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Old 08-27-2013, 11:08 AM   #136
2stoned
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Good math

Very true on the math.
Though that always seemed obvious.
I do not feel safe racing towards a moving, possibly inattentive or worse, vehicle at high speeds, only to find that they will suddenly try to block my path.
The shorter my encounter with those potential dangers the better.
Getting a little closer before you pass, may alert them, but also gives you a chance to read them.
Good post wraith...
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Old 08-27-2013, 06:38 PM   #137
Midnullarbor
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Wraith, thank you for taking the trouble to do the mathematics.

As you know, half-acceleration x time squared is the relevant basis for regarding relative speeds & distances.
But we have to be careful to avoid the GIGO effect.
A lot depends on how realistic the situation is.

Initial distance is crucial.
Earlier I mentioned "tailgaters" as starting from 40' back ~ this is not an out-of-the-air figure, but what I see everywhere out on country roads. The potential overtaker (car or bike) sits 2 car-lengths behind the front car . . . peeping around to see if the road is clear . . . then, eventually, "flooring it" and gradually overtaking.
That is why I use 40' [12m] at Time Zero.

Your high-powered bike gaining at 6.4 m/sec/sec [ 0.65 gee ] will, from 40' gain 28mph by the time your front wheel is reaching level with the car's rear fender, and nearly 37mph by the time your rear wheel clears past the car's front fender.
That is, very close to 9m distance [ = car + bike length ] . . . at an average speed of 32 mph . . . equals 0.63 seconds of "parallelarity danger" (if such a term exists).
Fairly straightforward . . . provided we ignore all the possible complications of reaction times & malicious intent by the driver, of course.

Now add 15mph to your average speed, and you are down to 0.43 seconds of overlap.
Yes, only 0.2 sec less . . . but that is a one-third reduction.



Most of us are not riding a 100+ horsepower [ 101+ Pferdestaerke, if you must ] sports bike . . . and where our own difference will be much bigger than one-third.
(Now look how the average relatively low-power car does the overtake . . . and the figures blow out enormously. And we see it everywhere!! Almost clueless drivers ~ and they think it's the "right" way to do it.)



Wraith, I am glad that you actually start your move from much further back ~ 22m [ 70' ] is a much safer starting position, even when you have a seriously quick bike which can make 0.65 gee in second gear.
I had earlier suggested 100' back, partly to suit lower-powered bikes and partly because the greater distance is more soothing & lulling for the driver in front. Perhaps even further back would be better ! (And certainly so for general braking/ reaction purposes.)


My apologies for the jumble of metric/ Imperial/ fps units.
Should all speedometers be calibrated in meters-per-second?
Though feet-per-second would probably look suitably more alarming to the average driver, who typically fails to appreciate the harsh realities of time & distance.
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Old 08-29-2013, 05:12 PM   #138
Midnullarbor
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Despite the benefits of a fast pass giving an easier overtake [road-space up ahead] and less time overlapping/ parallel to the car . . . the biggest advantage of a sneaky-quick pass (starting 100+ feet back) is psychological.

Since you are steadily riding "way back there", you are (mostly) not giving the strong impression that you are "pushing" or challenging the car driver who is in front. He may well be a potentially malicious Blocker, but his suspicions are a lot lower and he won't be watching you in his mirrors like a hawk.
You have an excellent chance of being beside him (and out of reach of his swerving reaction time) before he realises what you have done.



Of course, keep yourself well wide during the critical stages of the pass ~ but don't go too wide too early : you are wanting to use what the SMIDSY-aware riders call "the zooming effect" to camouflage your initial actions.
And flick on your turn-indicator just as you go by, to help give the idea that you had politely had it blinking from the start . . .



A good procedure for the single rider.
But a group of 2 or more riders were always going to have problems with Mr Malicious.
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Old 08-30-2013, 07:36 PM   #139
henshao
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http://www.advrider.com/forums/showthread.php?t=695861&page=122

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