Prius on highway - a bit of disappointment

update for sound deadening. I put some sound deadening materials on the floor and the inside of the wheel house behind the lower A pillar and it made a big difference in the noise in the car.I will see how it is on my commute tomorrow.also the stereo has a lot more bass after the sound deadening of the doors.

 

Hatchbacks are inherently louder than its sedan counterpart with the same amount of sound deadening material. Sound deadening materials are heavy because it has to be solid material in order to blocks sound. If you want enough material to do the entire car it'll probably be over 100lbs. This will reduce mileage. The Prius has been engineered to be light weight. Anything that can save weight has been implemented, including cutting back on the usage of sound deadening material. I went on a 100 mile road trip with a friend and his 2012 528i at speeds between 75-85 and managed 51mpg on MFD. Realistically about 48mpg. I set the DRCC at 90mph and just followed him. OST was 65F and I have full grill blocking.

 

That is the ONLY time I've ever achieved 50+ mpgs.
Cruise control was set at 76mph, driving through OH and PA.
My Prius definitely loves the interstate highway.

 

All the new freeways around here have heavy rain grooves!concrete. It's like having the window open!

 

the total weight I have added is 30 lbs. thehttp://www.raamaudio.com/products/RAAMmat-BXT-II.html is the heavy part the Ensolite-IUO-Peel-and-Stick weight is minimal. and I did cover all the door skins and inners and spare tire area.

 

I have just bought a Gen III Australian "Base" model Prius with 64500km (40000 miles) on the clock. My tank average is 4.9l/100km 57.6 mpg(UK) 48.2 mpg(US) 20.4km/l but that is only with 4 fills.

I've been pleasantly surprised at how good the highway economy has been without using any special driving techniques or modifications or suffering mortifications. Not super efficient, but not the blow-out is was expecting from a long, fast journey over hilly terrain with few flat stretches.

The baseline of sorts came from two return runs from Canberra to Sydney, a distance of about 280km (174 miles) one way. Canberra is about 620m above sea level (ASL) and Sydney sits at about 10m ASL. The route peaks at 756m a few times and remains above 600m for the about the first 165km (100 miles).

About 250km of that journey has a 110km/h (68mph) limit and I set the cruise control by GPS as the indicated speed was 114km/h. I tried to anticipate climbs by speeding up but as the speed dropped the CC thrust me back to set speed with maximum power. So this was no hypermiling adventure.

According to the HSI my two return journeys including a little city driving both used 4.6l/100km 61.4 mpg(UK) 51.4 mpg(US) 21.7km/l.

On one leg I recorded 160.5km (99.7 miles) 4.0l/100km 70.6MPG(UK) 59.1MPG(US) 25km/l with average speed 92km/h (57.1mph)! This was from a fill up near the end of the plateau just before a 600m descent over 40km (25 miles) and onwards to the centre (center) of Sydney. There were several long descents at 0l/100km to charge the battery on that run.

I used Google Earth to generate elevation profiles of the routes. This is inexact as the size of the GE window dictates the resolution of the profile and its calculation of the minimum and maximum slopes and total ascents and descents. Despite this, it is interesting to compare the profile with perception and see how much climbing you do in the process of descending 620m.

Here's my two blog posts with more details:
http://templeblot.wordpress.com/2012/02/04/prius-highway-1/
http://templeblot.wordpress.com/2012/02/15/prius-what-is-it-like-on-the-highway-part-2/

 

When my 2006 was "new" it wailed like a banshee on I-70 through Ohio. That was the only trip where the noise was almost unbearable so maybe your tires need to wear a bit more or the pressure changed.

Interstate trips ding my average & I 'm surprised how often & how long the Prius is the pace car. The round trip from Philadelphia to Atlanta earlier this month came in just over 50mpg helped by the commuter traffic in NoVa through Baltimore and a stretch on US40 through MD & DE. ~48mpg at speeds from 65-75mph is normal. RCC was on most of the trip.

The lower grill was blocked. I pulled the upper grill insulation when I saw inverter collant temp rise dramatically when parked at the rest stop.

Increase the tp to max. sidewall, block the grill, and slow down to bump the numbers up a bit.

 

I don't understand why anyone would expect miracles. No matter how good the technology there is a limit to how good the mileage will be over 70 mph. 48 mpg is not so bad when you'd be getting a whole lot less with any non-prius.

 

Here's my two blog posts with more details:
http://templeblot.wordpress.com/2012/02/04/prius-highway-1/
http://templeblot.wordpress.com/2012/02/15/prius-what-is-it-like-on-the-highway-part-2/[/QUOTE]

Hi Brad,

Welcome to priuschat from a fellow Aussie. Your experience pretty much mirrors mine over the same route, including the speedo and GPS being 4kms different at 110.

Recently I drove from Maldon, Central Vic to Sydney 5l/110kms on the way up and 4.6 0n the way home. It's mostly down hill from Yass to home.

 

What you're doing is only partial sound deadening. When I used to sound proof vehicles for competitions, we add about 250lbs of dynamat covering the entire interior. We gutted the interior down to the bare metal and add 2-3 layers of Dynamat and sound deadening fiber mats. What you're doing is similar to adding a pair of 6X9's for bass. What I'm doing is adding 4 15's for bass. Is it necessary to do that extreme? To quite down the interior down to high end Lexus level, yes.

 

Mid 40s is typical for speeds over 75, esp if there is significant wind. Michelin Primacy MXV4 tires will reduce the tread noise, but the improvement is minimal and you will lose about 5-7% in fuel economy.

 

BLAH BLAH BLAH

Yet another thread on how bad the Prius sucks.

I have owned many cars in my life. This car is amazing.

 

A bit unrealistic on the OP's part. He actually thought he could increase his speed to 75 mph and not expect to see a drop in fuel economy?

 

I like to drive over 75. What you lose in mileage you gain in time.

 

Not to mention the fact that it's a lot safer to keep up with the traffic. A lot of states have 75 MPH freeway speed limits and the traffic usually flows nicely at 75 to 80 MPH.

 

Pretty soon, it'll be too expensive to drive 75-80. Oh well, bring on mad max.

 

Other things being equal (they aren't), lower speeds are safer.

Even though I increase speed differentials by doing it, I choose lower speeds now for fuel economy and safety. The safety bit is a tradeoff, depending on what hits the fan.

 

That's pretty good mileage for this car at those speeds.