http://drewish.com/blogger/archives/2005/03/17/2sided_pov_toy.html
political statment aside…thats freakin awesome! those low rider racks are killer too.
I hope the text is reprogrammable. 
He doesn’t mention how fast he has to go to make the image persistent. I’d guess that with only one LED thingy per wheel that he’d have to be going pretty fast.
You don’t need to go incredibly fast. I’ve seen something like this give work at about 100 rpm.
That is fast. Bike racing cadence is 90.
Sorry, I got the terminology wrong. I mean 100 turns of the wheel per minute.
The POV thingy I saw wasn’t on a bike, it was a disc spun by a motor. It could display 3 flickery but readable letters.