I realized my aggressive Cooper Tires were wearing down when I almost went off Bear Creek road the other day. Good thing I know what to do when a truck starts to go sideways on a rain slicked steep road.

So bit the bullet and went down to the local tire dealer to put new ones on today. Decided to downsize the tire from 285 75 R16 to 265's.

I know they look funny but figured they would work better on the highway (where I really spend my time, not off-road) and be quieter.

So drove down to San Jose tonight to one of my jobs and checked the mileage and noise on the way down.

Normal mileage with this truck is about 15-18 depending upon speed.

On the way to San Jose it was over 20MPH. Nice. And I could hear the radio!

It'll be interesting to see what mileage I get on a longer run.

The difference may not be from the downsize , the new tires should give you an increase on the gas mileage as well as noise reduction .

IMO you have created more torgue and that is all you have done:)
your not really traveling as far on the same fuel load....your speedo is off 3.6% or at 60 MPH your really only going 57.8 there`s your extra mileage...again JMO

The aspect ratio on the tires is the same, i.e., 75 (265 75 R16) so don't believe that the speedo will require re-calibration.

Aspect ratio is a percentage of the tire width, ie 75% of 265mm, so same aspect ratio on different width tires is going to yield different sidewall heights.

I'll have to try a gps application for my iphone to determine if the speedo is off. The car originally came with 265's.

so if it was not changed when you put the bigger tire`s on...then no! its back to stock...if I`m read n ya right

stock tire was 265 75 R16 then you went with an aggressive tire 285-75 R16,now your back to 265`s..I posted a tire calcultor! give it a go

Like to try that, but where is it posted?

Click to view attachment

Click to view attachment

Just found this one ..I like it better,it calculates speed`s from 20 mph to 65

at 65mph your really only going 62.5 mph

Yep that's why I always ran narrow tires on my commute trucks. I used to get nearly 20 mpg in my v8 Crewcab and I ran 265s.

But low rolling resistance tires help even more. I have 285 low rolling resistance michelins on my Jeep. The section of 17 from Los gatos to Milpitas I'm clocking 28 mpg. Averaging 23..5 mpg combined. That's amazing to me as my smaller z with same size motor barely breaks 21 on same commute.

With the 285's, when running 70mph, like on the long trips up to Oregon, I was actually going closer to 74. Lucky I didn't get a ticket.

Went up to Sacramento on Friday afternoon. Averaged 20.6 on the way up and was 19.5 when I got home, about 330 miles later. Nice improvement and pretty good mileage for a big heavy truck.