tripping red lights

Equipment and On Road Behaviour, Laws and Rules. Cycling Promotion and Advocacy

Re: tripping red lights

Postby RonK » Mon Jan 21, 2013 9:39 am

hannos wrote:I cannot recall ever having a problem tripping lights on my carbon road bike. Granted, I do use alu clinchers so this would probably be what trips them.

Must be some special magnetic alu clinchers then.
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by BNA » Mon Jan 21, 2013 9:46 am

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Re: tripping red lights

Postby RonK » Mon Jan 21, 2013 9:46 am

fatherofmany wrote:Magnetic induction loops require metal in close proximity to disturb them. They are placed behind the white line because that's where the bulk of the metal is... in a car! I have found that if I place my bike back from the white line by about a metre then it is in the loop (if I can't see the cuts in the road where it is placed).

I haven't had too many probs with a metal bike but for the Carbon guys... the theory goes that a strong magnet will also disturb the magnetic induction loop.

I know it's a few grams :shock: but gluing, or taping a couple of rare earth magnets to the underside of the BB should be enough to set the loop off.

Let me know how it works if you try it.

FoM

I place my bike's bb over the loops, but some intersections have so many loops cut in it's impossible to tell which one is in use.

And my cf bike already uses several magnets including a powerful rare earth magnet for my cadence sensor.

But there are still some intersections where my bike is not detected.
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Re: tripping red lights

Postby kb » Mon Jan 21, 2013 2:27 pm

RonK wrote:
hannos wrote:I cannot recall ever having a problem tripping lights on my carbon road bike. Granted, I do use alu clinchers so this would probably be what trips them.

Must be some special magnetic alu clinchers then.

Doesn't have to be ferrous, just conductive. The eddy currents formed in conductive material near the loop generate their own magnetism.
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Re: tripping red lights

Postby RonK » Mon Jan 21, 2013 2:48 pm

kb wrote:
RonK wrote:
hannos wrote:I cannot recall ever having a problem tripping lights on my carbon road bike. Granted, I do use alu clinchers so this would probably be what trips them.

Must be some special magnetic alu clinchers then.

Doesn't have to be ferrous, just conductive. The eddy currents formed in conductive material near the loop generate their own magnetism.


Quite so - my comment was based on the suggestion to install magnets.

But here's an explanation why your bike may not be detected.

"The relatively crude nature of the loop's structure means that only metal masses above a certain size are capable of triggering the relay. This is good in that the loop does not thus produce very many "false positive" triggers (say, for example, by a pedestrian crossing the loop with a pocket full of loose metal change) but it sometimes also means that bicycles, scooters, and motorcycles stopped at such intersections may never be detected by them (and therefore risk being ignored by the switch/ signal). Most loops can be manually adjusted to consistently detect the presence of scooters and motorcycles at the least."
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Re: tripping red lights

Postby find_bruce » Mon Jan 21, 2013 4:19 pm

hannos wrote:I cannot recall ever having a problem tripping lights on my carbon road bike. Granted, I do use alu clinchers so this would probably be what trips them.

Yep - if you are positioned in the right area, depending on the sensitivity of the loops, alloy rims should be good to trigger the sensor.

Whether it does or not, at least in my experience, depends upon the intersection. 3 bike lights on Union St, 1 reliably detects both ways as long as you are within 50 mm of the marked sweet spot, 1 rarely detects either way & the third mostly detects bikes.

No doubt there are some technical differences between the sensors, but I do not know what they are.
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Re: tripping red lights

Postby AndrewBurns » Thu Jan 24, 2013 7:39 am

I'm not usually the only vehicle at the lights to trigger them but I know of two sets of lights that will simply not trigger for cyclists. Doesn't matter if I'm on my aluminium commuter or carbon road bike, I can see the loops so I place myself right where I should for maximum effect and get nothing. Once on a club ride through the city we had ~15 cyclists on the induction loop of one set of lights and it went through two cycles without changing, with an angry bus behind us we decided to just roll through when safe.
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