I remember I was in 8th grade when this came out and I was a huge fan of the old speed racer cuz I saw reruns of it when I was little, but never saw this movie because the new show that came out around this time wasn't that good. (I liked it enough to watch it but I knew it wasn't good.)
That might explain a little why this flopped. The older generation of fans was too old to go see it and there was no real new generation of fans that would watch this because they didn't like the new show.
Side note: There's an auto museum I visited recently in Orlando that has this movie's Mach 5 in it and it's for sale. I wanna cop it so bad.