Improving mpg above 65mph

[Uber_Otter]

I have a 06 scion Xa. On the highway I get 40mpg at 64mph, at 75-80 mph it drops to 30-32mpg. Huge difference, I need to get that 10mpg back. In Dallas the Tollway speeds are 70 posted and 75-80 in real traffic. Im looking at making vortex generators to clean up the underside first, then the back. I will be making clear turbulator tape to use to smooth out the air before door gaps, on the a pillars and around the mirrors.
Let me know if you guys have any suggestions. I will be taking pictures and letting you know what I find out.

[brg88tx]

i think the yaris has a little taller gear and i usually get about 38 mpg from 75-80. let us know how your aerodynamic experiment goes.

[Imagine]

It's a little motor, it's working pretty hard at those speeds. There's not really much you can do other than slow down a little and get out of the way of people that don't want to. Other idea would be start finding ways to make the car more aerodynamic at those speeds, that should help a little. Might be $$$ and make the car look funny though.

[schume]

As a former Geo Metro owner, I can speak from experience on trying to get good MPG at higher speeds. There are many things you can do, from simple to radical to try to squeeze out a few extra miles. First, you need to check if it's worth it. A simple formula to help decide what to do and how far to go.

1. Starting today, how many more miles to you plan on putting on your car before replacing it?
2. Take that number and divide it by your two different mileages (40 and 32) to figure out the total amount of fuel burned.
3. Multiply each total by the current price of gas
4. Subtract the big number from the little number and that is your ballpark budget for mileage improvements.

(example:
100,000 miles / 40 mpg = 2500 gallons of gas. 2500 x $3.50/gallon = $8750
100,000 miles / 32 mpg = 3125 gallons of gas. 3125 x $3.50/gallon = $10937.50
$10937.50 - $8750 = $2187.50)

So in the example, I'd try to spend about $2k on mileage improvements. I expect the price of gas to up in the future, so my money savings will increase accordingly as long as I stick to the initial budget.

For better mileage at speed, you need aerodynamic changes and/or weight reduction. There is no one magic aero mod that will give you 5mpg. But a combination of useful and practical changes should help.

I don't know how radical you're willing to go, so I'll just throw my ideas out that I would consider on your particular car. (not sure if some of these are possible since I don't have a xa to look at)

Rear wheel skirts
Side mirror delete
Front grill block/modification
Antenna delete
Belly pan

Experiment, test, enjoy the challenge. Let me know what you end up doing

[aca72]

How about:

6) Get the junk out of the trunk. This goes for you as well as for the vehicle. The lighter the vehicle is the less fuel it takes to move it.

http://www.yarisworld.com/forums/showpost.php?p=90486&postcount=2

[39+]

I am now getting 40.5+ (verified through tank refill/miles) on daily driving trips to work ranging from 4950-6000 ft altitude. I have 15-20 minutes slow/stop and go and run up to 85mph sustained for over 45 minutes in many cases (don't tell CSP!!!!). The ecometer is showing 41-42 most of the time, but I reset it occasionally.

The Yaris now has about 10K miles and is now getting better MPG.

I think that it all has to do with braking and slowing down. The more you do that, the less the mpg...

The ecometer is very helpful. :w00t:

[Bluevitz-rs]

Do a flat undertray first.

[Tom48]

Move into the right hand lane and slow down.

[advocate]

weight reduction weight reduction weight reduction weight reduction .

sign up for AAA and remove everything behind the rear seat. and that too if all you do is commute.

high PSI tires and light weight wheels are always good as well. get light weight lug nuts too.

[RETRO]

I have a 06 scion Xa. On the highway I get 40mpg at 64mph, at 75-80 mph it drops to 30-32mpg. Huge difference, I need to get that 10mpg back. In Dallas the Tollway speeds are 70 posted and 75-80 in real traffic. Im looking at making vortex generators to clean up the underside first, then the back. I will be making clear turbulator tape to use to smooth out the air before door gaps, on the a pillars and around the mirrors.
Let me know if you guys have any suggestions. I will be taking pictures and letting you know what I find out.
Buy a Prius:iono:

[advocate]

Buy a Prius:iono:

the prius is an overpriced piece of crap. anyone who buys one is a total hypocrite because the batteries are completely indisposable.

with enough work you can get a yaris to compete with a prius on MPG and save yourself 15,000 while you're at it.

[RETRO]

the prius is an overpriced piece of crap. anyone who buys one is a total hypocrite because the batteries are completely indisposable.

with enough work you can get a yaris to compete with a prius on MPG and save yourself 15,000 while you're at it.

Calm down it was a joke.

[McTimson]

Weight reduction will do very little for MPG at those speeds. Once you get past 45-50MPH (depending on the car), you're mostly dealing with aerodynamic losses, not weight.

Take a look at this calculator - http://ecomodder.com/forum/tool-aero-rolling-resistance.php - it splits up the frictional forces between aerodynamic forces and rolling forces, and shows how much of each you need at a given speed.

Play with the numbers, especially weight and CD, and look at the HP Aero and HP Rolling columns. The numbers show how much HP is required to move the car against aero and rolling frictional forces. You'll see that the faster you go, the aero HP requirements go up much faster than the rolling HP requirements.

Obviously, it's not perfectly indicative of real world performance, and you can't take into account gearing or anything in the drivetrain, but its a good tool to see just how much harder the car has to work at higher speeds.

So, if you really want to get better MPG at those speeds, aerodynamic mods are your best bet. If you don't want to bring attention to your car, bellypans are a good start, grille blocks aren't too noticeable if you do them well. Flat wheel covers, side skirts, and boattails/kammbacks can get you pretty nice gains, but are harder to make look nice.

Vortex generators won't do anything for you.