If you draw an imaginary line through the center of the neck to the ground, it will contact the ground in front of the tire contact patch. The measurement from where that line touches the ground and the tire contact patch is the "trail". It, along with the rake of the neck, effects how the bike steers. Ignoring other factors, increasing the trail will slow the steering and make the bike more self centering. That is why when you lower the rear while leaving the front stock, the bike will ride very straight and stable while going down the highway. Changing the rake of the forks without changing the rake of the neck will decrease the trail and make the bike more twitchy feeling. The increase in trail caused by raking the neck can be compensated somewhat by installing raked trees. Since they push the wheel out more, they shorten the trail measurement and bring it back to a more normal amount. There is an optimal amount of rake & trail for every chassis, but the engineering needed to determine that is WAY beyond my feeble mind.

Paul