A pass in the opposite direction. After working with the pup for a total of two hours he finally had a big improvement in his reaction to bikes. The fact that it took this long to get him to stop this behavior tells me that just having him pass a bike here and there on our walks would not have been enough. This was an all-out obsession of his. Seeing a person glide through the air on some hunk of metal with wheels had been a little too much for his brain to comprehend.
Later the same day I asked him to sit down in the driveway and I rode a bike in circles around him (no one was holding him there; he stayed on his own). Then I called him to me, petted him and then asked him to back up and sit down again. Once again I circled him with the bike, then rode the bike to the porch, got off and asked him to come. He ran over happily. That in itself was a huge improvement.
Even later the same day we went for a walk through town. A kid on a bike passed us a few times and guess what? No reaction whatsoever from Spence.
Major improvement. I am going to keep the bikes out on the porch and ride them often around him, asking him to ignore them. We will be working on this over the next few weeks. I want him to not give a moving bike a second look, yet at the same time not be afraid of them.