I rode a 2002 C10 for 9 years and 98,000 miles before moving on to a 2009 C14. I highly recommend Avon Spirit ST front tire. I used the 120/70ZR18 for years, with excellent results. It is a radial tire. I had both front and rear Avon Spirit STs, both radials, for years.
I'm installing them on my "new" C14 next week. Great tires, work well in wet and dry, and last a reasonable number of miles. Excellent handling on curvy roads, of which we have plenty in my four-state area (MD, PA, WV, and VA). Nick Diaz, Middletown, MD.