This is my first post so here goes.
I purchased my F-150 3 weeks ago and immediately disliked the factory 235-70-16 set up on it. This is a 2wd SC Flare and I don't have immediate plans to lift the truck. I want however to put the largest AT tire on the factory 16's that will not scrub on lock to lock turns without a lift. The other area of concern is the auto trans. and speedo recal. I have read the posting that say that it needs to be done electronically and also read the posts that say it can be done w-the speedo gear in the tailshaft. Does anyone have experience with what size tires will fit and not scrub on factory wheels, and the appropriate calibration (either electronically/ or gear teeth) for the auto trans to shift properly.
Thanks in advance for advice

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1998 F-150 SC Flareside 4.6 Wht/Grey Auto

 

I replaced my wimpy P235/70R16 tires with Bridgestone LT265/75R16 tires and had the speedo electronically recalibrated at the dealer. These tires are 31.6 in. diameter ( according to Bridgstone ) and I don't have a problem with the tires hitting anything. Truck looks "right" now. A word on the speedo recalibration, it took two trips to the dealer and about six hours of two technicians scratching their heads to figure out how to do the recal. First problem was dealer needed the CALIBRATION #, this used to be on a separate sticker on the driver door post, it is now on the tire info sticker on the drivers door post ( bottom right corner of sticker above a "C" ( 6 digit alphanumeric code )) Nobody told the service department about the move. This number is needed by the dealer computer to reprogram the vehicle computer. Second problem is the math! The tire size must be entered as revs/mile. My stock P235/70R16 tires had a number of 720 revs/mile in the computer. If we take 63360; inches per mile; and divide that by 720 revs/mile we get 88 inches which is the tire circumference. If we divide the 88 by pi ( 3.14 ) we get a diameter of 28.03 inches. Wait a minute, the standard diameter of a P235/70R16 Firestone Wilderness HT is 29.1 inches. I guess they figure in wear which would make the diameter less. So I took the 31.6 diameter of my new tires subtracted 1.1 from it, multiplied it by pi and came up with a circumference of 95.77 inches. Dividing 63360 by 95.77 came up with 661.58 or 662 revs per mile, which was entered into the computer. What fun!!! The lowest number the computer would accept was 650 revs/mile which translated to a tire size of 32.1 inches diameter. Don't know what you would do if you put bigger tires on.

The dealer can get this information from Ford by requesting Special Service Messages for your VIN # from Ford Oasis Computer.

Sorry for the long post. Might help someone avoid the same hassle I had.

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1999 F-150 XLT SC 4X4 5.4L
Air Box Mods and K&N filter
P265/75R16 Bridgestone Dueller H/T
Black DeeZee Running Boards
Vent Shades

 

easy to use tire calculator (including revs per mile)
at www.miata.net/garage/tirecalc.html ...
works with lynx (no java stuff)

 

I went from 255/70's to 265/75's. I don't think I need to recalibrate do you? Waht do I say to the cop if not?

 

What's the largest 16" tire you can put on a stock 2wd?

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1999 F-150 WS 4.2 5-speed, reg. cab, short bed, Sport Grill, Pioneer DEH-P4000 CD, Rockford's 5 1/4 in the corners, Tinted windows, more to come....

 

Sorry for the delay in the reply, but access is limited to mon-fri 7-3. I appreciate the great advice, however it looks like it is time for the big "dealer search", I talked to the most local dealer here and the service "geek" said that it can't be done. This guy told me that "all kinda code get into the computer and yer brakes wear out real fast." I think that as soon as I find a dealership that is willing to work with me on this speedo recal. I am in the market for some new tires. Again thanks for the replies.


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1998 F-150 SC Flareside 4.6 Wht/Grey Auto

 

Hey just wanted to say thanks to "jimd" for that tire calc. What a big help in determining tire sizes for comparison

 

one thing that should be noted is that manufacturer's specs on tire size don't mean crap. you must measure the tire on the truck from the middle of the centercap to the ground. this compensates for tire sag due to vehicle weight. manufacturer's dimensions are based on a particular wheel width (probably not what you're running, either).