i have an 01 4x4 with the 4.6 liter engine. i bought the truck with 265/75/16's on it and just went to 285's. the truck was actually pretty good on gas with the 265's and i got like 19-20 on the highway with a light foot. now with the 285's i am getting about 13 or 14 mpg on the highway. i understand that these tires are bigger and heavier but but would it really cause that much of an mpg loss or is there something else goin on? what kind of mpg is everyone else getting with 285's and the 4.6 engine? thanks a lot

 

Did you recalibrate the odometer/speedometer so you can get accurate readings?

 

Start by looking up the specs for each tire on weight, revs per mile and diameter.
You can reach a point where the rpm is so low that the engine torque cannot pull the weight 'on average'.
Look at your tach and see how much of the time the transmission might be running out of lockup or down shifted to third as indicated by the tach.
These things go un-notices until the fuel mileage is the first sign after a change.
The faster road gearing from the larger tire diameter often causes you to put your foot in the throttle deeper. This uses more gas by it'self.
Another example to think about is from total gear ratio.
If for example your rear gear is a 3.55; In OD the trans ratio is about .70, the final ratio is 3.55 x .7=2.485 through the 265 tire diameter.
Since the 285 tires are larger in diameter, the final road ratio is worse yet for you lose torque with the larger tires that causes the trans to try and make up for it without you noticing unless you pay close attention.
Only way to get the torque back is to lower the rear ratio.
Then it grinds out to be for example 4.11 x .7 = 2.877 through the tires. A difference of about 2.877 - 2.485= .392 to the good, but the engine still will rpm higher and go higher into it's torque curve making for better throttle response.
As for fuel mileage, it's all about how far the throttle is open as you drive as to what the overall mileage turns out to be, on average.
The larger tires will make the speedo more inaccurate so you can't use it for mileage calculcations and may cause shift points so change, somewhat.
My opinion is your truck's weight and engine torque can't pull the taller tires without more throttle and possible downshifting, that hurts mileage.
Good luck.

 

Bout what I get with 285's on a 03 5.4 Screw

 

im getting "13" mpg with 285
s 4.6l and i havent changed anything speedo wise

 

i get 14 with 35's

 

If you have a 4.6 you definitly need 4.10's. your stock gears are probably 3.73's or worse 3.55's. The 4.6 will wake up big time with gears. 285/75/16's are real close to 33" tires so gearing will be a great way to get your power and fuel economy back. My old screw with 33's and 4.10's got about 17 hwy @ cruise about 70 and the speedo was dang near dead on. With out gears it's like going up hill all the time hence the crap for gas mileage. I had toyo MT's and changed to AT's due to unsprung weight. The MT"s weight was 18 lbs more than the AT's and was killing the torque of the 4.6.

 

I put 285's on over the 265's, no noticeable difference in mileage. There was a 1 mpg drop at worst. The look was WELL worth the 1mpg drop, but my speedo is actually dead nuts on now vs gps!

 

My mpgs with the 4.6 dropped with the 285's. Im not worried about it tho since i dont drive far enough to be a huge deal right now. And i didnt really feel a huge power loss like everyone else says they do.

 

I dropped about 1 to 1.5 mpg when I put on the Firestone ATs. With the Kellys I dropped another 1 mpg. Currently getting right around 13.5/ 14 in mixed driving. All highway about 15.

 

285x16 is different than 285x 17.
17" tire is a bit smaller diameter in a 70 profile so will pull a bit better than the 16" higher profile will with the same gearing and weight.
Look up the specs.

 

Really not going to be major difference. In the TSR the 16s are only 1/10 of an inch taller. Admittedly the sidewall will flex a little more on the 16s, but not really enough to notice. I ran 265-75-16s on my 98, then switched to 285-70-17s with absolutely no difference in mileage.

 

well when i bought the truck the guy still had the window sticker from when he bought it and on there it said it had 3.31 gears. however, on here everyone is saying its probably 3.55's. anyways, if i went to 4.10's how expensive would that be?

 

To do the front and rear, it's gonna be expensive. Probably around 800-1000 in parts and 1000-1500 in labor if you pay someone to put them in. Thats just my guess, hopefully someone else can give a more accurate price.

 

If you have 3:31 gears; from my lecture above your worse off that in my example.
Not a wonder your suffering with the larger tires.
There is just not enough 'reasonable torque' to run them.
It's all a compromise determined by what you want to achive.
3.31 x .7= 2.137 final OD ratio. A far cry from a 3.55 x .7= 2.485 through the same tire diameter or a 4.10 X .7= 2.87.
Good luck.