Same here speedo is spot on with 285's. The 285's are only a 1/2" or 3/4" larger in overall dia.

I did not notice a change in mpgs but also have 4:30's and do tow about the same weight as OP.

 

I only had the 265s on for approx 300 miles so I can't comment on how they effected my mpg. I avg approx 16 mpg all highway with 265 and the best I've seen on my overhead display with the 285s was approx 16mpg as well. I know the display can be off but it was within .2 mpg when I did hand calculate a cpl tanks so I take it at face value.

 

They come stock with 265 and the speedo on mine is right on.

 

I believe when they had the recalls they replaced the 265 D with 285 E. I could be mistaken tho

 

Speedo on mine is fast about 3-4% with stock 265/75s. I would think moving up to 285/75s would put it right on.

 

657 rev per mile for the 265's and 634 per mile for the 285's. About 3% difference. Should also change RPM about 3% as well, though in the wrong direction for towing.

FWIW, my speedo is right on as per GPS with 265's. 2000 2WD V10.

 

That sounds about right, before I installed the 285's at 65 speedo was reading 67 to 68 mph. Now it's agree's with GPS and the roadside radar set up before road work zones.

 

we do know that different tires of the same 'size' MAY have different revs/mile depending on the tire and mfg, correct ?

That's why some mfg's with all wheel or full time 4 wheel drive say replace them all at once or at least have the new ones shaved down to within 5% of the old tires ! (but that would be dumb to do, correct? I mean buy new tires and then shave miles off them )

 

I agree that different mfger's of the same size tire vary!

And yes even part time 4wd should have all four tires replaced at once or it's just hard on transfer cases.

Shave tires?????? That's just absurd unless you like to throw money away and if so throw it my way.

So yes I would agree on all counts!

 

Jazz77 brings up a good point. I posted the original question and have 265 on now. I have noticed when driving on trips that my GPS, as well as those auromatic radar stations that show your speed, say I am going slower than my speedo says. Doesn't it make sense that it could be because the speedo is set up for 285s and I have 265s on it now? Just a thought...what do you guys think?

 

No, I don't think so, they come stock with 265's and my speedo is dead on.

 

all 3 of my excursions have been 3-4mph fast on the speedo with stock size tires. same goes for all my explorers they were exactly 3-4 fast, after putting 31" tires on them they are dead on.

right now with my excursion on 265/75s when the speedo says 75mph i'm actually going 71mph. same goes for my other fords stock..2-4mph is normal.

 

First, the radar stations are not necessarily very accurate.

I've compared the SGII (reading RPM & MPH via ODBII)
with both the dashboard and the GPS...

The ODBII/SGII was exactly the same speed as GPS reported.
The speedometer was 3 MPH FASTER @ 70-75MPH than GPS & SGII.
Edit: The Ex is 3-4 MPH slower than the speedometer says, I was tired last night :-)

The trip meter/odometer seem to agree with SGII reported trip distances.
I reset trip meter, lie-o-meter, and SGII with each fill-up,
and after 700+ miles on a tank they are both within 4-5 miles of
each other. AND the SGII is within a few tenths of a gallon of how
much fuel I take.

This means the lie-o-meter is close with stock 265 tires
while the speedometer reads below actual MPH.

When you go to 285 tires most posters claim the speedometer is now
correct - because the RPMs of the engine/tires is lower thus the
computer thinks you are going slower.
But, that would likely mean the ODBII/SGII and trip meter
would be wrong, apparently resulting in the popular position that
285 kills MPG, because you are actually going FARTHER with each
tank than the odometer/ODBII/SGII thinks you are.

I'll be needing tires shortly, and if I go with 285s, I'll borrow an AE
and see if I can re-calibrate things to compensate.

that's my 0.02 - ymmv