There are various ways to achieve better traction the easies being, a change in tire compound, but also the most costliest in the long run, since they'll wear out faster. I like to start from a neutral car and make adjustments as needed to the easist access parts
Alternatives you can try:
1) Softer shock springs in front give more turn-in, in the back give less turn but car won't spin out as easily.
2)Lighter shock oil all the way around should help out for those bumpy parking lot race tracks (we've all been there
3) A change in diff oil will help with traction by easing your acceleration, but it is the most time consuming. If you make a change here, might want to go lighter oil in the rear diff.
Check you HPI manual or their website and start making you adjustments from there.
I'm not sure if your new to rc or just new to on-road racing, but this track could be a blessing in disguise for you. It's low traction could be a valuable training course for you to work on accerating, braking and Line taking.
Hope this all helps and good luck
I have a great link to helping one understand car setup. I'll upload later tonight when I get back home.