[quote=AndyF Measure the diameter of each tire, sometimes they vary by quite a bit. [/quote]
get them within a 1/4 inch on the circumference with a cloth seamtress tape using air pressure, if possible
If they are more than a 1/4 inch now and you can't get them near that try swapping the big tire with the small tire on opposite sides.
Good luck, let us know what you find out
Do you have a manual valve body trans? If so are you starting in 2.nd gear and shifting into high gear as soon as the rear tires start to spin? If not try that and get the rear tire spinning as fats as possible to get them hot sooner