Tire size is specified by the manufacturer. They specify the size based on their frame geometry and other characteristics of the bike. If you have a problem with the rear wheel skidding you have to address the cause of the brake malfunction. It may be as simple as over application of the rear brake and under application of the front brake. You may have a brake that is grabbing due to contamination of the linings or a mechanical issue such as broken brake mounting hardware. You may also have misadjusted or worn front suspention forks. If the front end is diving excessively during braking the weight on the rear wheel shifts to the front making the rear wheel more likely to lock up and skid.