I bought a 2000 xlt used and it came from the factory (or dealership) with 265/75/16 tires. Now, what I have always noticed is that on highway trips, going uphill or into a strong headwind, I can forget about overdrive. It downshifts so much that I just turn it off. I just figured that it was due to the engine being gutless. But I'm curious if Ford SNAFU'd, didn't really put enough research into it, and put tires on this thing that were too big for the engine. Now don't get me wrong, they look great on the truck, but my milage sucks. And before anyone asks, no codes, no engine light or anything.

I see people posting here that get almost 20 mpg and am curious what size tires they have. I'm also curious what putting smaller tires on my truck would to. I know I would see an increase in RPM's, which, in theory, should decrease mpg. But I'm wondering if that would really happen.

Anyone? I'm stumped. I know this thing isn't really gutless because when I have to stomp on it, it flies . I love having a truck that's paid for, just wish I could get more miles out of a 23 gallon tank. Help?


Edit - I just realized that I have oversized tires on my truck and never knew it. Ok. So sizes for used appear to be 235/70/16 or 255/70/16. How much of a difference do you think I could see going to either of these sizes?

 

It is going to depend on your tranny and axle ratio as well. My truck is a 4x4 short bed with a manual tranny and 3.55 gears. I get about 16.5mpg running 70mph. If I slow it down to 55 mph I can get almost 19 if I am lucky. Driving around these back roads I can usually get 17 or so.

A lot of these guys that claim to get 20mpg are running 3.31 gears. Or they might have the automatic transmission which has a higher overdrive and will thus give you better highway mileage.

I forgot to mention I have the 255/70/16 tires.

 

I'll see what gears I have when I get home. Pretty sure I have 3.55's though. Also do have an auto. Right now I can only dream of 16 mpg. I need new tires though so I'm trying to figure out what I should do.

 

You were talking about how tire sizes would change your mileage. A shorter tire will effectively lower your gear ratio. (eg. 3.55 to 4.10) While a taller tire will give you a higher ratio, (eg. 3.55 to 3.30). So, theoretically, going to a taller tire will help out your mileage, by allowing you to run lower rpms at the same speed. However, usually taller tires are also slightly wider. Because they are wider, there is more rubber on the road at any given moment, thus causing more friction, and forcing you to use more gas. So ideally, you would want tall, skinny tires.