ive had several posts about power and fuel economy on my 04 screw . i may have power licked with the cat change. i have 275 65 18 tires now and sticker shows stock to be 265 60 18. how much will that change my speedo and odometer. it is 6.25 % more miles on my gps than on my trip gauge. should i trust my gps for miles and what is involved in making the speedo right?
it took 16 miles on my truck to get 1 mile distance different on my gps. truck was 16.0 miles and gps was 17.0.. if all thats correct and my math is right or at least close . 16 + 6.25% is 17.... 200 (trip gauge) miles and 15gal is 13.33mpg...... 212.5(gps) miles and 15 gal is 14.16mpg. all simulated trip mileage...i might not have a mpg issue after all and if it pulls fine in drive maybe all will be well if i can fix my odometer... thanks steve

 

using http://www.miata.net/garage/tirecalc.html

I get 661.0 stock and 629.0 new tire


Your truck reads 95.15% of your actual mileage traveled.

 

with that i guess my gps is closer than my odometer

 

so i just have to add 4.85% to my trip gauge mileage to figure mpg i guess.. so over a 5000 mile oil change i would actually be at 5242 miles