Hello all. I have a 2003 F250 SD SC 4X4 auto, 3.73's. It has the 235.85 General Ameritracs on it now. With an open rearend, it will leave a 78 foot blackmark(!) on dry pavement with only "slight" powerbraking! Anyway, I want to put some BFG's on it preferably 285.75's. I just drove it to Tennessee from WV (through the very hilly WV turnpike) and it jarred us to death. Some of it I believe is due to the 10 ply tires. I had 60 lbs of air in them down and 50 back. Anyway, the truck did great, averaging 14-15 mpg at speeds from 65 (Virginia) to 80 in Tennessee. Does anyone regret the 285's with the 5.4 and 3.73 auto combo? It does not seem to have too much pedal left in OD at 75 before it downshifts into third currently. If left on cruise control, it downshifts fairly commonly on my normal drive. If I drive it, I can avoid the downshift by losing about 2-3 mph on some of the hills. This is not bad. I had a 2001 D@!dge Ram with the 318 automatic and it was a downshift king. It would downshift immediately into second gear at 70 mph when it hit a sudden hill. I swore I would never have another automatic in a truck. The Ford holds it's own, though. Anyway, will 285's clear the factory mudflaps? Any input appreciated.

 

I have 265's on mine and 3.73's I won't go any bigger because I run 2,000 rpm's now at 70 mph's
That puts me at the low end of the power band
motor wants to lug all the time in OD.
I have the 6sp ,so I have to shift all the time when pulling my boat and up a hill

It will do it but you'll be on the low end ,motor will
want lug and tranny shift all the time.
Nice top end speed and fuel mileage might gain alittle .

Just My opinion.

Rich

 

I hear dave91gt, my dodge 318 was a downshift nightmare. I could of swore a few times that I had left the trans on the interstate. I love my new powerstroker though, climbs those arizona mountain 6%ers @80 loaded down like it is the plains of the midwest.

 

I just put 285s on mine....Nitto Grapplers...love them. i am leaving in 1 hour to drive from Scottsdale back to my home in Colorado...I usually get 15mpg.....we'll see. I will post when done. My rear end is differnt than yours though.

 

I have 315's on mine, but the 4.11 gears help quite a bit you may want to consider them. I typically turn about 2600 at 70mph and I can't imagine what the takeoff was like with stock tires.

 

dave91gt,

Glad to see a fellow West Virginian on here! I have 285's on my truck and I didn't notice to much differance. (But) I have 4.10 gears. I can pull a trailer and 4-wheeler all my gear up our little hills without much trouble.

Fitter

 

I'm going with 285 Bridgestone Revo's when it's time to replace the 235 Michelin's that are on there now. Also going with 16X8 rims in lieu of the stock 16X7's and a 2" leveling kit. I think the 265's with the leveling kit might look too skinny, so I may ask my tire guy to mount each (265 & 285) so I can see the diff.

Daryl

 

I recently put 285s on my 01 5.4L with 3.73 gears and 5 spd manual. I haven't noticed a lot of difference in power, but my fuel mileage seems to have "tanked". I used to get around 14-15 on the highway but I think I'd be lucky to get 13 now. Could be something else, but the mileage seemed to drop off right around the time I got the new tires. They're mud terrains so they might have a little more affect on fuel mileage than all terrains.

MJC

 

Your mileage is probably still the same but now your wheels are turning slower. For example, the stock Michelin 265 75 R16E rotates at 652 RPM at 45mph while the 285 75 R16D rotates at 634 RPM at 45mph. That's a 2.76% difference. Your odometer says you traveled 100 miles but you really traveled 102.8 so you're "loosing" some miles in your MPG calculations. Quick fix: 1) You could add 2.76% to your mileage figure when you calculate your MPG or 2) take it to Ford and have them recalibrate the speedometer.

 

n578md

You'll need to factor in the difference of the tire size. I went from 265's to 285's that made my milage off by 3.4% meaning that when I'm traveling 60mph I'm actually going 62.2mph. So what ever my total milage is, say 400 (per tank) 400 X 1.036 = actual miles 414.4


Don't know if this makes any sense or not, starting to confuse me..


Later

Big Mick

 

Interesting info... have you had Ford recalibrate for you or know someone who has? Just curious the cost of having Ford do it vs. getting the speedo calibrator from SuperLift? (~ $200)

Daryl

 

Thats too weird!

 

Yes, I went from 245 to 265 on my Chevrolet K2500 (The atrocities in my life never cease, my wife bought that truck, not my fault!) and I figured that out after looking at the RPM info, when I added the 3% difference to the miles travelled, it all came back to normal. I also changed my 255 tires to 235 85's on my 02 F150 and had the same problem plus it wouldn't shift right anymore (another atrocity, it was an automatic!). This time I took it to Ford and they recalibrated the speedo. Everything went back to normal, in fact my mileage was alittle better after the tire change because it took less engine RPM to travel at 60mph. Ford will charge you between $70 and $35 to do it depending on the dealership. I have a friend who had it done free of charge. It's only a 5 minute process if that. They plug their computer in, select the tire size from a list, save it and its done. The new service computers no longer need to have the RPM at 45MPH or tire circumference, they just have a list of "valid" tire sizes and 285 75 R16 is one of them.

 

great!.... Thanks!

 

On a side note, the service computers used to do most maintenance like speedo recalibrating is called a WDS (Worlwide Diagnostic System, I think). It looks like a laptop computer.