I've broken 340 before on straight highway driving ...from central texas to south texas and back ((had to run to central to pick up my work stuff I ended up forgetting)) 170 miles each way...plus the extra miles I drove when I finally got into both cities...prolly an extra 20...so actually more like 360 ....though I did end up running below the final line =P and it took $35 to fill er' all the way back up =P

but on average....I prolly get 18-21 in the city...which is all highway driving anyways...and quite a bit more when im on the open road

 

i got 11mpg on my last fill up, and loved every minute of it.

-hS

 

agreed, 94 civic for like 2000, its an investment in the long run that'll work in your favor

 

I get about 230 per tank and i drive pretty hard. i guess i ain't too concerned with the mpg as long as i enjoy the miles i've travelled.

 

this has turned into YAMGPT, but only worse, because of the amount of wildly inaccurate, and only moderately useful, miles per tank comparisons.

Ways to improve gas mileage (some of these have been mentioned):
* Check your airpressure. Underinflated tires have more rolling resistance than properly inflated tires, which lowers fuel economy.

* avoid long start ups. crank the car, put your seatbelt on, and drive.

* avoid short trips when possible. the car runs richer when it is first cranked until it gets up to normal operating temperature, and short trips don't allow the car to fully get up to temperature.

* avoid sitting in traffic if at all possible (i can't). fuel consumption without movement negatively affects fuel economy.

* avoid hard/fast starts.

* coast up to a stop in gear. when in neutral, fuel has to be added to keep the engine running. in gear, the movement of the vehicle keeps the engine running, and allows the computer to go into Decelleration Fuel CutOff (DFCO), in which there is no fuel being added. your mpg at this point is infinite (theoretically).

* slow down.

* roll your windows up at highway speeds (above 55mph) to reduce drag.

* clean/replace your airfilter

* change your oil on a regular basis.

 

I found this ironic, as i was driving at the speeds of 85-100 on the freeway i got 290 MILES on the freeway w/ just the warning light barely turning on. This was ALL FREEWAY from SAN JOSE TO Orange County. Can anyone explain this, my theory is that since i was so up in the RPMs (around 5ish) that i would be getting torque and that it would reduce the need to have gas burn so rich. Also, probably because i stayed constant in between those speeds. i dunno, someone correct me on this.

 

well i think there is something wrong with NY traffic, but maybe thats just me

 

oh yeah, & i get 190-200 miles per tank, which is between 12 & 12.5 gallons... i'll let you do the math.

 

Could you please tell me what the optimal speed to drive is? You tell me stopped is bad and then you tell me to slow down!

How about not telling people that their measurements are wildly innaccurate unless you are going to post things that aren't wildly general?

The reality is that a fair number of RX8's are broken in the fuel consumption area. Those of you with good mileage, congradulations, but don't think it is because of some superior driving skillz. Those of us with really poor mileage would acutally like to figure out what is wrong, since getting 17 MPG on the highway is a real problem.

 

I'm surprised no one mentioned it yet.

A sure way to raise MPG is to get lightweight rims.

 

you sure about that? im not doubting you, im just inquisitive... i need a little encouragement to spend the money on some wheels, & this might just be the extra little push...

i know that it will take less torque to get a lighter wheel spinning, but is it really even a factor considering that the engine is really pushing a 3200 pound car? i would love to see some actual data on this.

 

when you are sitting in traffic, your are using gas and aren't going any where. to calculate MPG, you have to move. you can turn your car on, leave, for 2 days, and come back to it having died from running out of gas. that's a whole tank of gas (15.9 gallons). distance moved, 0ft (let alone miles). 0 miles divided by 15.9 equal 0 mpg. when you are sitting still at a traffic light or in grid lock, you are getting 0 mpg. this isn't rocket science.

next, as your speed increases, wind resistance also increases. not a tough concept. a study in 1997 by the dept. of energy showed that fuel consumption at 70mph was ~8.2% greater than at 65mph. getting 17mpg on the highway? Slowing down 5mpg would increase your fuel ecomy to 18.394. Driving 70mph uses ~17% more gas than driving 55mph. That means 17mpg would go to 19.89mpg. by slowing down.

again, these aren't tough concepts.

now, miles per tank is a largely useless statistic because it is not common practice to 100% of the fuel out of the tank. and since most people don't fill with the exact same amount of fuel each time, this introduces a huge amount of error into this number. and if you can't use it compare with just one person, you definately can't use it to compare many people. by taking the number of miles driven and dividing it by the number of gallons taken to fill the tank up (the formula for MPG), this standardizes the number, and thereby makes useful for comparisons.

if you are still having problems understanding these simple ideas, i'll try drawing somethign out in crayon for you.

 

There is a HUGE amount of data in this sticky:

check it out and see for yourself

https://www.rx8club.com/series-i-wheels-tires-brakes-suspension-55/effects-wheel-size-weight-performance-51865/

 

Oh man....

Okay, so what's my fuel consumption at 1MPH? What is it at 20 MPH? What is it at 50 MPH?

Pumping losses in an engine are REALLY IMPORTANT. They go down as the throttle opens. At some speed, there is an optimum balance between aerodynamic resistance and pumping losses. This is different for every engine. 50 MPH might be the most efficent speed in one engine/car, it might be 100 MPH in the same car with a different engine. Your DOE study is an average, not for a specific car. One easy way to realize this is to do the quick math- drag is the square of velocity. Going from 65 MPH to 75 MH increases drag by 33%. Why doesn't average fuel consumption go up by 33% per mile? Because pumping losses go down.

The highest MPG I ever got in my 1993 Plymouth Laser 1.8L was 43 MPG. That was driving it from NM to AZ at an average speed of almost 100 MPH. Different cars have different efficency points.

My point was that "slow down" is not always an accurate statement. At some speed, "speed up" is an accurate statement. I doubt "highway" mileage is done at 20 MPH, which appears to be the speed at which I would supposedly have to drive to get 24 MPG.

I agree miles per tank is useless. If you read my post, I say "one gallon left." If you'd like me to do the math for you, this means 14.9 G used. If you'd like me to do the division, it means I get 13.5-14 MPG.

I'm an engineer by trade and I design systems that monitor engines. I know all about BSFC, pumping losses, and drag vs. velocity curves.

 

Can you point out the one that deals with lighter wheels and better MPG? None of those appear to discuss that.

Lighter wheels help you when accelerating, like any weight savings. Once you are at constant speed, the only effect is very, very slightly less tire frictional drag, but this is so overwhelmed by air drag that I doubt you'd see the effect.

 

yeah, ive actually spent hours in this thread, reading through the different links, etc. & have never come across anything that focuses on MPG, but thanks for the help. i'll keep digging through there.

 

well considering that you lose the highest percentage of MPG from accelerating... thus city driving has less MPG. The lighter wheels lower rotational mass and acceleration is easier... you can achieve the same acceleration as before but without using as much gas. I have no idea what you mean by "tire frictional drag" and how that correlates to a smaller/ lighter rim.

The real savings is in the city... where its stop and go... I'm not saying you're going to gain huge amounts of MPG, but its a non-invasive and foolproof way to "free Up" power and increase mpg.

 

so are you saying when im going down hill and pop it in neutral im taking up more gas than driving to a stop in gear?

 

yes

 

I agree with everything you say in your post, except this. Please provide some factual, legitimate, documentation to this process. I've been searching, but I can only find information hybrid engines employing this technique.

Also, even if coasting in gear does save you a minute amount of gas, you're also increasing wear on your engine and transmission. I'll take the (theoretical) negligible amount of mpg loss to gain improved mechanical life.

 

I have 2k on my 05' I get 15-17 hiway/city mix. Only thing that seems to help is hiway driving. More of it the better. If you are taking side streets don't. No way to increase millege in the city. Worst was 14. Best 20. I saw a guy saying to skip gears which I do regularly, but I doubt that it make much diff.

 

The bottom line is the best thing you can do to increase gas milage is to not have such a lead foot. I saw another posted on here complaining of his bad gas milage when he said "I only hit 9k once or twice a day, I don't drive aggressively"

 

I fill up when im in between a half and a quarter left to help safe a little bit of money filling up. I can go a week with that and warm up in the morning for about 7-8 minutes before i go to school, girlfriend's, food, mall, stop and go traffic. I dont take it on the highway much. Only to go up to the dealer.

I get about 17-19 id say and i have no mods in my car. I pound it on the back roads, too.
I've only calulated it like three times because i always forget to set my trip when i fill up.

I'm still getting used to the lower mileage because i had a 6 and i could go two weeks with work included in it on a half tank.

Oh well. The RX-8s more fun.

 

is it me or wasnt there something about short start ups are better and not warming up your car for long periods of time?

 

lots of good info here but back on topic...

im on my fourth tank with my revi and ive only noticed ~0.5mpg increase overall. however, on one of the tanks it was mostly highway driving with 5-10% hard backraod driving mixed in. i got almost 22mpg, which is a huge difference from my normal 17. i have gotten one tank at 23, but that was literally all highway (gas stations at the exit at both ends) with cruise control the whole way. my next best tank was 21 and i thinki can count the 20+ tanks on 1 hand so that was encouraging