Unless you're really good, don't even bother trying to attempt the hardest difficulty with the standard carts.
Save yourself the headache and complete all of Rouge's missions so you can unlock her alternate cart, Eggrobo. He's wicked fast and will blast you into first place easier than any of the other carts can.
It's a bit of work beforehand but if you find yourself stuck or can't win because you keep crashing, it will be a worthy investment. Compared to a near perfect and crashless run with Sonic's stock car, I was able to beat the hardest difficulty in a time that was 12 seconds better while crashing twice.