Here's one for you: when we bought the camper five months ago it was
equipped with three generic brand 195R14's and one 185R14. The two
mismatched tires were on the rear. I promptly dumped those and
replaced them with a decent pair of Michelin X reniforced 185R14's onon
the back. I am curious if a) the mismatched tires would have had a
bizarre affect on the engine or suspension (they were well worn) and b)  apart from
affecting the speedometer slightly if running the 195's at the front
and the 185's at the back would create a problem (none so far I think
after 10k). 

BTW the 195's were not reinforced so I elected to leave them up front.
I guess the previous owner was persuaded that a larger diam. tire
would make up for its lack of reinforcement.

DC