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Old 03-13-2005, 22:41   #1 (permalink)
liteflyer 1
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speedo error and how to fix?

I just went from R16 tires to R16.5 and have realized that the speedo
is off by appox. 10 mph. My parts guy says they no longer run off of
the trans were you could change gears and adjust the speedo readout
that way. He says that with the electronic speedos that the sensor is
in the rear axle and you do something to the speeometer itself. Anyone
know what to do to adjust it?

thank you
dave B.
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Old 03-13-2005, 22:41   #2 (permalink)
Mark Jones
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Re: speedo error and how to fix?

"liteflyer 1" <d.benson@frontiernet.net> wrote in message
news:52jf21pnegop24rvrgiisdqb95un7vvjqg@4ax.com...
> I just went from R16 tires to R16.5 and have realized that the speedo
> is off by appox. 10 mph. My parts guy says they no longer run off of
> the trans were you could change gears and adjust the speedo readout
> that way. He says that with the electronic speedos that the sensor is
> in the rear axle and you do something to the speeometer itself. Anyone
> know what to do to adjust it?

On many newer vehicles, this would require that the main computer
be programmed with the change in the final drive ratio. You will
probably have to take it to your local dealer and see if they can
program a custom ratio.


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Old 03-13-2005, 22:41   #3 (permalink)
lugnut
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Re: speedo error and how to fix?

On Fri, 04 Mar 2005 02:57:46 GMT, liteflyer 1
<d.benson@frontiernet.net> wrote:

>I just went from R16 tires to R16.5 and have realized that the speedo
>is off by appox. 10 mph. My parts guy says they no longer run off of
>the trans were you could change gears and adjust the speedo readout
>that way. He says that with the electronic speedos that the sensor is
>in the rear axle and you do something to the speeometer itself. Anyone
>know what to do to adjust it?
>
>thank you
>dave B.



The recalibration of the speedometer depends on your make,
model & year vehicle. Some can be recal'd with a switch
sequence while some require reprogramming the ECM or other
devices. If you have a '96 or newer OBD2 vehicle, it is
likely that you will need to get it done by a dealer or
someone else capable of re-programming the ECM.. Note that
it is important that this be accurate if you have antilock
brakes or traction control for them to work correctly.
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Old 03-13-2005, 22:41   #4 (permalink)
Matt Macchiarolo
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Re: speedo error and how to fix?

Note that
> it is important that this be accurate if you have antilock
> brakes or traction control for them to work correctly.


Not really...the ABS/TC senses the difference in speed between wheels, and
doesn't care how big the tire/wheel combination is as long as all 4 wheels
are the same.

But, the OP's tranny won't shift right until the speedometer is corrected,
and his odometer will be off as well.

Either it has to be reprogrammed for your tire/wheel combination, or you can
get a Superlift Truspeed unit, which corrects the signal.


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Old 03-13-2005, 22:41   #5 (permalink)
The OTHER Kevin in San Diego
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Re: speedo error and how to fix?

On Fri, 4 Mar 2005 16:39:01 -0500, "Matt Macchiarolo"
<matt@nospamplease.com> wrote:

> Note that
>> it is important that this be accurate if you have antilock
>> brakes or traction control for them to work correctly.

>
>Not really...the ABS/TC senses the difference in speed between wheels, and
>doesn't care how big the tire/wheel combination is as long as all 4 wheels
>are the same.
>
>But, the OP's tranny won't shift right until the speedometer is corrected,
>and his odometer will be off as well.
>
>Either it has to be reprogrammed for your tire/wheel combination, or you can
>get a Superlift Truspeed unit, which corrects the signal.


I put one of those units on my Superduty when I put the 35's on it.
Easy to install, PITA to get dialed in by yourself.. Lots of little
adjustments and test drives with my GPS receiver finally got it
correct.

The "ballpark" settings the instructions show are pretty close tho.

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Old 03-13-2005, 22:42   #6 (permalink)
Ernie Sparks
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Re: speedo error and how to fix?

Are you sure that, by increasing your rim size by a half inch your tire
circumference increased enough to raise your speed by 10 mph? That sounds
like a lot. There must be something else must be involved. Also, at what
indicated speed does this increase seem to have occurred....65 mph...100
mph...etc. Do you have a tach from which to check this increase? There is a
lot involved. I went from 9.50-16.5 to 12.00-16.5 on the rear of my truck
and the speedo finally registered correctly! Remember, the factory usually
sets speedos to record higher speeds than you are actually experiencing.
Some AAA locations have the ability to accurately check your speedo. Good
luck!


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Old 03-13-2005, 22:42   #7 (permalink)
David M
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Re: speedo error and how to fix?

On Tue, 08 Mar 2005 02:49:16 +0000, Ernie Sparks rearranged some electrons
to form:

> Are you sure that, by increasing your rim size by a half inch your tire
> circumference increased enough to raise your speed by 10 mph? That sounds
> like a lot. There must be something else must be involved. Also, at what
> indicated speed does this increase seem to have occurred....65 mph...100
> mph...etc. Do you have a tach from which to check this increase? There is a
> lot involved. I went from 9.50-16.5 to 12.00-16.5 on the rear of my truck
> and the speedo finally registered correctly! Remember, the factory usually
> sets speedos to record higher speeds than you are actually experiencing.
> Some AAA locations have the ability to accurately check your speedo. Good
> luck!


You can also use a stopwatch and highway mile markers.


--
David M (dmacchiarolo)
http://home.triad.rr.com/redsled
T/S 53
sled351 Linux 2.4.18-14 has been up 15 days 7:51

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