Tiger

I am currently experiencing problems with a tight rear wheel. Brakes, bearings and drive chain all have no problem. Drives under load for first 500-1000 yards then goes free. I've recently had an oil change...could the oil viscosity be causing the problem? I used the manufacturers recommended oil. Has anybody ever experienced such a problem? If so, please let me know what I can do to solve the problem. Cheers Big Ears.