Speedo and Larger Tires - Ranger-Forums - The Ultimate Ford Ranger Resource


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  #1  
Old 09-08-2009
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Speedo and Larger Tires

When it comes time for new tires I want to put taller tires on my 08 XLT. Maybe same width but a 78 instead of a 70 series I know the speedometer can be recalibrated for the taller tire, my question is if the battery goes dead or is disconnected for any reason would the re-progamming of the computer need to be redone or will it keep the changed tire size?

Thanks

George
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  #2  
Old 09-08-2009
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78 serious? lol. never heard of it.

if youre running like a 245/70, you could go to a 245/75 without any problems. i wouldnt bother reprogramming the speedo. not gonna have that much difference if any
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  #3  
Old 10-14-2009
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my '98 came with 265/75's I believe which are close to a 30.5-31'' tire....then I put 32'' tires on there, no speedo difference, now I have 33's on and its like 1-2 mph off. Not that big of a deal.
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Old 10-14-2009
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Quote:
Originally Posted by muscleford View Post
When it comes time for new tires I want to put taller tires on my 08 XLT. Maybe same width but a 78 instead of a 70 series I know the speedometer can be recalibrated for the taller tire, my question is if the battery goes dead or is disconnected for any reason would the re-progamming of the computer need to be redone or will it keep the changed tire size?

Thanks

George
245/75= 30.48 inches tall

245/70=29.50

so there wont be much difference maybe 1 mph or 2


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Originally Posted by backwoodsmudders View Post
my '98 came with 265/75's I believe which are close to a 30.5-31'' tire....then I put 32'' tires on there, no speedo difference, now I have 33's on and its like 1-2 mph off. Not that big of a deal.

the reason you didnt see a change from 265s to 32s is

265/75= 31.64 tall tires

32/11.50= 32.01

but thats a good way to help prove he wont need to change his speedo.

its not like your going from a 235/70= 27.95 tall tire to a 31/10.50= 30.97 like i did my speedo was way off.
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Old 10-14-2009
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Your speedometer will not be off by a set mph, it will be a percent of your speed.

Correct Speed = (Old Speedo Reading * new tire diameter) / (Old Tire Diameter)

The faster you go, the more it will be off.

Going from 29" to 31" puts mine off by around 5 mph @ 70 mph
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  #6  
Old 10-14-2009
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Anyone know how much it costs to get this done? Im worried about the odometer being off too
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  #7  
Old 10-14-2009
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But wouldn't that mean less miles in the end?

Shouldn't be too much to fix it.
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  #8  
Old 10-14-2009
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I think mine is off by about 4-5 mph. I went from 31" to 33" though. I just set the cruise on 59 by the speedo and ride.
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  #9  
Old 10-14-2009
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Quote:
Originally Posted by iHateTechnology View Post
But wouldn't that mean less miles in the end?

Shouldn't be too much to fix it.
Yeah, less miles in the end for sure.I was happy about that.
I had 33s on a 2.5L, and when the speedometer read 32mph, I was going 35, and when the speedometer read 55mph, I was really going 65mph.

Try icthusrulz's equation, looks legit.
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  #10  
Old 10-15-2009
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Quote:
Originally Posted by icthusrulz View Post
Your speedometer will not be off by a set mph, it will be a percent of your speed.

Correct Speed = (Old Speedo Reading * new tire diameter) / (Old Tire Diameter)

The faster you go, the more it will be off.

Going from 29" to 31" puts mine off by around 5 mph @ 70 mph
Yes, thank you for saying that, I meant to earlier. You know those stands on the side of the road with the radar that show how fast your not supposed to be going? Well drive by those after you switch your tires. At 45 your speedo will most likely be perfect but at 70 it might be 2 off.
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  #11  
Old 10-15-2009
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Quote:
Originally Posted by gsueagles6 View Post
Anyone know how much it costs to get this done? Im worried about the odometer being off too
On the rangers the speed is calculated by wheel speed sensors not a mechanical "speedo cable" so the only way to recalibrate it is by tapping into the electrical. Superlift has a box for $150??? I think to recalibrate it. You just send them your tire size and any gearing changes and they will calibrate it. Yes, over time the odometer might be off.
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Old 10-15-2009
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I'm almost certain you can get an ECU re-flash at the Ford dealer too (I know they CAN, but don't know if they WILL). Probably cheaper than the Superlift Box.
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  #13  
Old 10-16-2009
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Quote:
Originally Posted by icthusrulz View Post
I'm almost certain you can get an ECU re-flash at the Ford dealer too (I know they CAN, but don't know if they WILL). Probably cheaper than the Superlift Box.
I would think not because of liability reasons, as you are tampering with the vehicles stock form. And its a dealer....that would have to warranty anything that would get screwed up in the process
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  #14  
Old 10-16-2009
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Make the tire change you want, then borrow someone's TomTom or other GPS and go for a ride. Just make a mental note of the differences at 45, 55, 65, etc. That way you'll know whether you're 1 mph off at 45 or 3 mph off at 70 or whatever.
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  #15  
Old 10-16-2009
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Hmm with 33's my speedo will be at 92 and ill be at like 98mph GPS tracked.
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  #16  
Old 10-16-2009
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There isn't a single answer for Ranger speedometer correction.

1994 and earlier:
Traditional cable-driven speedometer/odometer
Adjustment Method: interchangeable gears at transmission or transfer case
Adjusts for: axle ratio and tire diameter.

1995~1997
Electric speedometer geared to odometer
VSS source: gear driven pulse generator on the trans or t-case
VSS wire to speedometer: Gray/Black
Adjustment Method: interchangeable gears at transmission or transfer case
Adjusts for: axle ratio and tire diameter.

1998~2000
Electric speedometer geared to odometer
Raw VSS source: the ABS sensor on the rear diff housing reads the tone ring.
Corrected VSS Wire to speedometer: Gray/Black
ADJ Method: (RABS trucks): flash adjustment in the Generic Electronic Module (GEM) using a dealer tool such as NGS+. WDS, IDS may also work.
Adjustment Method: (4WABS trucks): flash adjustment in the 4WABS Module (GEM) using a dealer tool such as NGS+. WDS, IDS may also work.
Adjusts for: tire diameter only.

2001~2003
Electric speedometer geared to 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: Gray/Black
Adjustment Method: flash adjustment in the Powertrain Control Module (PCM) using a 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.

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 a 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.


2007~2009 (Unconfirmed)
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 to cluster: Transmitted over Module Communications Network
Adjustment Method: flash adjustment in the Powertrain Control Module (PCM) using a an aftermarket flash tool. Dealer tools may also work BUT the adjustment range is probably factory limited by VIDBLOCK.
Adjusts for: axle ratio and tire diameter.
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  #17  
Old 10-16-2009
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Nice writeup!!! Great info!
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  #18  
Old 10-16-2009
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on my 2000. I have tires that are 1 size taller and wider then stock. Any reason why my speedo would be off so much. It starts around 55. the speedo says 75 but I'm really doing 80. corrects its self at 80ish. Found this out from a speeding ticket then tested it with driving next to my wife's car...
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