Thank you JonnyBoy; that is exactly what I needed.
The 275 is the section width in mm. That is the widest bulge of the tire, not the tread. You can convert it to inches by dividing by 25.4 ie 275 / 25.4 = 10.83" or about 10 11/16 inches wide at the bulge above the tread. The 35 is the aspect ratio of the tire, the % of the sidewall height to the width: 275 x .35 / 25.4 = 3.79", that is the side wall height. The nominal tire height would be 3.79 + 3.79 + 20" wheel diameter which is 27.58" or about 27 1/2" for the tire diameter.
I am looking for some 295 or wider for the rear at least 265 for the front.
Thanks for the info - David.