Bigger tires change odometer accuracy? - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 12-01-2012
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Bigger tires change odometer accuracy?

OK, i got 32 inch tires and adjust the speedo with my tuner and GPS - my question is will the larger tires throw off the odometer reading for mileage. which will then not give me accurate MPG readings...?????????????
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Old 12-01-2012
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Yes--if you get a tuner, you can adjust for tire size though.
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Old 12-01-2012
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Hmmm, I did adjust the mph with tuner.. would that also adjust odometer?
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Old 12-01-2012
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this is a very good question. never really thought of it. i would imagine the odometer and speedo would both be recailibrated when you calibrate the speedo seeing as they both use the same sensors to measure speed and mileage
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Old 12-01-2012
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Quote:
Originally Posted by dczys View Post
Hmmm, I did adjust the mph with tuner.. would that also adjust odometer?
It should yes.

Just go drive a mile on the interstate or somewhere with mile markers in order to use them as a gauge - then verify that your odometer also moved a mile.

Or use a GPS or smartphone App that records distance....
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Old 12-01-2012
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^^^^^^^
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Old 12-02-2012
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Depending on your model and setup. I'm assuming 4x4. Your speed signal will be coming from a hall effect sensor either on the transmission or the rear end housing. This signal is a pulse signal. The GEM (2wd pre-2001) or 4WABS (4x4 or 2001-up 2wd) will convert this pulse signal into a voltage that is sent to the cluster. This voltages splits to the speedometer and the odometer so they both read the same. I've noticed that factory readings are always off about 2 units between odometer and speedometer. Odometer usually reads dead on but the speedometer always reads about 2 mph faster than what you are really going.

If your a real accuracy stickler I would get your odometer to read correctly and then adjust the needle on the speedometer manually (removing and setting cruise to a known speed and re applying the needle).

Note GPS speedometers are acurate to about 0.1 of a mile.
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Old 12-02-2012
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Originally Posted by sheltonfilms View Post
I've noticed that factory readings are always off about 2 units between odometer and speedometer. Odometer usually reads dead on but the speedometer always reads about 2 mph faster than what you are really going.
That is not true. Not in either one of my rangers or any of my other 3 vehicles since then. Might just be your truck but your speedometer should be dead on.
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Old 12-02-2012
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well i tested it out..
zeroed the truck, GPS, and Ultragauge. and drove....
Truck read 30.2 miles
Ultra gauge read 29.9 miles
and GPS read 30.71 miles

i dont think its really enough of a difference to worry about
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Old 12-02-2012
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i dont think its really enough of a difference to worry about
Yep, good to hear - it looks like the tuner dialed in both the speedometer & odometer.
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Old 12-02-2012
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This is good to know. Never thought about the odometer not changing but glad to hear it does...
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Old 12-03-2012
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