LaCostaRacer

The gas mileage threads do get old, but lets liven things up?

Here's a quick ballpark method that doesn't even require a calculator- just answering a few simple questions:

1. Do you reset your MID each tank and fill up the tank each time? If so continue on- otherwise try this one tip before complaining about gas mileage because you really don't have much data to go by and need enlightenment.

2. Is your average MPH (calculated by the MID in addition to MPG that everyone always quotes) < 30 MPH ?

If so, use 20 MPG as your baseline and then subtract .5 MPG for every one MPH below 30 MPH.

If higher, use 20 MPG as your baseline and then add .5 MPG for every one MPH above 30 MPH up to 65mph. Speeds higher than 65 are capped at 35MPG and then decrement by .25 MPG for every 1mph higher.


3. Are you running with Oxygenated fuel during parts of the year for smog reasons (e.g. California during the winter months)? If so subtract one MPG from question #2


4. Are your tires under-inflated? If so subtract 1 MPG from your question #3 answer if below 30 MPH or 3 MPG if answer #2 is > 50 MPH

5. Are you running with high performance tires? If so subtract 1 MPG for < 30 MPH average speeds and 2 MPG for > 30 MPG speeds

While not scientific, I bet answering these questions will get you within 1-3MPG of actual mileage. I'm using my own data as a benchmark which involves a spirited, urban, and mostly flat commute. My actual MPG is a hair higher than the formula calculates in some cases and dead on in others. It seems withing 1MPG of actual in both urban and highway commutes though.

Hopefully others will try this out and comment- we might have to adjust the factors more based on terrain- I was trying to keep this very simple with no calculator needed.

Give it a shot

Red Voodoo

Damn it. I hate math.

LaCostaRacer

^ I hear you- fortunately doing a little math on question #2 gets you very close. The other questions are refinements mostly based on variables that people might have tire, gas type, etc. This formula reminds me of some of the wacky formulas the IRS uses for AMT, standard deductions, etc.

tmnhs81

h4qq

iTrader: (1)

...lol

thanks LaCosta, I'll do this as soon as my next fillup comes

YeuEmMaiMai

it's easier than that

I predict based upon experience that I will get between 24-25mpg mixed each time I fill up the tank. The car has been doing that consistantly for the last 94K miles....no more math involved other than the occasional spot check to verify that milage is what I am expecting lol. I also predict that I will get between 30-32mpg on the highway when I do my road trips.

LaCostaRacer

Yes, I didn't do the formula to predict my own MPG either. I use the MID for that because it is very accurate anyway.

This should help all those folks who feel the need to post how terrible their mileage is. There's a reason for bad MPG and it usually involves the start/stop cycles, and idle time per tank. The point here is AVERAGE MPH IS A HUGE predictor in MPG and it gets a little old when people complain about ,but fail to give the most important piece of data.

I hate cars

Sounds like fun. I'll try it next time I fill up and reset the MID. MPG is so MPH based it's unreal.

The only thing I really hate is #3. Oxygenated fuel only works to lean out carbureted cars. Fuel injected cars use the 02 sensor to bring the mixture right back to the normal range. But I guess that's a little off topic.

TypeSinNC

iTrader: (2)

I reset every time I fill up...not really sure why I do, I guess its gotten to be a habit

LaCostaRacer

Not much action on this thread today. I just entered some gas slips into FuelEconomy.gov so I had a chance to backtest the 'formula' better. I used Excel to run some numbers easier and tweak the formula.

I found out that the original formula might overstate mileage at highway speeds.

I also made a simpler formula that works better across the speed range:


IF Speed > 30 then
Predicted MPG = 20 - (30 - MID_MPH) * .5
ELSE
Predicted MPG = 20 + (MID_MPH -30) * .25

I back-tested the new formula and I'm usually within 1 MPG of actual in most cases. The formula may overstate mileage in a few of my cases where I was going on ski trips and did some climbing under load. The formula is dead on for my average commute which is almost always sub-30MPH average speed.

The MID is very close to actual mileage too ( within +/- .5 MPG), but the formula gets even closer in most cases.

So for those people stressing over gas mileage, you might want to see the 1994 film 'Speed' to get some nice techniques for keeping your speed up to improve mileage.

LaCostaRacer

bump for relevancy for high gas prices and lots of discussion on how to save gas

RaviNJCLs

iTrader: (4)

Thanks. But it is a lot easier to calculate miles driven / gallons = MPG.

TheChamp531

iTrader: (3)

Thankful for what you're tellin us but I'll let the MID tell us.

LaCostaRacer

Sorry for any confusion. This formula should reinforce how average speed has a major impact on mileage. I have read countless postings of people complaining about mileage but not providing the speed info. I'm happy to see Acurick's new thread showing how speed correlates to MPG.

The MID is very accurate for current MPG but won't predict future Mpg if you have to choose between two routes which show different average speeds but different distances.

Bearcat94

FWIW, Acurik's post has a formula as well.

MPG = -0.01(mph^2) + 0.9937(mph) + 3.4906


Should be easy for one of you fellas in college to take the derivative of that and find the exact MPH to get max miles per gallon.

AK1991

Me too! It is quite consistent, tank after tank, but it has become a habit for me...

mtxjohn

This "formula" is just ridiculous. The lower my average MPH the better MPG I get. Because air drag increases exponentially with speed.

The MID is a "DREAM-O-METER". I don't know why some people claim its accurate (wishful thinking?) but my 2008 TL's isnt even CLOSE. It reads a good 4MPG high.

Recent trip with 600lbs of cargo I got 438.9 miles on 12.998 gallons of gas.

That was a steady 60mph. On the way home we did 70-75mph and still got 32.5 mpg.

LaCostaRacer

^ I have no idea what you're saying. because you provide no actual facts to your statement You need to provide details about your average MPH speed and MID MPG to gain credibility in your assertion.

If you think about what you're saying, it would mean going an average of 20 MPH would be more efficient than going 40 MPH and that is clearly not true or accurate in a normal commute that involves highway as well as some street (start/stop) traffic.

LaCostaRacer

oops there was a typo in this formula with a - instead of a +. Sorry for any confusion:

V type should be + and not -
V estimated MID MPH based on 'steady 60 MPH' statement- probably less in reality
= 20 + (60-30) * .5
= 20 + 30 * .5
= 35 mpg

actual = 33.7 (formula still is pretty accurate within 1.3 MPG of actual)

mtxjohn

You would have no idea what I'm saying because I actually ACHIEVE excellent fuel economy instead of making things up.

Look through my post. I stated my actual MPG, (not the MID, which is a joke. It reads over 10% high on my car). If you start by reading the MID and assuming it is correct you have already failed. You are not helping these people who get crappy mileage-there is a wealth of information on the internet for anyone who wishes to look.

LaCostaRacer

Yes I saw what you wrote but you missed giving me WHAT THE MID showed for average speed was which is one major component of this thread and formula. All I saw was nebulous 70-75MPH references and then steady 60 MPH. The formula requires the AVERAGE SPEED. You can use the Navi-hack to see instant MPG data doing but that doesn't show your actual MPG either for a given tank.

Perhaps you fill up at different gas stations and have more variables going on. I fill up mostly in the morning and at the same gas station (Costco) 90% of the time.

All I can say is there are many people like myself that experience the exact opposite. I have 5.5 years of data showing how accurate the MID is with reality and it is also cross-referenced with speed data. In fact, I filled up today and here's a textbook example of this:

Miles: 243.7 Gals=11.94 MID MPG=20 Actual = 20.41
MID MPH = 31
Formula = 20 + (31-30) * .5 = 20.5

I would say this is a general example of my 5.5 years of findings with just 2 exceptions where the MID was off a couple MPG.

mtxjohn

Here is 40,000 miles of data on my RSX. I have averaged an astounding 50% MORE mpg than the EPA mixed rating on my rsx 36 vs 24. That's not a one-time fuel up or a short tank, thats my ACTUAL average including 5 months of winter temps a year in MN.

PS if you're going to post a claim about MPG it NEEDS to be a near full tank. And we need to see the MPG before and after that fillup because its very common for the cars to have a short fill of 1/2 gallon followed by a complete fill with + 1/2 gallon. So the guy who puts 8 gallons in thinks he got 35MPG and the next fill he gets 25mpg. I see it all the time on fuelly. His real average was closer to 30.

http://www.fuelly.com/driver/mtxjohn/rsx

Here is the more recent fuel ups for the TL which is my wifes daily driver.
I *think* the ave speed was 55 for the 33.8MPG tank.

http://www.fuelly.com/driver/mtxjohn/tl

This whole discussion of average speed is foolishness. There are too many variables to consider. In my VAST experience in my RSX I would say any average speed over 45 can kill your mileage. What I mean is for example-i have the cruise set at 60, and I'm coming to slowing traffic. ill drop it N and pull a GLIDE. Now I'm in a P&G situation and the lower avg speed actually boosted my MPG. It;s a simple fact that when you double your speed you square the wind resistance. Every car has an optimal speed, in my wifes CRV, per the scanguage 45 is best for that car. *generally* 55 is best for most cars. Anythign faster and you're wasting gas. But youre also wasting time. Acura built this sedan to MOVE not for MPG. The fact that it can get near 34MPG or better is just amazing to me. My MID stated 39MPG on that trip fyi.

I can see your point about ppl who idle, and that idling lowering avg spd having bad FE. You're 100% right about that but average speed doesnt give any indication of how we got there. If my avg speed lowered because of Pulse and Gliging and DWB (driving without brakes) then it vastly increased my mpg. If my lower average speed was due to idling and traffic well then it HURT my MPG. You can't assume anythign based on average speed with respect to fuel use.

I'm going to seriously question the validity of anyone claiming they regularly get 30's in their car as you can plainly see the real-world average is about 22MPG for TL owners on fuelly.

It takes quite a bit of skill to extract mileage from cars significantly above average. I have proof of my skill on fuelly.

LaCostaRacer

^ Well pat yourself on your back then. I have no problems getting 33+ MPG out of my TL (note this is a TL forum and not RSX) too with 4 people in the car a full trunk, AC on, driving 80 MPH, and no cruise control. I don't think of myself as having any unusual skills either- the TL is a great high speed cruiser.

In case, you didn't realize it- I ALWAYS FILL THE TANK too and have been for 5.5 years. I simply don't wait for my tank to physically empty before flling up- usually just before the light comes on. I never know what my schedule is so I like having 5+ gallons in the tank.

I have to say you have quite an 'attitude' for posting so few times. Heck 40% of your posts are on this 'pointless' thread alone.