ok, i got a question. And i'm new to the 4x4 world so this may end up sounding stupid!??

I'm starting to look for aftermarket tires
(BFG's mostly mud or AT)

i have 265/70-17 on the truck now!
i want to go bigger. from what i know i converted the tire size to inchs (most offroad tires are inchs.) and came up with:

265/70-17 is same as 31.5/10.5-17
(31.6/10.43-17 from calculater)

But my dad has 31/10.5-15 and my tires are about 1 t 2 inches taller?

Why is this? did i convert wrong?

(265 is how wide it is and its in mm's, and 25.4mm = 1 inch. then find 70% of that and thats the sidewall multiply by 2 and add in the wheels 17" and thats how tall the tire is.)

is this right?

Why is mine that much taller with little number change between the two tires?

thanks!
GotMud?




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2000 F150 XLT 4x4 Sport
SC, SB, 4.2L V6, 5-Spd - Silver Metalic Clear Coat -

Planned Mod's:

4"-5" Susp. lift
35" BFG's
SuperChip
K&N Air Filter kit

You can eMail me @: scott_isbrecht@hotmail.com
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"One Man, One Search, One Goal ... More Power!"
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thanks everyone!!!

Now i can sleep at night!! Ha,ha

after the lift and 35" tires i'll really be bigger then my dads!!

GotMud?

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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2000 F150 XLT 4x4 Sport
SC, SB, 4.2L V6, 5-Spd - Silver Metalic Clear Coat -

Planned Mod's:

4"-5" Susp. lift
35" BFG's
SuperChip
K&N Air Filter kit

You can eMail me @: scott_isbrecht@hotmail.com
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"One Man, One Search, One Goal ... More Power!"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 

Try www.4lo.com for conversions.

L8,

Mike

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99 4x4 XLT supercab 5.4L Flareside, Deep Wedgewood Blue/Med. Graphite w/Captain Chairs, Pioneer DEP-4000, Tint, K&N, Bedliner, 3" Catback w/3 Chamber Flowmaster, Superchip, 285/75/16 BFG A/T on American Racing Python wheels, Stull Billet Grill, Clear Corner Lenses.

'00 Expedition XLT, Silver w/Dark graphite interior, 5.4L, Stull Billet Grill and some other stuff. All in all she'll stay stock. Ok, maybe a Flowmaster 50 series soon.

 

You did the calculations right. However, one must look at the inflation of the tire. For your tires could be inflated to the max, whereas your dad's could be undlerinflated, which increases the footprint but descreases the height. Possibly if both tires were inflated to their load carrying max, the difference between the tires would be negligable. I have 285/75/16, which is 32.8, but at 40 psi, they are only 32.4.

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1999 4.2l 2wd super cab F-150 3.55 gears LS Mods: 3in body lift, 285/75 R16 BFG AT, suglid tonuea cover (white) 10 disk changer K&N Air Filter Tow package 6000 Lbs GVWR

Things to come: 4.10 gears, Flowmaster 40 series Delta, Superchip, Grill

 

GotMud-

The answer is very easy. Yes, rim size and inflation pressure makes a difference, but dont forget that metric-sized tires are exact (+/- 0.25"), while the english(?) sizes are not.

Much like a 2x4 piece of lumber is not 2"x4" (we americans are pretty dumb), a 31" tire actually averages 30.5" tall (different manufacturers produce different sizes).

BFGs 265/70/17 tire is 31.8" tall on an 8" rim. Their 31/10.5/15 tire is 30.8 on an 8" rim. Knock off another 1/2" diameter (equavalent to a 1/4" of wear) for wear, plus add some more for over/underinflation - you could be looking at a 2" difference (on the same rim size).

 

Loser1, I've got a truck kinda like yours.
What have you done about your speedo gear? I've already gotten a ticket. 84 in a 55. Woops. The transfer gear thing sounds pretty simple. But now, what do we do about our computers. Damn technology.

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1999 Red F150 4x4 5.4L XLT X-Cab
Towing Package
Corporate 9.75 Rear Axle, 3.55 Limited Slip
Corporate 8.8 Front Axle, 3.55 Open
K&N Generation II
Jet Chip
32x11.50 Super Swamper SSR
coming soon
Gibson Headers
40-Series Flomaster exhaust

 

RedBullSr,

Recalibration, let me see if I can remember the details.

I started with 255/75/16's (stock) the revolution per mile is (if I remember correctly) 694 rpms. Going to a 285/75/16 tire, the rpms should be 640. My local Ford dealership said the "computer" cannot be reprogramed.

After doing some research on "our" website I was able to give the dealership detailed instructions on how to reprogram the PSOM (programable speedo odo module). I also provided the rpms for the new and old tire sizes.

To make a long story short, the dealership told me, true or not, that they could only reprogram the PSOM to 687 rmps and not 640.

I left it at that, and just guess-ta-mate my mphs. I also look at it as my truck will be under warranty longer because the miles are shorter with larger tires.

Hope this helped,

Mike

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99 4x4 XLT supercab 5.4L Flareside, Deep Wedgewood Blue/Med. Graphite w/Captain Chairs, Pioneer DEP-4000, Tint, K&N, Bedliner, 3" Catback w/3 Chamber Flowmaster, Superchip, 285/75/16 BFG A/T on American Racing Python wheels, Stull Billet Grill, Clear Corner Lenses.

'00 Expedition XLT, Silver w/Dark graphite interior, 5.4L, Stull Billet Grill and some other stuff. All in all she'll stay stock. Ok, maybe a Flowmaster 50 series soon.