Since the other solutions were unclear or incorrect on this point, I did want to note that the achievement is for winning gold in all events
, not all races. I simply could not do anything on the Professional series, Legends event, Nurburgring race -- I finished 6th, but had enough points to win the event (golded the other 5 races) and both this achievement and the All Gold (Professional) achievements popped.
In terms of simply winning races, some obvious tips, and then some less obvious ones:
First, the game is much easier with all assists on and with the difficulty set to Easy. I did alright on default settings, winning a few races, but once I went to easy, almost all races were a breeze.
Winning or buying a few specific cars as soon as possible will help you on a large number of races. Some cars that were used to death:
* Lotus Exige Cup - all of the Lotus cars are solid performers at low HP, making them ideal for the Semi-Pro events
* Dodge Viper - many versions of this car, they are surprising solid at handling and braking, and can be used in a lot of races
* McLaren F1 - the production and race models are outstanding
* Lamborghini Murcielago - fast, and can be made a lot faster
* Porche R3 cars - obtainable fairly early and will do some damage on R3-caliber races
* Ferrari F333 - the best R1 car
* Konigsegg - a beast when upgraded
Generally, if you have the highest PI in the field, and you've gotten used to the game, you'll win most races without upgrades. If you need to upgrade, I suggest a few key improvements:
* Brakes. The key to keeping your speed up is to be able to handle turns, and crisp braking is key.
* Weight reduction. This improves most of your car's categories significantly, and is usually fairly modestly priced.
* Support Bars. Helps to keep the car from flying all over the place when turning at high speeds.
Other solid upgrades to improve handling include wider tires, better tire compounds, bumpers/wings, and shocks/struts. I didn't find that I needed to upgrade my speed/acceleration too much, but when I did, it was pretty straightforward (cost/HP analysis). Generally, intake/exhaust/fuel system are easy improvements.
As others have noted, you can hire drivers for this, but you win less money (making your car collecting take a lot longer) and it's just not any fun, either.