I have a '09 SCAB with the 4.6 but it has 235/75/17 Hankook AT tires. Not a lot of snow here yet but I have a feeling that these tires won't do well in snow or mud and I am wanting to put on a good AT tire.

I am thinking about 275/75/17 Cooper AT3's

I have searched a lot on here but no real diffninitive answer. I understand it probably wont help the milage or power but would that size of a tire just kill the mileage or make it so sluggish that I hate the truck?

It probably isn't that much more weight or rolling resistance but sometimes small changes that the truck arent designed for will make a big difference.

I have found a like new set of 255/70/17's but I think they would just look too small and disappoint me.

Thanks

 

I have a 2010 scab stx with 4.6l 3v 6 speed on stock size 265/75/18 I believe. I don't think it will be all that bad mileage will go down but shouldn't be anything crazy.

 

What would affect your MPG ...

• not flashing the PCM to adjust for your change in tire size.
  *And this would have to be done by an aftermarket tuner since the resulting diameter (33.2" - 275/75x17) is not within FoMoCo's valid IDS parameters.
• changing tire from Passenger to LightTruck.

As for "sluggish" ... Would depend upon your RAR. With less than a 3.55 you'd probably notice a negative effect.

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Which 4.6L do you have? 2v or 3v? That's important because the 3v got the 6-speed automatic that will be able to better compensate for a lack of effective gearing in your differentials with larger tires.

Joe is correct, adjusting your PCM to correct for the larger tire size will keep your odometer accurate and MPG calculations accurate. Larger tires on the ground will almost always yield a lower actual fuel economy though.