wider tire and traction

As far as slicks go, most Stock racers that are limited to a 9" slick use a 10" rim. This allows you to use more air pressure while still maintaining a full-width footprint and not wadding-up the sidewalls, which is not good. Of course, each application is different and you have to experiment with air pressures for your particular combo. I've heard pressures range from 14 to 30+ lbs! But it seems most are in the 18-22lb range. Radial slicks seem to like a pound or two more pressure than bias ply.

But you will get better results by experimenting/tuning your suspension than simply going wider. But it may not be cheap. There are a lot of Stock class cars in the 9's and 10's with 9" slicks.