What's the sweet spot?

In 4500 miles of mixed driving, I have found the sweet spot to be around 63 mph. I am averaging 55.5 mpg actual over that period. I suspect a slight downhill or tailwind may have been a factor in your 80+ mph drive. I have one 30 mile drive that seems flat, but I get over 60 mpg on it because it is actually slightly downhill. You really can't assess mileage on a short trip unless it is a round trip. I have also found that in town driving with moderate to light traffic and speeds below 45 mph give me the best mileage. I have gotten over 60 mpg when I do a lot of this type of driving. The keys here are to get up to speed briskly (counterintuitive), then feather the pedal to maximize the coasting and "golf carting". If you accellerate very slowly, your milage will not be as good.

I agree with you on cruise control. It will give you good mileage, but you can do better without it if you pay attention. I still use the cruise though, because its easier.

 

As kingofgix pointed out, the system is optimized for about 62.14 mph (or, 100km/hr).

This just simply means that if you were in those exact same conditions as the other day of driving at 80+, if you were going this speed, your MPG would've been better - by how much, only one can guess.

After driving 16,000 miles with this car, and a few thousand of those in Michigan where the speed limit is 75 and people drive 85, I've found my difference would be approximately from 47mpg on Michigan highways to about 52-53mpg here in Northern Virginia highways (where I usually have the car running around 65-70).

It most likely won't amount to a whole lot, but there is a difference - of course other factors include elevation changes, weather/winds, etc.

-m.

 

Oh, and as an aside, before this car I got 3 speeding tickets in the past three years in this area. Don't have that problem anymore

-m.

 

<div class='quotetop'>QUOTE(efusco\";p=\"45980)</div>

You're right as far as it goes - but there is a lower threshold where consumption goes back up again at lower speeds, when the fixed overheads (air-con, lights, other accessories) begin to dominate over the speed-related effects (air and friction resistances). We are talking about walking speeds here, I think. I definitely get more from my fuel at 30mph than at 60. But less than 10mph can get expensive, mainly because most of the energy goes via the HV battery, which gets charged in bursts, unlike normal driving where a lot of the engine's power goes directly to the wheels.

 

In my experience, the Prius gets best gas mileage / mileage to power ratio when your foot keeps the accelerator just below the point where your Prius starts producing that unmistakable CVT sound (high engine revs out of proportion to noticable acceleration).

That's my definition of the Prius sweet spot.

On the subject of cruise control, its use produces good gas mileage on reasonably flat land. But when you get into hilly areas, best mileage will be experienced without using cruise. You can usually maintain the sweet spot (my definition) by allowing your speed to vary one or two mph on hills. But cruise control on hills will insist on maintaining selected speed, damn the sweet spot.

Experience: 13,500 miles that includes almost daily drives through the hills of my rural environment, 60 mph flat rural highway, 75+ mph freeway, and then stop-and-go city driving (and back). These days I'm averaging exactly 50 mpg.

 

Re: Aerodynamics and the Sweet Spot

My AM-7 is coming up on it's first birthday (10/25.)

Seems there was a post back then about Coefficient of Drag that alluded to the aerodynamic moment at which the Prius starts "pushing air".

I remember the Prius' cD at .026 (just a tad under the Insight which is .025).

This supposedly tanslates to about 100 KPH or 62 MPH+change, after which the ICE and MGs will have to do some actual work to maintain speed.

Oddly, I found that the very best MPG seemed to happen on flat or "rolling hills" secondary highways at around 38 to 46 MPH with a little help from Cruise Control.

Comments?

Bob

 

MAGIC SPEEDS
Here are my critical speeds in my 04:
These are on flat roads, driver only, no large wind component.
31 mph is where the ICE must kick in to help acceleration
41 mph and above is where the ICE is on ALWAYS ON
54 mph = 54 mpg- I call this maximum productivity speed (pMPH)
any faster and mileage drops, any slower means slower.

Best acceleration is when the battery is NOT charging. Charging the battery wastes about 70% of the energy burned and then running the motor from the battery wastes about another 60% of what was stored.

So, if the speed limit is 35 - 45 mph I drive at 40 mph for maximum electric motor efficiency (99 mpg except when charging-most of which I get from coasting before stops).
If the speed limit is 55-65 I drive at 57 mph for almost max productivity.
If the sped limit is 65-75 I drive at 73 mph for about 48 mpg.
Results are an average of about 51-52 mpg.

 

Before I got my Prius in 12/03 I attended an educational session. I got the idea that the G2 was optimised at 100Km/Hr
and proudly stated this on an old site. Some one asked optimised for what? I thought it was that if you plotted time to destination versus speed this would be the max. As they pointed out that was BS. I still don't know the answer. I know that 35 MPH with the windows closed on a hot day with the AC turned off and wearing only your undershorts will get you near 1,000 mi on a tankful because some demented soul documented it.