OK, I see a lot of info on MPG data with tire size changes. It is well known that the speedo can be corrected with a tuner. Can anyone confirm without a doubt that the ODOMETER is also corrected by the tuner?

It would make sense that it is based on the speedo but I could also see it being based simply on rotations. I see a lot of posts where people are "hand calculating" their mileage. However if the ODOMETER is in error, then this hand calculation is also in error.

I guess one way to check this is to compare mile-markers to odometer? Are there any Tuner or OEM software guys on this forum?

Thanks - Dave

there is a formula to calculating mpg when your tire size is bigger then stock

Interesting question. Speed, as reflected on the speedometer, is simply a ratio of distance travelled per time unit. After using Stealth-2 to recalibrate my tire size, the speedometer readings exactly match the speed shown on my GPS. The two gauges are clearly using identical time units to define identical speed readings. Mightn't one therefore assume they are using the identical measurements of distance traveled?

Of course, a$$uming anything is problematic, and your question is still valid. :confuzeld

It's possible that the speedometer relies on different rotational counter than the odometer, but it's highly unlikely. The answer lies in a GPS that's also recording miles traveled. I've never tried to use my GPS for trip distance. But next time ... I will.

Speedometer and odometer both get their signal from the Vehicle Speed Sensor (VSS). If you accurately correct one, the other should be correct also.

Mine is corrected with the Hypertech, I get on US23 at MM80 and it logs 80 miles when I hit the Ohio border, thats as close to proof as I can get.

I corrected my speedometer with the Predator. Compared my speed with a $1800 submeter Gps unit. My speed off the VSS is right on. My Speedometer is 1 MPH high at 60.

Because I'm too much of a nerd I have attached an excel spreadsheet that will do the following:
1. Convert metric to standard tire size
2. Suggest gear ratio for tire size
3. Speedo calculation with different size tires
4. Tranny tooth gear replacement for new tires or gears.

User entry fields are in green. I hope this helps.

wow burnside had a little time on your hands...but good info

I first compared my stock tires over a 60 mile distance that I normally travel against my GPS and found both the odometer and speedometer to closely match my GPS. Then I measured my new tires at 32.25 to 32.5 inches tall and used my Hypertech Tirepaq to first adjust for the smaller size, compared the vehicles speedometer and odometer to my GPS over the same 60 mile piece of road, re-adjusted for 32.5 and again compared it to the GPS. I found that I couldn't see a difference when comparing the instantaneous MPH, but over the 60 mile run there was about a 1-2% discrepancy and I settled on the 32.5 inch tire diameter.

now that spreadsheet should be a sticky

ok yes im a little slow and just noticed it was already there... durr