as far as i know the more upgrades u get on ur car the better the handling/steering.....its a known fact......utha than the rims and muffler upgrade they help u with speed...dat bout it... i think

...lol
e.g course A DC2 has only 3 upgrades (exhaust, wheels and hood) plus the the version 2 special upgrade: turbo.. then when u have to renew ur card go to course D(Wheels, Muffler, Rear Wing, Front Body Kit, Side Skirt, Rear Body Kit, Hood)....equal in handling/steering and speed is a good combination.
do sum research on the cars and make combinations so u get a good and equal on everything on ur choice of car.....make theories on how u can improve the attributes of the car u get.
good luck