How to get people to understand that braking is the #1 cause of bad city mpg.

ECO and PWR modes only affect how far you have to push the accelerator pedal to get your result, not your maximum rate of acceleration.

 

Ya, I never understood how people don't grasp that concept either. I don't recall anywhere in the manual or on-line which said that switching to PWR mode gave the prius an extra 50 HP. Maybe people are just old racers where they think pressing the PWR button is like pressing the Nitrous button.

 

Actually for the plug-in the left pedal can be your friend if properly used to nicely charge the large battery downhill for later use. Of course in the flatland there is no advantage.

 

Thanks, this is a good explanation. I usually stayed in Eco mode since my initial post, but have started trying the other modes out and came to the same conclusion.

 

There are many MANY people out there that think that wrestling is real and the Moon Landings were faked.
You just aren't going to fix stupid, and I usually have better things to do than to try.

 

Plug-in or not doesn't make any difference. If you can travel safely without using the brake, you are better off than using it. Putting charge in the battery has losses so it is never as good as putting that same energy into momentum. If you need to brake to remain safe, you need that brake regardless of whether it would save energy or not.

 

Of course you would never use braking just to generate electricity. Fortunately most of the "hills" in our area (Sierra Nevada Mountains/Foothills and Coast Range) do indeed require an appropriate amount of braking. Even in the flat lands braking is required frequently when not on the freeway. And, of course, slowing down from freeway speeds requires appropriate regenerative braking. With its larger battery capacity and the opportunity to chose when to use the charge in the battery this makes the plug-in a definite mpg winner even after last night's charge is used up.

 

Or still married . . .

I love my wife dearly but would rather pay her gas bills than alimony. I still work so she has no clue about how I drive except for when I'm driving her somewhere:

• "YOU'RE LETTING A TRUCK PASS YOU!!"
• "We're not late. I'm dressed and the appointment is in 30 minutes (and 120 miles!)"

I wonder if WARP drive was invented by a married man?

Bob Wilson

 

Hey guys, that's an interesting discussion. I thought the best MPG techniques included not to go in the pwr section of the HSI. So I can accelerate faster now? That will be a relief

In the same idea, should I press the gas pedal a lot when climbing a hill? I live in a place with many many steep hills.

Thanks for your answer.

 

Stomping on the gas pedal will hurt fuel economy, but the real killer is not anticipating traffic and red lights.

It is OK to coast.

 

I generally use the Hybrid System Indicator display, and when accelerating try to keep it in the white zone flagged with "3", per the following:

It's not always possible, sometimes on steep hills you have to go into the PWR zone, but I try to stick to it.

 

You thought right.

I try to gain speed before the hill so that I do not have to floor the pedal.

 

For the very best MPG, that is correct. But based on the BSFC charts posted some time ago, I believe you can go part way in to the PWR section and still get extremely good MPG, while gaining a lot in driveability and traffic compatibility. No sense angering a lot of other drivers to save a little bit of fuel, when other techniques can save a lot more fuel without upsetting others.

Gaining speed before the hill, good opportunistic gliding, good driving-without-brakes style, and timing of traffic lights will save far more fuel than avoiding PWR on uphills.

With some hills, the car simply needs a lot of gas, d**m the HSI display. I haven't attempted to test what speed it can climb a 7% grade without going into PWR, but it seems it might be at risk of getting rear-ended by one of those 80,000 trucks creeping slowly uphill. And even if it isn't quite that slow, I still don't have the patience to spend an extra 30 minutes just to avoid hitting PWR.

 

1++

 

True, I already do it, but even this way, I can get below 20 mph, they are mountains not just small hills. I'm questioning myself since I have the car and I think it's best to go faster while going up to reduce the time the car is in pwr, but I was not able to test my theory yet.

 

The time it takes is not part of the mpg equation. If you go up a 1 mile hill slow and the mpg is 20 for one mile you use less gas for that mile than if you go up the 1 mile hill fast and the mpg is 10 for that one mile.

 

I know this but with the friction in the equation it's not linear.

 

Are you asking the why behind the answer ? I can try and give you a qualitative explanation based on a units analysis --

rpm is proportional to power; if torque is held constant, the change in rpm is equal to the change in power. That is the situation we are discussing going up a hill.

Piston friction is primarily a function of rpm, and is somewhat linear.

Power increases with the cube of velocity.

And there is the problem: An increase in rpm leads to a linear increase in ICE drag, but only a cubed root increase in speed.