89dieselkong

So I understand the theory behind having bigger tires means more rolling mass and weight etc. My question is though, having a bigger tire would mean that you should see lower RPM's at the same speed, so wouldn't that counter the weight/mass of a larger tires and make things equal out as far as MPG??

Thanks

06RAM2500

Takes more to get rolling and to maintain.

Dartmouth 12V

If you are looking at highway mileage only, the biggest factor is air resistance. When you go to taller tires, you will have significantly increased your resistance. The higher your truck is, the more air flows under it which adds a lot of drag. Additionally, wider tires will increase your frontal area by a lot. You will bring your rpms down a little which will help a little bit but it will not make up for the extra drag. If you want a truck with good highway mileage, put some small, narrow tires on it and regear.

In town, the issue has to do with accelerating. Our trucks are heavy so F=ma doesn't look too good for us. When you go to bigger tires, you significantly increase the rotational inertia which also hurts you. If you wanted the best mileage for in town, you should go with really small tires and gear so that you are running at the rpm that corresponds to torque peak in the highest gear at the highest speed you intend to go.

Yellow Yota

Yup. What he said.^

SIXSLUG

Just get 'em, you know you want 'em and fuel costs what it costs!

Hawkeye

Find out how far the tires are throwing off your speedometer? Use a GPS if possible or have someone with a cellphone drive next to you. You may find part of the MPG lose is because your speedometer is not giving you the actual miles you have driven.

89dieselkong

Thanks everyone, I don't have them yet, but was thinking of going to a 19.5" rim with taller tires. Other than that I am probaly going to keep the 235/85R16's on.