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-   -   Bike frontal cross section v speed perception (http://www.advrider.com/forums/showthread.php?t=951709)

gunsports 02-02-2014 01:35 AM

Bike frontal cross section v speed perception
 
Perhaps some of the experts can help here. Down here, one of the main causes of bike/car accidents is where motorists will stop to turn into or cross a lane, causing an approaching bike to collide with the car. One of the 'excuses' for their action is that; they did see the bike; but did not realise the bike was travelling so fast.

I am both a biker and cager. So, I started paying special attention to this 'excuse'. And it's true; at least by my observation. It appears that one can better judge the approach speed of the wider car, than the approach speed of the narrower bike.

More, I have noticed that; where bikes have additional riding lights; arranged in a form of a triangle with the riding lights on the extremeties of the bike; judging their approach speed seems to be better and more accurate.

Any thoughts?

scootrboi 02-02-2014 03:04 AM

Quote:

Originally Posted by gunsports (Post 23370015)
Perhaps some of the experts can help here. Down here, one of the main causes of bike/car accidents is where motorists will stop to turn into or cross a lane, causing an approaching bike to collide with the car. One of the 'excuses' for their action is that; they did see the bike; but did not realise the bike was travelling so fast.

I am both a biker and cager. So, I started paying special attention to this 'excuse'. And it's true; at least by my observation. It appears that one can better judge the approach speed of the wider car, than the approach speed of the narrower bike.

More, I have noticed that; where bikes have additional riding lights; arranged in a form of a triangle with the riding lights on the extremeties of the bike; judging their approach speed seems to be better and more accurate.

Any thoughts?

The changing size of the triangle sounds significant.

filmfan 02-02-2014 04:38 AM

The triangle gives our range-finding binococular vision something to work with.

With cars, there are generally distinct, widely-spaced details to judge with, for example the headlights, whether they are lit or not.

It let your brain compute the changing angles of those points, more precisely, the rate of change, which gives you a perception of the speed.

Kommando 02-02-2014 08:51 AM

Quote:

Originally Posted by gunsports (Post 23370015)
Perhaps some of the experts can help here. Down here, one of the main causes of bike/car accidents is where motorists will stop to turn into or cross a lane, causing an approaching bike to collide with the car. One of the 'excuses' for their action is that; they did see the bike; but did not realise the bike was travelling so fast.

I am both a biker and cager. So, I started paying special attention to this 'excuse'. And it's true; at least by my observation. It appears that one can better judge the approach speed of the wider car, than the approach speed of the narrower bike.

More, I have noticed that; where bikes have additional riding lights; arranged in a form of a triangle with the riding lights on the extremeties of the bike; judging their approach speed seems to be better and more accurate.

Any thoughts?

Combine the triangle of light with hi-viz, a white helmet, and lateral motion. Remain ready to avoid the pinheads who pull across in front of you anyway. I've been cut off while running code in an ambulance, so there's always a chance they're suicidal or something.

manfromthestix 02-02-2014 09:03 AM

I put some high-intensity LED driving lights down low on my fork tubes and feel that they dramatically increase my visibility, both from the added brightness and the triangle of lights now visible to on-coming motorists or those I'm following. I've read about the theory and thought it was plausible, then have tested it and now totally agree. This isn't the best photo of what I'm talking about, but it's all I've got right now - the bike is buried in the garage 'cuz it's frigging Winter here :cry.

http://manfromthestix.smugmug.com/ph...-FrVb6fq-L.jpg

The added light is also VERY NICE for night riding and the low-mount position doesn't blind on-coming vehicles.

Doug

74C5 02-02-2014 10:26 AM

We sense approach or departure by the rate of angular growth or shrinkage of an object. This was originally couched as angular acceleration....perhaps more true at night when one might be able to only see two taillights while overtaking a slow, or stopped, object. Headlamps poses a more complex issue with being unable to look at them directly if too bright (hence the inherent lack of wisdom for high beams on a bike 24/7/365).
If the angle starts small, when it becomes slightly larger is probably more difficult to perceive. If the angle is larger to begin with, I think we can all agree that growth is easier to notice.
Another factor is the squish likelihood. How often do people fail to notice the 60,000 lb tractor-trailer that will give another vehicle a really bad day. Inherently knowing that you will get seriously messed up tends to elicit behaviors that help with continuing your genetic lines......for most.:rofl
Then again, some people are just stupid and not only pull out in front of motorcycles but, trucks as well.

orangebear 02-02-2014 10:49 AM

i keep my head light turned off in good weather so that if i go over a bump a car driver wont think i have flashed him and pull out in front off me.

Idle 02-02-2014 11:31 AM

Honestly, I get left turners pulling out at the last minute in the pickup much more often than when on the bike. I don't bother honking the horn, I just let off the gas a little and then continue on. (in the truck)

I believe the reason is that I can't really weave in the truck like I do on the supermoto. So I think that even with even a large profile vehicle, speed can not be judged accurately.

I always drive and ride a little faster than the speed limit, and on the bike I'm always riding to distance myself from the traffic around and behind me.

That puts me in a position (on my own) where I need to make myself visible. I stand when cresting hills, and gently ride back and forth in my lane most of the time.



The nano-second I see a left turning car appear on a side street, or in a center turn lane, I swerve towards them, and then back and forth a few times as I close in.

It's far from a smooth subtle weave, I push on the bar hard, it's an abrupt change of direction, followed by more of them.

My headlight beam is doing a figure eight (fork mounted) so it's flashing around like a search light, just not a very bright one.

I've had people start to pull out that could have easily made it. They then do a "I'm sorry" wave, and it's returned with a "no prob, thanks for waiting and not killing me" wave.

It is the changing of profile and direction that allows our speed to be judged more accurately.

More lighting is always a good idea if it doesn't blind anyone.

manfromthestix 02-02-2014 01:47 PM

More lighting is always a good idea if it doesn't blind anyone.

That's why I went with the low fork-mounted LEDs. If I lived where there wasn't much traffic (or raced the Dakar or something) I'd have high-mounted lights, but here in Virginia there's a lot of on-coming traffic all the time. The Clearwater Lights "Glenda" model also have a cool feature in that you set the output on low beam to whatever you want with a rheostat switch, then when you switch to high beam they automatically go to 100% output. They are VERY bright on full power but not retina-burning when tuned lower.

I'm not so sure about all this weaving business... If it works for you that's great, but I think I'll stick to less dramatic methods of conspicuity. With all the traffic here I'd be weaving like a drunken sailor every inch of every ride.

Doug<!-- / message -->

scootrboi 02-02-2014 02:00 PM

This face has kept me visible for many years. http://farm4.staticflickr.com/3796/1...6b657b6c_b.jpg

foxtrapper 02-02-2014 03:25 PM

Quote:

Originally Posted by gunsports (Post 23370015)

More, I have noticed that; where bikes have additional riding lights; arranged in a form of a triangle with the riding lights on the extremeties of the bike; judging their approach speed seems to be better and more accurate.

Any thoughts?

I stumbled onto that decades ago with an old vetter fairing and the running lights down low. I frequently got comments about how visible I was, and how well they could judge me. From friends on their bikes, to cars at traffic lights. The difference was and is substantial.

Big Harley's carry this advantage as well, it's their stock lighting configuration. They also have physically large running lights.

erkmania 02-02-2014 05:35 PM

Quote:

Originally Posted by foxtrapper (Post 23374357)
Big Harley's carry this advantage as well, it's their stock lighting configuration. They also have physically large running lights.

And, riders that come in easy to see sizes, too. Right or wrong, I couldn't resist. :rofl






:hide

kiwi_outdoors 02-02-2014 05:50 PM

yup
 
Quote:

Originally Posted by gunsports (Post 23370015)
Perhaps some of the experts can help here. Down here, one of the main causes of bike/car accidents is where motorists will stop to turn into or cross a lane, causing an approaching bike to collide with the car. One of the 'excuses' for their action is that; they did see the bike; but did not realise the bike was travelling so fast.

I am both a biker and cager. So, I started paying special attention to this 'excuse'. And it's true; at least by my observation. It appears that one can better judge the approach speed of the wider car, than the approach speed of the narrower bike.

More, I have noticed that; where bikes have additional riding lights; arranged in a form of a triangle with the riding lights on the extremeties of the bike; judging their approach speed seems to be better and more accurate.

Any thoughts?

this is why they added ditch lights to locos on Caltrain (commuter rail, insecure right of way)

No False Enthusiasm 02-03-2014 06:25 AM

I can remember passing a old farm truck on a moonless night on a two lane Farm to Market Road. I could see oncoming headlights, but they appeared to be far enough away to insure my safe pass.

I accelerated but stayed in 5th gear. Just as I drew abreast of the pickup, I realized that the oncoming vehicle was much closer... I grabbed 4th and pegged the throttle...

The oncoming vehicle was a Jeep CJ-5, with headlights mounted closely together, just outside of the grill. The narrow headlights made the vehicle appear to be much farther away.

It was a hellova wake-up...

NFE

dduelin 02-03-2014 04:46 PM

Quote:

Originally Posted by orangebear (Post 23372305)
i keep my head light turned off in good weather so that if i go over a bump a car driver wont think i have flashed him and pull out in front off me.

Yes, I agree. I also do not wear a seat belt in the car so I can be thrown clear in case of an accident or if my car flies off the road into a canal I can swim to safety. Sorry, I couldn't resist. I hope your lighting tactics work for you but I'm not sure the lack of lighting is a good thing when the intersection does not have a bump.

Seriously, anything that increases our visibility to other motorists is a good thing and studies document this. Lighting, clothing and helmet color all are factors.

Still, if you hold up a pencil at arm's length it's width completely blocks from view a head-on motorcycle just 60 feet away. It is incumbent on us to chose positions of relative safety in traffic and expect the worst and act accordingly.


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