Can I use "normal" shoes/trainers with clipless pedals? Is it possible to use regular trainers/shoes (i.e., withou cleats) with clipless pedals?

A friend of mine mentioned he does this all the time. However, I cannot imagine how this would work. Surely the area of grip would be far too small to get any kind of purchase on the pedals.

We both have Shimano PD-R540 SPD pedals.
Yes, you can use them with normal shoes, but as you predict, it isn't very comfortable, especially if your shoes have thin, flexible soles. Also, there's a risk of your foot slipping off, particularly in the wet.

There are various options to temporarily convert clip pedals into ordinary flat ones.


Fly pedals 
BBB BPD FeetRest pedal adaptors (SPD only)