I just bought a 2008 F250 Super Duty Diesel and they came with 325/60-20 tires. The truck has 3:73 gear ratio and my mileage is bad around 13 unloaded on highway. Would my mileage increase if I went back to the original tire size 275/65-20?

What effect are the larger tires having on my MPG and speedometer reading? Thanks
Randy

 

mud tires or all terain? mud are slightly wose.... i am thinking of going up in sizes.......

 

discount tire and others have size comparison tools..
they tell u how much the speedo is off by making tire changes..

Tire Dimensions Made Simple - Discount Tire

Sam

 

Yes, a smaller tire will help.

First of all, those taller tires will make your truck taller, increasing wind resistance.

Also, more rubber on the ground increases rolling resistance.

 

tire size can have a drastic impact on fuel mileage.
basics;
the skinnier the tire = the less the rolling resistance,and better fuel economy.
the taller the tire = the higher the gear ratio which can help,but higher up in the air is no good for fuel economy either.
the shorter the tire = the lower the gearing,for better performance,but lower the fuel economy.
you really need to take your time choosing the correct tire size for your rig.

275/65/20 = 34.1x10.8/20
325/60/20 = 35.4x12.8/20

if you didn't correct your odo,then your odo thinks your traveling less miles than you really are now.making your fuel economy look worse than it really is.
however,you fuel economy will drop going to these tires.not so much for the little height up in the air,but the extra width.

you just added 2" of rolling resistance per tire for a total of 8" extra tread riding on the ground!
you can expect a big hit in fuel economy.to properly see it,you'll need to correct the odo,and hand calc 10 consecutive tanks.

wide tires contrary to popular believe,actually HURT traction as well,in everything expect one case.that being mud.and it has to be DEEP mud as well,otherwise the skinny tire will out perform the wide tire is every single other aspect.fuel economy,performance,traction.

in short,
big wide tires look cool,but hurt you in every single way.
(i like to the look too.don't get me wrong.)

 

I just traveled a little over 400 miles on 275/R70-18's, which are the size that comes from Ford, if I'm not mistaken. And I was getting 16.7mpg hand calculated. A little side note, this was the first long trip in my truck so I zeroed everything out after filling up and off I went. The lie-o-meter, in my truck at least, was dead on. I was a little surprised after reading a lot of post's stating how far off the trip meter was.<O</O