there's a lot of info about rake, offset, trail, etc. out there...I don't think you want to mess with changing your rake. your bike manufacturer chose the original rake for a reason and you probably want to stick with it because you could introduce unwanted shimmy or instability. that said...
Lennard Zinn, a frame builder, posted this answer to a question on VeloNews.com --- hope it helps.
"Very briefly, "fork rake" is the offset distance of the front hub from the center of the steering axis, measured perpendicular to said axis.
"Fork trail" is the distance between the wheel contact point on the road and the intersection of the steering axis with the road. Generally, greater trail means greater stability, and it is dependent on head angle, fork rake and wheel diameter.
In answer to your question, increasing the head angle from 73 to 75 degrees with the same fork does not change the rake. It does, however, decrease the trail and hence the bike's stability.
Trail is also reduced by increasing the fork rake with a given head angle.
Please see the Tech Report article in the July 1, 2002 issue of VeloNews. I explain all of this in great detail there, along with illustrations to further clarify it."
--Lennard Zinn