[UnCivic]

Stock tire size on a 6th Gen Civic DX is 185/65 R14.

The engine is a stock 1.6L SOHC. In 5th gear at 60mph, the RPM's are something like 2,500.

Since most of my driving is in 5th gear on the highway, in the interest of lowering RPM's at crusing speed to improve fuel economy, has anyone ever tried to increase the final drive ratio by using larger OD tires?

Since stock size is:
185/65 R14 OD=23.5 inches

Then, I think that the following might fit...
185/75 R14 OD=24.9 inches
195/65 R14 OD=24 inches
195/75 R14 OD=25.5 inches

I asked the guy at the local tire shop and told me that I was nuts. "That car is already designed for efficiency. Putting on bigger tires won't change anything."

However, how would cruising at 2,200 RPM at 60mph not use less fuel than 2,500 RPM?

Does anyone here have any experience with this type of lunacy?