How do you determine optimum tire size?
 

I've been looking at new tires and saw Sonic04Edge's thread on how he actually gained mpg's by increasing his tire size. I have a 3.0 with the 4R44E auto tranny and 4.10 gears in the back on 245/75/R16, so basically the same as Sonic04Edge's. Could I expect to see similar results if I went with the 32x11.5x15 tires as well? I know my current tires are too small because my RPM's at cruising speed are too high. I think a larger tire would get my RPM's down to where they should be, and look cool too.:biggthump Any one with ideas?

Theoretically you can reduce RPMs but it will cause your engine to work harder. The weight of the rotating mass will over come the reduced RPMs.

Well, at 60mph, I'm am running at 2500 RPM's in overdrive and I should only be at around 2000. Just trying to figure out where I could make changes to get some lower RPM's. I already want to change tires, why not go bigger, right?

I'd say do 33's. I loved my 3.0 with 33's and 4.10s, I was pulling 17-18mpg easy.

I'm looking for maximum tire minimum effort. I thought that to fit 33's, I would either need a bodylift, or some serious T-bar tweeking. Did you have a lift and/or a T-bar crank?

Maybe this can help you out:

http://www.therangerstation.com/tech...tirechart.html

I had just a spindle lift

think about your transmission.... that 4r44e has a hard time with larger tires until it is reprogrammed. mine had larger tires on it when i bought it (265/75/16) and it shifted pretty hard. luckily for me the ford place fixed it cuz of the warranty.... but after the reprogram it worked great. i have the same engine/tranny you do and the engine does fine with 32s... trans just didnt workout so well until i got it fixed.

OH....tranny doesnt like 35s btw

Thanks Crunchy for that chart. Yeah, when it comes time to change I may upgrade a little bit to 265 or 285's. Right now I'm on the high end of RPM's on that chart ideal for towing and the like. I'm also looking into a tuner so that would help me out too.

I'm pulling 18.5 mpg with 75% city driving. I have a 3.0 auto, 4.10s and 32s as well.