Just how accurate is your overhead compared to Hand Calc?

[joeyou]

Mine must be the only one that the o/h reads higher than actual. I don't write my numbers down but I always check at the pump and my hand calc have always been . 8 to 1. 5 mpg less than the o/h. For instance I filled up today and o/h said 17. 1 and hand calc was 15. 5. My truck only has 4k on it but I hope mpg gets better as it is broken in. My 93 and my 1996 both 2wd which I realize weigh less and have less resistance both got 18. 5-19. 5 doing the same driving that I am doing now.

You're not going to get the same mileage you did with your '93 and '96. My '95 averaged 21. 5 overall, my '99 averaged 20. 5 overall, and so far my 2004. 5 averages 17. 9 overall. They sacrifice fuel economy for more power and lower emissions. By the way, don't know why, but as time goes on my overhead seems to get much closer to my calculated mpg. I reset it at every fill up. Something you might want to be careful of is that if you're filling up when the tank is not close to empty you are going to compound error in the difference between your hand calculation and the overhead reading. My fillups usually take 26-30 gallons.

 

[JVolpe]

bpenrod,



I would go with the manufacture rpm number. With the GPS you can verify if it is correct. Every different rim/tire combination is going to vary a little. So I would probably start with manufacture number and then change if it is wrong.



If I hadnt talked with the other Ram owner I would have used the manufacturer rpm number, and it is close enough that it probably would not matter in the long run.