Corrected entry: To get Marty back to 1985, Doc has to time the Delorean's trip just right to have its hook hit the wire when the lightning strikes. Putting aside the wild notion of timing something to the exact millisecond, the alarm in the Delorean goes off while the car is stalled. Marty takes several seconds to get the car started again, which is going to throw off all of the calculations required to get the Delorean to the lightning strike and make Marty miss it.
Phoenix
10th Jan 2005
Correction: They were based on Marty accelerating at a specific rate; all he has to do is accelerate faster to catch up, though of course he has no idea how much faster and gets lucky.
Phoenix