Everyone knew that speed is one of the elements that could win you a race. In fact, most racers would spend most of their money to upgrade their car than to spend it on anything else. They always want to prepare for the next race since this is where they get their income.
In this game, speed is essential, but your skill is far more important as you need that to make sure that you won't crash in the game. Don't focus too much on the speed since there are lots of turbo that you can get on the road. Use the price money to upgrade your car in time for the next race challenge.