A lesson in SUV aerodynamics

[LVSteve]

Had to make a run to Hesperia and back yesterday, about 410 miles total. Forecast showed S or SW winds up to 25 mph with possibly bigger gusts would be blowing all along the route down I-15. Yep, my ears agreed as the wind was intruding on the normal silence of the interior of my SUV, a Mercedes ML turbo-diesel. I also noticed that the instantaneous consumption readout looked pretty sad on the really open parts of the freeway. Got to Hesperia with the trip meter showing 27.6 mpg. Not too bad, I thought. Let's hear it for diesel and cruise control.

My buddy and I picked up the stuff we went there to get, got some lunch and lottery tickets (hello to my distant cousin in Florida ) and set off to return. The following wind made a monster difference. There was barely a whisper of wind noise and on the flat the instantaneous consumption readout was showing bonkers numbers for a 5000 lb SUV of this size, over 40 mpg quite often.

We did get held up climbing the Baker grade by a huge oversized load that meant only one lane of traffic could get by. I'm sure the push and shove up the hill hurt the overall number for the day, but by how much I cannot say. Got back to Vegas with the trip meter showing 30.5 mpg for the whole day. Can't argue with that in a chunky vehicle. You also cannot argue with having over 400 ft lbs of torque and turbo when it comes to negotiating the mountains.

It is certainly way better than I could ever achieve in my gas powered Xterra that weighed 1000 lb less. Oh, and diesel was a bare five cents more expensive than regular last time I filled up at Sam's, a drop in the bucket when the cost is around $3.85/gallon.

 

[Autonomous]

Freight trains with empty, open cars can be slowed down by side winds.

 

[SMSgt]

I had a Mazda pickup that would not go over 55 when driving in a downpour. Could not push itself any faster against the rain.

 

[Rustyt1953]

Sounds like the ideal vehicle for a mime.

 

[swsig]

I keep detailed records of my fuel usage, and i can testify that wind direction can make a significant difference. My block shaped 2005 Toyota Sequoia normally averaged 18 mpg when driving from the DFW area to Albuquerque. However, on a trip to Albuquerque into a stiff head wind the entire way, I only averaged 14 mpg. The same wind was present as a tail wind on the trip back, and I averaged 22 mpg, the best I ever got with the Sequoia.

 

[Autonomous]

I had a Mazda pickup that would not go over 55 when driving in a downpour. Could not push itself any faster against the rain.

I'll bet a lot of the resistance was from the tires having to plow through the water.

 

[woodsltc]

I love driving my 2010 FJ Cruiser, but it has the aerodynamics of cinderblock.

It's a manual transmission with full-time 4WD .... get's an average of 19 mpg in normal conditions, add a stiff head-wind and it drops to 16 mpg. Still it's fun to drive so I plan on keeping it .

Don

 

[moralem]

I had to make a trip to rescue my SIL and little grandson when their F150 ecoboost went into limp mode because of a turbo code…..hauled my 20 foot trailer on 8000 lb axles behind my 2022 superduty with the 7.3l gas motor. Averaged, per the computer, 15.2 mpg from north Texas to Holbrook AZ. On the way back loaded, averaged just over 10mpg. Running 75-80mph.

 

[LVSteve]

Averaged, per the computer, 15.2 mpg from north Texas to Holbrook AZ. On the way back loaded, averaged just over 10mpg. Running 75-80mph.

Assuming drag rises as a cube of the speed, I think we can see why you only got 10 mpg.

 

[Shibadog]

Gotta love diesel-power and mpg’s. Wife’s Touareg and my Ram Eco, both with 3.0 TD’s will break 30 on the slab at 7-75 mph. Worst ever was the Ram pulling a TT into a headwind in west Texas. Instant readout ( normally 15.2-16.5 while towing) was in single digits��. When I stopped for fuel it was all I could do to stand��. That Western wind is Tough.

 

[Nevada Ed]

I had a Mazda pickup that would not go over 55 when driving in a downpour. Could not push itself any faster against the rain.

On our Nevada roads , if you are in the slow truck lane and you
get caught in a heavy down pour, you might not want to go too fast
since there is a chance of you car, hydroplaning, from deep water in the road ruts
made by the 18 wheelers.

You will know, when your car will not turn !!

 

[LVSteve]

On our Nevada roads , if you are in the slow truck lane and you
get caught in a heavy down pour, you might not want to go too fast
since there is a chance of you car, hydroplaning, from deep water in the road ruts
made by the 18 wheelers.

You will know, when your car will not turn !!

Those truck ruts drove me nuts the day I had to drive a Nissan rental with a track so narrow that you could not get the left and right tires into the bottom at the same time. Consequently, the car kept wanting to fall down into one rut or another.