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Old 03-17-2008, 09:04 PM   #1
DataDan
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The Vanishing Point

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 youíre 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 theyíre longer, you can speed up. Less obviously, the VP can help you read an unfamiliar turn and adjust your speed to match it. The VPís 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 youíre in it, and lengthen as you leave it. Approaching a point where the radius decreases, the VPís 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 VPís 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 youíll be able to adjust your speed to the situation. As you approach the turn, watch the VP. You donít 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 youíll close in on it. Slow down, and continue to slow as it gets closer. When the VP starts moving again, youíre 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 VPís progress, this time by accelerating as the VP leaps ahead.

The rules

When youíre out riding, you donít 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 VPís progress.
This technique works on all kinds of turns, even irregular ones that dish out a surprise when youíre least expecting it. In a decreasing radius turnóone that tightens up as you get deeper into itóthe VP will warn you by keeping the exit hidden deep into the turn. In a double-apex turnóone that seems to open up but then surprises you with a second curveóagain the VP warns you. You accelerate out of the first part as the sightline opens up, but the VP immediately closes back up, warning you of another curve.

A rider's-eye view

The following series of pictures shows the VPís 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 itís 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) youíre 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 deceleratingóoff 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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Last edited by DataDan; 03-28-2010 at 08:53 AM.. Reason: revised photo linkage
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Old 03-17-2008, 10:18 PM   #2
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Great post. I'm going to be trying some new-to-me roads this weekend and this will be a great technique to try.
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Old 03-18-2008, 04:02 PM   #3
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agreed. Many instructional tips make the mistake of presenting too much information - more than you can remember while negotiating a curve. I'm going to try this myself next time in the twisties..
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Old 03-19-2008, 08:45 AM   #4
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Great post. I think this is a very helpful concept for both newer & more experienced riders.

Especially for the new riders, I've noticed that some seem to want to "predict" how a turn will finish without being able to see what's beyond the vanishing point. You may want to take a turn at a certain speed because the last three turns were safe at that speed. If you "predict" the wrong exit to the turn, you can crash if you were going to fast for what ended up as a decreasing radius turn. Hopefully, the VP approach will allow riders to adjust to a speed that's safe for that particular moment and continuously adjust as the road changes.

The VP is an easy to remember concept that you can apply during your ride.
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Old 03-19-2008, 08:54 AM   #5
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Originally Posted by DataDan View Post
This series of pictures shows the VPís progress through a typical blind turn.
Busted! Turri Rd. Best 4.2 miles/14 tirns in the county. What's your best time Dan?
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Old 03-19-2008, 09:22 AM   #6
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Nice read, thanks.
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Old 03-21-2008, 10:03 AM   #7
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That was a great "road movie"!

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Old 03-21-2008, 11:38 AM   #8
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Good write-up and excellent movie, cool trailer.

The part in the movie where they beat the hell outta Cleavon Little gave me (when I was a little tyke) nightmares, though...
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Old 03-21-2008, 01:57 PM   #9
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I use The Varnishing Point all the time to tell where I started to sand the table from....
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Old 03-24-2008, 07:57 PM   #10
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Quote:
hiccup wrote: I'm going to be trying some new-to-me roads this weekend and this will be a great technique to try.
Quote:
vstrom_rider wrote: I'm going to try this myself next time in the twisties.
If you or anyone else has tried the VP technique, I'd be interested in your impressions. The rules are pretty simple, but they can have a positive effect on your riding.

While the rules tell you when to decelerate and accelerate, they can't tell you how fast to take a turn. So good judgment is still needed, and you can end up taking a turn faster or slower than you'd like. Which mistake did you tend to make more of, too fast or too slow?

How did it affect your use of brakes? Did you tend to use them more or less?

Keeping track of the VP imposes a visual discipline that keeps your eyes and brain ahead of the motorcycle. Did you notice that you experienced fewer surpises?

At the same time, you can't ignore the pavement between you and the VP. In his book Sport Riding Techniques Nick Ienatsch isn't talking about the VP, but his advice still pertains:
Street riders can't count on a perfect surface like roadracers can, so you need to scan the pavement, not just jump your eyes to the horizon. Scan constantly, moving your eyes from the path immediately in front of you to the farthest point you can see in the corner; as the corner unwinds in front of you, continue to scan to the farthest point.
And in his book Sportbiking: The Real World, BARF's GaryJ makes this observation about the DVD A Twist of the Wrist (by BARF's Keith Code):
During one track session, the eyes of the rider (a professional roadracer) could be seen rapidly scanning from left to right repeatedly during the execution of a single sweeping corner.
In fact, that left-to-right scanning while negotiating a turn is really forward and back along the rider's planned arc through the turn. So while you're watching the progress of the VP for cues to where the road is going, you're still mindful of potential hazards between here and there.

The point in a turn where distance to the VP goes from decreasing to constant is a crucial one. That's where you get off the brakes (if you had to brake) and roll on a bit of throttle. But the transition can also be used as a cue for steering. In the turn shown in the photo sequence linked in my first post, I steer a little bit to follow the gradual arc the turn makes from points 4 to 6. But at point 6 (the end of the turnout on the right), where the VP is now matching my speed and I'm looking at a constant radius section ahead, I make the steering input that will put me on that arc. Once leaned over, I'll add throttle to maintain constant speed, then, when the turn finally opens up, accelerate.


If you tried it, I'd like to hear what you think.
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Old 03-24-2008, 10:49 PM   #11
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I'll be adding this to 'The Pace' as a primary tool to work on and with while I ride. I'll post up later to let you know how it worked for me.

Thanks

Edit: I just bought the 2nd to last copies of GaryJ's Sportbiking: The Real World volume 1 & 2 from Amazon "Only 1 left in stock--order soon (more on the way)." they say.

And Motorcycle Roadcraft is out of stock, but will ship when it's in!

Thanks again

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Old 03-25-2008, 06:35 AM   #12
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Good read supported by good pics
THANK YOU!!!!
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Old 07-28-2008, 06:39 PM   #13
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Great post .... This is definitely something I can use while out on a .

Thanks again for the post
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Old 07-28-2008, 07:16 PM   #14
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as a newbie, i am so grateful to you veterans for posting all of this helpful riding/safety info. thx!
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Old 07-28-2008, 07:56 PM   #15
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Thanks for bumping this great thread.
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