I increased tire size from 17" stock to 19.5" tires. The speedometer is off by 2-3 mph; therefore, I presume the odometer and computer generated mpg readings are off also. Local mech wants $95 to recalibrate everything. First, is it worth the money to recal or is there an "app" for that that will give me a true reading of distance and mpg? Second, will recalibrating change engine performance to compensate for the larger tires? I have an Edge juice/attitude and already changed the tire size in that which does give me an accurate speed.Thanks in advance for your thoughts.

Most GPS mapping systems also show real speed you are travelling.Instead of spending the $95 on a recalc...get a Garmin or TomTom or other device or Mapping App for your iPhone/iPad if you have one.Not only will you get an accurate speedometer but also get a mapping system along with route marker and "Points of Interest"

I would get everything remapped to make sure the computer/tranny work correctly...

I am pretty sure that tuners (like a SMARTY or SMARTY JR) can recalibrate the speedo. I seem to remember that was an option on my Smarty JR. Not saying you should buy one just for that, but maybe if you get on one of the Cummins forums you could find someone local who could recalibrate for you.

Don, It takes about 5 minutes at most to recalibrate so I would talk to the shop about price. Having someone local fix your speedo with a Smarty product won't work since the 03-05 trucks go back to stock tire size when you reprogram them back to stock. Based on all the feedback I have seen I would sell the Edge product and buy a Smarty Jr or S06. They will allow you to calibrate your speedo and give you better towing performance, especially if your 04 is the 04.5 with 325hp. The Smartys aren't prone to failure or high EGTs like the edge products. If you have an auto trans the recalibrate is a good idea, but don't do it for the overhead mileage readings. The overhead is called the lie-o-meter for a reason, they are around 20% off on stock trucks and the Edge will make that error even greater.

If the Edge fixed your speedo, there's nothing more to it. You're done.

Speedo/odo recalibration thoughts | Good Sam Community

the_bear_II
Explorer
Apr 10, 2014
Most GPS mapping systems also show real speed you are travelling.

Instead of spending the $95 on a recalc...get a Garmin or TomTom or other device or Mapping App for your iPhone/iPad if you have one.

Not only will you get an accurate speedometer but also get a mapping system along with route marker and "Points of Interest"
e-light
Explorer
Apr 10, 2014
I would get everything remapped to make sure the computer/tranny work correctly...
Bionic_Man
Explorer
Apr 11, 2014
I am pretty sure that tuners (like a SMARTY or SMARTY JR) can recalibrate the speedo. I seem to remember that was an option on my Smarty JR. Not saying you should buy one just for that, but maybe if you get on one of the Cummins forums you could find someone local who could recalibrate for you.
AH64ID
Explorer
Apr 11, 2014
Don,

It takes about 5 minutes at most to recalibrate so I would talk to the shop about price.

Having someone local fix your speedo with a Smarty product won't work since the 03-05 trucks go back to stock tire size when you reprogram them back to stock.

Based on all the feedback I have seen I would sell the Edge product and buy a Smarty Jr or S06. They will allow you to calibrate your speedo and give you better towing performance, especially if your 04 is the 04.5 with 325hp. The Smartys aren't prone to failure or high EGTs like the edge products.

If you have an auto trans the recalibrate is a good idea, but don't do it for the overhead mileage readings. The overhead is called the lie-o-meter for a reason, they are around 20% off on stock trucks and the Edge will make that error even greater.
TurnThePage
Explorer
Apr 11, 2014
If the Edge fixed your speedo, there's nothing more to it. You're done.
AH64ID
Explorer
Apr 11, 2014
BillyW wrote:
If the Edge fixed your speedo, there's nothing more to it. You're done.

The edge adjusts the speed on the attitude monitor, not the dash.
tim_and_amy
Explorer
Apr 11, 2014
I agree, I would actually call the dealer. Ford charges $45 in Utah for that. They actually have it as an option in the computer to change tire size. That is all a smarty JR is doing.

Also, yes, you should have it adjusted, it physically changes the shift points, fuel economy settings and such.
As an example, when I went from stock 31's to 34.5" tires, my mpg showed towing at 12.5. I knew that wasn't right, by GPS and hand calc is was 8mpg. So that much difference can throw the PCM off by a bit.
TurnThePage
Explorer
Apr 11, 2014
ah64id wrote:
BillyW wrote:
If the Edge fixed your speedo, there's nothing more to it. You're done.

The edge adjusts the speed on the attitude monitor, not the dash.
I am falling wayyy too far behind!
Fulltimer50
Explorer
Apr 12, 2014
#1 Wheel size doesnt matter. Tire diameter matters.
#2 I have stock wheels and tires. My speedo is off 2-3 MPH.
Redsky
Explorer
Apr 13, 2014
A difference of 3-4% in your gearing is not going to make a significant difference to anything with regard to your vehicle's drive train. GM trucks come from the factory with a 3.73 or 4.10 rear end and that makes for a 25% difference in towing capacity but that is the only impact.

If you are showing 60 MPH on the speedo and have to remember that you are actually going 62 MPH it is no big thing. Same applies to driving 1000 miles per the odometer when you have really only driven about 960 miles. Your MPG will be understated by 4% but that too is no big deal.