Guys, I haven't been keeping up with new toys for our trucks so I need some updated people to help me out.

I have a '04 6.0 with an 8" lift and 37" tires. I have to deal with an inaccurate speedo and odo, and have done my best to roughly calculate the amount of error in these two gauges. I have a long commute to work that I had clocked before raising the truck, and it came up 32 miles on the odo. Now it reads right about 27 miles, so I see a 16% variance. Is that variance the same regardless of speed, and can I simply add the 16% back into my odometer readings to see what I am really getting out of a tank of fuel?

I also have a Predator on the 100hp program. Driving back and forth all week to work on this mostly highway route, my low fuel light is coming on anywhere between 290 and 320 clocked miles. This varies with how I have been driving the truck. For you other guys running bigger tires, are you seeing about the same thing? Like everyone else, I want to maximize mileage and am wondering if anyone ever came out with anything to recalibrate our speedo. I know the dealer is supposed to be able to correct for up to 35" tires, but I've got the 37"s and would rather get it exact if it is possible.

Thanks....

 

I have a truspeed from Superlift. If I remember right it corrects for up to 44" tires.

www.superlift.com/accessories/truspeed.asp

 

Do these also take into consideration gearing as well as tire size changes?

 

I also have Surperlift TruSpeed and set it from a GPS unit while driving, matched speedo to GPS reading.

Greg
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2003 Ford F350 6.0 PSD C/C S/B 4x4 Lariat FX4
120,000 Miles
Warn Manual Locking Hubs,ARE MPulse Cap
BFG All-Terrain AT 285/75R16, Superlift TruSpeed
Stock Air Intake,Zoodad Mod., 4" MBRP Turbo Back (No CAT) "JET SOUND"
SCT XCal2 and Tunes from Matt @ Spartan

 

I set mine by the gps as well but I'm sure the truespeed comes with charts telling how to adjust it for tire size and axle ratio. If that doesnt work you can use the mile marker signs on the side of the highway.

 

yeah i'm seeing the same number of miles per tank on my odometer as you and mine is lifted,so that's about right.
i know that with 35" tires if you divide the miles on odometer by 0.9 that will tell you the actual number of miles driven. i used mile markers for test this theory and it works.

 

Thanks guys....
I have 37" tires and 4:56 gearing.
I think it's in the ball park as is.... just want to validate the degree of error of nothing else.

 

I think the GPS is the best way to correct the speedometer but the way on the 99-08 superduty trucks the gear ratio will not change the speed signal.

I came up with my own in line correction box, I just cant talk about it. it is like the truspeed but does provide a user interface, which NONE of the others do

Good luck with getting that speedometer dead on again

kenny