I am on the verge of ordering a 2000 F150 4X4 5.4L Auto 3.55LS with 265/70/17. After the purchase, I plan on adding a 4" Rancho, 35" BFGs ATs and 4.10s. I can't wait!

My concern is reclibrating the computer for speedo, tranny shift points and any other computer stuff affected by the tire size and axle ratio changes (at this point I want to keep the engine RPMs, auto tranny shift points, etc.. like the stock configuration ... later on, I may play with these variables, but not now).

Does anybody know this info inside and out? I want to know what input does the speedometer require to display a reading? What input does the tranny require to determine the shift points? How does the speedo and tranny talk to each other in the computer? I have been trying to get answers from the local Ford Dealers, but they have been less than helpful.

Since I am new to this forum, I am hoping you can put me in touch with owners of 1999, or even better, 2000 trucks, that have set up their F150s like above. Specific questions I want to ask them include, which method is the best way to recalibrate computer - Dealer computer, Hypertech, Superchip or other method? Also, did they find out any info about the tire and axle changes affecting the vehicle's ABS braking system? Any other computer info problems encountered by tire size and axle ratio changes?

My original plan after purchasing the vehicle was to have the dealer recalibrate the truck for 255/70/16 tires (I still don't know if they can do it), then drop in the 4.10s and slap on the 35s.

If you do the math, the tire size and axle ratio relationship before and after the modifications stays very close to the same number, keeping the vehicle engine RPMs very close to stock. My feeling was it would trick the computer into thinking the vehicle was still stock which would keep, speedo, tranny and other computer stuff like ABS braking, functioning properly.

Maybe there is a better way to do the computer recalibration than my origional plan, keeping in mind my goal (at this point) is to maintain the factory engineered performance of the vehicle (I don't want to play with performance enhancements, like RPM or shift point changes at this point because there are too many variables - I want to do step A first, tires and axles, then step B second, performance enhancements).

If anyone knows some Ford dealers I could call that really know this computer recalibration info, I would appreiate it. I want to know what input variables like axle ratio, tire size, etc.. that the Ford Dealers have control over, and how complete the control is (or does the Ford Factory limit the range of control for each variable).

Thanks in advance for your help. I know this is a long post compared to others, but I don't know how else to convey my problem.

 

WOW already talking mods and don't even have your truck yet.
Defintely canidate for president. LOL
Seriosly get the 16" wheels 17" expensive and hard to find.
Dealer can recalibrate no prob.

 

Thanks for reply. Can't order 16s. 2000 Lariat only comes with 17s unless order 7700 # payload package which costs an extra $1000+ which I don't want. I am glad you responded. From some of your previous posts, I felt you had or could point me in the right direction for the hard facts. Can you help me out?

 

BKM,

Can't you order the truck from the factory with 4.10LS already installed? Wouldn't it save you some money?


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keith@myf150.com
http://www.myf150.com
Rocky Mount, NC

1999 F-150 XLT Styleside, Black On Black, SuperCab, Short Bed, 4x4, ORP, 4.6L Auto, 3.55LS

Mods: DrawTite Class III Hitch, Smittybilt Outland Grill Guard/Brush Guards, KC Daylighters, Custom Dual Exhaust w/ Dual Flowmaster 40's-Straight Out The Back, Airaid FIPK, SuperChips Chip, Bug Deflector, Pace-Edwards Roll-Top Bed Cover

 

The ABS/larger tire scare has popped up here from time to time only to be discounted from many a board member. Don't worry about it. The ABS system will work fine with your new set-up.

As far as recalibrating the speeedo/computer, I wouldn't worry about it either. By putting the 4.10 gears in, you should be pretty close to stock.

Obviousley you have put some thought into this. What percentage change did you calculate from stock to the 35"/4.10 setup?

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'97 F150 Lariat, Flareside, white/sliver, SC, ORP, 5.4 (FQR), Mods: 305/70/16 GY ATS, AR Baja wheels, dual exhaust, Smittybilt Nerf Bars, Edelbrock IAS Shocks, K&N Filter and Carbon Fiber Bug Gaurd. Rigged the fog lights too.

 

I'm glad to here about the ABS issue. My only concern is that I have heard unconfirmed rumours that the physical computer design has changed from 1998 to 1999 models. And that the 1999 and 2000 model computers are the same physical setup. I would love to hear this positive ABS news from a 99 or 00 owner.

Regarding speedo, are you saying my assumption about tricking the computer would really work????

Percentage change is as follows:

VARIABLES
255/60/16 (30.00 inches)
35 BFG ATs (34.60 inches)
Stock axle ratio is 3.55

34.60 / 30.00 = 1.1533 or 15.33% increase in tire diameter

3.55 X 1.1533 = 4.0943 (new target gear ratio - PRETTY DARN CLOSE TO 4.10S!!!)

Thanks for the help. Would appreciate all you can provide.

 

BKM Please remove the "copies" of this topic you have all over the board.
Thanks in advance.

 

Yes. PLEASE remove your copies. I even found a copy in the BEDLINERS forum. Sheesh! How completely annoying.

 

Thanks for taking care of this.

 

Wish I could. 5.4L engine gives you a 9.75 rear axle. Only ratios available from factory with 9.75 axle are 3.55 or 3.73. 3.73 only available with 7700# payload package. Aftermarket 4.10s are my only option. Can you help me?

 

I have a 99 2WD F150 with 35" tires and 4.56 gears. Currently my speedo reads 12% fast. I know the dealer can recal the speedo but I haven't gotten around to it since I put relatively few miles on my truck. But to answer your concerns, I have 4 wheel ABS and have absolutely no problems with this setup.

 

I also agree - all of the posts scattered throughout the board last night were annoying.

Anyway, it seems that you have taken care of all of your problems with the gear change. The math your doing seems to be right on. The final drive should be almost the same as stock.

Good luck with it and by all means let's see some pic's when you get it.