On a '98 and newer, the speedometer and odometer get their data from the
CAB (controller, antilock brake) rear-axle speed sensor. The PCM then
takes that number of revolutions per minute and translates it into a speed
signal to send to the gauges. It uses a lookup table to translate
revolutions to miles. This table is pre-set at the factory with the stock
available tire sizes (4 or 5), and cannot be altered - all you can do
(well, the dealer) is set the PCM to look at a different entry on the table.
There is a device that can be plugged into the line coming of fthe sensor
to "fool" the CAB and PCM, it's a little spendy and I don't get a warm
fuzzy interfering with stuff like that. A custom flash may also be able to
take care of a tire size difference, but that's even more expensive.
According to Ye Olde DML Tire Calculator, your new tires are 25.66" tall,
2.39" shorter than stock. Unless there's a stock tire size that's close,
you may be out of luck on a speedo adjustment.
nelsonjo@engr.orst.edu wrote:
> I was looking at the article in the october 01 issue of
> sport truck on their project quad cab
> dakota and it mentioned that they had told how to
> correct speedometer error on the
> dakotas in their august 01 issue in an article called
> "speedometer stress." Does any one
> have this information? if you do please let me know, I
> replaced my stock 255 65R15's
> with 275 40R17 tires on R/T rims on my 2000 5-speed dak.
> needless to say the speedo's
> a tad off.
>
> Totally unrelated: I was playing with my digital camera
> today, if anyone is interested in a
> pretty nice before and after shot of a dakota regular
> cab getting a full hotchkis kit and R/T
> rims let me know.
>
> Thanks,
> jon
>
-- -andy andylevy@yahoo.com Maintainer, DML FAQ - http://www.dakota-truck.net/faq/ http://home.twcny.rr.com/andylevy/dakota/ '99 CC 4x4 318 auto
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