountain descents, your front brake hand may get tired, or you may be at risk of overheating a tire and blowing it out, so it is best to spread the work between both brakes. Pumping the brakes, alternating between one and the other, will briefly heat the surface of each rim more and dissipate more heat before it spreads inwards to the tires. When sharp deceleration is needed, the front brake is more effective, as usual.
• When leaning in a turn, traction is shared between braking and turning. Using both brakes together reduces the likelihood that one wheel or the other will skid and dump you. The steeper you lean, the less you can brake, so moderate your speed before a curve. When you are leaning deeply, you need to release the brakes entirely.
• Long or low bicycles, such as tandems and long-wheelbase recumbents, have their front braking limited by the possibility of skidding the front wheel, since their geometry prevents lifting the rear wheel. Such bikes can stop shortest when both brakes are applied.

  Tandem caution: when riding a tandem solo (no stoker on board) the rear brake becomes virtually useless due to lack of traction. The risk of fishtailing is particularly high if a solo tandem rider uses both brakes at once. This also applies to a lesser extent if the stoker is a small child.

There is considerable disagreement as to which brake should be connected to which lever:

• Some cyclists say it is best to have the stronger right hand (presuming a right-handed cyclist) operate the rear brake.

• Motorcycles always have the right hand control the front brake, so cyclists who are also motorcyclists often prefer this setup. A moment of confusion in an emergency situation can be deadly. The left lever on a motorcycle operates the clutch, which will not stop you!

There are also observable national trends:

• In countries where vehicles drive on the right, it is common to set the brakes up so that the front brake is operated by the left lever.

• In countries where vehicles drive on the left, it is common to set the brakes up so that the front brake is operated by the right lever. The European Union has adopted this as a standard, even though only the United Kingdom and Ireland are left-side driving countries.

The theory that seems most probable to me is that the national standards arose from a concern that the cyclist be able to make hand signals, and still be able to reach the primary brake. This logical idea is, unfortunately, accompanied by the incorrect premise that the rear brake is the primary brake.

For this reason, I set my own bikes up so that the right hand controls the front brake, which is not the norm in the U.S.

I also do this because I'm right-handed, and wish to have my more skilful hand operate the more critical brake.

On the other hand, if you have already developed a preference, it is usually best to stick with it -- or at least, choose a few weeks of riding under undemanding conditions to retrain your reflexes. In an emergency, you must act faster than you can think. If you switch between a Mac and a Windows PC, where the same keys don't make the same characters, or between a clarinet and a saxophone where they don't make the same musical notes, you know how reflexes can trip you up. If you are used to skidding the rear wheel with the rear brake, switching the brake cables can result a flight over the handlebars. If you mostly use the front brake, switching the cables can result in rear-wheel skidding and increased stopping distance. These problems are most likely when first riding an unfamiliar bike, so, again, always test the brakes with a light brake application when you first start out. 

To turn a bicycle, you must lean inward toward the direction of the turn. The faster you are going, and the sharper the turn, the more you must lean. You have no choice about this, for a given speed and turn radius, the center of gravity of the bike/rider must be moved sideways a particular amount or the bicycle will not balance.

What you do have control over is whether you lean the bicycle more than, less than, or the same amount that you lean your body, to get the overall center of gravity to the place that it has to go.

• Leaning the upper body sharply while keeping the bicycle more upright

  This approach is popular with riders who are afraid of striking a pedal on the road. This is a particular concern for riders of fixed-gear bicycles, since they cannot coast through corners.

  This technique is also recommended by some racers and coaches as offering the possibility of recovering from a skid, but I don't believe it.

• Leaning the upper body and the bicycle together, keeping them in line as when riding straight.

  This technique has the advantage of keeping the steering axis, tire contact patches and center of gravity all in the same plane. This preserves the proper handling characteristics of the bicycle, and makes a skid less likely. You can verify this yourself by performing an experiment suggested by Jobst Brandt:

  "Some riders believe that sticking out their knee or leaning their body away from the bike, improves cornering. Sticking out a knee is the same thing that riders without cleats do when they stick out a foot in dirt track motorcycle fashion. It is a useless but reassuring gesture that, on uneven roads, actually works against you. Any body weight that is not centered over the bicycle (leaning the bike or sticking out a knee) puts a side load on the bicycle, and side loads cause steering motions if the road is not smooth. Getting weight off the saddle is also made more difficult by such manoeuvres.

  "To verify this, ride down a straight but rough road standing on one pedal with the bike slanted, and note how the bike follows an erratic line. In contrast, if you ride centered on the bike you can ride no-hands perfectly straight over rough road. When you lean off the bike you cannot ride a smooth line over road irregularities, especially in curves. For best control, stay centered over your bike."