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  #1  
Old 11-05-2009, 09:10 PM
NOLArat NOLArat is offline
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Default How do you recalibrate the speedo/odo for bigger tires?

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?
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Old 11-05-2009, 10:03 PM
rwenzing rwenzing is offline
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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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  #3  
Old 11-06-2009, 03:18 AM
STL STL is offline
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I corrected mine by swapping the rear axle with 4.10 gears
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Old 11-06-2009, 08:32 AM
NOLArat NOLArat is offline
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Quote:
Originally Posted by rwenzing View Post
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 .
So you think I can take it to a dealer and have them do it? I wonder how much they would charge...

Quote:
Originally Posted by STL View Post
I corrected mine by swapping the rear axle with 4.10 gears
That sounds expensive
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Old 11-06-2009, 09:04 AM
STL STL is offline
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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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Old 11-06-2009, 10:54 AM
rwenzing rwenzing is offline
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Quote:
Originally Posted by NOLArat View Post
So you think I can take it to a dealer and have them do it? I wonder how much they would charge...
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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  #7  
Old 11-06-2009, 01:08 PM
Fx4wannabe01 Fx4wannabe01 is offline
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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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Old 11-06-2009, 01:29 PM
turbo turbo is offline
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Quote:
Originally Posted by Fx4wannabe01
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.
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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  #9  
Old 11-06-2009, 01:54 PM
Fx4wannabe01 Fx4wannabe01 is offline
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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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  #10  
Old 11-06-2009, 02:06 PM
turbo turbo is offline
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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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Modifications
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Explorer overhead console
Explorer auto-dim mirror
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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
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  #11  
Old 11-06-2009, 08:10 PM
NOLArat NOLArat is offline
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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.
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  #12  
Old 11-07-2009, 10:52 AM
NOLArat NOLArat is offline
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Off the driver side door jam:

P235/75R15SL TIRES
15x7.OJ RIMS

Thats for front and rear
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  #13  
Old 11-07-2009, 02:33 PM
STL STL is offline
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235 is what I had stock then I went with 265 which is a 31" tire
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  #14  
Old 11-08-2009, 01:56 PM
Clem Clem is offline
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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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  #15  
Old 11-08-2009, 05:19 PM
NOLArat NOLArat is offline
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thanks guys, i'll just leave it as it is and make sure i keep that 5mph difference in mind when driving.
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