So today I realized that my speedo is off... A friend was following me on the interstate and called to ask why I was going 80 when in reality I was doing around 75... Also it's throwing my odometer off and only logging .95 of each mile I go.

I believe the tires on the truck are 31x10.5R15. How would I go about fixing this so my speedo is accurate and I'm actually logging a full mile?

2001 has the calibration in the PCM. It can be adjusted using a dealer tool but there are often factory restrictions in VIDBLOCK on how far the adjustment can be tweaked. An aftermarket flash tuner (SCT, Sniper, etc) can fix it or an aftermarket speedo calibration box could be wired in .

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2003 FX4 Level II, Supercharged 5.0L V8, Headers, Duals
BW4406 manual transfer case, Aussie Locker, Torsen L/S, 4.10's
Bilstein 7100 rezzies, Cadillac/Mustang rear discs, Duff traction bars
Keypad Entry, Lock LEDs, ABS switch, sway bar discos
Heated seats, Explorer EATC, Trip Computer and consoles

2003 XLT 2.3L M5OD-R1 reg cab, 2011 Taurus SEL, 2016 C-MAX Energi Plug-in Hybrid

I corrected mine by swapping the rear axle with 4.10 gears

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So you think I can take it to a dealer and have them do it? I wonder how much they would charge...

That sounds expensive

A good tuner cost $400 - $600 dollars the axle I got was $500 dollars.

Re gearing at a shop is $1K dollars

I would call the local dealer and ask them. Probably wont be super cheap but cant be really expensive either

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A couple of possible problems ... no, let's make that 3.

• The calibration MAY be set up so that VIDBLOCK doesn't allow that much adjustment. Then again it may not. No way to know without investigating.
• The dealer may not want to touch it because of legal liability.
• The tech might not know how to do it.

Cost is whatever they want to charge. I'd say $50 would be fair but that doesn't mean you can find anyone to do it for that. LOL

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2003 FX4 Level II, Supercharged 5.0L V8, Headers, Duals
BW4406 manual transfer case, Aussie Locker, Torsen L/S, 4.10's
Bilstein 7100 rezzies, Cadillac/Mustang rear discs, Duff traction bars
Keypad Entry, Lock LEDs, ABS switch, sway bar discos
Heated seats, Explorer EATC, Trip Computer and consoles

2003 XLT 2.3L M5OD-R1 reg cab, 2011 Taurus SEL, 2016 C-MAX Energi Plug-in Hybrid

I wondering why your speedo is off so much? 31's are 1/2" taller than what most likely came on your truck(245/75R16), which makes sense being .95 to 1 actual mile. Also makes sence because with larger tires, your speedo and odometer read slower than you are actually going.


So...tell us, what's your stock tire size? You can find that out by looking at your driverside door sticker. We find this out, we can determine how far off you are percentage wise. I think it'll be minor...very minor....as little as 2%. So minor, that I think you're needle is off just a hair and you shouldn't worry about it.

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'01 XLT disguised as a '03 Fx4 Level II.

I don't know, Shane -- I'm running 31x10.50's on my truck since it was lifted in May, and my speedo/odo are off by just a shade under 10%.

I arrived at this figure by comparing my MPH and ODO with my GPS on open, flat roadway with a 7 satellite lock (and, thus, a 15-foot circle of accuracy [which is about the length of my truck]). If I set the cruise at 70 MPH per the speedometer, the GPS reads 77 MPH; if I set the cruise at 40 MPH, the GPS reads 44 MPH.

Mathematical calculations (using odometer/trip-meter readings vs. gallons to fill the tank) bear this out: against previously observed MPG calculations and current (post-lift and larger tire installation) MPG calculations, there's a difference of 9.88%. This can be explained by the odometer (and, thus, speedometer) reading being off by 9.5 to 10% (allowing for marginal variation in computed MPG due to varying environmental factors, gasoline quality, driving conditions, etc).

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2001 Ranger XLT 4.0L SOHC
Silver Frost w/ Dark Graphite interior


Modifications
Summit 3" Body Lift
31x10.50 A/T tires
Explorer overhead console
Explorer auto-dim mirror
Explorer auto-headlights
Aux1 & Aux2 inputs on factory AM/FM/CD/Cassette
Door-dinger silencer button
Seamless retractable roof and passenger-side ejection seat with steering wheel mounted controls and safety interlock

Turbo...er Brian...you started out with 27" tires though(or some size about like that). The OP appears to be 4wd and 4wd edges(and 2wd with the 16" option) came with 245/75R16's which are 30.5" tall tires. Bumping up to a 31" tire is so small, it's hardly noticeable. In the OP's situation that is, not yours.

I know what you're saying though. And for what it's worth, before I was geared, my 35's showed 10% difference between actual speed and gauge speed. Now being geared, 4% difference the other way. lol.

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'01 XLT disguised as a '03 Fx4 Level II.

ah. didn't know the 4WD trucks started with a different size stock tire.

i'm still waiting for santa to send me a 4.10:1 rear, which should bring my speedo/odo back towards 'correct'

...also waiting for other things!

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2001 Ranger XLT 4.0L SOHC
Silver Frost w/ Dark Graphite interior


Modifications
Summit 3" Body Lift
31x10.50 A/T tires
Explorer overhead console
Explorer auto-dim mirror
Explorer auto-headlights
Aux1 & Aux2 inputs on factory AM/FM/CD/Cassette
Door-dinger silencer button
Seamless retractable roof and passenger-side ejection seat with steering wheel mounted controls and safety interlock

oh it's not 4wd sorry if i made that indication. it's 2wd and i won't be able to go get the stock tire size till the morning. all settled in bed surfing on my ultraportable big day tomorrow painting the grille and installing my gauge overlays so going to get to bed early.

Off the driver side door jam:

P235/75R15SL TIRES
15x7.OJ RIMS

Thats for front and rear

235 is what I had stock then I went with 265 which is a 31" tire

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With 3.73's and stock 235's, then going to 31's (30.5) it will show 5 MPH slower than actual speed. On an X anyway.

Ray

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White 2002 Ranger XLT Extended Cab 4.0 4x4 4.10 LS
5 spd,/BW1354e
K&N CAI 77-2529KP
Jet Chip
2 1/4" Exhaust
Explorer Dome Light
IN THE WORKS:
Sable Electric Fan


“If you do not know where you are going, every road will get you nowhere.”
—Henry Kissinger

thanks guys, i'll just leave it as it is and make sure i keep that 5mph difference in mind when driving.