FUEL

This is not a quick achievement, as you are required to earn all 3 stars on every career race in the game by beating the races at Legend difficulty.

AI Opposition
You will probably find that the AI racers are very frustrating when playing on the legend, do not be surprised if they...

Knock you just wide of a checkpoint gate or knock you off the track / over a cliff / into a tree.

End up sideways or brake/stop in front of your machine, bringing you to a standstill.

Rubber band you just as you get close to the last checkpoint / finish gate and then sneak the win.

The AI in 1st place pulls out a 500m lead if you make the tiniest mistake, or you get done over by the other AI racers.

You crash into random small objects that are very hard to see and come to a halt, miss a hard to see short-cut that all the AI take or mis-judge a corner and end up going from 1st to last instantly.

That said, when you do beat them its very satisfying.


General Tips
When it comes to the races themselves, there are a few general pointers to consider.

The machines start of cheap, but do get expensive towards the end of the game, so unless you have loads of cash, buy wisely, as you will need the high spec machines later on.

Do race the challenges and earn extra fuel/cash.

Do track down the "maverick" (purple) bonus vehicles when you unlock them, collecting any drums you see as you hunt them down, some of them are pretty good.

Be patient, some races you may well nail on your 1st try, but others will seem impossible and will take many retries.

Don't always go for the fastest machine, it may sound strange, but sometimes I found it better to go for a machine 1 step down as it had better handling and cornering speeds.

Consider using a balanced asphalt/offroad machine rather than a pure asphalt or offroad machine on some races. I found this helped mainly on road races, as it helped maintain a good speed if I went a bit offroad, it does also work on offroad races that have road sections.

Knowing the track really does help in this game, especially in the later races where there is poor visibility, so I would always race the entrie race on my 1st try. even if I was miles behind, just to get a feel for any nasty surprises that will get you when you are in 1st and about to win.

Use the GPS but don't always rely on it.
In some races it better to ignore it and take a direct route to the next checkpoint, and yo can often pull out a good lead or more likely catch up to the top 3 with an unplanned shortcut.
In other races, especially the low vis ones, its all you can use to make sure you are keeping on the track and maintaining a good speed.

Good luck