Yes, we have ballast in the rear as well as many other places throughout the car. We run the GoodYear Front Runner tires all the way around. The traction varies as the conditions of the salt changes throughout the day, there is always some slip as we make a pass.
The roadster actually is drifting quite a bit from side to side as it tries to cut through the wind. It makes fro a fun ride when you are "sliding" throught the course and passing the mile markers every 8 seconds!