Midnight Club: Los Angeles

Buy the lowest level motorcycle (the Ducati Monster), and max out its stats. The lowest bike is easy to control because it isn't incredibly fast, but it is nimble enough to avoid traffic on straightaways. In the customization menu in the garage, make sure that you choose the ability called "Zone" which slows down time during those crucial moments where you are about to collide with a car.

Go onto a freeway and challenge as many cars as you can. If you run out of boost, just challenge a car and then pause the game and choose to exit the race. it will ask if you want to repair your vehicle and if you choose yes it will repair the bike and refill your boost. from there just beat ten people on the freeway and you will be all set.

There is no need to go and race on the freeway once you have a motorcycle as you need to progress through the main story. Towards the end of the story, you need 25 wins on a motorcycle so you may as well do the story missions.

Mission by mission guide is in my walkthrough.

Once you have unlocked Group 2 Vehicles, the motorcycles become available, with the Ducati Monster S4RS being the first one. You can use it if you want this achievement early on in the game, otherwise, you can wait until Group 4 Vehicles are unlocked to get the best ones.

The Ducati 1098R, which is only available in the Complete Edition or the South Central Vehicle Pack 2 is the best bike in the game, which only costs $15,000 and is the fastest of all the motorcycles. The Kawasaki Ninja ZX-14 is an alternate option that costs $2,000 more than the 1098R, and the best among all non-DLC motorcycles that is a little slower, but handles a bit better.

It will take some time to get used to the bikes' handling if you have been only driving cars, due to their lighter weight, which makes them very risky, with them being able to accelerate faster and turn sharper for a very low price at the major expense of being more vulnerable to damage, being thrown off from whenever you crash and taking longer to get back on after crashing.

After getting a motorcycle, you just have to win 10 races with it, and the achievement will unlock. Afterwards, once you have unlocked Group 4 Vehicles (when you can buy the Ninja ZX-14 or 1098R), you will need 25 more wins to be able to challenge Oswaldo, the motorcycle champ.