Eh heh, sorry made a mistake in my previous post. You should
play Boost On to stand a chance against those cars on home turf,
not Boost Off.
The ditches are not supposed to make you faster in terms of
acceleration. They sort of act like those train tracks forcing your
car to move along a certain line preventing your car from swinging
in/out too much. So if you use those ditches properly, you should
be able to take those turns at a much higher speed than normal.
This means your average speed on the track should be faster.
You know the part with the 4 consecutive hairpins in the 3rd
section for Akina down? Yeah you can use the ditches on the side
you're turning to help you turn at a higher speed. It's not easy
though as the ditch is just next to the 'barrier' so you might
knock around like a pinball if you're not careful.
Other ditches are on the first 2 hairpins of the 1st section of
Akina down. They're on the opposite side of the turn. These 2
ditches end just before the hairpin. They sort of allow you to turn
earlier for the hairpin giving you more distance. It's because when
one side of the car is in the ditch and you try to turn, the front
wheels will come out first while your rear wheels are still in the
ditch. Because of this, your car sort of turns on the spot. Another
ditch you can use is at the hairpin just before the 3rd section.
It's on the side you're turning to.
It seems Akagi also has ditches you can use. I'm not sure whether
the ditches help or not but if you play Time Attack, you can see on
the analysis screen for Akagi that they take note of whether you
enter ditches or not. It's the same for Akina.