Yep their sure is, the radial has less rolling resistance and will roll over the bias tire. These two types of tires are built totally different. You can not mix them with out some sort of handling problem. I had this problem one time with my drag car. I crossed the line at 165, let off the gas and the car started to wobble all over the track, almost lost it. First run with a set of radial slicks on the rear and bias ply Mickey Thompson Sportsman front runners. Did not think much about the problem being the mix of Radial and bias at the time and made another run, only to have it happen again... only worse. Talked to some folks in the pits and they educated me on mixing the tires. I later confirmed it with Mickey Thompson, and asked them to send me some radial front runners speed rated for my car, that did not happen, they were not being made at the time. Ended up putting VW tires on the front, and crossed my fingers that one would not let go on an 8 second pass.