2 inches.
When I received my Evolution, I was pumped. The Evolution for Jimmy Nevarez and Joey Slaughter’s Cascadia were on display together. They were equipped differently. Mine was a 6x4 with 
duals. Jimmy’s was a 6x2 with wide based singles. For fuel mileage only purposes Jimmy’s configuration should win. It is important to quantify the difference. The trucks are for testing. One thing bothered me. My fifth wheel was on a platform. That would make my box height about 2 inches higher than the other trucks.
A couple of weeks ago we lowered the fifth wheel those 2 inches. This little difference has made a measurable difference. Over the last 15,000 miles my truck has been averaging 8.225 MPG. My first 3 tanks since lowering the fifth wheel have been 8.71, 9.049, and 8.291. They average out to 8.683. The sample size is too small to make long term budgets on, but it is definitely a measurable difference.
The interesting thing though, is if you extrapolate annual numbers. At shows I talk to owner operators who struggle to get 6 mpg. Some are really proud to be averaging 7 mpg. Others are getting a very respectable 7.5 mpg. If we estimate that owner operators average 120,000 miles per year, the annual numbers are eye opening. For my purpose I will estimate fuel costs to be $3.80 per gallon. I will throw in DEF costs at $2.70180 on my truck. Then have a fluid cost per mile.
| MPG |
Diesel |
Annual Diesel Expense |
Annual DEF expense |
Total Fluid Cost |
| 6 |
20,000 |
76,000 |
0 |
$76,000 |
| 7 |
17,143 |
65,143 |
0 |
$65,140.40 |
| 7.5 |
16,000 |
60,800 |
0 |
$60,800 |
| 8.225 |
14,590 |
55,442 |
180 |
$55,622 |
| 8.683 |
13,820 |
52,516 |
180 |
$52,696 |
These numbers show significantly increased profits as fuel is saved. Little things mean a lot. Fixed costs to save fuel can have a large return on investment. Lowering my 5th wheel cost about $850. It (very early yet) is showing a possible annual savings of $2,926. It will pay for itself in less than 4 months.
The Evolution is a series of little changes. Every little change makes a difference. Fuel is our largest 
expense. Lowering that expense by small percentage points can make significant changes in annual fuel costs. Consider keeping that truck for 8 years. The fuel savings between my truck and a 6 mpg truck over the lifetime will be about $168,432. Even the little change of lowering the 5th wheel will yield $23,408. Little changes mean a lot.