How-to Guide / DIY on Red Lights... by yours truly.
Those loops are induction loops. It works by generating a small magnetic field that large masses of conductive ferrous material will disturb and set off the sensor. Unfortunately, sport bikes usually have a hard time with this because of the lower overall iron/steel mass that it has. Can't produce a strong enough eddy current to trip the sensor. It also doesn't help that many sport bikes have a lot of their steel parts replaced with aluminum to reduce weight. This also decreases it's ferrous mass as well. Aluminum's paramagnetic properties is much too weak to make up for what's lost when swapped out in lieu of steel. My cruiser trips all lights very reliably since all that extra steel mixed in with the chrome gives it a very high conductive mass. Also those induction loops are very sensitive to speed changes. Theoretically, if your sport bike doesn't work passing through the loop slowly, you could go through it faster and will create a larger eddy current which may trip the sensor. Contrary to popular belief, just sitting inside a loop not moving isn't enough to trip the sensor since the tiny eddy current of the rotating mass of the engine isn't generally enough to trip the sensor. A large enough magnet helps because of it's ferrous materials and it's closer proximity to the ground.
Correct. Generally the sensitivity is turned down so large vehicles don't set off multiple sensors. You see issues with motorcycles at lights in areas where large semi-trucks and the like generally pass through. Also, the amount of detection for paramagnetic materials is almost non-existent for the sensors in the ground since they sense large eddy currents which reduce induction and paramagnetic materials generally need a magnetic field to work. Also when that magnetic field is present, the magnetic affect on the paramagnetic materials like aluminum are vastly weaker than a ferrous material like iron. You would have to max out the sensor's sensitivity to get paramagnetic materials to set off the sensors. They are designed for large ferrous materials to set them off. Our changing bikes to using lighter materials like aluminum kinda screwed the pooch for us and these sensors, especially since engineers who designed these bikes didn't think about induction loop sensors during design. You actually see issues with induction sensor lights and super cars as well. Many of the super cars have shed most if not all of the steel and iron in them and went to aluminum, titanium, and carbon fiber. I've seen Lamborghinis stuck at lights because the sensor wasn't sufficiently sensitive enough.I have heard that the reason some of those induction loop sensors don't reliably sense motorcycles is because the signal maintenance crews often turn the sensitivity down too much, so they won't false signal in the rain or from next lane crosstalk.
Actually, induction loops can detect non-ferrous metals. Any good conductor of electricity in the alternating magnetic field will absorb energy and be sensed by the loop. That's why rain or wet soil can set them off.