Fiberglass "aerodynamic" topper for Jeep Gladiator

I bought a (almost) new car! 2022 Gladiator Mojave. This will be my cross-country and snow car. It's also rated to tow 4000lbs which means I can dolly everything else my GF and I own, currently 7 cars between the two of us. 

I really wish the JT came with a 6' bed, but compromises must be made and this truck ticks more boxes than anything else. My main reason for a 6' bed is that my skis and snowboards are longer than 5' and I would like them inside the truck when I travel. Luckily the height of a topper gives a long enough hypotenuse to fit 180cm skis, and my biggest are 177cm. 

Toppers aren't great for aero. Toppers cost a lot more than the materials to build them. I do fiberglass work for my day job. I think I can solve this problem. 

My goal is to build a top with a 13° sloped roof based on my reading at EcoModder. Because I want to also use it as a truck in the summer, the roof will be easily removable, leaving the triangular sides attached. To maintain rearward visibility I'll install RV windows. 

Construction is going to be a one-by material frame covered on both sides with fiberglass. I'm reading a lot on teardrop trailer construction and combining it with my surfboard building knowledge. 

Day 1 began with laying out the lowest layer, that sits on the bed, as well as the front wall and RV window. 

Very cool!

Whoa, can't wait to watch this. I love people talented with skills I don't have. 

This should be neat. I thought you were going to ask where to get one, based on the thread title. A build is much more interesting.

Do you need to do anything about the gap between the cab and the shell for your MPGs? 

Nice! The Mojave is the one to have. 

Yes, this is far more interesting than I expected from the title.  I wonder, would a Gurney lip at the tail end of the hardtop solve more than what the slopped roof would solve?  

Woody (Forum Supportum) said:

Nice! The Mojave is the one to have. 

100% I had a Mojave that I supercharged, and it was a very nice truck. If I find a Gobi Mojave hood and cowl, I'll swap it over to the new one (it's a Rubicon). 

Are you building a bed topper like this?

Chandler and Glueguy: Thanks! I enjoy fiberglass work but I'm not much of a woodworker. I'm happy to try my hand at something different.

thatsnowinnebago: I may experiment with a seal there. Most of the ones I see on ecomodder have a slight gap but a few guys smoothed it all the way from the roofline to the tail. I can experiment.

John Welsh: Good detachment of airflow would help with a regular topper. The goal is to get the vehicle as close as possible from a side view to a teardrop shape. The front end is what it is, so I'm working on the back end.

Woody and Steve: Big fan of the Mojave. I wanted at least 3 wheel drive, coming from an XJ with two open diffs. Getting a real locker is going to be nice in the snow. The tall/soft suspension is pretty comfy but it still handles pretty well. Having 4.10 gears will be nice on the highway, as I've heard the 3.73 trucks don't like 6th gear as much.

Fasted58: Same concept! My friend yesterday made the same comment when I showed him what I'm doing.

Measure twice, cut once, realize you measured the wrong thing, be thankful that wood is cheaper than metal

Trigonometry is much harder when the sides of your triangle are 2.5" thick instead of infinitesimal

First side is practice and second side should be much easier

Compound miter cuts are hard. I am not a wood worker. The main frame and roof frame are complete. Now to add on a few more ribs and it'll be ready for foam and glass 

Nice!

Very cool idea. Looking forward to seeing the results!

So much scrap wood and dust. I did not have a complete plan before hand so the dust and cut-offs is wasteful. Thankfully it's all 1x1 that I ripped from 1x4s so it's pretty cheap. Today I finished installing the ribs and framed the back window. Time for fiberglassing!

Every day I'm more impressed with the in town fuel economy. Just need to increase the highway mileage up to XJ numbers.

Very neat build idea!

What about the weight youre adding, will that neutralize some of the mpg gains by the shape or no?

In reply to buzzboy :

That is very reasonable given the weight and shape of the truck!  We own a 2021 Wrangler Unlimited with the 2.0 turbo and it barely does better, though it delivers an impressive 24 mpg on the highway.

I saw that your plan is/was to make the middle removable while leaving the sides....  if the back isn't totally enclosed, having the sides might not be worth it.  You can't get to anything in the back except from the rear which is not the end of the world but definitely a pain. 

In reply to buzzboy :

Up to XJ numbers, lol. 

@Hybridmoments: Small weight isn't really that big of a deal for highway fuel economy. And I doubt I'm adding over 100lbs.

@loweguy5: 24 would be amazing but I can only get that below 50mph. It's impressive for a big lump like this

@jfryjfry: I'll mostly use it in the summer for surfboards, occasional drivetrain and brush. All things loaded from the rear. It will still be relatively easy to remove the whole topper if I find that works better for my uses. 

@Keith: Right?! This thing crushes the XJ mpg at speeds under 60mph, but over that the XJ is actually more efficient.

A friend of mine did a similar thing to his truck. He decided to see how much he could do to improve the aero for mpgs. Note the wheel covers, wheel gaps filled, airdam, and side skirts.

How much did it help? I see vortex generators too....

TurboFource said:

How much did it help? I see vortex generators too....

He tested after each individual modification / change, so while he knows...I don't. I do know the end result of all the modifications. If I remember correctly, he got 36mpg out of it on the highway. But there were some underhood modifications as well. Clutch on the alternator, pressureless cooling system, etc. He really geeked out over it.

That Dakota is sweet! I don't see going full ecomodder on my truck, but a few tips and tricks to help out with an MPG or two.

Really my goal is to build a topper, making it more aerodynamic is just a side effect.

Following this as someone who dabbles with the resins and fibers. I can't wait to see how you cover the large flat areas.

My go-to item for large flat lay ups is a 4' glass sliding door I keep around the shop. Wax it up, spray on gel coat and build up a glass smooth hunk of FRP.