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  #1  
Old 04-05-2010, 11:14 AM
mayalibre mayalibre is offline
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Default Speedo/odometer adjustment possibly required...

Hi -- I just bought a 2000 Ford Ranger XLT Supercab V6 4.0L 4x4 Off Road from Oregon and am getting ready to register it here in California. The previous owner put on very nice larger wheels and tires -- they are P255/70R18 (as opposed to the stock 16s). My question is: Do the larger tires/wheels affect the speedometer/odometer?

I feel like I'm going faster than the speedometer says. I took it into the dealer for another computer issue this morning (the airbag light was on, and since it was a safety issue everybody said the dealer was the only place). And I asked about the speedometer/odometer. They referrred me to a speedometer specialist -- they also said that when I get the truck inspected at the DMV it may not pass if the speedometer isn't properly calibrated.

The truck is new for me, so I'm only starting to get familiar with it. And I saw on the Ford Trucks forum that some speedometers/odometers are connected to the transmission rotation, whereas others are connected to the wheels. The transmission on this vehicle is stock. So could I be imagining having a problem I don't have?

I don't want to get hosed by a specialty speedometer place that will charge me $200 just to "inspect" something that doesn't need to be inspected. Can somebody give me guidance on what to do and where to go to get this looked at and/or adjusted for a reasonable price?

Thanks!
-maya
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Last edited by mayalibre; 04-05-2010 at 11:19 AM.
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  #2  
Old 04-05-2010, 11:17 AM
STL STL is offline
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Default Re: Speedo/odometer adjustment possibly required...

Ya larger tires over stock will affect the speedometer
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Old 04-05-2010, 11:23 AM
mayalibre mayalibre is offline
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Default Re: Speedo/odometer adjustment possibly required...

Thank you. I'm not surprised. Is there a reasonable way to get the speedometer/odometer adjusted so that it reads properly to pass the Department of Motor Vehicles inspection, without costing $1000? Thanks!
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Old 04-05-2010, 01:55 PM
rwenzing rwenzing is offline
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Default Re: Speedo/odometer adjustment possibly required...

Quote:
Originally Posted by mayalibre View Post
Thank you. I'm not surprised. Is there a reasonable way to get the speedometer/odometer adjusted so that it reads properly to pass the Department of Motor Vehicles inspection, without costing $1000? Thanks!
A good Ford tech can do it for you. For the years 98~2000, there are two possible locations where the adjustment is done depending on which ABS system you have.

Rear only ABS: Correction done in the Generic Electronic Module
4 Wheel ABS: Correction done in the 4WABS Module

In either case, the adjustment is made using a special dealer tool to reflash the affected module. It will help if you research the tire "revs per mile" in advance. Look it up for your tire size in the specification chart at the tire manufacturer's website. The tech will need that value to make the correction. Since it is a nonstock size, he won't have it in the shop manual.
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Old 04-05-2010, 05:35 PM
Fx4wannabe01 Fx4wannabe01 is offline
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Default Re: Speedo/odometer adjustment possibly required...

Your tire diameter is 32.1"....aka only .6" taller than what came on the truck stock(245/75r16). Taller diameter tires will lower the rotations per mile of the wheel/tire....aka speedo and odometer will read slower/lower than actual speed/distance traveled. BUT...Ford's are known to read a little faster than actual speed with stock tires....if anything, that diameter cured the "reads too fast out of the box" problem. I'd just leave it be.
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Old 04-05-2010, 06:52 PM
rwenzing rwenzing is offline
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Default Re: Speedo/odometer adjustment possibly required...

Actually, they're about 1.6" larger diameter yielding a 3.5 MPH lower reading than the factory indication at 70 MPH. Still, that is a relatively minor error and, as you correctly point out, partially offset by the slightly higher-than-actual reading of most factory Ranger speedometers. The owner would have to decide if the net error is worth the expense of dialing it in perfectly.
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BW4406 manual transfer case, Aussie Locker, Torsen L/S, 4.10's
Bilstein 7100 rezzies, Cadillac/Mustang rear discs, Duff traction bars
Keypad Entry, Lock LEDs, ABS switch, sway bar discos
Heated seats, Explorer EATC, Trip Computer and consoles

2003 XLT 2.3L M5OD-R1 reg cab, 2011 Taurus SEL, 2016 C-MAX Energi Plug-in Hybrid
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  #7  
Old 04-05-2010, 06:56 PM
Fx4wannabe01 Fx4wannabe01 is offline
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Default Re: Speedo/odometer adjustment possibly required...

Crap...thanks Bob. It's been a long week already... lol. 1.6" taller. My bad. lol.
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Old 04-05-2010, 08:33 PM
littleblue littleblue is offline
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Default Re: Speedo/odometer adjustment possibly required...

Quote:
Originally Posted by mayalibre View Post
Is there a reasonable way to get the speedometer/odometer adjusted so that it reads properly to pass the Department of Motor Vehicles inspection, without costing $1000? Thanks!
Unless they have changed things in the past 2 years, speedo calibration is not part of the CA DMV inspection. Usually it a visual inspection of the VIN, smog components and sniffer test of the exhaust to make sure it passes the smog inspection.
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