so i had 33'' tires and 4.88, by all calculations should have been very close to the factory impulse/mile rate with the stock speedo sender gear. I have measured the speed at the time and found that the speedo was showing about 6% more than the gps, never thought to check the odometer, i assumed it was showing more by the same amount. I just put new 35'' tires on and the speedo is pretty much on the money, (speedo=100kph, gps=99kph). Just out of curiosity i reset the trip on the gps and it turne out that 40.6km on the odo is actually 42.4km according to the gps (that's 4.4% more than what the odometer measures). I'll be using this correction factor as my mpg calculation. i'm kinda pleases that the speedo shows the correct amount although for the PCM would be nice to have the proper impulses/mile rate (dunno if it actually makes a difference though).
