Jim’s Tech Talk
By Jim Langley
I’m letting reader Phillip Young steer the Tech Talk sled this week because he took the time to share what seems to me to be an ingenious tip – and even provided photos. His hack is a new one to me, too.
It concerns how to get those annoying under-pavement red light sensors to detect your carbon wheel-equipped bicycle. I’m sure you’ve experienced intersections that seem to completely ignore you and your two-wheeler. And, I think it’s gotten worse when you’re on a carbon frame with carbon wheels. You sit there hoping a car or a metal bicycle will come along to trip the light.
Phil has what sounds like a better idea. Read on and then please comment and let everyone know what you think. If you have some red light tripping tips and tricks it would be great for everyone to learn about them.
For example, I know some riders lean their bikes so they’re almost flat on the ground to try to get something to trip the sensor faster. And, if there’s a pole with a walk button, hitting that button is a way to get the light to go green, too – though it’s not always safe to get to that pole.
Here’s Phil’s trick. He wrote:
“Would you please pass this traffic light safety tip along to the RBR readers with carbon rim wheels?
Carbon rim bicycle wheels usually do not trigger traffic signal light sensor coils buried in the pavement and this can be a safety issue. The non-conducting carbon rims do not change the magnet field around sensor coils, so the traffic light doesn’t change for you. (Aluminum rim bicycle wheels usually do trigger traffic signal lights if the wheel is positioned parallel to and directly over the pavement sensor coils.)
If the traffic signal light doesn’t trip in your travel direction and you have waited for 2 or 3 minutes, you may be inclined to run the red traffic signal light dodging traffic at your peril. [Editor’s note: I believe it’s legal to do this in most of the USA.]
How I Modified My Carbon Wheels
My carbon rim bicycle wheels would not trigger traffic light sensor coils buried in the pavement until aluminum foil tape was applied to the rim circumference with some foil tape overlap.
I Added 3M adhesive backed aluminum foil tape cut about the width of rim tape where the normal cloth rim tape goes. Please see my photos. The adhesive backed aluminum foil tape sticks well to the carbon rim material and weighs almost nothing. This should work on all carbon rims using inner tubes.
Push the aluminum foil tape down against the rim to get full contact and adhesion. Install the normal cloth rim tape on top of the aluminum foil tape. The foil tape also offers additional support to the rim tape over the rim spoke holes.
The rim with aluminum foil tape now reliably triggers traffic light sensor coils. The bicycle wheel rim with aluminum foil should be positioned parallel to and directly over the sensor coils buried in the pavement rewarding you with a green light.
May your travels be safe and green lights always be with you!”
Thanks very much for sharing, Phil!
Ride total: 10,036
Jim Langley is RBR’s Technical Editor. He has been a pro mechanic and cycling writer for more than 40 years. He’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Check out his “cycling aficionado” website at http://www.jimlangley.net, his Q&A blog and updates at Twitter. Jim’s cycling streak ended in February 2022 with a total of 10,269 consecutive daily rides (28 years, 1 month and 11 days of never missing a ride). Click to read Jim’s full bio.
Phil,
This is a great idea, and one that evokes a “why didn’t I think of that”.
I like the idea that it is thin and also provides support for the woven rim strip.
Now, the question is how to trim off a nice even strip of the correct width. I personally use ENVE 3.4 carbon wheels.
I have also seen metallic tape in other metals, such as copper.
Perhaps someone would know where to find a source of metallic tape that happens to be the correct width – at least for certain rim widths.
All my best.
I’ve seen fairly narrow adhesive copper tape used in stained glass windows. You might check a store that sells supplies for stained glass.
Why not put it under the for bed in your shoe? I would think that’s better than adding rotating mass to your wheel.
Yes, and you would think cleat bolts would help especially if someone uses SPD cleats.
My very basic understanding of electromagnetism, and how inductive loops work, is that size matters and mass doesn’t. That is, it’s not about the amount of metal, but the physical dimensions. An aluminum rim looks the same to the loop detector as a 622mm diameter sheet of metal. Your shoe looks a lot smaller so is much less likely to be detected. Other comments mention cleats – way too small to have any impact.
Where I live the sensors won’t even activate the lights while I’m on my STEEL bike! So either I push the walk button or after stopping and making sure traffic is clear I go through the red light.
Why not put it under the foot bed insert in your shoe? I would think that’s better than adding rotating mass to your wheel.
Excellent tip! Thanks.!
Also, Syborg’ idea sounds like it is easier and definitely worth trying.👍🏻
It may also depend on the sensitivity of the sensors. Here in Indiana we never can trip the sensors, even with aluminum wheels. My brother-in-law, who lives in Palo Alto, CA, says it’s possible to report sensors that aren’t tripped and they can be adjusted. Indiana is one of those states that permit you to treat a red light as a stop and go if you’ve waited two minutes for the light to change. Sometimes our estimate of the two minutes may be a little premature!
Illinois has the same dead red law. We have to wait 3 minutes. Goes for bikes and motorcycles.
Early one morning I rode up behind a group of cyclists waiting at a red light with no cars around. One rider was off his bike jumping up and down as hard as he could inside the sensor circle in the pavement. I overheard him explaining to his mates that the bikes were too light to trip the pressure sensors for the traffic lights and this was the best way to trigger them. I was very tempted to let this guy do jumping jacks in the streets for the rest of his life, but decided to educate him on inductive sensors instead so we were not stuck at this light forever.
I wonder if there’s enough steel in Speedplay Zero walkable cleats to trip sensors?
Living in the Upper Peculiar of Michigan I was not even aware of sensors buried in the pavement. We’ve had electrify for a number of years but are a bit behind in other tech…and that’s the way we like it. A big billboard near the southern approach to the bridge over the Straits of Mackinac: “Welcome to the Upper Peninsula same state different state of mind.”
For those using them, I would think there is enough metal in an SPD clip to trip the sensor.. Just need to plant your foot on it.
Your bottom bracket will have enough metal to trip most sensors. I am successful most of the time positioning my bike bottom bracket over buried sensors.
David – it’s highly unlikely that your bottom bracket is tripping any sensors – it’s way too small. But your complete drivetrain, including crankset, chain, etc. may be enough if the sensors are adjusted correctly.
I’ve done this successfully as well. Since chains are steel, I’ve tilted my bike to the right bringing the chain down to the pavement over the sensor wire.
I don’t know but my motorcycle doesn’t reliably trip the sensors with a lot more aluminum and ferrous mass than my bicycle. Sometimes I try and time it with a vehicle and sometimes I do a 270° turn.
I read a guideline on the magnetic sensors that showed that the place for one to line their bike up is across the middle of the circle. For a long time I thought that one needed to aline one’s bike along a side of the circle but that’s not it.
I think this aluminum strip approach will help but only if you’re in the proper place: right across the middle, not on one side or the other
https://www.youtube.com/watch?v=Sj-mNB6dLkk
No, you want to be as close to the loop as possible
Apparently that varies from state to state and even in this video it ca vary. At one point the moderator states that you want to be aligned on the right edge but later there is an image showing the “X” on the left edge.
In Southern California, where some places to have a bike like for bikers to line up on, it’s down the middle, not on the side, and there is a Department of Motor Vehicles thing (I can’t find it now), that clearly shows using the middle of the circle and that location does work on most of the lights I encounter.
This is an updated comment from an earlier comment based on different comments in this thread
Apparently that varies from state to state and even in this video it ca vary. At one point the moderator states that you want to be aligned on the right edge but later there is an image showing the “X” on the left edge.
In Southern California, where some places to have a bike like for bikers to line up on, it’s down the middle, not on the side, and there is a Department of Motor Vehicles thing (I can’t find it now), that clearly shows using the middle of the circle and that location does work on most of the lights I encounter.
Different states and jurisdictions have different specifications for pavement sensors. In Michigan, I have been in a group or more than 6 riders who parked over a sensor and it still did not trip. The “aluminum foil in the rims” would have zero effect on that situation. Amazing how many people think there is a weight sensor in the pavement.
Great piece Jim. Charles Wells and I have been playing around with this idea as well. I have been riding with copper tape on my carbon rims for over a year now in San Diego, CA, and I can attest that the tape does make a difference. It’s not 100%, but far better than before. We have found that positioning is also important in tripping the sensor. It depends on the type of sensor, but generally the best place is right on top of the lines of the induction loops. I did some testing one night on a circular induction loop with two wheels (one with tape, one without), and I found that the optimal position to place the wheel is directly on top of the sensor lines, tangent to the circle. To use the analogy of a clock, 3 0’clock and 9 o’clock were the best. This link is a great resource as well: https://www.bikewalknc.org/bicycle-detection-at-traffic-signals/. I hope this helps!
Thanks for the great replies, everyone!!
Jim
i think it has to be iron or magnetic to work.
steel cleats may be enough, if you can see where the sensor wire is. otherwise it may not be enough steel for it to be ‘seen’.
one thing i do is lay the bike over so the steel chain gets close to the sensor
more usually, i just look around for The Law and then go anyway.
Larry, no need for iron/steel or other magnetic material. We are inducing current in a loop, so the material just needs to be an electrical conductor. Most electrical components that use this phenomenon, such as transformers, speaker coils, etc., use copper since it’s one of the best conductors. The loop in the road is almost certainly copper, not steel. Also, the bigger the loop the better – a wheel is great, a cleat won’t work.
Thanks, a good reason to keep riding alloy rims. Home Depot has a good deal on lead Pb tape.
Intersections are dangerous at all times, imho the longer you sit there the more likely a distracted driver
will run you down. If it’s clear, I just roll,
a moving target is harder to hit..
Personally I much prefer to cover my bike helmet with tinfoil and then lie down on the sensor with my body aligned north to south. This allows proper energy flow while also preventing the UN helicopters from reading my brainwaves. Works a treat! That way they can’t track me after I jump the red light and proceed on my way.
YMMV
I have found if you ride right on the lines, that will trip them as well.
I have put magnets in my shoes under the liner. Plus the best place to trip the sensors in the road is where they cross paths
FYI. Most of these sensor “Coils” are actually within a single strip of plastic sheath,
Look for the cuts in the road surface that they place these ‘wires’ in.
In some places in the world (New Zealand) they often cut a diagonal grid, in others its a square or 2 squares.
It is very unlikely they will cut a circle as they often just use a concrete cutter to cut the channels and pust the wire to the bottom then fill with a cement/tar/butyl/epoxy/’add your countries filler here’.
The sensitivity is usually now set to pick up chains etc. but older traffic light coils do a poor job of picking up motorcycles.
One could lay their bike chain along a cut.. or wait 5 days for the light to change…
Check this out from Australia regarding their bike systems.
(I am about to help install a sensor in Wellington New Zealand… Very 1st thing I thought of (As an MTBer myself) is a full carbon bike with alloy skeletal pedals etc… (or a road bike all carbon and I have even seen Kevlar spokes… (luckily we’re not all that rich)