This might be more of a general automotive question but I just bought a 95 accord exr 2.7 v6 and I was checking the tire size posted in the door well and the tires on the car. They differ the car says it should have 205's and the car has 195's on it.

Is this a big deal? What kind of problems could it lead to or will it affect my performance or efficiency?

 

having different tire sizes will impact Gas economy, speedometer readings, transmission, braking distances all depending on the difference in size. What you have is not a huge difference, unless the sidewall height is like 45, then that would cause issues.

205-60-15 is the width / height / size of the OE Accord V6 95-97
if you want to upgrade to a 18" you can without issues, but the parameters will change ...
the sidewall will get thinner ( low profile ) to compensate the 15" --- > 18"
the circumfrence of the tire will increase 15" ---- > 18"
and the width of the tread will need to increase to have contact patch with the ground for proper readings of the speedometer
it's better to have the "right" size tire on for that vehicle

if you have aftermarket rims / mags on like 17" 18" there is a way to properly size the tire diameter with the width of the sidewall height and circumfrence

your best friend

http://www.miata.net/garage/tirecalcold.html

tells you what the avg speedometer loss / gain % is with any tire upgrade / downgrade

for your accord v6check out http://www.v6performance.net

<--- AKA cowgodv6