MPG - Calculated vs. computer?
 

Owner of a 2005 HCH manual, living in northern MD, somewhat hilly environment but I do mostly higway driving. I will start by admitting I do not read all posts, but I see a recurring theme of discussion about mileages exceeding 60+ and even 70's for HCH's. With that caveat, I hope this is not a redundant thread.

My question - are people manually calculating their mileages on a tank-by-tank basis, or are they basing their input to the forum based on the estimated mileage shown by the dashboard computer?

The reason I ask is that my computer typically estimates my mileage about 2-3 mph higher (consistently) than what I get by manually calculating based on miles driven divided by gallons pumped at the station. Example - filled up this week; 400 miles and 8.48 gal. This is a bit over 47. Computer said 51. I have not reset my Trip B odometer in almost 10,000 miles and show 48.4. But since I was only averaging 44-45 this summer with the AC on, I have to assume that real mileage is lower.

I do see improvements when I can drive on the MD eastern shore (can you say FLAT?). Is that a determining factor here? I saw 75 mpg on the computer once, but I had just filled up and practically coasted downhill to my house. My concern is that prospective buyers may be seeing mileage numbers that are somewhat misleading in our attempts to promote hybrid technologies (once again with the caveat that I have not read this entire forum database, and therefore may have missed statements about how mileages should be calculated by forum users.)

Regards,

Safety Guy

Re: MPG - Calculated vs. computer?
 

I have an 04 HCH, I use the actual data from the pump and odometer and I keep a meticulous log. Remember, the OSD shows a converted (from metric) reading. The MPG estimate jumps in .4 and .3 increments as that is what the rounding from the conversion delivers.

So, when your gauge reads 63.2 mpg, it could be as low as 63.05 or as high as 63.35 which is halfway to the next lower and higher increments.

I agree, I see about a 5 percent more ambitious reading on the gauge than the manual results compute.

My lpmg, as read on my Trip 2 gauge (never reset) is 54.1 my actual, via calculation, is 52.4.

Hope this information is useful.

Re: MPG - Calculated vs. computer?
 

I've monitoried this difference over the last 18 tanks (~9000 miles). The average error margin in the display over that time is 3.0 MPG. Hopefully folks are entering actual miles/gallons used into the database.

Re: MPG - Calculated vs. computer?
 

My own trip computer is usually optimisitc by 0.5 to 1.2 MPG, over the life of the car (about 15,000 miles).

I think that just about everybody in the very-high-mpg category does calculations by hand, using actual miles driven divided by gallons of gas.

Regarding prospective buyers coming into this site and having unreasonable expectations: I hope they would look at the average HCH MPG of around 46-48 MPG, understand the bias of most folks here who are acutely interested in getting better mileage, and set their own expectations somewhat lower (say 44-46). Then once they get the car, they will find that they develop some degree of more efficient driving skills, and get up to or above the average over time.

Re: MPG - Calculated vs. computer?
 

Some of the hypermilers use manual calculations, others use the computers numbers.

My computer is off by about 3MPG optimistic. I hear the computer update makes the reading more accurate. The numbers I put in the database are hand calculated. I think there is a field now where you can see how people are putting in their numbers.

Re: MPG - Calculated vs. computer?
 

Re: MPG - Calculated vs. computer?
 

My Trip B odo has not been reset since I purchased on April 1 and it shows 49.9 mpg and my hand calculated lifetime mpg is 49.3. Very close and within my tolerance level, being an engineer that is...I have done the computer update recall and did notice a slight betterment between hand and displayed miles pg. Have the AT-PZEV model being in MA.

Re: MPG - Calculated vs. computer?
 

Hi All:

___Not to bemoan the obvious but if you are calculating total FE over a tank, you really should use distance traveled over gallons purchased.

___If you are test driving an automobile of whatever sort, the FCD’s are probably good enough and better then you might have expected. You may not be generating much of an error over 1/10 of a tank vs. a whole tank and it is the comparative difference that you are interested in over that much shorter distance anyway. An Example. You refuel to top off, travel 50 miles and refuel to top off again. Are you going to show the same delta (let us assume you see a + 1.5 mpg delta over an entire tank) between the FCD and actual over 50 miles as you are over 1,000 miles or does the delta increase/build in over time/distance traveled? In the Accord, the delta builds in as your distance increases. The further you travel the higher the delta pushing to some finite difference between actual and calculated. It will not increase to infinity but approaches some built in absolute delta? In the case of the Accord, I think it is around 1.6 - 2.0 mpg. Since the NAVI was replaced in the Accord, I have consistently seen a 1.2 - 1.9 mpg overestimation by the TC vs. actual after 900 + miles. On the one short tank I have (I topped off at slightly less then ½ full the night before Katrina hit N.O. to save a few $’s), I only showed a .84 mpg delta after just 582 miles. I cannot say for sure if the delta builds in towards a specific over/under estimation with the HCH/Prius II/Escape HEV, etc. like the Accord but I bet it does? This would leave you with the FCD as a very good indicator over a much shorter distance by comparison to a whole tank.

___You can definitely use the FCD if you are calculating one segment vs. another as was the case of my first time behind the wheel of a Prius II. Here is that example:___The difference between segments will not show the FCD error at all because you are not measuring the actual, you are measuring the difference between segments via estimated gallons consumed and the FCD error should be equivalent in any given segment.

___Let me know if your hybrids FCD’s act similarly to that of the Accord as this would be an interesting piece of knowledge for future discussions …

___Good Luck

___Wayne R. Gerdes
___Waynegerdes@earthlink.net

Re: MPG - Calculated vs. computer?
 

My FCD generally begins to be off when it displays over 60, otherwise it's pretty accurate up to that point.
For example on my 69.2MPG calculated tank it said 64.
In the 66 calculated tank it says about 62.

Because of that I know that if it says low 60's I am doing OK.

Right now it's at 61 point something with 7 bars of fuel left so I'm a little behind, thanks to a relentless driving wind. I'd guess my calculations will come out to about 63-64 in the end.

Re: MPG - Calculated vs. computer?
 

now there is something i have been wondering about. how many bars are in the fuel display, and do they correspond to a certain amount of gas, say one per gallon? just wondering…

watch out. this will probably jinx me, but i am still holding right below 62MPG with 250 miles on this tank..... :cool: