Electric goKart top speed.

[EEDan1010101]

I'm working on a EV goKart with a motenergy ME1115 motor. The top speed while the wheels are off the ground is 51.8 the top speed in about a 1/4 mile straight away on the ground is 31.5
Is this normal? Even if the straight away was 2 miles I don't think the kart would reach upper 40mph so is it just an acceleration issue or power issue?

I am using a sevcon gen4 motor controller and I have the can-usb connection. Currently the motor controller is configured by thunderstuck for the motenery ME1115

 

[motomech]

Don't know, but you may like this site.;
http://www.etotheipiplusone.net/?page_id=2972

 

[EEDan1010101]

72 volt Sevcon Gen4 size 8
I think they are lithium batteries
The kart is around 300+ pounds with the driver.

These are the trip analyzer graphs for both trips.
This is with the kart wheels off the ground.

This is a test run around a parking lot

why is the mph almost half while on the ground. I understand weight and acceleration are factors. But is this something I can mess around with using the DVT software and CAN-USB connector?