Wow, the ARB rack was costing my 3-4 mpg!!!

[Arya Ebrahimi]

Ok, I just got home from my first highway trip without my ARB roof rack in almost 2 years.

With the ARB rack I was averaging between 9 and 10mpg. Speed didn't seem to matter, if I set the cruise at 55 or 75, I still got 9-10.

This weekend I averaged 14.6 on the way home and 13 on the way back(was in a bigger hurry on the way back). That's cruising at speeds ranging from 70-85mph, no cruise, just going with traffic.

The ONLY difference between these two situations was the rack. I can't imagine what I would get on a flat highway w/ the cruise set on 55.

BTW, my mileage in town is the same w/ or w/o the rack. I get about 9 regardless of driving style. If I hotrod w/ the OD off or drive like a granny w/ the OD on, it doesn't seem to matter.

I do have a CEL showing, but I forget what it's for(something to do w/ the O2 sensors, it's been on for over a year ).

Anyway, just wanted to report my findings as I was quite amazed when I got more than 280 miles on one tank w/o the orange light popping on.

 

[Tentsontop]

Seems odd a rack would suck that many MPG. I just put a big a$$ rack up. It's tapered in the front, but has plenty of wind grabbing potential. We'll see if my mileage changes.

 

[maximBJ70]

Its funny to think it that those little things will cost you so much. When I bought my 70 the PO warned me about losing out on fuel mileage with the rack on. Even the little Thule or Yakima bars will cost you a mpg or two. I didn't believe it either, but especially over 100kmh (ie.55) you really increase wind resistance with anything up there. Too bad 'cause they look so darn cool

 

[CodyRx7]

I dunno if that would be correct...

I have my ghetto rack up top with my 315 spare and its no more aerodynamic than an ARB would or wouldn't be.

I get between 12-16mpg regularly....the higher on the highway with less stop & go obviously.

 

[TX_TLC]

The ONLY difference between these two situations was the rack. I can't imagine what I would get on a flat highway w/ the cruise set on 55.

And that you went one direction on the road with the rack and the other direction on the road with out the rack. Meaning...is it up/down hill in one direction?

Also the weather can factor in as well...any wind? Seems like a large jump...but measure your mileage around town this week without the bar and that should help shed light on the situation.

 

[toylndcrusr]

Arya,

I recently replaced my 02 sensors (P0141 CEL) and got about a 3 mpg boost in fuel economy, so I am curious to see what your milage would be if you replaced your o2 sensors too.

 

[BLACKGOLD]

I'm not surprised. When I put the Confer rack on my Cruiser I have noticed about 2-3 mpg loss in mileage.

 

[Arya Ebrahimi]

And that you went one direction on the road with the rack and the other direction on the road with out the rack. Meaning...is it up/down hill in one direction?

Also the weather can factor in as well...any wind? Seems like a large jump...but measure your mileage around town this week without the bar and that should help shed light on the situation.

I'm not an idiot! This whole trip was without the rack. I sold the rack 2 weeks ago. I'm comparing this weekend's travel of ~500 miles roundtrip to my previous fuel consumption data.

My around town mileage has not changed noticeably at all since I removed the rack. I was rather dissappointed as that is where a large portion of my miles comes from.

 

[e9999]

one thing easy about aerodynamics is that Aero Drag goes up more or less like the square of velocity (not quite that simple but good enough for us here). Double the velocity, 4x more drag; 3x the velocity 9x the drag; etc.

So basically, don't worry too much about it at low speeds (town?) and limit speed on the freeway (plus that's good for your stress level.. ).

I leave the rack on mine cuz town doesn't matter much and when I'm going faster (freeway) I usually go places where I'd need it. (Plus I'm too lazy to take it off all the time.)

 

[TX_TLC]

I'm not an idiot! This whole trip was without the rack. I sold the rack 2 weeks ago. I'm comparing this weekend's travel of ~500 miles roundtrip to my previous fuel consumption data.

My around town mileage has not changed noticeably at all since I removed the rack. I was rather dissappointed as that is where a large portion of my miles comes from.

Ahh..I misread. Thought you drove somewhere and took the rack off and driving back with w/o the rack and you were comparing your "to" and "from" numbers.

 

[Grench]

Even removing the factory rack makes a difference. With the factory rack I got 14mpg. Without it I get 14.7. This is over multiple multi-tank trips, both cases -fully- loaded (~6,000 lbs) with ARB, rear tire, etc... I removed the rack and wing about 7 months ago and put LineX on the whole roof, so it isn't a -smooth- surface even now.

My wife's full stocker gets 16 on the highway - never had a roof rack or spoiler.

 

[Brentbba]

My INTI is costing me about 1mpg around town.

 

[FirstToy]

anything that adds frontal square footage and turbulence will reduce your mpg's. it's worth it if you need it.

the most aerodynamic vehicles have skinny tires, fared in, & very small frontal areas. minimal turbulence generators and a teardrop shape w/ a kamm tail.

anything outside of that, you are taking a hit on the coefficient of drag.

 

[re_guderian]

anything that adds frontal square footage and turbulence will reduce your mpg's. it's worth it if you need it.

the most aerodynamic vehicles have skinny tires, fared in, & very small frontal areas. minimal turbulence generators and a teardrop shape w/ a kamm tail.

anything outside of that, you are taking a hit on the coefficient of drag.

Think Honda Insight...

 

[FirstToy]

Think Honda Insight...

no, more like the GM EV. A tadpole w/ skinny tires is the most aero.

 

[L8Shift]

Think Honda Insight...

On your roof rack ...

(Sorry I couldn't resist, just the thought )

We could probably get one up there...tho

 

[cool breeze]

Yeah, you def need to replace the o2 sensors. I would look into those before anything if youre getting bad mielage, afterall they detect the properties of the engines combustion.

worth the money for sure

 

[j2custom]

roof rack

I get 14 mpg + even with the rack on. Stock truck with custom front bumper, 285 Michelins and a K&N filter. I did not check the mileage prior to install for a good comparison #s. I will be taking it off to repaint soon and will check then. I was planning on making a plastic, tin or aluminum wind diverter/deflector for the front of the rack soon too. Anyone have any experience with those on their racks?

 

[e9999]

best I can tell from a number of calcs is that I likely lost less than 1 mpg with a loaded roof rack (including upright jerry cans and a big luggage bag) going on the freeway at around 60 mph, this over long distances.
I attribute the relatively low loss to the low speed.

with a somewhat armored, fully and heavily loaded truck with camping gear for a week, full roof rack, jerry cans and luggage on top, 4 people inside, and pulling a popup trailer, I got 13mpg avg on the freeway last time...