I would like to record a bicycle ride to get all the feeling of the ride from ambient to mechanical bike sounds. However even if I didn't try I'm pretty sure that if mounted my Tascam dr40 it would be a mess for the noise of the bumps and movement in general. A windscreen is a must of course. Is there an effective way to decouple the recorder for unwanted noise? Or maybe small external mic for this usage?
Your two biggest problems are going to be wind and vibration. A bike's vibration is the worst type, short, sharp vibrations that rattle your teeth. A shock mount attached to the bicycle itself is not likely to block these vibrations. The best place to mount the mic on your body.
The second problem is wind noise. If you are riding at 3-5 mph, you are generating a 3-5 mph wind that the mic will hear. Natural wind will add to this. Foam or a dead cat fur will not block this noise. A blimp with a dead wombat fur is the best you can get. Maybe a harness to mount the mic on your back. Your body would block some (most?) of the wind allowing the blimp to do its job.
Since you are trying to pickup ambiance sound, a shotgun mic might not be the best choice. Maybe a dynamic cardioid pointed down and to your rear?
Someone with more experience may have better advice.