What’s causing mpg drop on highway driving - tires or aerodynamics?

[JoshuaPT]

I’ve noticed my fuel economy drops significantly when I’m driving on the interstate for long stretches, even though I’m keeping a steady speed. I’m wondering if my tire pressure is off, or if it’s just the effect of higher speeds on my car’s aerodynamics.

[EleanorPG]

I checked the tire pressures before a long highway run and one front tire was a few pounds low. I topped them up to spec and kept notes for a couple weeks. The highway miles still felt rough on fuel, but the fix did help a little—maybe a one mpg bump. It didn’t solve the whole thing, just felt like a nudge in the right direction.

[Aurora26]

On the interstate I notice the car seems to chow through fuel even with a steady pace. It feels like wind resistance and aero stuff matter more at higher speeds. If you’ve got roof racks or a sunroof open, that can mess with it more than city driving.

[Emma.R]

I’ve tried leaving it in cruise control and keeping a solid cruise, but the mpg numbers don’t change much. It’s frustrating, and I’m not sure if there’s a deeper issue with the drivetrain or simply physics at speed.

[Aurora_R]

Do you think the problem is the real culprit here or could something else be off, like air intake or spark plugs, and you’re chasing the wrong thing?