I know this MPG topic has been beaten to death, and I apologize for bringing it up again, however I would like to propose a new approach to understanding this MPG issue. I am not an RX-8 owner (yet), but have been following this forum for quite a while. Like many others, I too am interested in trying to understand the cause of great variation in mpg among RX-8 owners as well as relatively low mpg in many cases. (I have a daily commute of 85 miles).

It is very possible that there may be a combination of several factors causing this MPG situation. There is a type of quantitative analysis called Multivariate Regression which takes multiple factors into consideration and calculates their relative importance in determining an outcome, in this case, mpg. I’d be happy to conduct the analysis as a fellow RX-8 supporter. I just need as many RX-8 owners as possible to answer the survey below.

Based on my prior forum reading, I’ve come up with a several potential factors impacting the mpg. We’ll have to keep the responses very simple and straightforward. (Answers as explanations won’t work). Please participate……..

1. RECENT Combined City/Highway Average MPG = ___________
(Calculated Correctly and One Number please, not a range)

2. % Highway Driving = ______

3. Driving Style =
A. Easy going (Don’t normally use high rpm range, only occasionally)
B. Average,
C. Above Avg (Use Upper RPM range quite often and accelerate hard)

4. VIN Number (last 6 digits) = ___________
(NOTE: If you already entered your VIN on the thread “Let's compare VIN numbers and fuel economy”, I can get it from that thread).

5. Model (eg. Base, GT, etc) = ___________

6. Automatic / 6 speed = _____________

7. Octane (Number) of Fuel Used = ____________

8. DSC/TCS = Yes / No(Don’t Have or Fully Disabled)

9. Miles to Date = ___________

10. Approximate % Time Driving with Windows Open = ___________

11. Approximate % Time Driving with AC on = ___________

12. State = ______________
(I’ll later convert to Geographic Region)

Hope like hell I didn’t miss anything. I know this will be a pain – that many people have already responded to many threads regarding mpg. However it is very difficult to test one theory (eg. VIN # or Octane), when so many other contributing factors may also come into play. The analysis I am proposing takes all these factors into consideration simultaneously and identifies those which are important in determining mpg. If you are interested please respond. If you are not interested, well, please also respond………the more observations the better. I’ll post the results soon after receiving enough observations. For those that want to flame, hey, it’s my first post – have fun.

IMPORTANT: When responding, please complete all entries. If one thing is missing, such as Octane, then your entire response cannot be used. Thanks in advance for participating.

mod edit: results thread https://www.rx8club.com/showthread.p...4&page=1&pp=15

 

1. 16.2mpg
2. 40%
3. B
4. 106206
5. GT
6. 6 speed
7. 92
8. fully disabled
9. 834
10. 30%
11. 2%
12. NM

 

1. 16.8 MPG
2. 40%
3. C
4. 101102
5. GT
6. 6 speed
7. 93
8. Yes
9. 8400
10. 0%
11. 25%
12. NH

Observation: This only reflects my milage for my last fill-up. When I'm traveling my mileage increases significantly due to all of the time spent on the highway (20-24 MPG). Likewise I have seen horrible fuel economy on track days (7.5 MPG) or when I have been fooling around (13 MPG). Will this variation skew your results?

 

I'd emphasize to respondents that all their answers be specifically related to the 'recent MPG' answer to question 1.
-jd.

 

1. RECENT Combined City/Highway Average MPG = 22
(Calculated Correctly and One Number please, not a range)

2. % Highway Driving = 85%

3. Driving Style = B
A. Easy going (Don’t normally use high rpm range, only occasionally)
B. Average,
C. Above Avg (Use Upper RPM range quite often and accelerate hard)

4. VIN Number (last 6 digits) = 101212

5. Model (eg. Base, GT, etc) = GT

6. Automatic / 6 speed = 6 Sp

7. Octane (Number) of Fuel Used = 91

8. DSC/TCS = Yes

9. Miles to Date = 4800

10. Approximate % Time Driving with Windows Open = 10%

11. Approximate % Time Driving with AC on = 5%

12. State = AL
(I’ll later convert to Geographic Region)

 

1. 14.80
2. 15%
3. A
4. 108837
5. GT
6. 6 speed
7. 91
8. Yes
9. 2914
10. 1%
11. 5%
12. CA

 

Speed Racer: Regarding your concern about skewing the results. As long as your responses to the questions regarding % Highway and Driving Style (?'s 2 and 3) are based on RECENT driving (in accordance with your RECENT avg. mpg), I believe the results should be o.k.

 

JDL is correct:

PLEASE NOTE: As JDL stated; All responses should be specifically related to the 'recent MPG' answer to question 1.

ie. % highway driving, etc. should be based on RECENT driving.

 

Here's another take on the issue. What if the speedo's are.."optomistic"? say 1.5 mph off. That would reduce the MPG. I think before you can establish a baseline. You need to use another method of calculation. If the speedo's are at fault, then all the data collection in the world will not show a thing.


my .02 yen

 

1. 22.9
2. 80%
3. Average
4. 105899
5. Sport
6. 6 speed
7. 93
8. Yes
9. 5000
10. 10%
11. 20%
12. Virginia

 

"What if the speedo's are.."optomistic"? say 1.5 mph off. That would reduce the MPG. I think before you can establish a baseline. You need to use another method of calculation. If the speedo's are at fault, then all the data collection in the world will not show a thing."

Good point Matt. I have a couple comments in response.

1. If the speedos are optimistic 1.5 mph, I believe that would actually yield a higher mpg, thus reducing the problem people seem to be having. For example, if the speedo read 50 mph too high, then the odometer reading would show much higher mileage, thus yielding a terrific MPG.

2. One of the goals of my proposed analysis was to better understand the great variation in MPG among RX-8 owners. If everyones speedo reads 1.5 mph too high, then everyone is impacted the same. Though the MPG results for everyone would be a tad bit higher than reality, it would not cause variation in MPG among owners.

3. I'm assuming the optimistic 1.5 mph reading occurs at roughly 60 mph. That equates to a 2.5% error, or similarly, for someone getting 20 mpg equates to 1/2 mpg. This is not near enough to muddy the results of the analysis.

 

1. 21.35 MPG
2. 85%
3. B
4. 101129
5. touring
6. 6 speed
7. 92
8. No
9. 7800
10. 5%
11. 2%
12. MD

another part of driving style that may be important is average speed / or normal cruising speed. mine is probably average 72, usually in the 75 +/- 5 range. Sometimes 68, less some times in the 90s. I'm not sure how my throttle use is as an 'average'. in town driving it's very easy going,1200RPM starts. usually. Then there's a hopefully daily 9K redline short burst. My fuel buying was 87 for several tanks; the last 4 have been premium. The MPG figure I gave is the last tank which was on the 3rd full premium tank since switching back from 87. Our local temps have been in the 45-60 range mostly recently. Running close to 32PSI; 5w/20 oil, usually no passenger or extra luggage -all possible factors as well.

 

1. RECENT Combined City/Highway Average MPG = 18.3

2. % Highway Driving = 10%

3. Driving Style = B

4. VIN Number (last 6 digits) = 106908

5. Model (eg. Base, GT, etc) = GT

6. 6 speed

7. Octane (Number) of Fuel Used = 91

8. DSC/TCS = Disabled (DSC off, but no squiggly lines)

9. Miles to Date = 1500

10. Approx % Time Driving with Windows Open = 0%

11. Approximate % Time Driving with AC on = 98%

12. State = Florida


How about adding spoiler/no spoiler and front lip/no lip?

But there are more variables to consider: Ambient temps, humidity, length of traffic lights (here in Tampa bay, some red lights are 3 minutes long), amount of time idling, Hills/no hills,
average MPH...just to name a few

 

1. 15mpg
2. 5%
3. B
4. 107764
5. GT
6. 6 speed
7. 91
8. fully disabled
9. 1500
10. 50%
11. 50%
12. California

 

1. 17.5mpg
2. 20%
3. B
4. 104226
5. GT
6. 6 speed
7. 89
8. yes
9. 1950
10. 20% (sunroof open 75%)
11. 5%
12. OH