What MPG are you using for the compare??
 

It disturbed me that one of the AH drivers IMO is posting false MPG figures

"34.9 MPG on NAVI, 33.8 MPG 'Trip A', 32.46 'at the pump"

he is posting the NAVI #s instead of gas pump figures.

Why would anyone rely or post what the computer guesses at instead of true miles/gallons ???


Will post this also in general but is this common reporting by AH owners??

Re: What MPG are you using for the compare??
 

NAV figures should actually be more accurate as satellites can pinpoint your true position. Your car's figures are based on the diameter of the wheel and revolutions -- which may not be 100% accurate. For all practical purposes, it's all gravy. Don't worry too much about it.

Re: What MPG are you using for the compare??
 

not worried too much just like comparing apples to apples.

yes tire dia changes and using the std. 10/32" tread thickness - 2/32 which is considered worn out = 8/32*2 = 1/2" in overall difference from BEST to WORST case in tire size. This difference on a 215/60/15 which is 26.157" using that as a center line for the tread would make the worst case inaccuracy of 25.907/26.407 = 1.93% difference.

32.46 (pump) * 1.0193=33.08 (worst case %) vs navi of 34.9

would find it very interesting if the driver on his next long trip (200+ miles) & compare his odom vs the mileage markers then use that difference and compare to his NAVI info. My Jetta, strange as it may seem, travels 1.025 miles more when I compared the odom vs mile markers on a 700 mile trip I took.

also if you traveled in a 100 ft circle for 1 mile how far would the NAVI report your distance traveled???

just wondering how good satellites and computers are getting at tracking us.

Thanks for your time and hopefully future info from AH owners.

Re: What MPG are you using for the compare??
 

I've got some issues with the whole reporting method business as well. I guess the best thing to do is just not worry about it but sometimes that is easier said than done. I always post using pump figures because that seems the most fair in the long run to me. Still the car and navi displays are better as far as compairing one tank to another. Tank fill issues make the at the pump method worthless for compairing one tank to another.

Now wouldn't it be cool if you could graph more than one method...........Hello J, how about a major upgrade allowing for more than one method to be input into the Gen 2 database? Too much work?

Re: What MPG are you using for the compare??
 

I forgot about one tank being different from another. my TDI has the vent mod thus when I fill up at the pump my tank is 100% full and there is no difference tank to tank. Also when you fill up 5-10 times your avg. tank and milage will level out and be very accurate.

ever since my C5 vette said I had 60 miles to empty and then ran out of gas I don't take much stock into computer guesses.

Re: What MPG are you using for the compare??
 

I think you should only use the numbers to compare against yourself. Maybe you can use others numbers to set goals for yourself. It's realy not a competition so who realy cares what one person posts vs another.

Re: What MPG are you using for the compare??
 

Tom you are absolutely correct, your attitude shows your maturity. I'm not quite as mature and do view the database as a competition. There is no way I'd be driving in 98 degrees heat with no air if there was no competition.

Re: What MPG are you using for the compare??
 

Hi Iboomalot:

___I use topped off tanks to topped off tanks via the legal cal’ed pump and miles traveled per the legal odometer. There is no better solution for consistency although you can argue accuracy until the cows come home due to the OEM’s non-exact odometer’s and tire wear. NAV units boot up way to slowly to take into account any movement before at least 3 birds are locked up and a continual distance track can be measured. I am not even considering when they lose lock and show you ½ or more miles away before they get educated and jump back on course ;) Heaven forbid when they tell you to take one route with their “Locked to Route” feature enabled (most OEM NAVI solutions do not allow you to change this :() and you take the alternate. That jump is always worth a tenth or two and I see it every day at the I-355 and I-55 junction just north of Joliet, Illinois. Another … I should upload a screenshot of the bread crumbs when I take a non-digitized road into my work location. You would think a drunk was driving though a 20 acre field instead of a single dual lane road into the exact parking lot and many times the exact parking spot each and every day.

___Jason, they should be more accurate but they are not in many instances unfortunately :( Another aspect that will never be accounted for by an OEM or non-OEM NAVI solution: The change in distance between the far right and far left lanes of an interstate through a turn. I have measured this more then once while on night shifts in the Corolla. Moving from lane to lane to cut off the corners (Inside lane at all times) shows a .5 - .6 mile difference over 93 miles then just taking the right lane all the way home. NAVI’s haven’t a clue what to do with that difference?

___Good Luck

___Wayne R. Gerdes
___Waynegerdes@earthlink.net

Re: What MPG are you using for the compare??
 

There was a similar issue a few weeks ago re: greenandblue's odd tank. Someone there also brought up the point that over multiple tanks, any fluctuations in how full the tank is get worked out- the deficit from one tank is made up in the next. Unfortunatley that makes it hard to look at short-term subtlies.

IMO, I'd take the odometer mileage over GPS. Even if its not as accurate in absolute terms, its more repeatable in its error, and that can be reliably accounted for. GPS has many variables out of the operator's control- satellite lock, time between fixes, algorithm used to calculate distance between fixes, yadda yadda. The 'bread crums' mentioned before allude to the non-repeatable nature of GPS fix errors. Up to 10 meters (?) for EACH fix...compound that and BAM- you've got an issue (of course, the errors can be considered to be largely statistical in nature and can average to ~0).

That's why DOT built differential GPS for coastal mariners- to find the local instantaneous error and send out a signal that corrects for it.

When the Navy switched from 80s vintage radar-and-imagery guided Tomahawks to GPS guided, there was a few meters' worth of dropoff in precision...it hit the 1st or 3rd window from the left instead of always the 2nd. But the change was there.

Re: What MPG are you using for the compare??
 

There are always going to be issues with accuracy no matter what way you measure it and for what purpose. I honestly don't think it's something to be worried about.

Re: What MPG are you using for the compare??
 

a possible 6% drop in MPG rating isn't to worry about but Iam a big Technical person and would like to see a standard put in place for reporting MPG is all.

Since ALL cars have a speedo and all cars have a gas tank and all roads have mileage markers to calibrate your speedo too I can only see one sure way for direct comparisons to other vehicles on the road and thats using mileage and pump #s.

Its your site so you can run it like you want I just noticed some people posting NAVI #s that were consistanly 4-8% higher in MPG than there pump #s

I guess I could only post when I do HWY driving and up my #s from 42.8 to 48+ but I won't :D

I do thank you for this site it puts Hyrids into perspective and how driving habbits can improve or reduce MPG.

Re: What MPG are you using for the compare??
 

Since I don't have the NAV system in my Escapes, I use the odometer and pump method. Sure, you will get some variations from tank to tank but ultimately you still get total miles driven and total gallons of gas purchased. The former over the latter gives you a darned good figure for lifetime mileage.

I use an Excel Spreadsheat to track my mileage and on both Escapes after 4 or 5 tanks you could see the plot of lifetime mileage approach where it is now and pretty much hold there. The individual tanks vary quite a bit but the lifetime average mileage stays pretty flat.

And anyone who thinks there isn't a competition going on here - I remind my wife all the time that she is killing the mileage in the '05 since she started driving it. See the numbers below, you'll see. She's learning though....

Re: What MPG are you using for the compare??
 

Ditto.
Ditto again; I use one I got from this list which computes the difference between manually computed gallons/odo readings mpg and the HAH mpg readout (non-Navi). Last tank was dead on--both 34.0; more typically, math mpg is a bit lower (.05 to .1), though I'd say at least a third of the time the HAH readout is lower than the math, and occasionally the difference either way is larger, around .2. Pump variations and fill levels could easily account for these differences. I accept the auto shutoff at each pump and don't add more fuel, a "constant variable," I guess. I agree, that over 10 or 20 or 100 tanks, the overall average should be accurate enough to let me know what car and driver(s) have done.
"Two sailboats heading in generally the same direction is always a race, even if one of them doesn't know it" may apply to the mpg discussion here. The fellow who sold us our HAH is a neighbor, and he will drive our HAH in for service and bring it back, saving us a chunk of time since we live 40 minutes from the dealership. He drove it in today for 15K service (already!!). My wife just said "you're kidding, right?" when I mused that I'd lose 5 mpg on this tank by letting him drive the HAH in for service. Have to admit that the Greenhybrid database and my struggle to get to and stay in the 34 mpg group was as great a concern as overall fuel economy. Still happy to have free service delivery and return... I surely can make up the lost mpg on a planned road trip to Tucson :=).

To return to the sailing analogy, I'd say what we have here are several boats heading the same general direction; some of the skippers are just cruising, and some are applying every sail and rig tweak they know to squeeze out another tenth of a knot in boat speed. The database contains people with a mixture of purposes. If I understand Jason's position, the database is more a cruise than a regatta, reflecting a variety of driving conditions and purposes, resulting in a big picture of hybrid performance. Drivers within the database can, if they like, set performance targets by observing what other drivers post, or not. I've been motivated by some of the mpg reports and hypermileage discussions; my mpg has improved because of them. When someone in a comparable boat cruises right past me, I want to know "how are they doing that?" I may decide that the effort is not worth the benefit and keep on cruising, or I may join the regatta and see whether there's any way to match xcel and other hypermilers ( the answer is "no," by the way). I see nothing wrong with encouraging drivers who are posting impressive numbers to conform to the math mpg norms used by the other drivers who have a regatta going inside the big cruise. The emphasis would be on "encourage" given the broader, non-competitive purposes of Greenhybrid.
Lewis