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 Motorcycle Safety
 Roadcraft
 Limit point in curves
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rioguy
Ex-Member

Posted - 06/30/2009 :  5:02 AM                       Like
This is something new I learned from Roadcraft that works very well.

You can see it explained and demonstrated in this video:

http://www.youtube.com/watch?v=Rb2gZVuoNU4

Here is a good explanation of it.

quote:
Assessing the vanishing point, limit point or arrow head.

Find a good bend, it doesn't matter if it is to the right or to the left, and look for the point where the two verges appear to meet. This is the vanishing point, limit point or arrow head.


If you enter a curve and you seem to be catching up to this point then you are traveling too fast. If your speed leaves you feeling that you are remaining the same distance from the vanishing point then you are at the right speed for the curve.
Your trainer will be more than happy to explain the principles involved in assessing the vanishing point.
If you carry too much speed into the curve you can be faced with some very serious problems. Most riders will try to sit the bike up and brake and in doing so, lose control of it. If you do manage to steer the machine, the excess speed will mean that you cannot lean the bike sufficiently to complete the curve, and you may well find yourself rapidly leaving the road.
Always lose your speed on the approach and build time into the process. Practice this discipline until you have perfected the technique, and this can only be done at speeds you can manage, so keep a large safety margin in the early stages of development.


In practice, I found it took quite a bit of time to really learn it. However, now the road tells me visually if my speed is correct for the entry and when I can accelerate for the exit. After a lot of practice, I found I can ride a difficult section of twisties without ever looking at the speedometer or advisory signs. (Not recommended until one gets very proficient at the technique.)

Combining this with aggressively searching for clues about the nature of the curve before entering it has improved my riding a lot and has also increased my speed through curves in a safe manner. (For those who are riding too fast, it may slow them down.)

A comment on the videos: It seems as if the instructors are talking too much to allow the students to make their own decisions. Is this normal, or is it just done for the viewers of the video to learn the techniques? It would be very distracting to me.

However, I find if I make commentary to myself in a similar manner, it really helps. Then when I turn off my mouth, the commentary seems to automatically run in my mind.

advancedbiker
New Member
13 Posts


BIDDULPH, STAFFORDSHIRE
United Kingdom

Honda

VFR800

Posted - 06/30/2009 :  7:11 AM
Commentary on the clip.....

In this particular clip the rider had a problem with bend assessment and had never heard of limit points. I only had 2 hours with the rider, hence the amount of commentary.

Whilst on the subject of limit points, great observation aid, but it can rarely be used by itself. As you mentioned, look at the street furniture, trees, telegraph poles, vehicles going around the bend you are approaching, either travelling in the same or opposite direction. This gives you a heads up on the curvature of the bend, but then you must look at what is after that bend. So now as part of Roadcraft you are formulating your riding plan. Also on the approach to any bend, do I enter it with the right amount of speed, correct gear to allow me to balance the throttle whilst going round it. It is an art and when perfected gives you a lot of that feel good factor,

Regards

Nigel
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rioguy
Ex-Member

Posted - 06/30/2009 :  8:13 AM
quote:
Originally posted by advancedbiker

Commentary on the clip.....

In this particular clip the rider had a problem with bend assessment and had never heard of limit points. I only had 2 hours with the rider, hence the amount of commentary.

Whilst on the subject of limit points, great observation aid, but it can rarely be used by itself. As you mentioned, look at the street furniture, trees, telegraph poles, vehicles going around the bend you are approaching, either travelling in the same or opposite direction. This gives you a heads up on the curvature of the bend, but then you must look at what is after that bend. So now as part of Roadcraft you are formulating your riding plan. Also on the approach to any bend, do I enter it with the right amount of speed, correct gear to allow me to balance the throttle whilst going round it. It is an art and when perfected gives you a lot of that feel good factor,

Regards

Nigel



I can see where it would be difficult with only two hours with a rider. The limit point was a very difficult concept for me until I got it after a lot of miles of practice. It took about 1,000 miles in twisties to get it where it's internalized. (Nobody said Roadcraft is easy.)

Strictly limiting the discussion to limit point and setting "road furniture" aside for the moment, I break it into 3 stages.

1. As I approach the curve, I see how far the limit point is from the point the road starts the curve. After gaining experience, I've been able to adjust my speed to within a few mph of the speed at which the limit point won't move when I enter the curve. (In practice, I use all available information to set the entry speed.)

2. As I enter the curve, note the movement of the limit point. If it is moving closer, I can just delay increasing the throttle for a moment until the limit point freezes. If it's moving away, I can increase throttle sooner.

3. In the curve, I use very subtle throttle changes to keep the limit point stationary. Throughout the curve, I'm saying "limit in" or "limit out" which correspond to a very slight throttle reduction or increase.

4. As the limit point starts to "run away" I say "Limit out, limit out, limit out" which tells me to increase throttle in proportion to the rate the limit point is moving out until I reach the speed I will maintain on the straight following at the point I'm on the straight.

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gymnast
Moderator
4263 Posts
[Mentor]


Meridian, Idaho
USA

Harley-Davidson

Sportster Sport

Posted - 06/30/2009 :  9:01 AM
Advancedbiker. I have a terminology question. By "limit points" do you use the term to mean the same thing as "sight distance limits in horizontal and vertical curves"?

Edit- In a less technical sense, is the term "limit point" synonymous with the term "vanishing point"

Edited by - gymnast on 06/30/2009 9:16 AM
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Cash Anthony
Female Administrator
1466 Posts
[Mentor]


Houston, Texas
USA

Honda

Magna 750

Peer Review: 1

Posted - 06/30/2009 :  9:11 AM Follow poster on Twitter  Join poster on Facebook as Friend  
My concern about the video as a demonstration is that not only does the rider cross the center line numerous times (demonstrating a lack of control or concern), but also the emphasis on watching limit points as a way to determine whether to roll on through a curve or not seems to me to over-ride the necessity for watching for hazards and obstacles and new danger zones when your vision is limited.

The only other reference in the video besides that limit point is the street signs -- that also were intended to notify the rider of one type of change of conditions coming up, i.e., the road's changing path. Both of these gave the rider only one kind of information.

There were multiple opportunities for disaster as those riders went speeding by doorways into walled yards, entries in hedgerows, bicyclists and pedestrians who were possible "issues" and who were given no commentary at all. Nor any change of lane positioning in advance of those (as opposed to changing positions to set up for the curves). Nor any slowing, or checking of speed, or even a moment's verbal notice.

Riding can't be a matter of finding one theory that you like and focusing on it, even for training purposes, unless you're on a closed course or a private road. If you're out there where the reality is, your riding needs to reflect that "big picture" all the time.


Cash
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(Deleted or Lost)

Posted - 06/30/2009 :  11:45 AM
Cash,
Your points are valid, and we should all bear them in mind, all the time.
In a training session one is usually especially focused on a specific technique one is learning, indeed one has to, until that technique is 'internalized'. This process is probably more familiar to new riders,when it sometimes seems never ending that as soon as one has 'got it', there's something new to 'get'. Those of us who have been riding for a long time, would do well to remember when learning a lot of 'new stuff' from Roadcraft, that we are back in that situation, and adjust our riding accordingly. We should be able to retain all our other skillls in active deployment, while concentrating on a new technique, but we'd better work at it.
Cash's warning is wise and timely.
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Niebor
Ex-Member

Posted - 07/05/2009 :  11:45 PM
I went out today to see what all the fuss is about regarding "street furniture". I found this spot along the road and found myself looking very closely at this situation:

[URL=http://s83.photobucket.com/albums/j292/Niebor/MS%20Practice/?action=view¤t=furniture1.jpg][/URL]

The stated purpose of street furniture is to give a clue of the curves coming up. Of particular interest is the curve that cannot be completely seen yet. Because of the camber of the road which appears to be almost flat, the yellow line gives no clues. So what else is there?

The angle of the guardrail is perhaps the best clue as it certainly follows the road. If you look at the telephone wires, they usually, but not always follow the road. The trees along the right side of the road give a good indication of the angle. Then there is just one yellow warning sign indicating that it is probably a sharp curve.

There were no speed advisory signs prior to this curve, but the speed limit was 35. Would you slow down, and if so, when? Where would you position yourself in the short straight to get a better view of the curve? A hint to the solution is given in the next picture which is taken from the right tire track in the same position.

[URL=http://s83.photobucket.com/albums/j292/Niebor/MS Practice/?action=view¤t=furniture2.jpg][/URL]

In the right tire track, a tree hides the good view of the curve. The guard rail is no longer visible and the warning arrow is no longer visible. The other clues are still there

The general rule is to position yourself far enough from the inside of the curve to get a good view of the road ahead. This inside position might be appropriate due to the oncoming traffic. If I chose this position, Id consider slowing down because of the reduced forward visibility.

Looking the other direction was interesting.

[URL=http://s83.photobucket.com/albums/j292/Niebor/MS Practice/?action=view¤t=furniture3.jpg][/URL]

The yellow line disappears from view as the road crests. There is a road to that continues past the straight portion to the left that one could think is the main road and enter this area at too high a speed. But there are some clues. Again, there are telephone wires along the edge of the road showing it might turn right. Another clue is the tree line curving to the right. As this situation The view might open up a bit by moving to the left tire track shortly. A safe approach is to slow down as this car is doing while the view opens up.

I found it difficult at times to work these new mental skills. When that happened, I just reverted to the "old school" methods I'm comfortable with. The process has merit, it's just that I'm kind of an old dog, these are new tricks.

I think I'm beginning to see a pattern here. Mental skills gather information about the road ahead. Position the bike in the lane so as to create the most forward visibility if there are no other hazards. Base on the information, adjust the speed so you can stop on your side of the road in the road you can see. Select a gear that allows you to progress smoothly, without changing gears in the curve if possible.
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Nigel A
Male Junior Member
68 Posts


TAUNTON, Somerset
United Kingdom

(None)

Formerly BMW 80RT

Posted - 07/06/2009 :  1:14 AM
Good illustrations, Niebor, and you have also hit on a good point that positioning can affect the extent of view into the bend, but that that positioning is also affected by the need to have the optimim position for safety first and then for view.

A further point of interest is that in your pictures you can see across the bend which makes this more of an 'open' bend, as opposed to a 'closed' bend where a hedgeline (for example) comes straight up from the edge of the road and there is no view across the bend.

Nigel (advancedrider) is also completely right, of course, that observing the limit point is one point of information. However, it is the key to ones speed into and through the bend. Yes, focused concentration is often needed to observe the point at which the limit point starts to 'move away' because that gives you the clue as to when the bend is starting to open out. However, all this is interlocked with (as mentioned) positioning and the relationship of power (throttle) to the steering. These are critical relationships and all have to come together in harmony for a smooth entry, progession through and exit from a bend. I would put an illustration in here but clicking on the 'picture' icon does not take one to a directiory from which one could select an image.

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(Deleted or Lost)

Posted - 08/29/2009 :  10:20 PM
I had a delightful, and very instructive, ride today. I have a hundred mile loop I call 'The Big Block' that I ride fairly often.
It has about 35 miles of 'county two lane' twisties, followed by 20 miles of bendy US Highway and Freeway, followed by about 25 miles of severe 'technical' twisties (some of those bends are sub 10mph), and finally 25 miles of rural freeway.
I did the first 35 miles of 'county two lane' twisties, and then stopped for a break in a beautiful town square for a cigar and to re-hydrate. While there, I thought of just turning around and doing that same road(s) in the reverse diretion (I've actually never done that before). That made the return journey effectively an unfamiliar road.

I've been gradually working on internalizing Limit, or Vanishing Point perception seamlessly into my hazard scanning pattern, and I decided this would be a good opportunity to 'commit' to using it as a principal element in choosing the speed in bends.

I was happily amazed at the result. There were about ten instances where other hazards mandated a lower speed, and these seemed to be incorporated 'automatically', but overall, relying on the behavior of the 'Limit Point' resulted in a much more confident and smooth passage through the bends.

Before I committed to using it, I quite frequently had reasons to slow down partway through long bends, because of being unsure how the bend was developing, and similarly I frequently felt like I was 'coasting' under very light throttle while I waited to see how the bend developed.
It was a subtle difference, but a very significant one, when using the Limit Point. I always felt confident that I was at thr 'right' (safe) speed, and any adjustments happened positively, smoothly, and 'automatically'.

I do think the couple of months spent observing the Limit Point, without actually using it, were very important in making it work so well when I eventually committed to using it as an 'internalized' control input.

I made a little better progress through the bendy bits, while actually feeling, and being, safer as well. The occasional hazard that suddenly appeared was handled even less dramatically than before - I judge that as confirming that I was actually riding more safely, too.




Comments and advice would be welcome.
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gymnast
Moderator
4263 Posts
[Mentor]


Meridian, Idaho
USA

Harley-Davidson

Sportster Sport

Posted - 08/29/2009 :  11:17 PM
quote:
Originally posted by gymnast

Advancedbiker. I have a terminology question. By "limit points" do you use the term to mean the same thing as "sight distance limits in horizontal and vertical curves"?

Edit- In a less technical sense, is the term "limit point" synonymous with the term "vanishing point"



In that "Advancedbiker never addressed my question, would The Meromorph care to address it? In your latest post as well as in several of the other posts above, neighbors for instance seems to relate (with excellent illustrations) to sight distance limit point and appropriate speed selection in a horizontal curve situation. A vertical curve situation would be hills or grade differences where the sight distance vanishing point or the "limit point" presents a similar speed selection situation.

Noting the vanishing point or limit point and conciously adjusting speed accordingly to perceived conditions without reference to monitoring the speedometer is a skill that is a product of actively practice and implementation of the search and scan process. Practice will, hopefully lead to subcortical implementation of this important riding skill.

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(Deleted or Lost)

Posted - 08/30/2009 :  12:09 PM
quote:
Originally posted by gymnast

quote:
Originally posted by gymnast

Advancedbiker. I have a terminology question. By "limit points" do you use the term to mean the same thing as "sight distance limits in horizontal and vertical curves"?

Edit- In a less technical sense, is the term "limit point" synonymous with the term "vanishing point"



In that "Advancedbiker never addressed my question, would The Meromorph care to address it? In your latest post as well as in several of the other posts above, neighbors for instance seems to relate (with excellent illustrations) to sight distance limit point and appropriate speed selection in a horizontal curve situation. A vertical curve situation would be hills or grade differences where the sight distance vanishing point or the "limit point" presents a similar speed selection situation.

Noting the vanishing point or limit point and conciously adjusting speed accordingly to perceived conditions without reference to monitoring the speedometer is a skill that is a product of actively practice and implementation of the search and scan process. Practice will, hopefully lead to subcortical implementation of this important riding skill.




Yeah, Limit Point and Vanishing Point mean exactly the same thing. I much prefer the Limit Point term, however, because, while Vanishing Point is an accurate description, Limit Point also incorporates the concept that this is the limit of your direct vision of what is coming up. It's a small but important distinction that has a real (at least for me) psychological impact on how I use it.
That statement, perhaps is the answer to your original question.
Yes, it's essentially the same as "sight distance limits in horizontal and vertical curves".
There is one distinction I would make, however. I place a greater emphasis on the use of the horizontal curve Limit Point for speed selection, and tend to treat the vertical curve Limit Point as an adventitious Hazard, more a reason to decrease speed for Hazard Avoidance, followed by dismissal of the Hazard when view is regained, than as a speed setting mechanism.
There are two reasons I do this.
1) Frequently it presents as 'dead ground', which certainly presents a Hazard to be planned for, but usually also still allows Hazard Assesment and Planning to be continued beyond it, while stil having to cope with the near-field Hazard. Of course, I have encountered major drop-offs in hilly country where the vertical curve is a true Limit Point.
2) If there is traffic, then while the road surface is not visible beyond a crest, often the tops of the vehicle(s) in front can still be seen and their behavior can indicate whether there is a real Hazard active in the Dead Ground.

I hope that answers your question.
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