OK I just upgraded my tires from 225-75-16 to 265-75-16

Since I have not corrected the speedometer by reflashing the computor I believe I read some where that my speedometer now reads 11% slower than I am actually going.

I just manually checked my gas mileage. It shows a drop from the 18-19 range to about 16.5.

I know to expect some drop in mileage with bigger tires. But I am wondering how accuate are my mileage calulations now that my speedometer and odometer are running slow.

Would not my odometer show less miles than I actually traveled? And therefore show an exagerated drop in miles per gallon?

Any math wizzards out there that can tell me what the amount of error is or how to figure it?

 

From 18.5 down to 16.5 = 11% reduction.
That is consistent with the 11% speed/distance change, if that is accurate.

 

Then you are saying that in actuallity my MPG has remained the same (more or less) but the drop shown is the result of the 11% error.

 

Could be. It all hinges on the actual error (%) you got for the tire difference.
Measure the diameter difference. Then we can figure the error.

 

I'll do that tomorrow. Thanks.

I guess another way is to just get the damn speedometer reflashed and see if my mileage goes up. But I don't like going to the dealer for much of anything.

 

will bigger tires/wheels void the warranty?

Also, if you re-gear, will it fix the odometer?

 

Calibration will be good for your auto tranny, too.

 

No. Speed/distance signal comes from the left front wheel.
Well, at least on mine it does. Manual trannys may be different. I don't recall.