I've bicycled for over 20 years on the rural roads (never in the city) around western Wisconsin wearing various types of headphones without an issue. I ride about 3,000 miles a year.
I tried my Ety6 once, and that was scary. Total isolation.
Earbuds work the best, with the Yuins being my favorites. You can still hear ambient noises, like cars, but hear the music well enough. A windy day will cut back on the ability to hear the music. The Fii0E5 give a bass boost that helps. It certainly is a compromise, but a necessary one.
In the past I've also tried PK100's, iGrados, Koss PortaPros and an untold number of Sony cheapies. The PK worked well, since they are open, but the sweat tore up the pads. The iGrados are just uncomfortable but I do use them on cold days as they double as warm earpads. With a lot of bending the PortaPros worked well to but again the sweat ran through the pads.
Of IEM's I'm guessing that the PL50 may be a good choice, depending on the tip used. They lie flat to the head and wrap back around the ear. They're comfortable.
Back off topic (sorta):
The question of bicycling and listening to music is one I've given a lot of thought too. As noted, I've been doing this with cassette, CD and now mp3 players. It gets me out on the road. Without the exercise and de-stressing that bicycling provides, I would certainly have health problems. But, let's face it, bicycling can be boring, especially if you're riding alone ( riding with others has got to be one of the more dangerous things to do on a bike, most accidents I hear about are with other cyclists ). Without music, I just wouldn't ride as much.
And I do listen to music. When podcasts starting getting popular a few years ago I listened to those. But I found the concentration needed was too distracting and have cut back.
Hearing is the most overrated sense when it comes to bicycling. Presumably, better hearing should alert you to traffic. But you cannot hear many cars when they are coming up behind you. Some are just quiet (like a Prius). Other times wind noise totally obliterates most sounds, including cars.
Sight is a far better sense for identifying traffic. Many hardcore or enthusiast bikers don't have rear view mirrors. A mirror will tell you far more accurately than your ears what traffic is coming up. Is there one car or a line? Is the car weaving around, in your lane or starting to give you some space? Hearing will tell you none of this.
As you can see above, I don't ride with IEM's. I do believe that hearing does play a part in a bicyclists safety. I just don't think it is as important as some contend.
