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Old 08-14-2018, 04:35 PM   #1
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Speed/Od-ometer: Has anyone bothered to recalibrate?

I finally got around to watching my odometer doing lots of hwy miles, esp when I noticed South Dakota (or therabouts) posted every 0.2 miles. It was all seat of the pants, in my head, using imprecise interpretations of my trip ODO tenths display -- haven't had a chance to do a more definitive test. (The rough number I came up with was that my ODO will show 93 miles for every 100 I actually drive.) Anyway, I realized I was way off.

Running 285/75 R16s (32.8") with 3.73 gear ratio, I realized I was both breaking the speed limit at times and that my ACTUAL MPGs were going to be different (higher, phew!) than my previously calculated MPGs.

Everything's relative of course, so for personal planning it doesn't really matter if my *actual* MPGs are different from calculated MPGs, and I can (try to) remember to drive "under the speed limit" ...but for resale at least, it seems like due diligence requires accurate representation of vehicle miles.

I wish I knew what tire size the previous owners used and/or when they switched, but c'est la vie.

I was just wondering if any of you have been in the same boat, and whether/how you went about correcting the Speedo and resetting the ODO, esp if you don't have full history on prior owner's tire size.


Muy Bonita - 2000 Ford E-350 V10 Quigley with 285/75 R16s, SMB-West RB50, manual PH
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Old 08-14-2018, 05:08 PM   #2
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And while I have read this post,

and other internet stuff about subtracting engine idle hours from total hours, etc... which seems ... very ballpark.

I was also hoping to induce folks' thoughts on how whether or not it seemed important to you, or whether it presents a challenge at resale. I haven't called a dealership but costs of options to recalibrate seem high.

Does SMB or Quigley recalibrate the speedo before ship-to-customer? Or did they in 2000?


Muy Bonita - 2000 Ford E-350 V10 Quigley with 285/75 R16s, SMB-West RB50, manual PH
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Old 08-14-2018, 05:11 PM   #3
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I would not worry about the POs tire size. Just work with what you have. Most gps units will have a display that shows your speed. That will give you a very accurate, although not perfect, comparison to your speedo. Have counted milepost markers myself before gps units.

It is not possible to change the odometer numbers. It is possible to calibrate the speedo. Other forum members have done it. Mine was done for me by Agile when I had the 4x4 conversion done.
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Old 08-14-2018, 09:14 PM   #4
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Speedos are calibrated to the original tire size when new. My 32 in tires introduced an error that was corrected when I re-geared to 410's. At one time I thought Chris at U-Joint offered a black box of some sort that allowed you to re-calibrate, you might check his website. My scan gauge also has a speedo built in that I seem to remember can be calibrated.
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Old 08-14-2018, 10:13 PM   #5
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Agile uses (or has used) a box that would convert speedo pulses to correct for tire size, I forget the brand....I talked to Ramsey about this a few times...

I'm also pretty sure that a dealer can fake gearing settings to get larger tires to be mostly correct on the speedo....

Starting in 2008, I think it got harder to modify the speedo settings; after playing with 1der's auto enginuity setup we could not do anything with my van's speedo calibration. I called their tech support and they mentioned that Ford does not give the aftermarket folks access to all the modules and starting around 2008 the speedo calibration is in the ABS module??

..just some related info....hope this helps...
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Old 08-15-2018, 12:36 AM   #6
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I use one of these boxes. They work fine. Mine is a "dakota digital".

If you do calibrate, keep in mind that most vehicles are a bit generous when displaying speed. I calibrated mine to be dead on with GPS speed. This means I need to remember to drive a bit slower in the van, if I don't want to get a ticket. -- I should probably fix that.

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Old 08-15-2018, 08:31 AM   #7
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UJoint sells an black box ie ERA(electronic ratio adapator) made by Abbott Enterprises. I have one in my van and got my speedo dead on compared to GPS.

Abbott does sell them directly also, as I know of another person who bought one from them.
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Old 08-15-2018, 12:13 PM   #8
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When I regeared my van (2007 model, believe the year makes a difference in how it has to be done) from 3.73 to 4.56 I just took it to the local Ford dealer. They plugged in to it with their computer and a few minutes later my speedo/odo was calibrated to the new gear ratio.
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Old 08-15-2018, 02:31 PM   #9
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Thanks everyone for your insights and info.

I do need to get a scan gauge (another research project, if only reviewing forum threads and the rest of the online.

Since I'm kind of dying to get an Agile RIP kit installed (though won't be this season) may wait for those mods.

But good to know someone's had a reasonable experience at the ford dealer ... my rigs a 2000, as noted in my signature, so presumably escapes the year 2008+ constraint.

I thought I read someone on the forum say that SMB recalibrated their rig before it went out the door, but maybe that just all depends.

so quigley conversion (in 2000) would have just left stock tires on the car?

thanks all!
Muy Bonita - 2000 Ford E-350 V10 Quigley with 285/75 R16s, SMB-West RB50, manual PH
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Old 08-15-2018, 02:43 PM   #10
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My 2009 SMB was definitely not recalibrated. I heard similar - that newer vehicles are more challenging to make tire size corrections. I don’t really care about the mileage discrepancy; it’s 13% off, and since it was a new build with oversized tires since “new”, I know the actual odometer vs. displayed miles. I use my ScanGauge on the highway to keep my speed in check; 13% doesn’t really matter until you get over 45-50 mph, but it’s enough to get you pulled over at 65-75.

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