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Thread: Two "4 second rules"

  1. #31
    Nickname: Droid
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    I like the discussion, but I fear we are loosing people at this point. But I do want to comment:

    1. Yes, I have on occassion, on a road I am very familiar with, under traction conditions I know(or assumed and was right, a "calculated" risk) doubled the posted speed for a corner. Not at the entry, but certainly by the exit I have attained 70 mph on a few 35mph posted turns. Once, on a Buell XB12 I managed to hit the rev limiter before exiting a corner in 2nd gear, which I'd guess was in excess of 60mph on a tight right handed turn. It was on a turn posted as 20 mph, probably because the turn had another road intersecting to it, but the sightlines were all clear. It is very possible.

    3. No actually, there are many ways to determine an "expected" apex for a turn before getting to the turn entry. Read the terrain in the turn area, read the road slope/camber, read the turn FAR before you get there, perhaps 1/2 mile before in some cases, read the "treeline"; if you see a LOT of trees perpendicular to your direct ahead line of sight, its a tight turn. If you see trees at an angle to your direct ahead line of sight, its a broader turn (learned this in the unmarked turn/twisties of south central Missouri), read the shoudler painted line, read the centerline, read from traffic exiting the turn. READING a turn starts FAR before you ever get to the turn, taking in data that clues you to the turn setup. All that reading before the turn helps set up your apex choice before the entry.

    I got caught on a cresting RH decreasing radius turn in Missouri. I did not read the "falling" tree line to clue me when riding uphill to the turn. I got in, it got tighter, and a truck in the other lane. I looked to the exit, maintained speed and pressed HARD on the right grip. Dragged my boot edge, centerstand and my passenger boot edge, and made the turn. My mistake was I did not read the terrain before getting to the turn, but I adjusted and made it. Not to brag at all, but just saying it is possible to adjust.

    I'll have to claim ignorance on Grodsky's four second rule for blind corners until I find what was printed by Larry on that subject. Larry was a very competent cycle safety expert, but also a very competent rider who could describe techniques we can really use. Based on what the OP said, "Grodsky's informal tests seemed to indicate 4 seconds was the time needed for good experienced riders to stop in a curve when there were not any road surface problem.". I underlined "time" because as it relates to braking, especially in a curve. Back to 35 mph, or 51 feet per second, if in a curve and the rider had to suddenly stop, 1/2 sec is spent in simply reacting and starting the braking process. There goes 26 feet. A good straight line stop, clean dry pavement, from 35 mph is about 50 feet and about 2 seconds. So we've gone 76 to 80 feet through the turn. Larry is generous with his "four second" guide, taking 1/2 second off for reaction/application. leaves 3.5 seconds for braking, about 1.5 second longer than a straight line stop. So now we're into more like 100 feet to come to a stop from 35 mph.

    You easily see the potential problem if the speed at entry is 70 mph. Because braking from speed is not linear to start speed. 70 mph braking is not twice the distance of 35 mph braking. More like four times the distance, especially in a curve. But very few riders consider braking performance in these terms, and fewer still practice any braking skills, until its pucker time.
    Last edited by ANDYVH; 05-09-2013 at 08:46 PM.

  2. #32
    Registered User AKsuited's Avatar
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    Quote Originally Posted by ANDYVH View Post
    You easily see the potential problem if the speed at entry is 70 mph. Because braking from speed is not linear to start speed. 70 mph braking is not twice the distance of 35 mph braking. More like four times the distance, especially in a curve. But very few riders consider braking performance in these terms, and fewer still practice any braking skills, until its pucker time.
    Indeed. The formula for kinetic energy, the energy of a moving body, is 1/2 m v2, or one half mass times the square of the velocity. If everyone kept that firmly in mind, there would be fewer wrecks on and off the road.

    Harry
    2003 R1150RT - Silver

  3. #33
    Kbiker BCKRider's Avatar
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    ANDYVH, I STILL think the "four second" rule for blind corners or hills has lot of viability and should be more widely known. I am most certainly not a "speed limits must always be obeyed" kind of person. But I am very interested in ideas which decrease the odds of my demise when riding. I have no problem with those of you who double or triple "suggested speeds" when you have the sight lines to know that is not only fun but safe. Blind corners are just the norm on all the back roads I've ridden. I thought a "4 second rule of thumb" might be a reality check for those of you who like to go fast around the twisties or crest hills at speed.

    My hope is that this thread gives you something to think about. You wouldn't read it if you were not pretty "safety conscious." Try counting seconds around blind corners or topping hills at your usual speed. I'm most certainly not telling you how to ride. I am asking you to analyze your riding in those situations if you hadn't given it much thought. The decisions (and consequences of those decisions) are always your own.
    Doug
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  4. #34
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    It seems we are at odds on this 4-second issue. Yes the MSF says 4-seconds is your Immediate Path of Travel scan/search range, and the MSF does not define that as only straight line riding, so it certainly is applicable for cornering. I am not saying, and have not said, that Larry Grodsky's 4-second sightline guide for cornering is not viable or reasonable.

    I just got Larry's book "Stayin Safe". On page 118 he describes the basis for his 4-second guide. In the follow paragraphs and page he describes much what I said earlier about braking capability (not saying I know what Larry knew, just that my MSF training principles do relate to what known safety pros publish). On page 119 he details the braking capabilites required for the speeds some of us like to carry into turns, well sighted turns and blind turns. What is most telling, is what he calls "response envelope" and how long that can get as speed increases. The response envelope is also the total distance required to stop. It relates to our natural response time. In clear straight line stopping its about 1/2 second. But Larry details that as speed increases, the response "zone" (that time/distance we cover in transition from throttle to braking) rises in almost direct proportion. So if you double your speed, you also double your response zone.

    Taken into a curve, at twice posted speed, your visual lead of 2-seconds (MSF minimum), could become six to eight times/distance in response envelope. At 60 mph in a turn posted at 30 mph (likely not a blind turn), that equals 528' to almost 704'. At 45 mph in a blind turn posted at 20 mph (45mph = 66 feet per second) that equals to 528'. Clearly NOT safe if you are expecting everything to be all right through the turn based on what you CANT see. Larry says it like this, "However arbitrary these figures, it's apparent that riding fast on the street takes more nerve than skill."

    A VERY telling statement when you consider how many riders have FAR FAR LESS skill than nerve.
    Last edited by ANDYVH; 05-15-2013 at 04:09 AM.

  5. #35
    Registered User LDB's Avatar
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    I have a commercial license good for anything up to 80k doubles and triples. For anything large enough to fall under HOS rules I like a 10 second rule as much as possible. For bikes and 4 wheelers I like a 5 second rule. 4 seconds is marginal in some situations although certainly better than the old 2 second rule that used to be popular. Those are obviously geared more toward following distances. You often can't get that much in peripheral safety margin.
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  6. #36
    Registered User amiles's Avatar
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    I think that it is important for the rider to keep several things in mind even when leaving a very long following distance. That driver that is entering your road from an intersection, ramp or driveway up ahead, if alert & conscientiously trying to drive safely, will see you approaching, do a mental time speed distance calculation to determine whether to pull out ahead or behind you. The very different frontal area of a motorcycle vs that of a car complicates this calculation as to the available distance for a safe merge. The speed of the motorcycle will more than likely be mentally calculated based on the speed limit and or the observed speeds of passing traffic. If the oncoming vehicle (you) is closing at a significantly higher rate of speed, the driver's calculation of a safe entry will likely be incorrect & cause a conflict with you.

    Seems strange reading that motorcyclists are concerned with aggressive drivers. The pot calling the kettle black?

  7. #37
    Registered User WalterK75's Avatar
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    The British police riding manual, Police rider's handbook to better motorcycling, recommends that you be able to stop in the distance you can see ahead of you. That distance constantly changes due to curves, traffic and hills. A blind curve is just that, blind. How can one adjust to 4 seconds ahead if it is blind? Can you stop in the distance ahead that you can see?

    Further, in reference to blind curves no one can see what is hidden there. There is a blind curve I ride almost every ride. What is around that curve? One time it was a vehicle coming in the opposite direction in its lane. No problem. Another time it was a small amount of gravel exactly where I needed to ride based on my chosen line and lean into the curve. At another time, a few small branches from a tree. I do not know what I'll find. It could be a slow truck, a road crew, an animal crossing the road.

    How can I know what to expect on new roads with new blind curves? The 4 second rule is impossible to determine until after the fact. "Can I stop in the distance I see before me?" is the way to go. On page 47 of the above police rider's handbook it says, "Adjust your speed according to how well you can see, the complexity of the situation and the distance it will take you to stop. You must always be able to stop within the distance you can see to be clear" and on page 81, "Never ride so fast that you cannot stop comfortably on your own side of the road within the distance you can see to be clear."

    Good thread. I'm pleased that so many think about this issue and ride accordingly.
    Walter

    G. K. Chesterton wrote - "The traveller sees what he sees, the tourist sees what he came to see."

  8. #38
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    Quote Originally Posted by BCKRider View Post
    ... I AM STILL WAITING for someone to substantiate (or refute) Grodsky's "four second rule" on blind corners. I would submit that counting seconds (for whatever reasons) is a tool easily available to all of us, whether in our car or on our bike. I would also submit almost all of us are awful at judging distance when in a moving vehicle. Seconds (not car lengths, or feet or meters) should be what is taught and what experienced drivers/ riders talk about. That is the subject I'm still broaching.
    Good morning Doug and all... Interesting discussion here.

    Doug, I think Grodsky's four second rule is probably a good rule of thumb for total time to stop. Keep in mind that, as we teach in the MSF program, there are three items involved in a stop: Perception, Reaction, and Actual stopping distance. Most of the instructors I work with pretty much agree that the two second following rule is not viable simply because most riders do not actively practice emergency quick-stops and swerve maneuvers. Essentially from perception to initial reaction, application of brakes, (assuming the brakes are not being covered) tends to be something over 1 second if you have very good reflexes., Given the age demographic of most riders, the reaction times are probably degraded even more. Then you have the actual stopping distance to deal with.

    As far as how I ride, the slow in fast out rule is appropriate. If I enter a blind curve, I always slow to a point that I can stop in the sight distance. This rule served me very well a couple of years ago when entering a tight 140 degree outside curve (2-lane country road) leaning a good 30 degrees probably doing 15 mph at that point, and came face to face with a large combine in the middle of the road with the knives up at chest level pointing at me. Did a quick-stop in the curve and had no problems of any kind. Combine operator made the comment that he probably needed to get out of the road. Indeed !.

    Distance judgment is problematic too. I tend to think a lot of drivers (and riders) have very poor depth perception due to vision problems. Many do not seem to have a clue that vehicles cannot stop in one car length from 75 mph on a freeway when following within 1 car length.

    Several comments above note the problem of trying to maintain a safe distance to the vehicle in front, and other drivers pulling into the gap. That happens, but generally if you are moving approximately the speed of the surrounding traffic it is a minimal issue. I personally like to ride just slightly faster than the prevailing traffic which does two things: First, it keeps most of the action I need to worry about in front of me, and secondly, It will make a lot of drivers notice you just a bit more. It also will not attract unwanted LEO attention.

    As far as intersections, I always assume any vehicle in the intersection does not see me or cannot estimate my approach speed. Slowing way down and covering brakes saves a lot of pucker factor.

    Ride safe out there: You are invisible and everyone is out to kill you. Act accordingly in the combat zone.
    Doug, 2011 R1200RT Polar Metallic
    MSF #127350 NAUI #36288

  9. #39
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    Just to add another rule of thumb (or speed). Every 10 mph is about 15 ft per second so 20 mph=30 fps, 60 mph=90 fps, 80 mph=120 fps etc.

    A football field or an average city block is 300 ft long so at 60 mph you need just over 3 sec to stop inside a football field so should be scanning that distance. Make your own visual realities to compare and no need to count when you can relate to something you know.

  10. #40
    roamingbeemer roamingbeemer's Avatar
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    Very good thread. I think about how to stay alive on the road a lot. IMHO, the 4 second rule, 12 seconds, or any general rule needs flexibility depending on the situation.
    I watched Jay Leno on Youtube riding an Indian and going pretty fast on the right side of the road and lane passing many driveways and it made me very uncomfortable just watching him. Harder to see him, he would have no time to react, and he can not see in the drive ways and/or intersections at all.
    I am a Very conservative rider on the highway and I am always looking for the threats so I can position the bike to reduce the risk. If on a two land highways with traffic coming the other direction I will put myself a little closer to the cars ahead of me so a car coming the other direction can not start an overtake with me in the way.
    With traffic from the other direction you can put yourself on the right side of the lane so you can have an escape path but this limits your visibility to see into driveways and intersections from the right so at times using the car ahead as a blocker helps. Of course a little closer does not mean close. This is using the 4 second rule I believe.
    With no traffic form the other direction I always ride so I can see into intersections and driveways by being closer to the left. Of course watching for any left turning vehicles ahead where you may need to modify the plan. I will try to use a car ahead of me as a blocker for a left turning vehicle too or slow down if necessary. This would be the 12 second rule per the MSF.
    I guess it is a matter of constant threat awareness and putting your bike in a position to reduce the risk using many generalized rules to assist out decision making. It has worked for me so far in several countries and riding environments.
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  11. #41
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    Thumbs up

    Quote Originally Posted by roamingbeemer View Post
    I guess it is a matter of constant threat awareness and putting your bike in a position to reduce the risk using many generalized rules to assist out decision making. It has worked for me so far in several countries and riding environments.
    Agreed, there are lots of time and space rules of thumb etc that one needs to consider, even in a vehicle, and that was a good way to sum it all up for me.

  12. #42
    Registered User greenwald's Avatar
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    Smile

    Quote Originally Posted by BCKRider View Post
    This post comes from my last re-reading of "Stayin' Safe," a book of columns by the late Lawrence Grodsky for "Rider" magazine. I would highly recommend the book, but what follows are my interpretations.

    1. What is unfolding 4 seconds ahead of you requires your fullest attention and often immediate action. (12 seconds ahead is what you would like to see and often can't.) So are you aware of everything 4 seconds ahead of and off to the side of your bike? And since you probably don't have a second hand mounted on your faceshield, try counting. (One thousand one, one thousand two... or One Mississipi...) This is a very good reality check.

    2. If you are really safety conscious, you want to be able to stop in any "blind" situation, whether that is a curve or a hill. Grodsky's informal tests seemed to indicate 4 seconds was the time needed for good experienced riders to stop in a curve when there were not any road surface problems. Cresting a hill can be a more insidious problem unless you take into account the possibility of a hidden driveway to your right or a vehicle crossing the centerline. Again, count the seconds to what you can see.

    There are many riders who violate the second rule - and some of them have been doing it for many miles and years. I don't understand why they are still alive. Maybe they can tell us how Larry and I are wrong. At any rate, I am not telling YOU how to ride. Just offering some thoughts which make sense to me.
    Doug - I applaud you embracing Grodsky's lifetime of work dedicated to safer riding. He left us too soon, courtesy of those damned 'forest rats.'

    The 2, 4 and 12 second following distances were never 'rules,' but rather recommendations, and for good reasons. As MSF instructors, we enlighten novices to these suggestions, and in doing so, we emphasize the dangers of being too close in traffic for effective reaction distance, as well as promote situational awareness ("head on a swivel").

    As you can see from the multitude of responses to your original post, much can be discussed and learned in the interest of becoming a safer rider.

    Thanks for posting.
    Last edited by greenwald; 01-12-2014 at 05:55 AM.
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  13. #43
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    "Much to be learned" is for sure the one thing we all can agree on. A second might be that lots of real world experience can make a difference. I'm sure most of us would say we still learn new stuff even at our "advanced age"

    The contributors to this thread appear all to be riders with lots of miles and years of experience- and they're still doing it despite what is between them probably hundreds of instances when injury or death was possible. That's too many escapes/avoidances to be all dumb luck and says that one can likely learn something from any of them- even if their way of thinking about the event and describing it isn't yours.

    A friend of mine who wrote a few best sellers made his reputation studying and explaining to to others the different ways humans learn- what works for your own education is what ultimately matters- just as long as you get educated enough to tilt the odds in your favor. Learning from the "other guy" beats learning the hard way.

  14. #44
    Kbiker BCKRider's Avatar
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    Thank you, amiles

    What a pleasant surprise to see this thread revived after six months! Clearly there are very different ways of thinking about these matters - and probably what counts most is that we ARE thinking about them.

    While I am always interested in specifics, probably one's attitude is more important. I try to remind myself every time I get on the bike or in the car that my MAIN GOAL is to arrive at my destination with body and machine intact. Hopefully the specifics of speed, bike placement, and situational awareness flow from that one simple idea.
    Doug
    1992 K100RS

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