I think BHibbs' explanation was a good one. Do note #7 of the instructions (cited above) required to recalibrate the speedo:

Enter tire manufacturer's specification of revs/mile (tire revolutions per mile). If not available, use Formula of: 63360 Divided by the Circumference of the tire measured in inches.

63360 is the number of inches in a mile (5280' x 12"). The speedo is programmed based of the size of the tires shipped with it. Do the above calculation, then do the same thing with a proposed taller tire, subtract the difference and you would arrive at how many fewer revolutions of the wheel the new taller tires need to turn, in order to cover the same distance as the OEM tires.

Wise thinking young grasshopper. Should you have the foresight to do the calibration at the same time (or very near) when you get the taller tires mounted, it would give you documention as to the accuracy of the miles displayed, should you decide to sell your truck and the question arrises.

While I can't say with absolute certainty, I am reasonably sure when the computer is adjusted for the new tire circumference, all the other related functions will be adjusted as well.

 

I would never have thought that when I started this thread some time ago that there would have been 100+ responses to it. when I get my truck next week I will post some pictures of the bigger tires I have desided to get. I have desided to go with the bfg 285/70/r17 . I have also already bought that daystar 2.5 inch front lift. I will post pics with stock tires with new tires and later with new tires and lift kit. I am not sure how long it will take me to get the lift kit in because I haven't desided if I am going to put it in myself or not.

 

Good deal!!!

 

is it still possible to crank up the torsion bars on the 2004 to lift the front?

 

I am not sure but I thought I heard someone say the new 2004's do not have torsion bars with their new suspension. someone let me know if I am wrong.

 

You are correct...that's why the daystar is the best option for a level truck.

 

what is involved with the daystar lift and where do can you get it?

 

the daystar lift is mounted above the front coils. you compress the coils slightly and bolt it on above them. it involves bolting 2 pieces onto each coil. this will level the truck out. it has been said that you can do it yourself if you want. i talked to the daystar people at the off-road expo this past weekend and they made it sound super easy. keep in mind, daystar is not a lift kit per se, it is a set of spacers. check out daystar's website:

http://www.daystarweb.com/

 

I don't know that I agree Daystar being the "best" option for a level truck. If you have a 4x4 and are going to stay with OEM (or nearly so) sized tires, then it might be worth your while to investigate removing the blocks in the back (first) and replacing the shackles with the 2x4 ones. I have not crawled under the trucks to see first hand if this will work, but I was told by a Ford mechanic it can be done this way. Anyone that knows for sure, please chime in here.

As for lifting the front end; spacers have been around for some time now, and in my estimation, they are not the best solution, but rather a cheap fix. The coils are engineered to compress and expand to given dimensions at predetermined rates, and are designed to utilize shocks made to work within those specs. The best option (for those that can afford it) is to get new custom springs wound to factory specs, but taller in height and shocks designed to work properly with the taller springs.

I don't mean to be a wet blanket at the Daystar party, but we have those here that are new to lifting and altering suspensions, that I believe should be aware of the tradeoffs involved with using spacers. Ford spent huge money engineering the best riding truck ever -- it would be a shame to screw that up using a budget solution. Donahoe Racing is going to offer a better solution soon. I am sure other lift companies will follow suit quickly. Personally, I think one would be wise to be a little more patient about lifting the '04 F150s.

 

Billstein will be offering a good new lift. I saw saw a custom lift on a 2004 F-150 Scab at the off road expo. It used all Billstein parts and was done by Off Road Unlimited. I emailed Off Road Unlimted to see when they are going to post pics of their awesome truck. There will be many other options available besides the Daystar spacers.

I think if it is just for looks and not off roading, then spacers are fine. If you are lifting your truck to take it off road, you should think about putting in different coils and spending the money to do it right. i would imagine (though i may be completely wrong) that the ride with the spacers would be a little more rough and bouncy, no matter on or off road, because the springs are partly compressed to begin with. they lose some of their travel which can comfort the ride. just my opinion, no proof here.

 

A few more thoughts of this subject...

I remembered a friend had once used a Superlift TruSpeed Speed Signal Recalibrator (read more here) on his first modded Excursion, so I did a quick search to see if they had anything for the new F150. Sad to report, nothing for any Ford newer than '01 listed, but it did remind me there are some other issues related to changing tire height. From Superlift:

"Virtually every vehicle manufactured since 1992 is equipped with an electronic speedometer that uses a sensor to read vehicle speed rather than a mechanical cable. This speed signal is a big factor in the overall performance equation. The speed sensor sends its signal to the Engine Control Module (ECM), the Powertrain Control Module, transmission, and if applicable, the anti-lock system "brain." When tire height and/or axle gearing is altered, these control units receive erroneous information. In all but the most extreme cases (really huge tires), an incorrectly calibrated vehicle will operate, but not at its peak. For example: if a vehicle is factory equipped with 28" tall tires and they are changed to 35s, a 20% change has occurred. Unless remedied, the various control systems will "think" that the vehicle is traveling 20% slower than it actually is. To make matters worse, newer computer-controlled vehicles have become extremely sensitive to changes in tire diameter and axle gear ratio. The reduction in performance can be difficult to gauge, but it is real. Plus, the number and degree of malfunctions increase as speed signal inaccuracy increases."

Interesting eh? I have not had time to research further, but I know a SpeedCal unit is used by the Mustang guys, and S&S makes another for HD bikes, Stewart-Warner produces calibration devices; so there may be other calibration devices available for those with an interest.

 

Here is a link to a good explanation and illustration of the speedometer correction process -- follow the link here.

 

this whole process of lifting the truck and putting bigger meats on is more complicated than i thought. dang. i will do it eventually, but a novice like me sure won't lead the way on the new F-150. it is a good thing that we have a lot of good truck shops here in SoCal. they aren't cheap, but they do great work.

 

There really is an art to setting up a suspension right. Most people take for granted the engineering efforts that went in to making the new F150 one of the nicest riding trucks ever produced. The wheel openings are such, that many will be able to get by with oversized tires and very little in the way of a lift. This new truck design is able to accomodate what once would have required lift heights that you would have been hard pressed to avoid altering the suspension geometery in a way that was detrimental to ride quality. The patience to allow the aftermarket time to catch up with demand will reward you with much better thought out suspension products, a far broader selection of custom wheels, and most importantly, the mechanics and installer enough practice with fitting the componets and finding out what works best for the new F150s.

 

Hey Jason, any progress with the Daystar kit to report?