Calibrating The Speedometer
 

Two tickets and a drop in mileage, I think my speedo is off by about 7 mph. How do I fix this? Never calibrated a speedo before.

Superchip programmer can fix that

cheaper fix

well there is the truespeed calibrator

Rickson Truck Wheels and Accessories

There's at least a half dozen different brand of boxes out there that do this. The dealer can also do a flash for you that will recalibrate this.

Now I gotta ask the real question here. I see your runnin an Auto tranny, RUH ROH. How big a tires are you runnin. You know that if your speedo is off then so are your shift points on your tranny. No problem for us manual tranny guys but could be disasterous for an auto if those are off to far.

Just put on new Dakota P265/75R16. I didn't change tire size. Tranny works, truck rolls forward and backwards.

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Reflashing the computer resets for a new tire size?

The dealer can do a re-flash to adjust the computer to the tire size you want. If they are smart enough to figure it out that is.

Something does not add up. At what speed is it 7mph off??

What is the gear ratio and what was the tire the new one replaced?

For instance, if your speedo was correct with 245-75/16 and you went to 265-75/16 that is an increase in unloaded diameter of 3.75%. Or, at 60 MPH indicated, you would be going 62.25 MPH.

That does not account for loaded radius, ect.

If you are 7MPH, something is clearly wrong. We need more info.

Dave

yeah the only way to throw your speedo off is to change tire diameter or to change the gear ratio in the pumpkins

Well you could use a GPS or a Scangauge II...:w2:

How does the ScanGauge II detect actual MPH?

It reads it off the ECM which is calculated from the VSS.

Thanks for the input regarding the speedo. After changing my tires my wife was using the truck and noticed a big difference from the speed trap signs (digital readouts). Then I had the opportunity to drive a "newer" rig and the trannyshifts felt totally different. After driving a while I started noticing a drop in mpg.

This gauge is controlled by the instrument cluster circuit board based upon the cluster programming and electronic messages received by the cluster from the Powertrain Control Module (PCM) over the Chrysler Collision Detection (CCD) data bus.

The Smarty can also recalibrate it for Tire Size

Right, but if it just reads from the VSS, it must get the same signal the speedo does. In order to correct for tire size there has to be a way to tell the computer the tires are larger. The ScanGuage II allows you to do this?

it getsin information from the PCM. But like in all the rigs I used it in the ScanGauge II was dead on the money compared to the speedometer. If the ScanGauge II is off you can calibrate it too.

:sos:i just had a dealer recalibrate mine for 285s and now my truck takes off in 2nd gear instead of 1st. now my truck is pulling 2 codes,p1693&p1698 dealer told me these are chrysler codes that control the trans. if anyone has any idea how to fix this issue without spending big $ i appreciate any help you can offer.