DataDan
Mama says he's bona fide
Sightlines in a blind curve can provide valuable clues about what to expect
One of the first challenges faced by a novice sport rider in the Bay Area is dealing with inscrutable roads that climb the steep mountains and zigzag through the thick woods where the best riding is found. But the panic triggered by a decreasing radius or gravel-strewn apex might make you question your decision to take up a sport that seems, diabolically, intent on spitting you into the abyss. A skill that can help tremendously as you explore our idyllic riding environment is learning to read the road so you can anticipate those unpleasant surprises. One effective technique called the vanishing point is taught to riders in the UK and recommended in a British book, Motorcycle Roadcraft.
From any spot on the road, the VP is the farthest bit of pavement you can see ahead of you. It could be miles away on the horizon, at the summit of a hill you’re climbing, or right in front of you where the road disappears around a blind turn. It usually moves forward but will come to a stop as you approach a sightline obstruction. This technique uses the VP and its apparent motion for cues about what to expect of the road ahead.
In its primary application, the VP sets a speed limit of sorts: Maintain speed that allows you to come to a stop on your own side of the road in the distance you can see to be clear. The Brits call this the safe stopping distance rule. The length of clear roadway, surface conditions, your motorcycle, and skill determine how fast you can go and still be able to brake for a hazard lurking just out of sight. Because the distance you can see changes continuously, safe speed changes as well. Approach a blind turn or crest where the VP is stationary and you will rapidly close in on it. The margin of safety it represents is shrinking, so you must slow down to maintain that margin. On the other hand, when it jumps into the distance as your sightline opens up, you may be able to accelerate.
The key to reading blind turns
Basic stuff, so far. When sightlines are short, slow down; when they’re longer, you can speed up. Less obviously, the VP can help you read an unfamiliar turn and adjust your speed to match it. The VP’s cues result from simple geometry: the sightline around a blind turn is shortest where the turn is tightest. Sightlines will shorten approaching the tight section, remain at a fixed distance ahead while you’re in it, and lengthen as you leave it. Approaching a point where the radius decreases, the VP’s forward progress will slow because your view is blocked where the curve wraps around the hillside, embankment, or other obstacle. But within a section where turn radius is constant, sight distance will be constant too, and the VP’s progress will match your speed through the turn. When a turn begins to open up, sight distance will increase and the VP will jump ahead.
Using these cues from the progress of the VP, you can anticipate difficult turns that might otherwise surprise you, and you’ll be able to adjust your speed to the situation. As you approach the turn, watch the VP. You don’t know how tight the turn is yet, but the VP will show you where it becomes tighter. It will stall where the turn tightens, and you’ll close in on it. Slow down, and continue to slow as it gets closer. When the VP starts moving again, you’re nearing a constant radius section. Begin to roll on the throttle and maintain constant speed as the VP stays a constant distance ahead of you. Finally, your view through the curve will open up where you can see the next straight, and the VP will quickly leap into the distance. Again, match the throttle to the VP’s progress, this time by accelerating as the VP leaps ahead.
The rules
When you’re out riding, you don’t have to worry about the geometry as you negotiate a turn, just remember the basic rules:
A rider's-eye view
The following series of pictures shows the VP’s progress through a typical blind turn. The first is an aerial of the turn, which will be taken as a left-hander from bottom right to top left. Notice how the turn tightens up. At first it’s gentle, but the turn radius gradually decreases and reaches its tightest point about two-thirds of the way through.
In the first 5 shots (taken at 10-yard intervals) you’re quickly closing in on the VP, the last bit of pavement you can see where the road curves left around the embankment on the inside. The VP is moving ahead, as you can see by the warning arrows that are revealed, but more slowly than you are. Consequently, you should be decelerating—off the gas, a bit of brake, and downshifting.
In shots 6 and 7, the VP stays about the same distance ahead, cueing you to a fixed-radius section, so you can begin to add a bit of gas.
In shot 8, the VP is moving away from you, and in 9 the turn exit is in full view, so you can begin to accelerate.
The final pic is the same aerial as before, but with sightlines drawn in. Notice how tightly spaced the VP is for the first few sightings and how sightline length increases when the view beyond the tightest radius opens up.
Discovering and riding new roads is part of what makes sport riding fun. Developing the skill to read them and anticipate their twists and turns will take the anxiety out of the unfamiliar environment and make it even better.
One of the first challenges faced by a novice sport rider in the Bay Area is dealing with inscrutable roads that climb the steep mountains and zigzag through the thick woods where the best riding is found. But the panic triggered by a decreasing radius or gravel-strewn apex might make you question your decision to take up a sport that seems, diabolically, intent on spitting you into the abyss. A skill that can help tremendously as you explore our idyllic riding environment is learning to read the road so you can anticipate those unpleasant surprises. One effective technique called the vanishing point is taught to riders in the UK and recommended in a British book, Motorcycle Roadcraft.
From any spot on the road, the VP is the farthest bit of pavement you can see ahead of you. It could be miles away on the horizon, at the summit of a hill you’re climbing, or right in front of you where the road disappears around a blind turn. It usually moves forward but will come to a stop as you approach a sightline obstruction. This technique uses the VP and its apparent motion for cues about what to expect of the road ahead.
In its primary application, the VP sets a speed limit of sorts: Maintain speed that allows you to come to a stop on your own side of the road in the distance you can see to be clear. The Brits call this the safe stopping distance rule. The length of clear roadway, surface conditions, your motorcycle, and skill determine how fast you can go and still be able to brake for a hazard lurking just out of sight. Because the distance you can see changes continuously, safe speed changes as well. Approach a blind turn or crest where the VP is stationary and you will rapidly close in on it. The margin of safety it represents is shrinking, so you must slow down to maintain that margin. On the other hand, when it jumps into the distance as your sightline opens up, you may be able to accelerate.
The key to reading blind turns
Basic stuff, so far. When sightlines are short, slow down; when they’re longer, you can speed up. Less obviously, the VP can help you read an unfamiliar turn and adjust your speed to match it. The VP’s cues result from simple geometry: the sightline around a blind turn is shortest where the turn is tightest. Sightlines will shorten approaching the tight section, remain at a fixed distance ahead while you’re in it, and lengthen as you leave it. Approaching a point where the radius decreases, the VP’s forward progress will slow because your view is blocked where the curve wraps around the hillside, embankment, or other obstacle. But within a section where turn radius is constant, sight distance will be constant too, and the VP’s progress will match your speed through the turn. When a turn begins to open up, sight distance will increase and the VP will jump ahead.
Using these cues from the progress of the VP, you can anticipate difficult turns that might otherwise surprise you, and you’ll be able to adjust your speed to the situation. As you approach the turn, watch the VP. You don’t know how tight the turn is yet, but the VP will show you where it becomes tighter. It will stall where the turn tightens, and you’ll close in on it. Slow down, and continue to slow as it gets closer. When the VP starts moving again, you’re nearing a constant radius section. Begin to roll on the throttle and maintain constant speed as the VP stays a constant distance ahead of you. Finally, your view through the curve will open up where you can see the next straight, and the VP will quickly leap into the distance. Again, match the throttle to the VP’s progress, this time by accelerating as the VP leaps ahead.
The rules
When you’re out riding, you don’t have to worry about the geometry as you negotiate a turn, just remember the basic rules:
- When the VP is getting closer, slow down. Roll off the gas, and brake if necessary.
- When the VP is staying a fixed distance ahead, maintain constant speed with a little bit of throttle.
- When the VP is disappearing into the distance, roll on the gas and accelerate, again matching the throttle to the VP’s progress.
A rider's-eye view
The following series of pictures shows the VP’s progress through a typical blind turn. The first is an aerial of the turn, which will be taken as a left-hander from bottom right to top left. Notice how the turn tightens up. At first it’s gentle, but the turn radius gradually decreases and reaches its tightest point about two-thirds of the way through.
In the first 5 shots (taken at 10-yard intervals) you’re quickly closing in on the VP, the last bit of pavement you can see where the road curves left around the embankment on the inside. The VP is moving ahead, as you can see by the warning arrows that are revealed, but more slowly than you are. Consequently, you should be decelerating—off the gas, a bit of brake, and downshifting.
In shots 6 and 7, the VP stays about the same distance ahead, cueing you to a fixed-radius section, so you can begin to add a bit of gas.
In shot 8, the VP is moving away from you, and in 9 the turn exit is in full view, so you can begin to accelerate.
The final pic is the same aerial as before, but with sightlines drawn in. Notice how tightly spaced the VP is for the first few sightings and how sightline length increases when the view beyond the tightest radius opens up.
Discovering and riding new roads is part of what makes sport riding fun. Developing the skill to read them and anticipate their twists and turns will take the anxiety out of the unfamiliar environment and make it even better.
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.... This is definitely something I can use while out on a :ride.
