Delhi Rd? You've only got the Lane Cove National Park nearby. It has seal roadways from Delhi Rd at the bottom to Lane Cove Rd at the top, but you might find singletracks have been carved out by renegade MTB hoons.

Might be something in Garrigal National Park (near the Roseville Bridge) for you tho. Very steep climbs either side of the creek, and lotsa walking tracks that you could probably use as singletrack.