I can tell if I am going fast or slow by the wind in face and by how fast the landscape passes by. You can easily measure your rpm if you have a watch (I don't have one). Count how many times your pedals go around in 15 seconds and multiply by 4. For some reason though I know if I am pedalling fast or slow without measuring. I also feel if my heart beats fast or slow and maps can tell me distances quite accurately and they are beautiful to look at.

What I really want is a handlebar TV!