Don't believe that 30 PSI number. Most folks are running their H3's at significantly higher pressures. I run at ~38 PSI on my 285's. I hear a lot of chatter for running at 40 PSI as well.

 

No wonder you MPG sucks, you've been running your tires underinflated!

Read the siedwall of your tires, the bozo that slapped a sticker in the door jam did not work for the tire maker.

 

So you are the guys blowing by me in the H3's on the highway! LOL I usually try to set the cruise at 70 and I seem to get somewhere around 17 or 18 (without roof racks on).

 

On my last long trip in the Alpha I got just over 16 mpg, going about 70-75

 

I had actually had them at 36-38psi before we left and dropped the pressure to 30psi after we got back and they seem to be doing better....we are going to take the roof racks off soon, since we don't put stuff on the roof!!! Maybe some new tires will do it...but last 3 cars everytime we needed tires we ended up with a new car!!! LOL!!

 

A roof rack will significantly impact your mileage. It could easily knock 1-2 mpg off of your average. Dropping your speed down to 65 or 70 will probably save another 1-2 mpg.