Which is to say: whenever there was a choice to be made between sticking to the spirit of the Speed Racer cartoons and concerns such as realism or remote plausibility, the movie chose to peel off in a cloud of dust leaving rationality far behind. I didn't have the objections I had to, say, the flimsy logic of the Matrix movies, because the rational part of my brain realized that there was no place for it in the theater and wandered away.
To ask whether any sensible race car designer would spend the weight to include a catapult for flinging a hornet's nest at other cars would be as fruitless as asking why Wile E. Coyote doesn't just order some food from the ACME Corporation.
I did have one intrusion of rationality--when Royalton mentioned getting his start programming on a Commodore 64, I tried to put that and the '43 Grand Prix into a chronology together, but couldn't make them fit well.
I'm not sure I'm eager to see it again, but I had good fun seeing it once.