I've never really played the first two "Tony Hawk's Pro Skater" games - I've only began to obsessively play it from the third game onward, but Tony Hawk's Pro Skater HD brought me back to the first two games. So, it might be a newbie question, but here goes: is it possible to chain together street and vert tricks without using the Revert which was added in THPS3?
Back in Tony Hawk Proskater 1(original game, not hd), you were unable to perform a manual. In the second game, they added the manual, but you are still unable to manual after performing a tick from a pipe. Even if you pressed down/up, up/down before landing off a pipe, you cannot combo that trick. Street tricks/rails can be chained with manuals by pressing up/down, down/up as mentioned in the other answer.
I have played all three games mentioned and I am also finding inconsistencies with chaining using manuals in the updated HD game. It seems as though the HD re-make is not polished enough to consistently record a manual after performing excessive grinds/street tricks. Also, it is impossible to chain a manual to a vert trick in THPS HD, unless you buy the Revert DLC Pack, and then it is possible to chain the tricks using a revert move.