Currently I have 285/75/16's on my truck. I am going to put a 3 inch body lift on and would like to put 315's on. I have a couple of questions for you guys who have big tires like this. First, how far off will it put my speedometer? It's only about 4 or 5 off now. How do I get the speedometer re-calibrated and how much should I expect to pay? Second, will the oversize tires screw up the transmission shift points or anything else? I have heard rumors of this. And last, what about new gears? I know I will lose some power and mileage trying to turn that large of tire, but I do have the tow package with 3.55's. Any suggestions? Thanks.

Lok N Load

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1997 F-150 Supercab 4X4,
Royal Blue,
4.6 V-8, Tow Package,
Wheels and Tires,
Performance Exhaust,
Smitty Nerf Bars,
Alpine CD,
Alpine 5 Channel Amp
PPI 5 X 7's,
Boston 10" Sub,

 

Well LokNLoad I think that in one aspect that you're in luck. Since you have a '97, to recaliberate your speedo, you can go to your dealer and order a different computer chip for like $20. (Someone else will have to shed some more light on this subject, because I've never done it myself)
As for gearing, yeah you will notice a great deal of loss in power, but there are a lot of guys on here who run 35's with the 3.55 gears. Good luck and take plenty of pics.

 

loknload,
prepare yourself to be driving a dog...trust me, i made this mistake several times as a younger man...the 4.6 is a great motor, like mine alot...but, that's a lot of tire to be turning...you should consider going to 4.56 gears, 4.10's would be much better than the 3.55's, but, i think he 4.56's are called for here...expect to use 4-lo off-road where 4-hi used to work fine...you've probably already felt some power loss with the 285's...expect lots more...i don't think the tow package is going to make much, if any, difference here...you're still trying to pull big rubber with a 4.6 and 3.55's...best of luck with your decision, Rich.

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-1999 F-150 4X4 XLT SC
-4.6, auto
-3.55LS
-Westin chrome nerf bars
-dual straight pipes
-hikerdadrich@aol.com

 

Yep, gears gears gears. Don't wanna burn up your tranny. And it will do it.

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2000 Ford F-150 Extended Cab Flareside 4x4 Lariat
5.4L;auto;3.55LS;Black/Silver;ORP;remote keyless;floor-shift 4wd;Class 3
Mods so far:
Lund X-Terminator bug shield; Vent Shade Vent Visors; GTS headlight blackouts; Westin Black nerf bars; Pendaliner bedliner; Genuine Steel Products (Longtek Engineering) black Grille/Brush Guard; GTS Tail Blazer II Slotted taillight covers; Clear corner lenses; under hitch backup lights (for now); 2 KC Hilites Daylighter 6" 150W black round off-road lights; Crank torsion bars to level truck; Change gold 4x4 stickers to silver
Pending
2 Polk Audio EX10 10" subs under rear seat
Wish list:
Roll bar; Lots of lights; Flowmaster 40 Series single to dual exhaust w/ 18" SS tips out back; Aluminum dash kit; Change factory striping to silver & black; White gauges; Optima red top battery; Hidden winch; Kenwood or Alpine TV/CD/AM/FM/DVD system; Viper alarm w/ remote start; Remote 5-spd Rancho RS9000s; 4" suspension & 3" body lift; 36"x12.5"x16" BFGoodrich All-Terrain T/As; 16"x10" aluminum wheels; 4.56 gears; Custom tonneu cover to fit around roll bar; A 18' - 26' boat to tag along behind

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