changed from 195/60/14 to 185/70/14; no rpm differance.

I put a taller and narrower tire on. Was suppose to be a 4.25% differance in the speedometer. I drove it on the freeway and noticed no differance in the rpm at 70 mph. With both size tires it turned about 2450. I expected the rpm to drop,even just a little. I know the taller tire is about an inch taller. Shoudn't the rpm drop enough to notice on the tach? I was going to recalculate the odometer for correct milage but this doen't make sense. I guess I will just figure out the milage with no adjustment for the taller tires. In theory it should get better milage. I don't know if this was worth it.

Check your speedometer against a gps. Your Car still thinks its going 70mph. Your just fooling it with bigger tires.

Your speedometer reading versus your rpm wont change with taller tires. Your actual speed versus rpm however will as well as throwing your odometer off by 4.25%. Your car doesn't know you changed tire circumference and is not calculating a new reading. Your wheels are spinning the same rpm in gear in relation to the engine rpm as they were before.

According to the tire size calculator web site, the tire will turn 833 rev. per mile instead of 868. With about 35 less rev. per mile, should'nt the engine be turning less? A manual trans. is a dirrect lock up with no slipping? If the wheels are turning less, isn't the engine turning less?

Yes, but in relationship to what?

Like others have mentioned, check your speed against something external to the car and you'll see you are traveling faster at the same rpm.

I understand it now. When I tried to compare the differance in the odometer reading it was closer to 5% differance instead of 4.25%. But the tire size calculator web site says 4.25 so thats what I will use when calculating the mpg. I am cuurious what the differance will be with the taller tires.