MPH VS MPG

As I was driving home yesterday, I had a thought come to me. I was not able to do the math myself, SO, I am asking here. I know some of you bright engineers out there are going to know this and spread the word.
The question I asked myself was if the Miles Per Hour value is off on the swing, does that change the odometer reading? And if that reading is not correct, would that not change the MPG value for the scoot? And if it does, and it appears that the MPH is always a little higher than actual, are we getting less MPG or more MPG?
I have considered that the two reading may be independent of each other. I don't know if the electronics for the speedometer and the odometer are controlled by the same computing chip. That bit of information will be helpful in knowing whether the question is even valid.
Thanks for taking the time with this.
Gary

Let me add a bit of a twist into this discussion -

My wife and I ride together a lot. We fill our tanks before heading out and when we stop to refill - our trip A odometers do not read the same distance, they may be off by as much as .6 miles over a 180 mile distance.

During a recent 825 mile trip where we both rode the exact same routes. I managed to add an additional 3.8 miles on my bike.

Dale, this might be very relevant... IF your and your wifes' odometer differ... say... you read 60 mph and she is reading 60.1 mph. would that influence the odometer reading as well... I rode with a friend several days last week on some round trips of around 200 miles. We filled up together about 4 times and compared MPG each time. He has an 08 and I have an 03. Our odometers never agreed and as you said it was about .5 miles difference for the near 200 miles. I didn't really pay close attention at the time but now after hearing your experience, starting to really wonder about this.
I may just have too much time on my hands.
Gary

I do not know if the speedometers agree or display the same value, just that the odometer which measures distance covered, are not in agreement.

The speed (time) at which a distance is covered does not affect the distance covered. In other words - 60 miles is 60 miles whether you are travelling at 30 mph or 60 mph. In the case of 30 mph it will take 2 hours to cover 60 miles, at 60 mph the same distance can be covered in one hour. In either case it is still 60 miles.

How does the odometer of the SilverWing work? I'm not sure, but believe it is electronic and that the sensor is on the rear wheel. Is it the same sensor for the speedometer, again I do not know.

I doubt the difference in MPG will be very significant.

Dale said ... "I doubt the difference in MPG will be very significant." That is an understatement... I just want to add... if two bikes leave together and travel between the same two points and arrive together ... the odometers should read the same. As you said Dale... the distance doesn't change if we change the speed we travel or the time we take to travel. Distance = Average Speed X Time. Almost everyone I have read about on any forum mentions that the speedometer for most vehicles is inaccurate. May be insignificant , but inaccurate. That being a given, distance reported by the odometer can be questioned and if that report is off, then the MPG is affected. I agree probably VERY INSIGNIFICANT, but some inquiring minds want to know.
I am sure you understand now, why my wife is in no hurry to retire with me.
I await some reaaalllly smart brilliant engineer lady or guy to put this to rest. I won't be able to sleep tonight until this is settled. NOT REALLY. Just stirring up stuff.
I have probably begun the process of being booted again...

As I have pondered this (not continuously) I am also perplexed. It would seem that the odometers are not entirely 100% reliable. They are not so grossly out of whack that it causes me to not want the bike, but a perplexing issue none the less.

I do not know how the odometer works. The sensor for the speedometer is indeed at the hub of the rear wheel. Is this same sensor used for the odometer? How is the speed calculated? How is distance calculated? Does the tire circumference affect the algorithym used to calculate? Does circumference affect both in the same way? - I have no clue.

Without being privvy to the drawings and program data for the chipset it is not a simple thing to figure out how or where (even if) there is an error.

Yeah, that is just what I thought,,,, we think just alike... now that IS scary. Thanks for having fun with me...
Gary

This subject has been discussed at length on another site .The general consensus is that the speedometer is out but that the odometer is accurate . It is also thought that this is done on purpose to make us think we are faster that we are .I guess they think that we can't handle the truth. There is only one speed sensor for both .Except on my bike as I have one for the speed control .

Excell,

I agree it has been discussed (to death) at length and I also agree with the general concensus is that the speedometer is inaccurate, but disagree with the odometer being accurate.

Two riders on 2005 SilverWings (my wife on hers and myself on mine) fill the gas tanks and reset the Trip A odometer. They travel the same route one behind the other until they decide to stop for fuel. They refill the tanks and record the miles travelled. One bike has some how travelled farther by a few tenths of a mile than the other bike. It would seem that the odometers are not as accurate as the general consensus would have us believe.

I personally don't care about the speedometer error and actually don't worry over the odometer inaccuracies. But, I don't agree that the odometers are necessarily accurate. I have a small notebook full of annoted mileage stats on our two bikes and it is a rare occurance when we both have travelled the same distance according to our bikes odometers.

Now it is possible that there are external factors that are somehow contributing to this small deviation, but it would be hard to quantify and even harder to understand how those factors are so consistent.

I guess you could check it with a GPS thats what we did at the Ford dealer that I used to work for . I would have to agree that one of your bikes is out .

I was typing this as Excel posted his... go figure...

Dale, in your record keeping journal, do you record any consistency in the odometer readings. Is one bike ALWAYS reading more than the other, or, do you get results that vary in difference?

I promise this is the last time I am going to bring this up. Too many people dying already...
I want to propose a test. For the sake of science, I am willing to sacrifice my time and money (gas money) to gather some data. I want some feed back on my hypothesis. Do you think this would be a valid test for measuring the distance from point A to point B and return? Most riders I know accept the GPS readings as more accurate than the scoot. At least the MPH. I think that the speed and miles are both probably inaccurate on the scoot.

My proposal:
After resetting my trip meter on the scoot and my GPS both to 0.00
Take a trip beginning at my house going 50 miles out, taking a reading on both devices, then returning to the Goolsby home place and taking both reading again. Speed and time will not be any influence on either reading. Both should read the same (assuming my tires don't leave the ground) even if I don't end up with exactly 100 miles. I will take the reading of the meter that reads 50.0 miles first as the turn around marker.

My goodness... I am starting to feel like a Capt. Kirk boldly going where no man has ever gone before... probably just my blood pressure meds.

Since you are both talking about such long distances it may be because one is weaving more than the other. I know it may sound silly but it may also be true. If you weave more than the other rider it could add up to about .5 mile over a distance of about 200 miles. It is just a thought though but seems to make sense.

I know for a fact that all Honda Silver Wing odometers are exact to the nano-mile. :ROTF:

Opalsboy wrote:

I was typing this as Excel posted his... go figure...

Dale, in your record keeping journal, do you record any consistency in the odometer readings. Is one bike ALWAYS reading more than the other, or, do you get results that vary in difference?

I promise this is the last time I am going to bring this up. Too many people dying already...
I want to propose a test. For the sake of science, I am willing to sacrifice my time and money (gas money) to gather some data. I want some feed back on my hypothesis. Do you think this would be a valid test for measuring the distance from point A to point B and return? Most riders I know accept the GPS readings as more accurate than the scoot. At least the MPH. I think that the speed and miles are both probably inaccurate on the scoot.

My proposal:
After resetting my trip meter on the scoot and my GPS both to 0.00
Take a trip beginning at my house going 50 miles out, taking a reading on both devices, then returning to the Goolsby home place and taking both reading again. Speed and time will not be any influence on either reading. Both should read the same (assuming my tires don't leave the ground) even if I don't end up with exactly 100 miles. I will take the reading of the meter that reads 50.0 miles first as the turn around marker.

My goodness... I am starting to feel like a Capt. Kirk boldly going where no man has ever gone before... probably just my blood pressure meds.

That should do it ,I await the results .

Yes, as pointed out, the odometers are inaccurate. Other factors that will affect the distance traveled by two bikes on the same route include whether you ride on the inside of a curve or the outside, because te radius along the inside of a curve is slightly less than the radius along the outside. But just for discussion sake, let's assume that the odometer is accurate to 98% (meaning there is a 2% error).

If you travel 150 miles and use 3 gallons of gas your miles per gallon is right at 50. (150/3 = 50) However, if the odometer is showing that you traveled 2% more miles (2% of 150 is 3 more miles) then the error would make it look like you got 51 miles per gallon. (153/3 = 51) It would work the same way if the odometer showed fewer miles traveled, except it would reduce the calculated miles per gallon to 49 mpg. (147 miles traveled divided by 30 gallon of gas = 49 mpg)

You will note that the assumed 2% error in the odometer reading resulted in a 2% error in the miles per gallon (1 mpg difference out of 50 is 2%).

Now I don't know whether or not the odometer error is in any way related to the speedometer error. They may be entirely unrelated, but maybe not.

ahhh that last calculation should have read: (147 miles traveled divided by 3 gallon of gas = 49 mpg)...

Jeff do you think the odometer error is less than 2%? Is that based on GPS confirmation? It would be good to know...

TA DAH !!!! Here is the actual GPS to Odometer data collected by GHG on 7/15/2009. I changed the parameters just a little. I received a goat skin pad for my scoot yesterday, so I forced myself to ride a little farther than the 100 miles to give my pad the old Butt test at the same time.

I traveled in a circular route around my area. The total distance was a little over 140 miles. 142.36 miles GPS, 144.9 miles Odometer.

Information collected was: Odometer Mi,GPS Mi, Difference, error/GPSMi Error expressed as %

Odometer mi GPS mi Diff error/gpsMi Expressed
as %
1st Data 20.5 20.18 0.32 .02 2.0

2nd Data 37.1 36.28 0.82 .02 2.0

3rd Data 65.7 64.43 1.27 .02 2.0

4th Data 144.9 142.36 2.54 .02 2.0


Jeff you can see that the 2% error is pretty constant. I did do a little observing as a side event. I noticed that the speedometer is more accurate at slower speeds. The error seemed to increase by 1 MPH per 10 MPH above 30 MPH,

I did a little figuring to help decide if this 2 % is significant. Just fun stuff an old man finds to do.

If you have a 10,000 mile warranty and your odometer is 2% early. That is one less tank (200 mi) of gas you get to use.

The difference in the MPG is almost exactly 1 MPG. ( 50 MPG Odometer, 49 MPG Actual by GPS)

This exercise has not been to increase or decrease our enjoyment of riding our Scoots. For me, it has just been a mental exercise. That is about all I have left to exercise any more. And that is slowly turning to mush.

Explaining the MPG data. FOR MY BIKE ONLY....

I get consistently 210 Mi (Indicated) per tank. For 4.2 gal tank that equals 210/4.2= 50 MPG

Using the 2% error my GPS will indicate 205.8 miles and for the same 4.2 gals of gas. 205.8/4.2= 49 MPG.


Dale, you and your wife need to check your scoots by GPS and see if there is a constant error in yalls readings. Not that it is going to change our arrival time in the arms of our Lord.

God bless... everyone

Gary

I don't have a GPS - OH the horrors! I am a map guy.

I also don't download music I really like holding the physical album or cd.

I'm a dinosaur.

Album???? Where do you get those any more? And what do you use them on? I though they had gone away. CDs are going to be a lost breed very very soon.

As I was making my little exercise trip today, I was playing MP3s through my GPS. I listened to a Gospel group The Holcomb Brothers. I have two digital albums of theirs that I listen to. Heard each twice while riding. Good music. Take my mind off the heat. It is only 101 F here today.
Gary

Audio Technica AT-LP2D LP-to-Digital Recording Audio Turntable System with USB

Lately I am really getting into hip-hop from the guys at www.reachrecords.com

But this is really a departure from the topic and I apologize.

I will continue to not worry about the deviation (delta in engineer talk) between our odometers and the speedometer and GPS. I enjoy riding too much to let that bother me.

Ditto ... and .... DITTO.
Gary