From what I remember this 'glitch' can occur with many cars however it is the most noticable with the FD(since it can jump the 'longest'). What happens is when you get to the jumps with an opponent, you can land on top of their car while doing the jump, however you will appear to remain in a elevated state. While "on top" of their car you head into the next hairpin without without touching the ground. From here on, you can do the remainder of the hairpin jumps without even touching the ground without the use of your opponent,,, and for the rest of the level you will be a few inches off the ground. I doubt this has any effect when it comes down to speed, it's like you are still driving driving on asphalt, but instead you are in the air.