Thunder Twins has been bring sound systems on bike fun rides for about 5 years now in Portland and we have tried A LOT of different things and learned much. Pre-amps, amp/speaker configurations, splitters, and FM transmitter.
A lot of people have asked me about using FM transmitter on bike rides lately and I really have wanted it to work but have to say FM transmitters have a number of downsides that make them sort of lame especially for dance music.
Our Thunder Twins setup(3 or 4 sound systems) have experimented with FM since last year. At this point, we plan on using it for is our upcoming Dropout Bike In Filmfest April 16th but not planning for rides.
Stuff we use:
2 watt transmitter.
Sounds systems range from 100 to 400 watts.
Why it sucks for bike rides:
1. Interference, lots of static. Cause everything is moving around. Even when people walk between the transmitter and receiver it will make some static.
2. You can't have sound source(aka magnets) near the transmitter, creates electro magnetic interference....noise.
3. Lack of Bass, even when setup in flat non moving place, there is a noticeable loss of bass response.
4. Noticeable delay, which has a few factors. Most digital music players have a conversion delay in FM receiver. So with a mix of digital and analog receivers it can sound like a racket. Mostly if there is one or two louder system.
5. Battery is Non regulated power, so as your battery get's lower it sounds worse.
6. Typically in a ride you go out of range, buildings, and etc.
In summary it just don't sound good.