You on a road bike? Most of Greylock Road is an unpaved road that I'm sure is probably quite beat up via dirt bikes/atvs... I would guess that you'd want a mtb if you were to go up Greylock road to the old Adams road... The easy access to Rockwell road is from Rt 7 (from the west) which is a lot longer coming from Hadley. The road from North Adams is shorter but a bit steeper than the southern approach to the summit.

You could ride the Ashwillticook rail trail though for a bit which parallels Rt 8 all the way to Adams, MA...

Maybe Pete has more up to date info.. I live west of greylock so normally getting to the visitor's center on rockwell road is fairly straightforward.

You can cut through the Berkshire mall to get from Rt 8 to Rt 7 but it is a fairly short but steep hill that you have to go up and then down to get to rt 7. (there are also ways to cut over north of the mall too..)

Jay