Huge MPG change?

[BUZZHEAD]

Welcome to the 15 MPH CLUB
It is the vehicle I wanted ,ever since the 1989 JEEP COMMANCHE PICK UP I had.
I have had five JEEP wranglers between getting this awesome truck.
You cannot have this much fun in a HONDA CIVIC.

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[Gren71]

it's not the shape of the mirror that concerns them, it's the interaction of that mirror with the rest of the side of the truck that has the bigger impact. Similar for the bumper - yeah, there's weight there to consider, yeah, most after-market do expose the fronts of the front tires, but it's the interaction of the shape of that bumper with the rest of the truck that determines drag losses.

In another thread im going to do an experiment where i go back to the oem bumper with the ugly air dam pieces on it.

I recently got JLUR rims to put on my JT MAX TOW (11in diameter, its like a giant tuna can) and the fella i got it from happened to be an engineer. We talked about jeep geometry a bit and ended up talking about the aerodynamics of the brick. The fella made the point that if you did the math the small air dams make up a very small part of the total area of drag made by the JT.

im of the same line of thinking as papa where it has to do with the whole package, not just that one piece of the equation.

 

[Jeeperjamie]

In another thread im going to do an experiment where i go back to the oem bumper with the ugly air dam pieces on it.

I recently got JLUR rims to put on my JT MAX TOW (11in diameter, its like a giant tuna can) and the fella i got it from happened to be an engineer. We talked about jeep geometry a bit and ended up talking about the aerodynamics of the brick. The fella made the point that if you did the math the small air dams make up a very small part of the total area of drag made by the JT.

im of the same line of thinking as papa where it has to do with the whole package, not just that one piece of the equation.

I feel the same way. Air flow needs to go up and over and around the side of the jeep so what ever you put on other than OEM has to be able to that. If it stops air flow or pushes it up or down then it's going to cause drag. I'll bet even the skid plate plastic or metal would have some sort of affect if removed. I have considered mounting the metal one I have to see but need the hardware to do it. I am currently running without either installed.

 

[NachoRuby]

You cannot have this much fun in a HONDA CIVIC.

Is that Civic an Si or R?

 

[Iamstubb]

I had those steps, until I hit a rock wheeling and cracked one. It was a good hit, minor damage. I prefer the rock rails. But yes, adding 100lbs rock rails and a 100lb horse stall mat for the bed and 100lbs of bumper and winch and 50lbs of gear, well now my 1550lb payload becomes 1000lbs payload with me in the Jeep. Yet somehow when I am on the scales I am darn near gvwr!

I figure if I am going to do any serious wheeling, I will switch them back out. It was an easy swap that took less than an hour. In the mean time the steps make it easier for the folks and Mrs. to hop in.

 

[Stratus109]

You couldn't have picked a heavier tire unfortunately. They are sturdy at least. I always tell people if yr not wheeling often or at all and its a street truck get the lightest tire u can for the size. Same with the rims. Unsprung weight is a sob.

 

[kdaa25]

If you got 3.73 gears then that's expected. I got 4.10 gears on my Sport Max Tow and I get around 17.2 to 17.5 on 37 12.5 17. You also picked one of the heavier 35's, yours weigh more than my 37's do and if you went with a stubby bumper or any bumper that doesn't close in the gap between the fenders and the bumper then air is getting up inside those fenders when you ride and that's causing wind resistance. The higher you go up in lift then the worse it's going to get, plus the added weight of the bumper didn't help either.

That's why I chose a full width bumper with high clearance ends to close back that gap between the fenders and the bumper, plus I took weight of the tires, bumper and winch into account as well, even down to the types of lights I decided to mount. Believe it or not every little detail matters when it comes to aerodynamics, even lights. Lights bars block air flow and push air up instead of around the jeep, especially light bars put above the windshield. Just saying and giving a few tips, I'm sure someone will try to contradict what I'm saying but after building a few of them you get an idea of the do's and don'ts. Mine as it sits to give you a idea of what I'm talking about. I have never had a problem pretty much staying above 17 Mpgs and on occasion above 18 on longer trips. A few days I've been at 16.7 and those were colder days when it was below 32° in the morning and no higher than the 40's in the evening.

Would love to see your setup for comparison

I like your bumper setup. What's the brand of your bumper? Thanks

 

[seven30]

Welcome to the 15 MPH CLUB
It is the vehicle I wanted ,ever since the 1989 JEEP COMMANCHE PICK UP I had.
I have had five JEEP wranglers between getting this awesome truck.
You cannot have this much fun in a HONDA CIVIC.

The JT is a great truck. The Comanche was legendary. I have both.

 

[Jeeperjamie]

I like your bumper setup. What's the brand of your bumper? Thanks

Rugged Ridge Spartan High clearance bumper.

 

[Maddaw]

I feel the same way. Air flow needs to go up and over and around the side of the jeep so what ever you put on other than OEM has to be able to that. If it stops air flow or pushes it up or down then it's going to cause drag. I'll bet even the skid plate plastic or metal would have some sort of affect if removed. I have considered mounting the metal one I have to see but need the hardware to do it. I am currently running without either installed.

I have also found that aerodynamics play a huge part in the mileage. I have 3.73gears, 2.5 lift, 35s, steel bumper, winch, and bed cover and get an expected 15mpg. With my half rack and RTT(sits flush to roof line)on the bed and the cover removed I get 16.7mpg. So even though there is an extra 500lbs on the vehicle, the change in the draft over the top of the vehicle adds and extra 1.7mpg. I noticed this when I installed it but didn’t believe it until I removed the rack and tent for storage and lost the mpgs.

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