Originally Posted by Floyd
I have a 2018 Thor Vegas 25 three. I'm wondering if anyone has tried increasing the fuel economy by changing out the rear tires. Does anyone know if a larger circumference tire will affect the fuel economy? I'm trying to get the RPMs at 70 miles an hour on or below 2000. Every vehicle I own except for this Vegas will run on or below 2000 RPMs at 70 mph. Has anyone else out there tried to reduce the RPMs of the vehicle through this means or any other?
Tires are a miniscule part due to the restrictions of size we have.
Differential gearing is what you're after for a greater ratio change.
A final drive ratio is what changes rpm.
Unless you live in Kansas or some flat spot,
Different ratio will eat up your savings on the big hills.
A downshift you didn't have before.
Use the wrong final ratio and you'll have the dreaded 'hunt and peck' transmission trying to find a spot it likes.
Below 2,000 rpm might not be a mpg good thing.
Everyone thinks of doing the ratio change with tires or gears but it's an expensive science.
I changed to taller tires on my expeditionary vehicle, then had to change gear ratios so the rpms would stay below 3,000 when on any slope. There was no gear induced torque to keep the tires turning, so I had downshifts.
27" to 31" tires required 3.73 to 4.10 gears to make up for the extra rolling length/lack of torque in the 31's.