[FTC]: Wheels slipping on the field

Hey everyone,

We have 2 rear motor drive. with front 2 being omni and back 2 being 4 inch normal wheels. One problem we are encountering is that on the playing field the back two four inch wheels always slip and do not turn accurately. Do you guys have any tips/suggestions for improving traction on the wheels? Perhaps applying something to the wheel.

Thanks for your help!