I'm having the same problem and I have three POV's installed on the wheel, scary cause I bought 9 kits in total for some friends and even with three on my bike and running at 31kms/h (19 miles/hour), I was only able to see two letters and not that well. I turned off two POV's, I then turned on an extra one and ran at the same speed at still nothing, just a bunch of fast moving lights but no coherent text to see. I asked a passer by if he could read something without knowing what the text said and after a run he told me that he was able just see two letters, 'LO' out of a text that is supposed to say 'LONDON ATHENS 2010'
Interestingly when I was testing it at home with my hand I could see the text but I was close by, in the street it was a very different story, no satisfactory results whatsoever. Help please.