- The car had to be able to go 100+ mph despite its size and heft.
- The car had to be able to accelerate from zero to 60 in 5 seconds.
- The car had to be able to turn corners at speed. Lots of Hollywood cars can't turn or can't turn very well. To navigate the streets of Chicago (where the car scenes were filmed) at speed, this car needed to be agile. So it has a complete, real-world steering system.
- The car had to be able to jump up to 30 feet and then land completely unscathed.
The braking in particular is interesting. To make the car turn, they put extra brakes on each rear wheel and then mounted big hand levers on either side of the driver. To turn sharply to the left, the driver can brake the left rear wheel separately with the left hand lever. This is very much like the braking system seen on tractors to help them maneuver sharply in the fields.
Once they had the test frame running, it was time for the jump tests. The whole front end collapsed the first time around and had to be completely rebuilt.