Keeping to the left of the...
Keeping to the left of the lane in town will give you a bit of breathing room if a car should pull out of a driveway or street in front of you.
One aspect of street riding we see many riders struggle with is where they position themselves in the lane of traffic. Where you place yourself on the racetrack is for the most part more easily understood, as the requirements are solely performance-oriented. Throw in the unique features of, for example, a road clinging to the side of a mountain, as well as the unexpected characteristics of a public road, and the optimum lane position could be totally different from what you would expect.
In general, the center of any traffic lane is best avoided. Cars leak fluids and drop small parts, and that refuse all collects in the center of the lane, making it slippery with oil and a potential source of flat tires. The slipperiness is especially true at intersections, and doubly so in wet weather. Most traffic situations will require you to be in either the right or left portion of a lane, so there's usually no reason to be in the oily center in any event.
In the city, the left lane is usually the safest option, as you will be farther away from cars turning in and out of driveways and side streets. Especially avoid running up the side of traffic in the often unused right lane in slow or stopped traffic—you'll be a prime target for a car turning left through a break in the traffic. Staying in the right-hand portion of the leftmost lane offers a number of other advantages: As you come up on a car, you'll be in the driver's blind spot for the shortest amount of time. Keeping to the right gives you a bit of a cushion to oncoming traffic. And you'll be able to change to the next lane quickly if needed. Many riders take the extra precaution of moving to the left of the lane briefly when overtaking a car. This has the benefit of both minimizing the driver's blind spot and also leaving the largest possible space to the car at all times.
The right portion of the leftmost...
The right portion of the leftmost lane on a freeway is generally the safest option as it leaves you clear of merging and exiting traffic, yet asserts your use of the entire lane should an errant driver decide to use that real estate.
On the freeway, a similar approach can be utilized. The left hand lane—including the carpool lane—is generally the safest option, leaving you clear of cars merging and exiting. Use the same technique as in the city when coming up on cars: Keep to the right of the lane until you're near the car, and move to the left of the lane to overtake. Likewise, when a car is overtaking you, keep to the side of the lane closest to the car so its driver is not tempted to move over into your lane. If you're worried about getting too close, you can move to the opposite side just as the car comes level. In all cases, keep alert for the actions of the cars around, and consider the blind spots that each driver is dealing with. Your goal is to stay out of those blind spots as much as possible.
In a right-hand canyon turn,...
In a right-hand canyon turn, use a late-apex approach to allow you to see as far around the corner as possible for as long as possible. This also lets oncoming traffic see you earlier.
When it comes to twisty roads, it's important to note some characteristics that most share. Roads that have a lot of turns are generally built that way to dodge hilly terrain, leaving a hillside to one side of the road, and a dropoff on the other. Driving or riding on the mountain side of the lane leaves shorter sightlines than in the opposite direction, and you can make a ride much more enjoyable by using this fact to your advantage. A perfect example is the Pacific Coast Highway. This road snakes up the coast, clinging to the side of the mountain that juts out of the ocean. Traveling northbound has you hugging a steep cliff in many areas, with short sight lines. Southbound, the view is much better, from both a tourist and safety standpoint. When planning a ride, use this fact to your advantage when choosing which direction to ride on particular roads.
In any event, your lane position on a curvy road is determined more by the direction of the turn—right or left—rather than the topography. In right-handers, keep to the left of the lane on the entrance, leaving the maximum sightline around the corner. Apex to the inside as you would any corner, but stay to the inside of the turn on the exit. This leaves you clear of any oncoming traffic that is potentially on the wrong side of the road, and also gives you some room for error if you misjudge the corner. Running a bit wide will still leave you in your lane, as opposed to crossing the double yellow and into oncoming traffic.
Just because your wheels are...
Just because your wheels are in the correct lane position doesn?t mean the rest of you is as well. Leave plenty of room at the apex in left-hand turns so you aren?t exposed to oncoming traffic.
In left-hand turns, stay right on the entry for a clear view into the turn. When you head for the apex, shy away from the centerline to keep well clear of oncoming traffic. Don't forget that your wheels can be in your lane and yet your body can be over the centerline, exposing you to a car in the other lane. Leave plenty of room for cars (and yes, bikes) coming the other way. There's a lot less room on the exit of a left-hand turn than a right-hander, so plan accordingly with restraint on the exit until you can clearly see the course of the road. On most twisty roads, lane position and line choice is more a matter of optimizing sight lines than using a classic swooping style from the edge of the road to the apex and back again.
In any situation, choosing the right lane position is a matter of considering line of sight for both you and the drivers around you, and in the twisties balancing that with the optimum line choice. Get that right, and you'll be safe as well as make good time, whether it's getting to work or jetting down your favorite mountain pass.