Electric go kart
 

I am going to build an electric go kart this summer, but I am having trouble finding the correct motor to use. I was thinking of using only 1 Motenergy ME1003 PMDC Motor and running it at only 24-48 volts. I know that some other models can run at up to 72v getting around 3700 rpm. The combined weight of the kart and the rider is about 300kg. I am looking to go at least 40mph. What is best for this application?