No, its not air pressure, the tires are about 89.25 and 90.50 different in diameter. Tried different pressures from 14 to 20 psi. With the new tires it goes straight. I think if I had a spool it would be a steady pull from one side to the other, but with the sure grip, I am guessing here, locking and unlocking, it is absolutely scary over like 60 mph, all over the place.