Jim, I do it by the month using "real" miles (odometer miles) as opposed to computer miles whether they are from a program, an ELD, or the truck's ECM, and using real fuel put in the tanks instead of the numbers the ECM spits out. Not perfect but about as close as you're going to get without being super scientific.
We chunk all that information in a database so we can extract information however we want to look at it.
My best trucks are 2015/2016 Freightliner Cascadias.
The best advice I can give anyone is to reach out to your Detroit rep, not your salesman (although s/he can get your Detroit rep for you) and ask him/her if the spec you are thinking of is fuel efficient, then build your truck around that drive line. I would expect the same goes for Volvo, Mack, and Navistar.
Unfortunately there is no real roadmap to success when buying Paccar product, although you are likely better to buy Kenworth than you are Peterbilt if Paccar is a must have.
Jim's right about the X-Line Energy tires. We've tried several other brands, and they just don't do as well as the Michelins.
As for trailer skirts, we have found that they cost us fuel, but here's why ... we run mostly north and south, and quite often lighter one way. Prevailing winds are from the west so we are always being pushed sideways with the skirts on. If we were running long distance east and west, I would definitely have them on because they do make a difference by about 1/2 mpg (Imperial).
My worst are two shit-ass old Peterbilts.
Best thing you can do with old Peterbilts is burn them. Forego the insurance recovery, and pay the environmental clean up fee. Honestly, you'll be money ahead at the end of the day ... LOL
I do have a poignant story to relay ...
I have a younger brother. It's not my fault. I had no say in the matter. We are somewhat competitive.
Over the years he has always been the one around here to spec and order the trucks. That was until he ordered some '07 and '12 Peterbilts. That was the last time I let him order trucks. They were junk. Unfortunately no research went into what we were buying by either the Peterbilt salesperson, or my brother. What we ended up with was 1980's Billy Big Riggin' trucks, and that shit doesn't sit well with new tech.
Fast forward to the next round of buy-ins. I did literally months of research myself. Spoke to dozens of people whether they were owners, techs, engineers, and so on. What I ended up with were Freightliner Cascadias. All my sales facility really did was add up the numbers, and send me a bill.
The Freightliners performed flawlessly. Better than expected actually. Eventually it's my brothers time to buy new trucks, as he has his own fleet on with the company, and there is no denying the value of the Detroit drive line. However, he won't buy Freightliner because I do. So he buys Western Star, but insists on spec'ing them himself. What he ends up with are 1980's Billy Big Riggin' trucks with a shit load of modern tech in them. Anyone care to guess what they get for fuel mileage ???
If you guessed between 6.0 and 7.25 mpg (Imperial) you win a gold star.
It gets even better though ... or worse depending on your point of view ... the drivers he has in two of these trucks are Old School - Old School, as in they are way smarter than any computer, and no way is any machine going to tell them how to drive. One of them can manage 6.5 mpg (Imperial) when he is light, and the other has yet to break 6.0 mpg (Imperial), and that truck has 800k on it !!!
Times are changing quickly boys, girls, and them ... very quickly.
