Roof top tent mounting heights vs MPG

Hey guys, I know you're all sick of MPG questions, so I apologize in advance.

I've had a 19 DCSB OR since September, I love it. I've actually been really impressed with the mileage I've gotten on this.

I mounted a RTT a couple weeks ago on a KBB rack. Since then, I've noticed a ~4mpg hit that is worse at highway speeds and ~8mpg hit with any crosswinds or headwinds. I didn't have any hit in the mileage with just the rack. I can hear a decent amount of turbulent air flow with the tent on now, and I notice that when I am just coasting, the truck slows down noticeably faster. I've also noticed that it has trouble holding 6th at ~65 (no issue before) and is now using 5th much of the time.

So, it seems like all this is because of how high up above the cab the RTT is sitting and acting like an expensive sail. My rack is the KB voodoo rack with the tonneau cover attachment. I don't have a tonneau cover on currently.

So, let me answer a couple of questions preemptively; I know I shouldn't care about mpg, I know that none of us bought the truck for good mpg, etc, etc, etc. I'm not looking for opinions about mpg. I am concerned about the 4mpg hit adding up to quite a of difference in not only gas cost over the next 200k miles, but also increased wear on the engine having to work harder to maintain a given speed.

I'm considering getting rid of the tonneau cover adapters and getting the regular adapter for the rack, this will lower it by ~2 inches at a cost of $80. It will still stick up over the cab. I could also get low enough racks that it will be even with the cab, but

My question is how big of a difference should I expect? If I lower it the 2 inches, how much of my gas mileage do you think that will bring back? Should I skip the lowering ~2 inches step and just get bed bars that will place the tent at cab height? Is the ~4-5 mpg hit just what I should expect for having a ~200 pound tent in the bed permanently? I read others posts that say they didn't really say any noticeable drop with the addition of a tent, but it was immediate and very clear for me.

Thanks for your help, really enjoying learning from this community. I'll include a picture of my truck so you can see the current height of the tent.

 

Shouldn’t be that big of a hit at that height, perhaps it’s more of a weight thing. My RTT sits a bit lower than yours but I haven’t seen as big of an mpg hit as you.

 

I have seen a bit of a drop in fuel mileage. I believe it is a combination of weight and aerodynamics.

 

Move it lower. Under cab line to be exact.

 

You can mount the kb voodoo rack with the cover attachment without the cover actually on?

 

I guess my question would be, are you planning to never remove the tent? Gotta be prepared incase on the way home from work you need to pitch a tent? Really need to flex on the Starbuck Baristas. Why not just take it off and put the tent on when you plan on using it? This should get you just about all your mpgs back, alleviate all the additional wear and tear you're concerned with, and not cost you a penny.

 

My Yakima mounter on top of my shell well above the cab took a 1mpg hit.

 

I think you’ll get about 1 mpg increase for every 1 inch of lowering the thing.

 

I fly to the gas station!!!

 

When I first put on my rtt, I noticed a pretty consistent -2mpg effect. I have a cbi bed rack, which puts it halfway through the roofline (maybe a little more)
Im geared and have 35s with armor, mpg is nothing. like nothing. Is what it is though. If the MPG is hurting you, take it off and store it when you arent using it. If you lower it below, you may get better MPG, aero dynamics and all that stuff. But you wont be sure until you try it. If I was you, just carry more fuel in cans in the bed if you are worried about range. Also, If you are traveling at significant altitude I could see the increased weight being harder on your truck, causing the airfuel ratio to be a tad diff, but not 4-5 mpg difference. I say get the lowest bars you can, try them, and if that does not help you, go back to the one you originally had.

 

I lost about 1 MPG with mine mounted as shown. Just the ladder sits above the roofline.

 

what bedrack is that?

 

Mine didn’t change at all with or without.

 

#BuiltnotBought

 

Bahahahahahaha! The bender in the kitchen has me rollin'! Well done.

 

12-14mpg on a 5000 mile trip 70-75mph. I sold it and will stay in a hotel or spike camp next time.

No bike up top on the way back and made no difference. The RTT is a gas hog

 

No shit, that's horrendous!
Hotel was free with those numbers!

 

My RTT sits flush with my cab...for almost 2 years I've kept it on my truck full time because we have extremely limited storage space at our small house and nowhere for me to put it, unless I stash it outside in the backyard. Definitely noticed an MPG hit even with the tent flush with the roof line, especially at highway speeds with crosswinds. It makes my brick-like aerodynamics that much more brick-like.

I recently put a 100lb steel bumper on the front and decided that the RTT is coming off and going in the backyard to be reinstalled when needed...my MPG with tent and stock bumper was at ~15mpg on a good day. With the 100lb bumper on now + the tent, I don't wanna know what it was going to be.

Without the tent and with the bumper I've stayed right about 15mpg, so no change. No change is better than worse change I guess lol

 

Exactly! If I'm ever 2+ hours from a place to stay I'll bring an old school tent

 

Yeah no shit.... You put a one foot tall wall above your roofline.