Speedo calcalator.....

YellowCrewCabber · Post by **YellowCrewCabber** » Thu May 07, 2009 6:30 pm

Yes!! I do have another question. Since I have stepped up to 30 inch tires, how far off is the speedo now? When it's indicating 70 mph, I'ts either Sunday morning or I'm about to get a wreckless driving ticket.

Post by **HenryJ** » Thu May 07, 2009 6:35 pm

Axle Ratio/Tire Size Calculator

From our website homepage.

blaz · Post by **blaz** » Thu May 07, 2009 7:10 pm

Ok, seeing that this was brought up. Is there any advantage in getting the truck's computer corrected for the larger tires? I don't mind that the speedo is out, and with a five speed I control the shift points. Is there anything else that I am missing, ABS?

Post by **HenryJ** » Thu May 07, 2009 7:30 pm

VSS readings are use in temperature calculation, SVC for the radio, Transmission functions, many PCM, TCM and BCM functions use the readings to make calculations.

How much is a change in tire size going to affect these calculations? The difference may be very small , and perhaps negligible.

I think the speedometer being off and the mileage calculations would be the biggest inconvenience.

If you don't need a programmer, the dealer should be able to correct the PCM with a flash from the TechII. Most will have a minimum charge. I paid as little as $22 once. It takes longer to turn it on and plug it in than it takes to make the corrections. Keep in mind that they can only select tire sizes that were available in an OEM configuration.

PGH04ZR5 · Post by **PGH04ZR5** » Mon Jun 08, 2009 6:53 pm

I have noticed my Speedo is off between 3-4 MPH over what my GPS says. I took a look around but couldn't find the answer I was looking for in another thread, is this making my MPG read higher or lower than is really is?

Post by **HenryJ** » Mon Jun 08, 2009 7:01 pm

MPG will read higher than it actually is. Mine was the same stock. Almost 10%, IIRC. Kind of like they over compensated for the optional offroad tires. Thought I was getting exceptional mileage. Once corrected it came back down to the advertised mileage on the window sticker.