Poor Gas Mileage

[pepepeter]

Originally Posted by rav4two

We run the front tires at 37 PSI and the rears at 35.5 PSI. I've gotten a "zero tie" alignment, have removed the crossbars, used a polymer wax that creates a super-slick surface, and run Mobil 1.

What is a zero tie alignment???

[JuneBug]

Originally Posted by pepepeter

What is a zero tie alignment???

I think he meant to say "zero toe" alignment. No toe in or toe out.

[ravenuer]

Originally Posted by JuneBug

I think he meant to say "zero toe" alignment. No toe in or toe out.

That's interesting because I was taught that almost all cars were specd with toe-in. Purpose being the resistance of the rolling tires would tend to "force" them back to a more zero toe. (not sure if that makes sense?) So if it was set at zero toe, it would tend to move to toe-out on the road.

[pico]

Originally Posted by rav4two

[...]used a polymer wax that creates a super-slick surface[...]

Since you are clearly interested in streamlining, there is a non-intuitive downside to a very slick surface. In some cases it creates a boundary layer that actually hinders air flow. The case is where the airflow is fast enough to sheer the boundary layer and cause eddies all across the layer which raises drag considerably.

On the 2011 RAV4 (and perhaps earlier) you will find a small, flat, perpendicular extension at the top of the headlight lens. I cannot prove it, but it might be there to break the otherwise laminar flow of air over that part to obviate a local 'sticky' laminar flow.

Engineers of the new all electric RAV4 redesigned the front, and combined existing parts from other (international) models of the RAV4 in order to improve its streamlining. They report that they reduced it half a point, which is the same as removing an athletic training parachute from an existing RAV4. That's a huge improvement.

And a data-point - the side window 'rain shields' create resonating drag on the RAV4. I removed mine after finding that. Will put them back on if I find it makes little-to-no difference.

Have you tried folding down the side mirrors for highway cruising? It might help - or not. Another non-intuitive thing.

[rav4two]

Originally Posted by ravenuer

That's interesting because I was taught that almost all cars were specd with toe-in. Purpose being the resistance of the rolling tires would tend to "force" them back to a more zero toe. (not sure if that makes sense?) So if it was set at zero toe, it would tend to move to toe-out on the road.

Junebug has it right. It's a zero toe alignment. A FWD biased vehicle like the Rav is almost exclusively FWD, so there's no rolling drag to induce toe out when driving along using throttle. There might be a little bit during coasting, and it's okay to run a small amount of toe in, like a 32nd on each side. But it really seems to help the Rav roll along very easily. Like in our garage, with the Rav in neutral, it'll roll backwards at about an inch a second from the slight slope that you can't even discern.

[rav4two]

Originally Posted by pico

Since you are clearly interested in streamlining, there is a non-intuitive downside to a very slick surface. In some cases it creates a boundary layer that actually hinders air flow. The case is where the airflow is fast enough to sheer the boundary layer and cause eddies all across the layer which raises drag considerably.

On the 2011 RAV4 (and perhaps earlier) you will find a small, flat, perpendicular extension at the top of the headlight lens. I cannot prove it, but it might be there to break the otherwise laminar flow of air over that part to obviate a local 'sticky' laminar flow.

Engineers of the new all electric RAV4 redesigned the front, and combined existing parts from other (international) models of the RAV4 in order to improve its streamlining. They report that they reduced it half a point, which is the same as removing an athletic training parachute from an existing RAV4. That's a huge improvement.

And a data-point - the side window 'rain shields' create resonating drag on the RAV4. I removed mine after finding that. Will put them back on if I find it makes little-to-no difference.

Have you tried folding down the side mirrors for highway cruising? It might help - or not. Another non-intuitive thing.

I believe the perpendicular sections of the headlight are to deflect airflow around the external rearview mirrors.

And while true that airflow and drag is more complicated than just slickness of surface, I've read a number of articles that indicate that slickness helps, including at least one SAE journal article (I'll see if I can find that link). But you are right that typical boundary layer interactions don't seem to make sense in this case. Hmmm. . .

[ravenuer]

Originally Posted by rav4two

Junebug has it right. It's a zero toe alignment. A FWD biased vehicle like the Rav is almost exclusively FWD, so there's no rolling drag to induce toe out when driving along using throttle. There might be a little bit during coasting, and it's okay to run a small amount of toe in, like a 32nd on each side. But it really seems to help the Rav roll along very easily. Like in our garage, with the Rav in neutral, it'll roll backwards at about an inch a second from the slight slope that you can't even discern.

OK, makes sense. My background in cars goes back looooong before todays newfangled stuff!

[JPL]

I bought an 06 RAV4 V6 Sport last year with 60 000 miles on it, and I too have been tracking all my fill-ups using an excel file. I love the power from the V6!

In the summer, I've averaged 19MPG in mostly city driving ( 70% city 30% highway). I've always used 87 octane gas. My trips were mostly from home to work and back. That's 8 miles to work and 8 miles back home, short trips. When driving on the highway, the best I've done was roughly 21.5 MPG.

In the winter, it's a totally different story. With the winter tires installed, and leaving my car parked outside all winter, I've averaged about 15MPG. The worst I got was 13 MPG. All this with normal driving habits, nothing abusive. I must say that I keep the heater on in the car almost all the time in the winter, I hate the cold!

Overall, my mileage is decent in the summer considering my driving conditions (city driving, short trips). The winter however, it's brutal.

[doane2u]

JPL: Don't know why your highway mileage is so low.. is it highway or freeway? Do you have a lot of stop lights?

On freeway trips I've averaged about 27-28 mpg with steady driveing at about 70 mph and using the cruise control.

My short trips/commute in town are not too great, about 15-16, but I tend to have a heavy foot and the acceleration factor hasn't worn off.

It would be interesting to fold the side mirrors in and see if it's quieter and gets better mileage, but I wouldn't risk the danger of no side views or getting a very expensive moving violation ticket.
I can just see the scenereo with a highway patrol pull over:

O Can I see your drivers license sir?

R4 What's wrong officer, was I doing something wrong? I'm sure I wasn't speeding?

O No sir.. but I noticed both your side mirrors are folded in?

R4 Oh... that.. I was seing if I could reduce my gas consumption a bit.. funny, I didn't even see you coming..

O Uhh... ya gotta be kidding, right?

[Rickl]

Originally Posted by JPL

In the summer, I've averaged 19MPG in mostly city driving ( 70% city 30% highway).
When driving on the highway, the best I've done was roughly 21.5 MPG.
In the winterI've averaged about 15MPG.
The worst I got was 13 MPG.

I also agree that your mileage seems low. I have reached 28 MPG(us) in highway driving compared to your 21.5. (30% more)

My city/highway ratio is about the same as yours and I have averaged 19.3 MPG over all seasons compared to 19 MPG for your summertime driving.

My worst winter mileage was 15 MPG compared to your 13 MPG (15% more).

Perhaps we have a Metric Mix-up here, or you spend a lot of time parked on a bridge somewhere near Montreal.