A fixed blade would be preferred, always, unless you practice drawing your folder in low light, low temperature, gloved etc. conditions; under duress, while on your bike, or off your bike lying on your back in the mud with an animal (wild, or human attacker).
Anything is better than nothing though so if you do have a folder you can still draw it as an impact device. No need to get completely fixated in using it as a blade only.
Emerson Knives has neat wave feature that is supposed to open the blade as you draw. Those of you with Spyderco; there's a zip tie mod that will do the same.
http://www.thebackyardpioneer.com/2012/08/07/spyderco-zip-tie-mod-a-gear-review/
Above all though, riding in groups, if possible, is always best. Everyone stay safe out there! :)