Why is it that the headlight on motorcycles invariably seem to “flicker” as it passes you going in the opposite direction? I also notice this in my rearview when one is behind me.
Car headlights, as far as I can tell, do not do this unless they are loose or something. Is this by design? Do all motorcycles do this? And if it is by design, is it meant to be more attention-grabbing to make the motorcycle more noticeable for safety?
Mods, please close thread. My google-fu was very weak. Questions answered.
Thanks.
Just for completeness, there are two reasons a headlight does this. The first is that the rider may have installed a device to make the headlight flicker for added visibility.
The second is that the wheelbase of motorcycles is considerably shorter than the wheelbase of a car, and the suspension is usually not as forgiving, either. You know when you’re driving on the freeway and your wheels are going “bump bump bump” because the surface isn’t level? On a bike that same road can make your teeth chatter while all your organs are trying to trade places. This will also make the headlight appear to flash, as it is tilting up and down.
To answer for those who are reading this thread, what you’re most likely seeing is the result of a “headlight modulator.” If you’re noticing the flickering headlight, then they are working exactly as they’re designed! They are installed by riders that want to be noticed.
I’d argue exactly the opposite. M/C headlights have appeared to flicker since the 1950s, long before IC-based modulators became available.
Front fork “stiction” and a short wheelbase couple to produce a continuous rocking motion in the frame. This nods the rigidly-mounted headlight up and down.
Modern lamps with their aggresive lenses means there is a very sharp difference betwen the main beam which is normally angled slightly down towards the road, & the level-and-above part of the beam which is quite dim. Nod that beam edge up & down just a few degrees at just a few Hz and you get a strong flickering effect.
Add in some vibration if the engine is a primitive Harley-style V-twin design, and you’ve got all sorts of perceived pulsations going on from an utterly constant light source…
If I pay $20,000+ for a new Harley the headlight better not be flickering unless I want it to!
The ones I see flickering around here are a random flicker that leads me to believe they’re the modulators, not vibration from the engine or suspension.
Note that in California it is illegal for cars to have headlights that modulate their beam but motorcycles have a specific exemption to the vehicle code allowing for this.