Speedo Calibration After Tire Size Change - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 05-14-2010
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Icon5 Speedo Calibration After Tire Size Change

Ok, I'm mainly just inquiring to make sure I understand this and to decide on the best action to take.

My truck info: 2004, 4x4, 4.0L, Auto tranny, 4.10 gears

Stock tire size: 245/75/16's

New tire size: 33x12.5x15

From the info I've been reading about, my new tire diameter is actually about 32.5-32.7", so that makes a difference of about 6.2-6.3% in diameter.

According to manufacters specs.. my stock tires had ~686 revs/mile
my new tires have ~636 revs/mile

From my understanding, I can go to a Ford dealership and have them plug something into the computer and re-calibrate it, but I also have something called VIDBLOCK that might not be able to compensate for such a large tire.... for about $100.

Or... I can buy a tuner... I think XCal2.. or SGI5 or something similar to do it myself, but those can cost $300-400.

Info I gathered from Bob from searching old threads:
2004~2006
Cluster microprocessor controls speedometer and digital odometer
Raw VSS source: Output Shaft Speed sensor fits into a window in the transmission extension housing where it reads a toothwheel machined on the output shaft.
Corrected VSS Wire to cluster: Gray/Black
Adjustment Method: flash adjustment in the Powertrain Control Module (PCM) using an aftermarket flash tool. Dealer tools such as NGS+, WDS, IDS may also work BUT the adjustment range is probably factory limited by VIDBLOCK.
Adjusts for: axle ratio and tire diameter.

My question is... what is my best option? Will dealer be able to calibrate correctly for my new tire size... or are they too big and be limited by the VIDBLOCK?... leaving me no choice but to buy a tuner? Correct me if I'm wrong, but since I have the sensor... I can't just change out the ring gear thing with one with more teeth to correct the problem?

Any advice, help, answers, suggestions would be appreciated. Just trying to save a few bucks. FYI, I don't plan on going any bigger on tires... and probly won't change gearing any time soon either, that is why I'm weary of buying a tuner, that might only be used once or twice for such a steep price. Sorry so long, I just want to provide as much info as possible so someone can help me. Thanks in advance.
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Old 05-15-2010
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all you need is the little box from superlift or a tuner
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Old 05-15-2010
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Speedo is wrong from the factory. Atleast mine was, a bump in size corrected it.

Get out on the highway and do 60. A mile marker should pass by every minute.
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Old 05-15-2010
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245/75r16 = 30.5 tire

OnlineConversion.com - Bigger Tires

If your speedo says 60 on the new tires you will be gpong just shy of 65
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Old 05-15-2010
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Quote:
Originally Posted by RLong31 View Post
I can't just change out the ring gear thing with one with more teeth to correct the problem?
The teeth are on the transmission output shaft, machined on I believe, and I'm sure there is only one output shaft part number used for each Ranger transmission. Besides that, even if you could somehow exchange the output shaft for another with a different tooth count, doing so would require a complete trans teardown.
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Old 05-15-2010
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I have noticed that my speedo seems to be almost correct. I run my GPS and noticed before I got bigger tires that the speedo was off. Now it seems to be just about right. I'm a little more concerned about my odometer being off. I can adjust my speed for any difference I guess. Am I putting more or less miles on with the bigger tires?

What do you all suggest as the best tuner? The SCT, XCal2, Bully Dog? Or any others I'm not thinking of.
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Old 05-15-2010
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your putting on more i believe because if your speedo says your doing 60 and your really doing 65 then for every hour you drive your putting 5 extra milmes on the truck that the odometer is not reading

also if you want to double check what i said next you fill up reset your trip odometer on your truck and on your GPS and when you fill up again check and see what the difference is

i knonw mine is way off because my stock tire was 225 70 15 and now im running 31 10.5 15
but i too would be interested in the solution to this
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Old 05-15-2010
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^^^ wrong its less read the first line you typed. if your speedo says your doing 60 thats what your odometer is reading. not you actually going 65 so you put less miles on your truck if your speedo is slow. if you are doing 60 and your speedo says 65 then you are putting more miles on your truck.



But yes a dealer should be able to fix this we just did it in my buddys tahoe at the dealership he works at
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Old 05-15-2010
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When my speedo says 60 on the freeway my girl drives next to me and she says her speedo says 70 on her stock 4runner so I know mine is off for sure
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Old 05-15-2010
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Wasn't there a website that told you how many revolutions your tires were doing? How do you calculate it so that I can put it in my tuner to get my speedo as close to stock as possible?
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Old 05-15-2010
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Originally Posted by rangerboy101 View Post
Wasn't there a website that told you how many revolutions your tires were doing? How do you calculate it so that I can put it in my tuner to get my speedo as close to stock as possible?
For the exact measured revs/mile for any particular tire, look it up under specifications at the tire manufacturer's website. You can also Google several tire size calculators and most of those will give a generic revs/mile for any size and that's close enough for speedometer calibration.
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Old 05-15-2010
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^^Agreed, I googled bf goodrich revs/mile and goodyear revs/mile... and that's how I found mine.

Any suggestions on which tuner to get?
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Old 05-15-2010
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Cool thanks for the help Bob. As for what tuner to get, I have the Xcal 2 and it's nice. I got mine for a little cheaper than a new Xcal 3 would cost so that's the only reason I have it instead of the Xcal 3. Both are great tuners though.
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Old 05-15-2010
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Alright, with my new tires my revs/mile are 614. The stock ones are 662. I'd put the new tires revs/mile in my tuner correct? Or am I thinking backwards and I really have to put the old tires revs/mile in the tuner?
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Old 05-15-2010
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614 revs/mile and 4.10 axle ratio if that's what you're running now.
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Old 05-15-2010
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That's what I thought. I'm pretty sure I read somewhere that the speedos are 3mph off from the factory? I'll try and find that thread.
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Old 05-15-2010
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Never mind. It was you that said that Bob on another forum haha.
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Old 05-15-2010
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What does the xcal3 do that the xcal 2 cannot? anybody have the 3?
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Old 05-15-2010
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Quote:
Originally Posted by rangerboy101 View Post
That's what I thought. I'm pretty sure I read somewhere that the speedos are 3mph off from the factory? I'll try and find that thread.
I think that most owners find that the factory speedometer reads 1~3 mph higher than actual at highway speeds when using a GPS or radar for comparison.
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