Subaru Forester Owners Forum banner
1 - 20 of 53 Posts

·
Registered
2022 Forest Green Premium
Joined
·
52 Posts
Discussion Starter · #1 ·
Has anyone used the adaptive cruise tbehind a mobile home or semi trailer to take advantage of the improved mpg?
How well does the system keep a set distance? How much improvement did you see in MPG?
 

·
Registered
2005 2.5X 4EAT 2017 2.5i Prem CVT
Joined
·
591 Posts
It may not be quite as precise as a radar-based ACC, but it's still pretty good. No ACC is good enough to play NASCAR driver out on the highway, however.

I'm perfectly content with my ACC distance in the middle position and eeking out a couple extra mpg the safe and easy way - 35 psi tires and ethanol-free gas!
 

·
Registered
2022 Forest Green Premium
Joined
·
52 Posts
Discussion Starter · #5 ·
When drafting manually, I tend to stay 75-100 feet back, sometimes more if I can't exactly match my non-smart cruise control. Not as much gained for mpg, but also will not get you arrested for tailgating and will leave you time to hit the brakes in an emergency. Most adaptive cruise systems have a similar vehicle distance minimum and maximum, for similar safety reasons.
 

·
Registered
2005 2.5X 4EAT 2017 2.5i Prem CVT
Joined
·
591 Posts
Given that so many experienced truckers have left the business in recent years I give them a lot more space these days. Especially the Stevie Wonder Institute For Trucking! (aka Sure Wish I had a Faster Truck)
 

·
Registered
2018 Forester XT Limited CVT
Joined
·
1,287 Posts
I suspect some of any MPG increase from safe drafting is because most semi and recreational vehicles drive at slower speeds, which translates to better mileage
On my fuel economy chart, the biggest spike (all the spikes are road trips with lots of highway driving) was when the car was pretty new and I was getting used to all the new features. I did use the ACC but also kept it at the speed limit. I didn't draft, but I do think the lower speeds (less aero drag) contributed quite a lot to the increased economy.

These days I will help out with my foot but back then I would let the car figure things out, and it would hang too far back and accelerate too slowly (oh yeah I had it set to accelerate slowly, that'll contribute as well) if a car was turning or something.

OT: I have the same mug, but with my first name instead of yours.

The red line is the 9-fill average. Just ignore it because there are different driving categories (eg city and hwy, winter and summer, etc) all averaged together.

Slope Rectangle Font Parallel Plot
 

·
Registered
2015 Forester2.5i Premium CVT
Joined
·
1,431 Posts
ACC can’t be set to a close-enough following distance for effective drafting. (1) Thank God! and (2) imagine the lawsuits against Subaru. Because Subaru would lose them all.
 

·
Registered
2017 Foz 2.5i CVT
Joined
·
2,446 Posts
Like the above poster says, I think a broken Eyesight windshield experience will help you lose interest in any tailgating habits. It was a PITA to get a replacement for our '17...and the only other broken windshield I've had in the last 10 years was in my old '09 Foz which got a replacement. Now my son has the '09 and is driving it with a cracked windshield.
 

·
Registered
2022 Forest Green Premium
Joined
·
52 Posts
Discussion Starter · #13 ·
Then what is the point of the adaptive cruise I'd you can't sit back like 100 feet from the car in front of you and let the technology maintain speed and distance. A distance which should prevent the likelihood of any accident or road debris, and which, per some, helps improve mileage by like 10%.
 

·
Registered
2017 Foz 2.5i CVT
Joined
·
2,446 Posts
100 feet is nothing for rocks that are thrown up and Subaru windshields break easily.

In the late 1970's I did some hypermiling in various vehicles, including drafting, folding my sideview mirrors, big tire pressures, slippery oil, etc. None of those old vehicles had cruise control and if I wanted to draft (aka tailgate) now, I would prefer to control the gas pedal myself.

The cost of one Eyesight windshield is far more than you would save in your whole ownership period with the Subaru via drafting. And if you are gonna use adaptive cruise to follow closely, you will wear out your brake pads prematurely and further cancel out any savings. Brakes are not cheap these days either.

And pissing off other drivers in 2022 is not someplace I want to go. We have road rage shootings in Detroit.
 

·
Registered
2019 Forester Sport Lineartronic® CVT
Joined
·
502 Posts
Then what is the point of the adaptive cruise I'd you can't sit back like 100 feet from the car in front of you and let the technology maintain speed and distance. A distance which should prevent the likelihood of any accident or road debris, and which, per some, helps improve mileage by like 10%.
100 feet is too darn close at 65-70 mph. 65mph is 95fps.
 

·
Registered
2017 Forester XT Touring
Joined
·
1,183 Posts
I agree with @rdclark - Even the minimum setting (which on my FXT is closer than I should be following) isn't close enough for effective drafting. Years of motorcycle riding and feeling the turbulence off of every type of vehicle has shown me this. You have to get really close to get in the "bubble" of air that makes for effective drafting. Just outside of that, and the turbulence will negate any real effect.

That said, the tractor trailers that have the panels on the back to smooth out the airflow are a bit of a different story. But I think that does more to negate the drafting advantage as well, as you're now just in smoother air that loses the "bubble".
 

·
Registered
2015 Forester2.5i Premium CVT
Joined
·
1,431 Posts
There are many people in the world with a weak grasp of math and physics. Many of them have driver’s licenses. They cannot estimate distances. They cannot even roughly calculate stopping distance at a given speed. Many of them are the same people who vastly over-estimate their own skill as drivers. Some of them have difficulty with durations as well, thinking that one second is a significant amount of elapsed time.

If you are following another vehicle at 100 feet at 60mph, and that vehicle swerves to avoid an object in the road, or a bad pothole, you will have 1.47 seconds to also avoid that hazard. Count to two. Oops, too late!

This is why recommended following distance is a least 3 seconds at highway speeds. And it’s a good idea to practice estimating this — just watch the lead vehicle pass a fixed point, then count the seconds until you pass it — to develop a solid grasp of what that distance looks like.

It may be possible to gain some benefit from the disruption of standing air by a lead vehicle even at a minimum safe following distance. This is not drafting, but at least it’s not stupidly dangerous and might help fuel efficiency a little bit while still letting you see the road ahead.
 

·
Registered
2022 Forest Green Premium
Joined
·
52 Posts
Discussion Starter · #19 ·
So ACC is a dangerous and irresponsible technology. Got it. Maybe everyone should tell car manufacturers to stop adding the unnecessary cost to vehicles.
 

·
Registered
2017 Foz 2.5i CVT
Joined
·
2,446 Posts
So ACC is a dangerous and irresponsible technology. Got it. Maybe everyone should tell car manufacturers to stop adding the unnecessary cost to vehicles.
ACC is fine. Drafting is dangerous and irresponsible :) Your whining about the laws of physics is not going to make a difference. You clearly have some lessons to learn.

This is not a good time in automotive history to smash a new car or even to need a new Eyesight windshield.
 
1 - 20 of 53 Posts
Top