Why isn't the fuel economy better?

[lastsnare]

Originally Posted by White Shadow

Hold on a second.....so you're saying that you can average 35% better fuel economy than your car is rated for on the highway? Seriously? Would you be pissed if I raised the BS flag?

I agree, this sounds highly questionable.
I think that the mpg can only accurately be calculated by filling up the tank, setting the odometer to zero, running the tank down to near empty, filling up again and seeing how many miles you went and how many gallons you put in on the 2nd fillup. I can easily see that instantaneous mpg might be something crazy if you are driving along and suddenly let up on the gas or coast. But an average mpg for a whole tank is probably the only way to accurately determine the fuel economy. Because, after all, 99mpg isn't impossible for a few seconds while you are coasting, but that isn't going to save you any money at the pump unless you can do it for a whole tank repeatably.

[fatoni]

Originally Posted by White Shadow

No, I guess you didn't say that. I obviously confused you with Mmnhamsandwich who did say that.



Never said it did. But Prius tires are tires meant primarily for fuel mileage, which is what I said. Those tires have a small contact patch, low rolling resistance, and are relatively light weight. All are contributors to helping increase fuel economy.

its all good. i didnt see what he posted either.

tires arent what causes the size of the contact patch. its primarily a function of weight and tire pressure. whether it was on prius tires or 275 hoosiers, the tire the contact patch wouldnt really change in size.

[RaceR]

Originally Posted by OrbitalEllipses

And it'll cost twice as much. Nice comparison.

Point was fuel consumption..
In UK GT86 is 25K
M135I is 30K

[OrbitalEllipses]

Originally Posted by RaceR

Point was fuel consumption..
In UK GT86 is 25K
M135I is 30K

Yeah, for a base model maybe...Germans gouge you on options.

There's a $20K USD difference in the base models those cars here. Heated seats? $500. Bluetooth? $750. iPod/USB adapter? $400. Navigation, alarm, handsfree (smartkey) entry? $2700. Bam, you've made a 1 Series M that costs twice as much as the BRZ and has comparable amenities. Yeah you're getting more, but you're paying more...whether it be a powerful AND more efficient engine, or the typical BMW accouterments.

[RaceR]

Originally Posted by OrbitalEllipses

Yeah, for a base model maybe...Germans gouge you on options.

There's a $20K USD difference in the base models those cars here. Heated seats? $500. Bluetooth? $750. iPod/USB adapter? $400. Navigation, alarm, handsfree (smartkey) entry? $2700. Bam, you've made a 1 Series M that costs twice as much as the BRZ and has comparable amenities. Yeah you're getting more, but you're paying more...whether it be a powerful AND more efficient engine, or the typical BMW accouterments.

Again. Point was fuel conumption (vs engine output)....

If we did not have insane HP taxes in Norway, but only CO2 like we have. Price difference would only be 15-20% extra for M135I (with many options!) compared to 86. (Since the 86 is quite bad on fuel consumption)
In many other EU countries without stupid taxes price difference is not that much.
yeye.. If you wanna talk about the M135I this is a better thread to do it in.

[OrbitalEllipses]

Originally Posted by RaceR

Again. Point was fuel conumption (vs engine output)....

Again, point was that HERE the difference in money is what gets you that.

THIS car (the 86) is overpriced across the pond. Hell, it's overpriced here. I'm not saying it's a great engine either, it's just half as much as the one you're talking about so it's kind of expected that consumption vs. output isn't going to be as impressive.

[fistpoint]

Originally Posted by White Shadow

Okay, so I was right...the Accord does get better fuel economy. With the automatic transmission, the Accord is considerably better. With the manual transmission, there's not a huge gap, but it's still better, which is what I expected.

BTW, why do you find the city MPG shocking?

When I originally posted I thought the mpg difference was 1 closer. But it still highlights what the OP is talking about. It seems V8's are getting all the newfangled technology that increases mgp while the 4 and 6 cyl cars have basically stagnated(well, more so the 4 bangers, 6's have improved).

By "shocking" I meant a modern V6 that can't do 20 city when a heavier(250+lbs) 420hp V8 vehicle comes damn close(the auto V8 GT). It shouldn't be close at all with such huge hp differences(278 vs 420).

The 4 bangers of today from nearly every maker except BMW are still similar in mpg to that of 20 years ago. Yes I realize the cars have increased in weight, but so did the BMW's They just have magic engines I think.

Originally Posted by White Shadow

Most people do care about their fuel economy. It may not be the most important aspect of their car, but they still care to some extent.

I agree with this 1000x

If the FR-S got RX-8 mpg numbers, I wouldn't even spend another second considering buying one and find something else.

[White Shadow]

Originally Posted by fatoni

its all good. i didnt see what he posted either.

tires arent what causes the size of the contact patch. its primarily a function of weight and tire pressure. whether it was on prius tires or 275 hoosiers, the tire the contact patch wouldnt really change in size.

You might want to read this article:

http://www.performancesimulations.co...on-tires-1.htm

Sure, weight and tire pressure are the biggest factor when it comes to contact patch size, but all else equal, a wider tire will put down a larger contact patch than a more narrow tire. I did notice that you said "wouldn't really change", so I suspect that you already know that wider tires generally mean wider contact patches.

[White Shadow]

Originally Posted by lastsnare

I agree, this sounds highly questionable.
I think that the mpg can only accurately be calculated by filling up the tank, setting the odometer to zero, running the tank down to near empty, filling up again and seeing how many miles you went and how many gallons you put in on the 2nd fillup. I can easily see that instantaneous mpg might be something crazy if you are driving along and suddenly let up on the gas or coast. But an average mpg for a whole tank is probably the only way to accurately determine the fuel economy. Because, after all, 99mpg isn't impossible for a few seconds while you are coasting, but that isn't going to save you any money at the pump unless you can do it for a whole tank repeatably.

True. An even more accurate method is to do that over the course of several consecutive tankfuls. A running consecutive total is always more accurate than just one tank....or a partial tank for that matter.

[White Shadow]

Originally Posted by fistpoint

I agree with this 1000x

If the FR-S got RX-8 mpg numbers, I wouldn't even spend another second considering buying one and find something else.

The poor fuel economy of the RX-8 is something that always steered me away from those cars. I never could understand how such a tiny engine could return such horrible fuel economy (for its size). The other thing that I don't like is the weak torque output too. Those rotaries just aren't very good when it comes to torque.

[fistpoint]

www.fueleconomy.gov/feg/make.shtml

Searching by make, I am sticking with my original claim that BMW simply makes magic 4 cylinder engines considering the 240hp numbers equal most manufactures sub 200hp 4 bangers. Magic engines.

"Lt. Dan, you got a magic engine!"

[carbonBLUE]

Originally Posted by White Shadow

You might want to read this article:

http://www.performancesimulations.co...on-tires-1.htm

Sure, weight and tire pressure are the biggest factor when it comes to contact patch size, but all else equal, a wider tire will put down a larger contact patch than a more narrow tire. I did notice that you said "wouldn't really change", so I suspect that you already know that wider tires generally mean wider contact patches.

fatoni is correct, if you ran a 215 wide tire at 35 psi and a 275 wide tire at 35 psi they would put down the same contact patches, now if you ran 28 psi in the 275 wide tires, your contact patches would greatly increase.

This is because of the simple fact of PSI, Pounds per square inch. If you have 35 psi in a tire and a car weighs x amount at that corner of the car, the weight of the corner of the car will only imply so much downward force on that wheel. ie 500 lbs in one corner only the contact patch would only be 14.9 square inches. now if you were to let some air out to 28 psi, the tire's contact patch is now 17.9 square inches.

now those measurements are all relative but gives a simple explination that wider tires doesn't automatically mean a wider patch of contact unless the pressure is set accordingly.

[ame="http://www.youtube.com/watch?v=r_IWa_qlt3g"]2013 Scion FR-S - YouTube[/ame]

in that test they probably didnt use less tire pressure to take advantage of the bigger wheels, which resulted in the same cornering speeds because the contact patch didnt actually change because the same air pressure was used, if they had let a few lbs of air out the car would have made a faster lap time regardless of the fact that the wheels were indeed heavier.

[getbent]

Fuelly shows the 2012 BMW 328i at 25mpg average, whereas the FR-S and BRZ are at 28mpg average. Just because they are rated for 34mpg in the EPA test doesn't mean they actually acheive it in the real world.

There isn't anything magic about Turbo engines, they take just as much gas as a bigger engine to make (big) power, its just that they don't use so much when low output is needed.

[Deslock]

Originally Posted by White Shadow

I don't get it, I really don't. These are lightweight cars. They aren't all that powerful or fast. They don't make a lot of power or torque. Yet the fuel economy ratings are lower than some other cars that are 1000 lbs heavier and more powerful & faster.

Am I alone in thinking that these cars should be rated at least 25 city and 35 highway, at the absolute minimum? I mean, a freaking BMW 328i is a boat compared to the FT86, yet it has the same city fuel economy rating and gets 4 more mpg on the highway.

Maybe I'm being too critical, but I honestly thought that such a small and lightweight car would be more fuel efficient, especially with a 2.0 engine that makes modest power.

Small displacement N/A cars tuned for engine responsiveness and high specific power have never had especially impressive EPA fuel economy ratings. On the other hand, they often exceed them.

After 5000+ miles in my BRZ 6MT (mostly short-around-town trips and only 1221 miles highway), I've averaged 29 MPG:

32-36 MPG highway
25-29 MPG in town (27-29 if I drop two of my fill-ups)

That's 50-70% more than what my RX8 got, 30-40% more than my old 2L WRX, and is also better than what people report with the 328i.

Anecdotal, but on par with what others seem to be getting.

Originally Posted by RaceR

On every day driving- below 5000 RPM a 136hp 116I beats the 200hp 86 with good margin. Compare 4000rpm!
yeah, the character of a 116I is very boring, and the GT86 is fun at high RPM. But that is not the point..

I've never felt the "everyday driving is below 5k RPM" argument to be especially persuasive. It's true that we spend most of our time at low RPMs, but that's simply because most of the time we don't need more than 30-50 hp. When I want to pass, I drop it into 3rd.