80-85mph highway mpg?

Make sure you come back and tell us what you got.

Mike

 

We should make it sort of a pool on here. You can choose what you will set the cruise at and we will all take a guess.

 

I'm gonna lay my wager on 36.3 mpg.

 

I think that's a good guess. But, I also think the number is dependent on the temperature. And without knowing the temperature, I'm guessing 35.2 MPG. I'll also bet that it isn't above 40MPG. I'm also assuming that the screen will read an average speed of about 85MPH. (You can also assume that I'm hedging my bets a lot).

Mike

 

Temps will play a part, but if he's continually running the engine around 3000 RPM's, I don't think they will make that much a difference. I would be more worried about winds, especially cross winds.

 

Austingreen has 17" wheels though yeah?

 

The temperatures should be in the 70s. I have about a 20 mile ride to SH130, which means the engine will be warmed up.

I have motegei sp10 17" rims and continental DWS 205/50R17 tires with 30,000 miles on them. These are slightly larger than the stock tires, making the spedometer slightly more accurate. I'll set the cruise control to 88 mph but report also gps speed. There will be a passenger and slight payload of stuff in my trunk and subwoofer, etc, probably about 3400lbs total weight.

The stretch of 85 mph speed limit is 40 miles. I'm not sure if I need to go the full distance. People have had to slam on the brakes, as there are wild hogs in the area of the new road. Hopefully I won't see one. I'll hit the trip odometer once reaching 88, but leave it running as I exit and come back going the other way.

Anything I should standardize before the test run? I'm guessing I'll get in the low 30s but have no idea. The trip odometer reads 1-2 mpg better than I actually get from gps distance and measured gas at the station.

 

My official guess is 33.9. Have fun!

 

Very close.

I had a morning meeting cancel and did the run.

Mileage for the loop 32.2 indicated. Going south and uphill was 28.2, coming back was 37.2. Those rolling hills seem to really drop the mileage. I set cruise control at 85mph, because I could see from the 80mph road that mileage drop a lot even going 80. GPS had me at 86mph. As I said, I have slightly larger tires than stock.

Temperatures may have hurt a little I started at 77 degrees finished at 81, but they hit 82 during the run. I prechilled the car, and had AC off during the test.

Some other information about SH130. The road is very pretty, with rolling hills and wide turns. There is an area marketed animal crossing, and I did see 1 road kill. I"m sure people will slow down at that area at night. I was going the speed limit and no one passed me. Not a single car. Most that I passed were going between 70mph and 80 mph. The slowest vehicles was a tundra pulling and airstream trailer, and I think he must have been going at least 30 mph slower than me.

 

Good info! I didn't assume rolling hills (I assumed it would be a relatively flat run), oh well. Still, 32.2 indicated is likely 30 mpg, which is better than most cars EPA highway.

 

Ouch! What kind of rubber do you have?

I wonder what you'll get with the standard 15" wheels and tires.

 

Thanks for taking the time to do this test. I still thought you'd do a little better (maybe about 3MPG better), even with the rolling hills, because I already assumed you didn't have really steep hills, plus it was round trip, so things tend to average out.

Mike

 

I had no idea how hilly it would be until I went out there. I did play with trip B while driving south and seemed to get in the mid 30s on the flats, and had 11mpg on the steepest hill. I don't think the battery can assist much at this speed. I stayed with full bars the whole time. It was a very unscientific experiment. I mainly wanted to see the new road. Those without after market tires and rims will likely do a little better than me. There were some strong winds, and I think the grippier tires helped my feel more comfortable driving those speeds though.

I would say my actual was probably 30-31 mpg at 86 mph (gps). I think it would have been much better if I had averaged 80 mph and slowed a little on the steeper uphills and gained it back after. The prius isn't really the kind of car that you want to drive over 80 anyway, but it gets fairly good mileage when you do. I may take this road once or twice a year to go camping near the end. Its about 5 miles out of my way for that, and has about 40 miles of 80-85mph roads. Say I do only get 30 mpg, I'll only use about an extra 2.5 gallons a year. I expect I would slow a little and get closer to 40 mpg though.

 

Continental procontact DWS with about 30K miles on them 205/50R17. I don't think the tires had much of an affect, but the wheels are motegi sp10 which are less aerodynamic. My tires do hurt city mileage.

I blame the wind and rolling hills, but really 30 or 31 mpg is not that bad, unless you compare it to a prius going 60mph - and I could have quite safely been going 60 mph on this road. Bottom line is you probably want to go less than 80 if you are traveling uphill in a prius and want good gas mileage.

Hey its the last free week to run this road. A week from now I expect ferraris going to the f1 race to be hitting it hard, I think that it would have been much better on the flat.

 

Did you watch the HSI much? If so, where was the gauge at during flat segments and and what about slightly uphill? I assume it was all the way to the right if there was too much slope.

 

thanks for running this!
yeah, 80 mph seems to be the magic number for this car if you don't feel like driving like grandma. going above that is like a serious cliff going down.

 

I had it in eco. THe HSI never went into the red power part, but was right up to it on most hills. Slight uphills were at about 80%, down hills were close to 50%.

 

I think also this might be due to an exponential increase in wind resistance versus speed (it isn't linear). I believe I saw a chart somewhere (and I'm always too lazy to go look for it) where the exponential really starts kicking in past 60 mph for your average car.

 

right

 

Energy to overcome drag increases with velocity squared - it will be twice as much at 85 mph as 60 mph. There is also energy to overcome rolling resistance which is fixed. If rolling resistance is 1/3 of the energy at 60 mph, it will take 5/3 the energy at 85 mph vs 60 mph- if its 55 mpg at 60 it should be 33 mpg at 85. I can't remember exactly what the number at 60 mph is, or percent of rolling resistance so correct these with something more accurate if you have it.

But I think I did worse. Power required goes up at velocity cubed for drag. I think the power requirement pushed the ice into a less efficient range.