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Carbon Rims & Stoplights?

Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

Carbon Rims & Stoplights?

Old 05-11-15, 11:04 PM
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halcyon100
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Carbon Rims & Stoplights?

I am considering getting some carbon wheels, but worry about not triggering traffic lights.

If you ride regularly on carbon rims, have you had problems triggering stoplights? I have aluminum wheels on a carbon fiber road bike I use for commuting and I generally trigger lights. Maybe a few times a year there will be issues with the stoplights on my commute route. I won't be putting the carbon rims on my commuter bike.

If you have had problems triggering lights, what has helped?
The bike I would put the carbon rims on also has a carbon fiber frame and carbon fiber cranks.
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Old 05-12-15, 12:14 AM
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I've never triggered a light on any sort of bike I've ridden regardless of the wheels.
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Old 05-12-15, 12:46 AM
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Ok. This truly is a new one on me and takes hand wringing to level JEDI MASTER!

It was my understanding that lights were triggered by weight so unless you are at some tipping point between being too light with carbon and just heavy enough with alloy I think I would be most concerned about how heavy the alloy wheels are in the first place!
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Old 05-12-15, 12:50 AM
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lights (at least in the continential USA), to my knowledge, were never triggered by weight, at one time they were, and in many cases still are, triggered by changes in a magnetic field. now, many are triggered by movements monitored by cameras.

so now, in some cases, waving your arms like an idiot in the direction of the overhead wire holding the camera may have some affect.

Last edited by hueyhoolihan; 05-12-15 at 12:56 AM.
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Old 05-12-15, 12:56 AM
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Originally Posted by hueyhoolihan View Post
lights (at least in the continential USA), to my knowledge, were never triggered by weight, at one time they were, and in many cases still are, triggered by changes in a magnetic field. now, many are triggered by movements monitored by cameras.

so now, in some cases, waving your arms like an idiot in the direction of the overhead wire holding the traffic light may have some affect.
Yes, but perhaps not the one you desire...

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Old 05-12-15, 01:00 AM
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It won't make a difference. Motorcycles oftentimes don't trip the sensor, so your bicycle likely won't either-- regardless of the rim material.
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Old 05-12-15, 01:05 AM
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Old 05-12-15, 04:49 AM
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What is a traffic light?
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Old 05-12-15, 07:43 AM
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those things we ignore
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Old 05-12-15, 07:48 AM
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In my experience traffic lights either have enough cars present to trigger the light for you or lack enough cars to care about the traffic light being triggered.
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Old 05-12-15, 08:01 AM
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Bikes won't trigger the light unless the traffic engineer has the sensitivity turned really far up. You can see the cameras on top of some of the lights. Otherwise I just hit the crosswalk button. Sometimes, if I'm riding home late at night (Midnight -2 in the morning) I'll just look both ways and cruise through the intersection. (The other direction has the constant green.)

I think it's legal to go through a red light if you have been sitting there long enough to go through one set of light changes? (In my intersection, my light won't turn green unless I specifically hit the crosswalk button or if a car is actually in the "go straight" lane, so sometimes I can actually watch people turn left beside me but never get the green myself.)
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Old 05-12-15, 08:04 AM
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Originally Posted by corrado33 View Post
Bikes won't trigger the light unless the traffic engineer has the sensitivity turned really far up. You can see the cameras on top of some of the lights. Otherwise I just hit the crosswalk button. Sometimes, if I'm riding home late at night (Midnight -2 in the morning) I'll just look both ways and cruise through the intersection. (The other direction has the constant green.)
+1.

Look left, look right - go through when there are no cars. Otherwise you'll be sitting there until the tires deflate...
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Old 05-12-15, 08:14 AM
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Originally Posted by Bob Dopolina View Post
Ok. This truly is a new one on me and takes hand wringing to level JEDI MASTER!

It was my understanding that lights were triggered by weight so unless you are at some tipping point between being too light with carbon and just heavy enough with alloy I think I would be most concerned about how heavy the alloy wheels are in the first place!
Most use eddy current sensors. Their loops (you can often see the cuts in the pavement) magnetically couple to nearby conductive objects which changes inductance.

Carbon fiber is electrically conductive, although epoxy usually is not.
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Old 05-12-15, 08:39 AM
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Here's your answer - get out your credit card!

New Device Lets Bicycles Trigger Traffic Light Sensors | ECS Redcat Blog
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Old 05-12-15, 09:25 AM
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Thanks for the feedback.

Most of the stoplights in my area are either camera-activated or sensor-activated (metal detecting). I'm not worried about the camera-activated lights. With the metal-detecting lights, I have found that if I roll my wheels directly over the sensor, I can trigger the light most of the time. I have heard that the metal in aluminum rims is generally sufficient to trigger lights. I'm just not sure if the amount of carbon in carbon rims is sufficient. I wrote to Enve to ask their opinion. The person responding just said that carbon is not as conductive as metal and you have to be careful to place your rim right over the sensor. I was already aware of those two things.

The stoplights I worry about are the ones where I am in the middle lane (going straight) and am in between a left turn lane and a right turn lane. I can't easily get over to the crosswalk button and there is usually enough car traffic at those intersections to make it a bit dangerous to treat the light like a stop sign.

I've read about that loop device, but don't want to go in the direction of adding weight to my bike.
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Old 05-12-15, 09:30 AM
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Originally Posted by halcyon100 View Post
I can't easily get over to the crosswalk button
You can. You just don't want to.
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Old 05-12-15, 10:07 AM
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First ride on FarSport 60mm wheels last night and I could not trigger an electric gate (same style sensor as lights) to get out of a neighborhood. Aluminum frame, and I'm accustomed to laying the bike on its side across the wires to get it to open every time. Before the CF rims I had HED Belgium rims. I would have thought it was the frame that aided in triggering the sensor, but maybe the rims were really doing it.

My big steel cargo bike will trigger it by just riding over the wires.

And I've heard lots of people think they were triggered by weight. The wires in the pavement in California have looked the same for at least the last 40 years. What kind of sensor could actually detect weight and be reliable enough to be buried under pavement for years at a time?
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Old 05-12-15, 10:16 AM
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Originally Posted by anotherbrian View Post
What kind of sensor could actually detect weight and be reliable enough to be buried under pavement for years at a time?
One built with alien technology discovered aboard the ship stored in Roswell. Timeline fits...
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Old 05-12-15, 10:18 AM
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Traffic lights are triggered by cameras (the ones around here never detect bicycles no matter what, although supposedly their sensitivity can be increased, it just hasn't been) or electromagnetic induction in which case yeah aluminum rims parked over the sensor will trigger them regardless of frame material (see the link for where to put your bike to trigger the sensors). Some of the induction loops here have been disconnected, so you see the sensor and park over it but the camera which is the actual signal will never see you.

It is never weight. If motorcycles don't trigger them it's probably because they are between the sensors rather than right on top.

In WA we just got a 'dead red' law passed that basically lets you run a red light that you are not triggering.

From the above link:
Extremely low-weight wheels constructed of carbon fiber with no metal in the rim are sometimes used by racing cyclists for competitions. Carbon fiber is a conductor, but the loop conductivity of the wheel is affected by the materials used to bond it into shape.
so yeah the epoxy might mess up the conductivity.
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Old 05-12-15, 10:18 AM
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The eddy current sensors can be triggered by a wheel placed on the loop, as indicated in 13. They are not triggered by bike frames: too small and too far away. Lower sensitivity loops can be triggered by laying the bike flat over the loop. Frustratingly, when streets are repaved, the loops are seldom remarked, which makes it impossible for bike or motorcycles.

Some local municipalities are painting symbols on the exact spot on the road where your wheel needs to be. In difficult cases such as the OP describes, you have to pull forward into the crosswalk, wait for a car to pull in behind you and then motion them forward so they would be over the loop. Many hang back. Probably afraid of bikes.

Left turn lanes are a particular PITA, since there are no crosswalk signals for them and even if there were, you wouldn't be able to get to them. There are a couple local intersections where of the two opposing left turn lanes, only the one with cars in it gets the arrow.

Traffic engineers can respond to cyclists' pressure, but only if there's money available to go out, run tests, make markings, and adjust sensors. Usually there's not. Probably takes a crew of 3 half a day to adjust one intersection.
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Old 05-12-15, 10:29 AM
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Originally Posted by anotherbrian View Post
First ride on FarSport 60mm wheels last night and I could not trigger an electric gate (same style sensor as lights) to get out of a neighborhood. Aluminum frame, and I'm accustomed to laying the bike on its side across the wires to get it to open every time. Before the CF rims I had HED Belgium rims. I would have thought it was the frame that aided in triggering the sensor, but maybe the rims were really doing it.

<snip>
Here's your answer.
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Old 05-12-15, 11:31 AM
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OK, slightly unrelated and maybe peculiar to southern California, but I see drivers ALL THE TIME pull up to an intersection and leave enough room for a whole extra car between them and the cross walk. Is there some legitimate reason for this that I don't understand? Maybe some logic that reads how many cars are waiting for a light?

It's handy for me on a bike because I can pull right in front of them but it seems farcical that it would have any impact on the light cycle.
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Old 05-12-15, 11:38 AM
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Originally Posted by halcyon100 View Post
Thanks for the feedback.

Most of the stoplights in my area are either camera-activated or sensor-activated (metal detecting). I'm not worried about the camera-activated lights. With the metal-detecting lights, I have found that if I roll my wheels directly over the sensor, I can trigger the light most of the time. I have heard that the metal in aluminum rims is generally sufficient to trigger lights. I'm just not sure if the amount of carbon in carbon rims is sufficient. I wrote to Enve to ask their opinion. The person responding just said that carbon is not as conductive as metal and you have to be careful to place your rim right over the sensor. I was already aware of those two things.

The stoplights I worry about are the ones where I am in the middle lane (going straight) and am in between a left turn lane and a right turn lane. I can't easily get over to the crosswalk button and there is usually enough car traffic at those intersections to make it a bit dangerous to treat the light like a stop sign.

I've read about that loop device, but don't want to go in the direction of adding weight to my bike.


It the sensing mech is magnetic, it won't detect aluminum. Ever heard of an aluminum magnet? Steel spokes, hub components, and any other steel components would affect a magnetic sensor.

I have no clue about other detecting technologies.
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Old 05-12-15, 12:53 PM
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Originally Posted by RoadTire View Post
It the sensing mech is magnetic, it won't detect aluminum. Ever heard of an aluminum magnet? Steel spokes, hub components, and any other steel components would affect a magnetic sensor.

I have no clue about other detecting technologies.
I suppose one might read the thread before posting. Or not. Some of us post to learn. Others just post.
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Old 05-12-15, 02:29 PM
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Just carry a cast iron frying pan in your jersey pocket. Seems like the easiest solution to the many problems of upgrading to carbon rims.
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