It will be a tough question to answer without knowing what car we are talking about. But the question is why did you not go back to the dealer an complain? While you where there you could also ask the question, they should know...

No, those tires are so close to the same size, it really wouldn's make a difference.

Most likely, depending on how the transmission is geared. Your wrong-sized tires has a slightly larger rolling diameter not. The sidewalls are each... (195mm * 5% ...) 9.75mm bigger, so the actual diameter difference is 19.5mm, or more than 3/4". I could go through a lot more math but here is the net result: 1) Your effective gear ratio is taller. While not as bad as starting out in 2nd gear, your engine WILL have to work harder to counteract the larger diameter. Saturn S-series were geared over-tall and thus would be an undrivable nightmare; they need all the gear they can get so smaller-than-stock tires are better. 2) Your handling will suffer slightly as there is a little more sidewall flex. 3) Depending on the car, there may be some clearance issues. Most cars have large enough wheel wells that this shouldn't be a problem, but this is not universal. Some cars may rub the tire, especially if you drive where/how I often do. 4) Your speedometer and odometer readings will be off slightly. But back to the original question, refer back to #1 above. If the engine has to work harder, it'll use more gas to achieve the same performance as you originally had. While some may say that the larger tire means that you'll be able to achieve the same speeds at lower RPM thereby saving gas, they forget about the increased torque requirement (power is a product of torque AND RPM) that more than obliterate any such gains. Oh, and they didn't do their job right. Did you AUTHORIZE them to install a tire other than the specified size? Did they consult you before making this modification to your vehicle? Or were they just blind/incompetent? When I get tires, I tell them EXACTLY what size I want and if they balk or don't have it, I go elsewhere. Start talking rolling diameters and revolutions per mile and they start shooting straight with you ;)