Flush Topper adds 2.1mpg at 70mph in a Gen 1 4x4 Tacoma

My old tacoma I had for three months before I put my topper on and I tracked my mileage for every tank both before and after

Pre cap was 19.7
And post cap was 19.8

No real difference

 

Cool...I was curious about that. Mine's been on since I bought the truck so I've never done a before/after.

 

I usually get 15 or less during the winter with the cap on. If I travel highway I can get near 17 doing about 70.

This past trip I got 17.3 with open bed (ranging from 7-80 mph). When I filled up and drove no faster than 60 mph I got 18.8.

If you want the best gas mileage don't drive fast and keep it around 2k rpm

That being said I drive 80 @ 2500 rpm for the better part of 15 hours to get to Florida (I like to save the extra hour for sleep )

btw OP, notice the "load" difference too? less fuel in the tank means less weight to carry as well.

 

If you drop your speeds down to 50 I would expect to see you around 21mpg given your %'s. "Engine Load' is affected by aerodynamic drag about 50x more than weight at highway speeds. Rolling resistance from tires makes up quite a bit more of the "load" than weight does when driving at highway speeds.