I'm extremely skeptical about both the mileage reported by the onboard computer, and the mileage reported by people on this and other forums. If you add anything that negatively impacts airflow or adds weight, you are likely negatively impacting your fuel economy. A roof rack, roof top tent, lift, larger and/or wider tires, MT's instead of AT tires, external moley panels, bull bar, extra lights, sidesteps/sliders, etc. etc., they all impact MPG negatively. Your average speed for a trip will also impact MPG, in an exponential fashion (or at least not linear). Add a headwind, climbing altitude, colder temps, etc., and there can be some major differences in one drive to the next even if you haven't changed anything on the vehicle itself.
All that being said, I wouldn't expect an impact of 30% for adding a low-profile roof rack. You need more data.
In addition, the only accurate way to measure MPG is to first fill the Grenadier and record the mileage. Then drive. When you fill up again, you know accurately how many gallons you used and you can subtract the new mileage to figure out how far you drove. In my experience my real economy has been substantially less than what the computer shows me getting.
This is why for me, the Longranger extended fuel tank is my most important mod.
All that being said, I wouldn't expect an impact of 30% for adding a low-profile roof rack. You need more data.
In addition, the only accurate way to measure MPG is to first fill the Grenadier and record the mileage. Then drive. When you fill up again, you know accurately how many gallons you used and you can subtract the new mileage to figure out how far you drove. In my experience my real economy has been substantially less than what the computer shows me getting.
This is why for me, the Longranger extended fuel tank is my most important mod.
