Cruise Control on Long Trips-My first sub 50 MPG Tank

I always thought that you can do better manually and not on cruse. When I use the curse, I am usually driving on the flats. I also use the eco mode toggled off on the display.
52+

 

Similar speeds in the summer, Ark-Indiana and return, about 48-49 mpg

BUT
Similar and slightly faster speeds in the WINTER, Ark-Big Bend Natl Park and return, 43 mpg or so. At that point, the car was very new, and we were just getting used to driving it.

So, especially if it was cold and you were using "winter gas", well, maybe you are not doing so bad after all.

 

As I've said before don't use cruise control if you want mpg. Cruise control doesn't know how to hypermile. It can't anticipate approaching down hill or up hill and adjust acceleration or braking. It will accelerate hard and brake hard to keep the speed at the set speed. It will not allow margin of of error in speed. When you set speed at 70mph, and the speed drops to 67 going up hill, it will accelerate hard to get the speed up to 70. This kills your MPG. Cruise is great but MPG will suffer. When I take long trips, I don't really care about poor mpg so I always use cruise control. I do cancel the cruise when going up hill or down hill though.

 

Are you sure the CC uses braking to slow down? I thought just costing.

BTW, I got 43 MPG in my first longer hwy trip, ~500 miles, some hills, 75 MPH, 4 people, CC and heater most time (temp 30-50F).

 

I have radar cruise control so it brakes as well as accelerates. For the normal cruise it will use regen to slow down the car to keep its target speed but only with little more regen than coasting.

 

I drive an almost new II...and I'm just learning how to drive it, but I do a lot of interstate driving with it. I have yet to see my first 50 MPG trip while using the cruise control (46-47 MPG in 1200 miles) I've even lamented that this crazy little car doesn't deliver the mileage that all the Prius fanatics say it does.
Well....I disengaged the cruise, and the A/C and so far I'm at 55MPG over the last 80 miles of mixed driving. So...I guess it's a trade off.
Relax and enjoy the trip and pay the extra gas, or do the hypermiling thing.

Depends on where your priorities are I guess. I'm still learning.....

 

My suspect is your higher speed. 70-74mph makes it tough to hold 50mpg.

 

I find it hard to get 50mpg as well except in certain limited circumstances. I'm still experimenting, but my current theories of why I'm getting poor mileage is as follows:
1) Anything above 66-68mph leads to a dramatic dropoff in MPG
2) Going against the wind
3) Using watered down fuel from "El Cheapo" gas stations on the interstate, such as Loves, etc.
4) First 10 minutes of driving is always in the 30's
5) Cruise might have something to do with it on hilly roads. But my Prius V with radar & LKA practically drives itself on the interstate. I could never imagine not using it on long trips.
6) I also found keeping it in ECO mode helps with mileage. This also helps with the cruise on, i.e. it doesn't accelerate as hard on hills.
7) Perhaps the A/C being on has some effect, but I haven't noticed anything dramatic.
8) What about the alloy 17" wheels that came with my Prius V? I always wondered if that killed off a few MPG. Hard for me to know for sure though.

 

For those with V/ATP, you can draft behind big rigs safely. Set your distance to 3 bars. If you're lucky enough to find a big rig driving at 70mph, you can easily get mid 50's. If you draft behind a truck doing 65mph, you can get high 50's. If you're patient and draft behind a truck doing 60mph you can get low to mid 60's. I find that 3 bars on the distance is very safe. It allows 3-4 seconds between you and the vehicle in front of you. Setting at 2 bars will increase your mileage but reduces following distance. I think 2 bars is still safe because it has 2-3 seconds between you and the vehicle in front of you. I wouldn't set the distance at 1 bar for any speed faster than 65mph. There's not enough reaction time.

 

Air temperature, vehicle warm-up, and wind are suspects:

In these tests:

• 82-86 F - warm summer day, no AC or heat except for the extreme right edge data point.
• two opposite direction runs - to 'normalize' any wind effects. It is not uncommon on a long distance trip to drive into a head wind of a high pressure center and a day or so later, the return trip drives into the head wind of the back side of the same high pressure center.
• warm-up costs - even with the significantly improved, engine coolant warm-up, the first 15-20 minutes still includes warming up the transaxle oil.
• river bottom - flat land with not more than 10-15 m altitude change over the route with no significant grades. Hills can push the engine into less fuel efficient regions.
• indicated and speed calibrated - use of GPS to adjust for actual speed and distance in fuel calculations. A true speed of 70 mph hits 50 MPG and anything faster rapidly falls off.

Your data suggests cooler than 82-86F and we need to know the winds. If you'll check the weather climate data for the dates traveled, you can look up the wind speed and direction as well as temperature.

I would recommend backing off so 70 mph is your new 'maximum' and try 65 mph when opportunity avails itself . . . say using a semitrailer truck as a pacing vehicle followed at a safe distance. When going up hills, try to back off a bit too:


You really want to avoid pushing the engine into less fuel efficient regions starting at the 2,500-3,000 rpm boundary:

Anything over 3,200 rpm kills MPG and can easily happen when climbing a hill in cold or cool weather into a headwind:


GOOD LUCK!
Bob Wilson

 

I sure agree. 65 MPH+ and hilly terrain equals lousy gas mileage, no matter how much you try to hyper-glide! Slow down your speed and enjoy the MPG. If your schedule will not let you slow down, leave earlier?

Happy Motoring!

Tom

 

Cruise Control on flat highways works well. On hills it tends to be less efficient, since its priority is maintaining speed, not conserving energy.

Regardless of CC, high speed is a mileage killer. The mileage the OP posted is in the ballpark of normal mileage given the reported speed.

Tom

 

I'm not sure that I would advocate "drafting" off of another vehicle...especially in a Prius. I ride Motorcycles a lot, and so I have a tactile appreciation of what the wind is like behind a large truck. It seems to me that if you get close enough to a large truck to effectively draft off of it, then you're much too close for safety---even with the fancy radar. I don't have direct experience with the Prius, but I do know that if a truck sees you disappear behind his/her mirrors, especially at night, then they're apt to shake you off their tail.

When somebody tailgates behind my truck, I patiently wait for a patch of gravel....

That usually fixes the problem!

JMHO.

 

Any time you're driving behind a big rig, you're drafting. You can be 20 cars length behind a big rig, you're still drafting. You're talking about tailgating where there are only 1 or 2 car length between you and the car in front of you. That's just stupid and unsafe. Drafting is safe if done right. Mythbusters already proved that drafting in a safe distance can still cut up to 40% drag. The way you word it is like NEVER drive behind a big rig no matter how far ahead it is. In a Prius with DRCC set and 3 bars following distance, There are enough room for at least 3 cars to cut in front of you at the same time. The Prius's radar cruise will never allow you get close enough to deem unsafe without it activate the brakes, even if set at 1 bar. Hell, even if you set it at 1 bar, there's still enough room for at least 1 car to cut in front you.

 

When I say "pacing vehicle," I mean far enough back that road debris is easily seen and avoided. The occasional rock can be seen 'bouncing' and driven around or avoided. In my world, at least the distance between power poles and enough space that others can pull in front without having to worry about slamming on the brakes.

The goals are:

• 65 mph on cruise control - there are trucking companies who have 65 mph as their target speed and moving vans have learned to avoid breakage.
• close enough that following traffic will see the truck and change lanes to pass the truck instead of tailgating you.

If you are closer to the truck than another trucker would be, you are too close. If you are back a bit from that, you'll find driving much less stressful.

Be predictable and if another high-ballin' trucker wants to pass, be courteous and even give him a little speed slack so he can get around you and your pacing truck ASAP.

This is not tailgating but significantly back . . . a car length per 10 mph or whatever the current recommendation is.

Bob Wilson

 

Hey...I really don't want to ruin anybody's little hobby, and if you think that drafting is OK...knock yourself out...no pun intended.
The only thing I'm saying is that IMHO, it might not be as "safe" as you think it is.
Let's consider a few FACTS. (not just my goofy opinions)
Most states mandate following distances, or at least suggest a 2-second separation between cars...for most open road driving conditions.
A Prius is 175.6 inches long---we'll call it 14.63 feet just to keep the math simple. Your "3 car lengths" is about 43.9 feet.
Lots of room if you're doing about 30mph.
At 70 mph, you're talking about less than 1/2 a second of separation.

Like I said...if you think that's cool...I'm happy for you. Since my biggest vehicle is a GMC Sierra, I usually don't have many idiots trying to draft off of me, and I usually try and be nice when somebody does tailgate me.......I just throttle down and wait for him/her to pass. Very rarely, I have to do a quick jink to the right and give them a some gravel to remember me by...
Be warned. I have some friends that drive professionally, and they DESPISE drafters.
The only dog I have in this fight is that I now drive a Prius too.

Peace.

 

While I don't have access to MythBusters -- except when visiting relatives, where I have seen them make major errors -- reviewers over on CleanMPG indicated that MythBusters found these large savings only at extremely unsafe prostate-exam-type following distances.

 

Last year I drove from Chicago to Maine and back without any use of cruise and achieved low 50's tanks at speed averages of high 60's. This past October, the wife and I took the car to Cape Cod and back, with added luggage weight, and higher headwinds, colder weather and got only low 40's tanks. The biggest difference is my wife likes to drive with cruise on all the time and in lower 70 mph speeds.

When I took over the driving shifts I shut the cruise down and hovered in the mid to high 60 mph speeds. I instantly began inching up the MPG stats. While cruise is a better manager of speed, a conscious effort to manually control the car can pay dividends (along with not going over 70mph). One is just more aware of engine throttling. Cruise could care less about MPG efficiency.