I just upgraded my tires from LT245/75/16 to the BFG's 285/75/16.Much nicer and meaner,I was wondering what effects this will have on actual mph on speedo and did I actually lower my gear ratio or increase it with larger tires.The truck doesn't seem as quick on takeoff as before but I really haven't stomped on it either.

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99 F250 XLT LD 4X4 S/C,5.4,3.73 Limited slip,Bright red clearcoat ,4whl abs,remote start w/keyless entry and alarm,chrome rims,tinted,westin nerf bars,factory tonneau,superchip,K&NGen II fipk,pioneer in dash cd,pioneer amp,infinity kappas all around,Lund front runner bug sheild.Gibson split rear,stull SS grilles.

 

You've introduced about 7% error into the speedo & odometer. So, when your speedo says you're doing 60, you'll actually be doing a little more than 64mph.

Your effective gear ratio is now about 3.65 instead of 3.73.

Better check my math to be sure though!

 

Barlitz, could you post or send me a picture of your truck? I am considering the LD, with the same tires as you. I'd like to see how it looks. Thanks,

--Sean

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Happy Off-Roading!
Huntington Beach, CA
Soon to have '01 ORP
Administrator www.clubsi.com
RIP: '94 Ranger Splash S/C 4.0L 4x4 Auto

 

Nomo,

How did you get 7%?

Regards

Sean

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2000 F150 XLT 4x4 Extended Cab

• Deep Wedgewood Blue
• 4.6L Manual Trans
• Ford Tonneau Cover
• Magnum Bug Deflector
• Panther 16x8 wheels with 285/75 R16 BFG All Terrain T/A
• 'Superchips' Performance Chip
• K&N FIPK (With custom mod)
• Westin Side Bars (Black)
• 3" Jardine Cat-Back Exhaust with Crome Tip
• Clear Corners
• Tinted Font Side Windows

 

This should help you. Just know the original gears, original tire height and new tire height.
http://members.home.net/mjbobbitt/f150/tirecalc.html

 

Nomo's 7% figure is correct. Take the diameter of the old tires and divide that by the new tire diameter. Rounded off, it's .93. Subtract that from 1.00 and you get .07 or 7%. The ratio is more like 3.47:1 if you still had the old tires.

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98 F-150 XLT 4X4 ORP Super Cab Short Bed, 4.6, Auto, 4.10's, Magnacharger supercharger, Superchip, Gibson single cat-back, 80/100w German head lamps, Warn HS9500i winch with semi hidden mount, Wrangler dual battery kit with red & yellow top Optima batteries, Torsion bars cranked up 2.5 turns. Needs one more door.