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Old 12-22-2018, 04:03 PM   #1 (permalink)
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2019 Chevy Silverado - Aerodynamic Fenders

2019 Silverado Front Air Curtains Improve Aerodynamics | GM Authority

Fenders and other mods help improve aerodynamic efficiency by 7%.
Better than moon covers?

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Old 12-23-2018, 12:04 AM   #2 (permalink)
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And yet it's supposedly rated worse for MPG than the previous generation?
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Old 12-23-2018, 01:32 AM   #3 (permalink)
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Well... As we all know, none of the modern cars since the 80s on so have gotten lighter or more fuel efficient, in general. You've got the hybrids doing double ecological damage with up front lithium battery mining and production, then crippled with a ten year life. Just more unnecessary, dangerous junk like wifi and such.

In Japan, Panasonic sponsors AA rechargeable battery race cars and races. Seriously lightweight and goes for dozens of miles. No reason to exceed 1000lbs with a carbon fiber shell like F1 race cars.

Then again, I do need the new truck's 12,000lbs towing ....er, let me think....er..... Right.....not!
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Old 12-27-2018, 11:59 AM   #4 (permalink)
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This new Silverado is 200-300 pounds lighter across the board than the 2018.

In the comments section of a TTAC article, an aerodynamicist chimed in that air curtains are typically worth about -.005 Cd. According to Hucho, that's about what a full skirt will get you.
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Old 12-29-2018, 11:31 AM   #5 (permalink)
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Aero only REALLY matters on other than short trips (above three hours) AND when the average speed on the trip (engine run time versus miles) is above 35.

(If you don’t have these numbers for your vehicle, don’t pretend to understand what I’ve just written).

“Wind-Handling” is a better term than “aero” for what GM is up to.

Being able to remain upright and lane-centered is what counts out on the road (it’s no longer “the open road” anywhere in the US).

For general FE purposes this in the reduction of steering wheel corrections by count PLUS degree of application and duration.

(Read that again).

Wind-handling at speed (pickup top speed of 65-mph) means any adverse steady predominant wind, or sudden cross-gusts. The former is the weather forecast, the latter is other traffic, in main.

Reduction of the work load is directly related to retention of fine motor skills throughout the day. It is those skills that mean best MPG for a given situation. How the truck is being used. Loaded or towing. (Other conditions don’t exist; such as empty bed and solo driver).

The “need” for a pickup is simple. One is a farmer, rancher or contractor. IRS miles per that.

Or, that one regularly (weekly) carries gear which for reasons of safety cannot be carried in the passenger cab or in an enclosed trailer (generator, fuel cans, etc).

That pretty well covers it.

Aero treatment as above REALLY helps in getting down the road.

I left ABQ for AMA day before yesterday in the Peterbilt (579 with EPIQ package) pulling an empty Utility-brand box van with fully-boxed TRAILER TAIL and skirts. Ran the usual GPS-corrected 67-mph. With a port stern mild tailwind (enough to make the cab silent) I was at 12.4-mpg much of the way. 11.3 by the end of the 325-mile run. Crossed both cities. IH-40 all the way. TARE is 34k.

There’s aero, and there’s aero. What looks great for straight-on winds (due solely to sleed) is attractive to us.

But what really counts is from winds in any direction. And that which eases steer functions (a somewhat protective barrier?) is to be commended. Yeah, it’s a bit of a stretch.

OTOH, I was being passed by flattop large cars with vestigial wings on the cab pulling reefers. I know for a fact they weren’t above 5.5-mpg.

And were working a whole lot harder than me.

As my tractor was shedding winds (lessened effect) theirs weren’t. As we were both pulling boxes (and there’s a legal limit to how far back one can slide the tandems from the kingpin; without reference to a weight-balanced load; farther back is best for crosswinds yet it may not be legally possible or otherwise ideal) the crosswind effect was a great deal harder for them.

Compared to them, I wasn’t working.

A front tire air curtain on a pickup is desirable. More so is independent front suspension for lower ground clearance and stability. The combination only helps cement the desirability or one brand and spec over another.

That workload will eventually cause a big rig (or badly specd pickup) to move out of the eleven foot wide Interstate lane. I see it all the time. Too fast, and too stupid.

Highway MPG is about steady-state. No braking or acceleration events. No lane changes. Cruise control on coming down entrance ramp, and engaged until exit ramp.

That means a speed below the crowd. Always. These days the governed trucks are at 66-mph. So, 64-mph works for best time. And it’s at the edge already for safe travel in a pickup. And only when one can keep that without encroaching on the space barrier.

Plan the start time for the trip to be early, AND all stops.

Traffic volume is what kills things. One just gets slower and slower. There’s no choice in the matter.

Do any of you think you maintain 50% cruise control “on” time? It’s seriously harder than you think. My truck notes it.

As a front air curtain is more than daunting for an amateur, luckily most of the rest isn’t (given some fabrication skills and willingness to hire some out). And still remain fairly low key.

The given is ALWAYS separation distance from other vehicles. No exceptions. (And no MPG claims worthy of note otherwise).

That 11-12 I reported above includes cancelling cruise when being slowly passed by another big truck. Not re-engaging until he’s about 700’ out. And then on a downslope where possible.

Same for the usual cretins (everyone) passing and then stalling ahead of me. Have to cancel to get them away. Same distance.

Somewhat the same in leaving a construction zone. Or small town on a US highway. Takes miles and miles before my space between the packs of morons is established. Means I’m running no more than 60 until the crowd from behind (who had stupidly bunched up) is well away.

“Aero” lessens the penalty in all of this. That’s it’s real “worthiness” once one knows what vehicle outputs to monitor and has also adjusted to traffic volume (the continual problem).

Had some fun with a pair of Airstream owners I know. Sent screen shots of MPG. 4WD Diesel one tons. Past that it’s a bad choice of tow vehicle, they each barely get 11-mpg on average. Half the engine size and less than half the combined weight. Rubbed it in with salt. (I’ve tried and tried to get them to optimize their rigs — I average 15-mpg with my significantly longer trailer — but, that’s America today. Men too scared to learn tools or their use. Forget driving skills. Everyone is Jackie Stewart to hear them tell it).

I also called and left a voice mail for the equipment manager (a VP) as this was the first time in 46k miles I’d pulled this exact spec trailer. That the difference was notable even from others that were close.

Aero allows one to fine tune skill at the wheel. (It’s not a substitute despite the prevailing attitude on this forum).

As to those running 55? Learn to manage what’s overtaking. Get out of the way. Safety first, FE second. Your future is in your mirrors. Work to minimize “time” spent with vehicles alongside. I’ve seen that done exactly twice in the past eight years.

And if I ever see BamZipPow out there (I know he manages traffic) I’m going to have some serious fun with him. Why? Because who is out on American roads is so unbelievably easy to predict that a variance will sit you straight up. (But dont worry. You’ll never see it).

I’m thinking I’ll start the trailer tail to wagging once I’m in the left lane and starting the pass (having hung back and now just the two of us; I start the pass 350’ feet out). That’ll slow him down and he’ll be halfway onto the shoulder. Then it’ll get weird. They say when the going gets tough, the weird turn pro. Should be some fun with two weirdo pros going at it.

The rest of you wouldn’t be any fun. He knows how to keep those tenths. Despite a problem. So unless you’re also fascinated (ha, dissociated) in doing both — meeting a high speed death challenge AND not killing the day’s accomplishment— your prudence would go into override mode.

I use this as an example. (BZP a great guy. If I could raise him on CB is the only way I’d start that trailer tail wagging side-to-side: “Look out!! Crazed pill head driver a’comin’ “). He’s used to smoothly managing that traffic. His aero rig makes that much easier.

Cart follows horse.

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Last edited by slowmover; 12-29-2018 at 12:19 PM..
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Old 12-31-2018, 01:24 AM   #6 (permalink)
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Quote:
Better than moon covers?
Completely compatible with Moon covers.

If you observe the spray spiraling out of truck's front wheelwells on the freeway in the rain, you can see the energy involved in the air circulating into and out of the wheelwell. Now, air doesn't get thrown out that far into the ambient flow because it doesn't have the mass; the wheel disk is swept by the ambient air flow. So I suspect the air curtain manages air the wheel disk doesn't see.

The dimensions are interesting, height and width, and it only covers the top third of the tire. I wonder if the roof of the air curtain slopes upward to the top of the wheelwell. Those raised ribs are vortex generators to maintain a coherent jet of air.
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Old 01-04-2019, 07:47 PM   #7 (permalink)
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The real mind blowing thing about the wheel/tire is that the tire where it hits the pavement is at a standstill, moving 0 mph. While at the top, the tire is going twice as fast as the vehicle. Aerodynamics in the simplest of forms is still pretty tough to understand, what is really happening with the wheels is just nuts.
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Old 01-04-2019, 11:28 PM   #8 (permalink)
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There are two little vortexes jetting out from just ahead of the tire contact patch. They're pretty inconsequential.
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Old 01-06-2019, 03:19 PM   #9 (permalink)
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Quote:
Originally Posted by freebeard View Post
There are two little vortexes jetting out from just ahead of the tire contact patch. They're pretty inconsequential.
...plus two rolling off the top, and one off each side. These vortices are the result of the entrainment that reduces a moving wheel's drag compared to a stationary one.

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Old 01-06-2019, 06:24 PM   #10 (permalink)
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My favorite illustration of that:



There's clear separation of the top, middle and bottom.

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