Testing testing and more testing , i don't know how familiar you are with tuning or the tuning part of these forums . But basicly if you like to drive you're own cars in online races you need to either learn to tune them youreself to make them competitive or start testing different tuning garages .
Finding a tuner that fits you're driving style might take some time but it is good fun , testing cars and racing against the clock .
Personally i useally use the odd car to race online and sometimes it works great sometimes i fail miserable , but i still get a good laugh .
also the more difficult the car ( that hated 550pp yellow bird in my garage

) will give you more sadisfaction for coming in 4th orso the winning all the time in that boring M3 , but thats my opinion .
Hope this kind of answer is something you we're looking for , if not i appoligise seeing i misunderstood then .