cross-country (mpg's) vs. 17x7 and 215/45x17's

What made you put on 17x7 wheels and 215/45x17 tires? I know the OEM tires stink but I think you went a little over board.

 

<div class='quotetop'>QUOTE(FBear @ Jan 3 2007, 12:58 PM) [snapback]370155[/snapback]</div>

Overboard? Not at all. I, and many, many others have done it too.



moredes15 So far my average is about 48 mpg with the same size tires/wheels. This is a mix of city and highway though. I have not taken any really long trips to get a good highway only number. I'm also an aggressive driver so I oculd probably get even better if I eased up on the gas pedal.

 

Given your amount of extra weight and the big jump in rotating mass I would say you were pretty much on par if the temps were cold.

With stock wheels and 3 people/luggage in my Prius I averaged 47mpg last summer going from Sacramento to Seattle and back. Durring the winter I was averaging 44mpg. I'm sure I could do better now that i understand "gliding" better.

Now with the 17s and a speaker box I am averging 43mpg in the winter. My 17s are only 3lbs/ea heavier than stock.


Ohh, EPA highway rating is 50mpg. 60mpg is City.

 

Hi Mordes15,

I wonder what your tire pressure was on those 215/45x17's ?

As F8L said the 60 mpg EPA rating is for the city EPA cycle. The highway is 51 mpg. And that is at 55 mph.

Many of us run higher airpressure with our 185/65-15's as that gives better tire ware, as well as better mileage. Allot of us run 42 PSI on the front tires and 40 PSI on the rears. We set the air pressure carefully (like in the morning before the sun can shine on the black rubber). The max pressure on the 185/65-15's is usually 44 psi. The pressure settings on the door appear to be well under what should be run on the Prius to give maximum tire life.

I do not know if anybody has found out what the best pressure for the 215/45-17's are on a Prius. What is the load rating of those tires? I think the 185/65-17 are very close to the load rating required by the weight of the Prius. If that is the case with the 215/45-17's, it probably would be prudent to bring the air pressure in the tires up some above the pressures on the door.

 

From an Easterner's point of view your mpg on the surface sounds a bit low. The EPA estimates are modelled on outdated Los Angeles driving, not mountain climbing. A turbocharged engine would have held its own on your route but there is no way a normally aspirated engine will be as efficient at 4000' as it is at sea level. I've been in cars where the turbo kicks in on 1000' mountains in PA. I would have guessed 40mpg for your trip. But then again the gas out there is probably very different from what we have here so maybe that is the best that can be done. Now that I said it you'll probably get a flood of posts proving I'm wrong.

 

<div class='quotetop'>QUOTE(F8L @ Jan 3 2007, 07:39 PM) [snapback]370425[/snapback]</div>

Cold yes, but size weight no. I was able to get 52 mpg on the much heavier Scion tC wheels. The size and weight factor are exagerated by people on this board. One's driving style is THE BIGGEST FACTOR. I'm not saying that the size and weight don't have an effect, but it's minimal.

 

Hi Moredes15,

One other thing is that your trip was east to west, into the the prevailing wind. On average this could have added 10 mph to your airspeed, or from 85 to 95 mph airspeed.

That kinda airspeed would jive with the mileage you got.

 

<div class='quotetop'>QUOTE(moredes15 @ Jan 4 2007, 07:37 PM) [snapback]371042[/snapback]</div>

Actually it's the opposite. I generally do NOT use cruise control. The Prius cruise control system seems to be quite aggressive at maintaining the vehicle's speed, and seems to use more gas then necessary. I get better mileage when I don't use the cruise control, and many others have gotten similar results. A quick search of PC should get you a few threads to get more info from.

I think the primary culprit in your case is your heavier foot and the low temperatures. People in more temperate climates (like us here in Florida) tend to fare better than our more northern neighbors becuase of the higher winter temps. On the flip side, Northern states tend to fare better in the summer, as we are required to use A/C, which imparts a HUGE hit to mileage.

My advice is to just keep driving until you find a style that feels good to you. Then whatever your mileage is, just be happy. You are probably getting much better use of your gas than everyone around you.

My mileage has ended up averaging 47 mpg over the 30,000 miles I've put on my '06 so far. Not bad considering how I drive.

 

There is no doubt in my mind that the biggest reason for the mileage in the high 30s is your overall speed. The mass of the wheels contributes little to fuel consumption at a constant speed, but the tire width adds aerodynamic drag, and your relatively high speed (70 - 85 mph) is the biggest culprit. Those of us who get 50 mpg plus on the highway are travelling at or less than 65 mph, on generally flat terrain.

 

<div class='quotetop'>QUOTE(moredes15 @ Jan 4 2007, 04:37 PM) [snapback]371042[/snapback]</div>

When I lived in San Diego, my commute was about 25mi each way; about 2mi of city driving, 23mi of highway (with net 600ft climb), and a tiny bit of surface street again. A map of my route is at http://preview.tinyurl.com/2fxxa3

I'd just set the cruise at 65mph and go. I routinely got high 40s, sometimes hitting the low 50s. This was on stock wheels and tires, in a 2005. I was happy with those numbers, as I traded in my 1995 Subaru Legacy L sedan, which turned in 22mpg on the same commute. (Granted, when I drove the Suby with my new habits learned from the Prius, I got 30mpg on some runs here in Albuquerque!)

Worst milage I got in SD was going back and forth over the hill from Ocean Beach to the airport -- short (no time to warm up) and all up and down (no useful gliding).

My long-distance driving out in the Southwest (I live in Albuquerque now, and have driven to Phoenix, Las Cruces, etc) usually finds me driving 75-80mph and seeing milage in the low 40s, with some exceptions -- the 6500' climb from Phoenix to Flagstaff is a killer, the more so when I had a roof rack and a couple hundred pounds of Ikea stuff in the car.

<div class='quotetop'>QUOTE(JimN @ Jan 3 2007, 06:21 PM) [snapback]370480[/snapback]</div>

Hmm. I moved from San Diego (sea level, although I commuted to 600' elevation every day) to Albuquerque (elevation 5000' or so), and I didn't see much difference in either power or milage. The hot summer with lots more A/C usage made a much more visible dent in my milage stats.

I wonder if the fact that the Prius (mine's a 2005) uses a pretty high compression ratio, along with the ability to continuously vary the gear ratio, helps alleviate the aspiration issue?

At higher speeds, one might also wonder if wind resistance is dropped by the same small amount that engine power is?