I'm playing on hard, so maybe that also has something to do with it, but in order to beat the gold cup race, I basically crawled my way through the first 2 laps while making sure to crash into as many of the explosive crates as possible (whilst avoiding the regular ones). This way I could blast through the final lap without too many obstacles left. Don't worry, the A.I. (if you wanna call it A.I.) will patiently wait for you. Dozens of times I've come in second with a complete time of less than 1:40. I finally won the race with a time of around 3 minutes. Really fantastic design there.