I know these are stupid questions, please be patient... I inherited a 1976 Dodge Cobra motor home. I am trying to determine the length of said RV. Every paper I have received including the title does not have the size indicated. Is there a way to determine the actual size without chalking the length on the sidewalk and measuring the distance? On tire size, I am finding 8.75R16.5LT M/S are hard to find, most dealers around me do not carry half sizes. How does one find which tires are compatible? Can you go up a size, like on car tires?