Tony Hawk's Underground Cheats

This isn't much but it helps with beating Eric within the time.

ok- you have to get all the green fist icons while following Eric around
Jersey. The hint is that you DO NOT have to do everything he does,
meaning you don't have to grind the things he does to get the icons, and
to get the icons all you have to do is skate near them.

P.S the Fire That He Drops HURTS, so either go around it of jump over
it. (normal jump wont do it so bonless over them )

Unlock by completing Story mode on the Normal or Sick difficulty settings.

Moon gravity is good and perfect rails are good

Start at the entrance of the stadium (where the parked trucks are located, and where you get into the contest. From there, look at the tape. You should see it above the glass dome behind the subway-like spline entrance. Go down left from here and wait for a vehicle to drive out of the tunnel. Skitch it towards where you started from. Make sure you are on the left side of the car. When you are about to pass the subway entrance spline, get of the vehicle and spline the entrance from the side. This will launch you across the dome into the secret tape.

To do 'perfect manual' at the main menu go to options and go to 'cheat codes' and put in 'keepitsteady' then pick your game.
When your playing press start and go to 'options and go to 'cheats select perfect manual and press 'a' button

When skating in Manhattan, it is possible to ride in the back of the DC trucks driving around the city. Skate behind one and jump into the back when you get a chance. Doing so will allow you hitch a ride around the block.