Gas mileage, odometer, what gives??

[MakarskiJA]

Okay, slight irritation here,
Ive done my share of reading on the forum and come to the conclusion that my speedometer is off by the BMW 7.5mph, okay, thats fine. The odometer over the course of a 95 mile trip is off by 15 miles short. Gas light comes on at 105 miles and I fill with 3.5 gal. This come up with roughly 31mpg riding conservatively. Factor in the maybe 18 miles that arent showing on the odo and you get 35 mpg. No where near the 48 or so that the factory says it should get. I need to get my Garmin 60CSX fixed so I can get some better numbers but does anyone out there have any ideas on why:
1) Im not getting the gas mileage that I think I should?
2)or what I'm doing wrong in my calculations?

I have a speedo-tuner on order that I'm going to try for kicks and I will let ya'll know how that goes.

Nothing in the engine is aftermarket, stock computer, exhaust, tire size etc.

[wswartzwel]

you running gasoline, or ethanol? in town? interstate? cruising or burning up the corners at high speed.

Mine varies from 30- to over 50 mpg depending on elevation and type of gas, type of riding.

[RBMann]

I used a speedo re-calibrator until installing HID headlights. Some kind of voltage feedback burned out two re-calibrators.

My mileage was spot on but the speedo read +10%. The problem for me with the re-calibrator was it changed speedo and mileage at the same time, since they both use the sensor.

At what speed are you 7.5MPH off?

I have also seen gas mileage from 28-54.

[MakarskiJA]

We have a Marathon here in Madison Heights, VA that has NON-Ethanol gas that I'm using to fill up. Like I said I've been riding conservatively a little in town but mostly highway doing 55-70 depending on what road it is. At 60mph I seem to be running about 53-54. My fiance was following me and asked why I was going under the speed limit. We did this with both a honda and a volvo with the same speedo results. I've still been getting comfortable on the bike so I havent really been burning much of anything. Starting to get my lean angles over more though as I ride it a bit more.

[MakarskiJA]

Originally Posted by 2wheelmike

Something else to consider is tires. worn tires shouldn't make that big a difference, but it does contribute to error. The next time you buy tires, try the next taller size 190/55. It went a long way towards correcting the speedometer for me, but mostly I liked the turn-in much better and the chicken strips are now nice a even F/R (seems good). If you have an R12S-specific hugger, you will likely have interference though. The odometer will also be affected, so this might be bad if your odometer is correct (as determined by GPS). Does your phone have GPS?

My tires are 180/55 Michelins with only about 1000 miles on them. I haven't been real hard on them and neither was the previous owner that I bought it from. I've got a speedo-tuner on order so the error wont be a problem. I'm hoping that will put my mind at ease and "fix" things and that it may just be a math error. I'm fairly new to the street bike world so I was curious if there was another factor I'm overlooking or havent already read on the forum.

And no, I have a dumb phone, no GPS... the woes of being a poor college student

[EenyBear]

From one enthusiast to another...

The normal culprit for speedo variance (from past observations) is some sort of change to tire/wheel total diameter.

If the bike is new to you, check that first. it may also be that the speedo needs to be calibrated (perhaps for the first time).

As for mileage... nobody ever gets the manufacturer's stated mileage. It can be higher or lower depending on many... many... many... variables ranging from tire inflation to the RPM you have selected for a shift point to road surface to ... well, if it's important to find an answer along this line, the lads here can add to the list. I bet we can easily get over 20 reasons for mileage variation without trying too hard. Some you can manage and some you live with.

Here's an easy one. When the bike is stationary and idling, you are getting 0 (zero) mpg. Therefore the more you idle (city riding) the lower your mileage on average. Simple - yes - but often overlooked, surprising as that may seem.

Two identically tuned and equipped bikes can get different mileage based on inherent subtle mechanical differences as well as something as mundane as rider weight. Not to worry. Get the speedo calibrated (I must say I don't know much about this process...) to soothe your mind. Then concentrate on smooth shifting, proper tire inflation, clean lubrication fluids blah blah blah. If the engine is running smoothly and you are having fun don't worry about 33 vs 35 vs 28 mpg.

Best of luck with your bike. I wish you many hours and many miles of safe, enjoyable riding.

$0.02

PS:I say all this because we have all thought about mileage at one time or another and many still do.
PPS: I have learned that there's a wide gap between riding for best mileage and riding for best fun.

[Nitro]

30-35 miles/gallon is about right on a well tuned bike.

[EenyBear]

Originally Posted by RBMann

At what speed are you 7.5MPH off?

That, Sir, is an insightful question.

[twodear]

The one thing not specifically mentioned is state of tune. MakarskiJA, your writing gives me the impression that you've already done the basic checks but I'll say it anyway...spark plug condition and heat range can make a big difference as can the timing of the ignition sensor on the front of the motor. So too can the O2 sensor mounted in the Cat.

[ckcarr]

Originally Posted by MakarskiJA

No where near the 48 or so that the factory says it should get.

Where did this number come from specifically. Because I've never seen one that high. I could get 45 mpg in Utah 6th gear flat road cruising at 4,000 feet elv. But most are in the 30-35 mpg range or worse as Nitro says...

[MakarskiJA]

ckcarr- Every spec sheet I've read on the R1100S has said 48 on average. Perhaps I just have a case of noob. Even the stock bike manual calls out 55mpg at a constant 55mph.

TwoDear- I will have to check the plugs and O2 sensor like you have suggested. I havent gotten around to doing that yet. Oil was changed not long ago, previous owner kept a pretty well maintained maintenance log for the bike. Even noted the day the seat was changed from stock to corbin to a seargent. Honestly I've been debating just going ahead and changing all the fluids in the bike so that I KNOW whats in there. I did drain some oil one day cause I topped it off a little too much and it was black as tar but flowed well. According to logs the oil was changed about the same time the tires were a little over 1000 miles ago. I checked the tire pressure and its about 32Front/35Rear.

Come to think of it the temp may be having a big effect on it. its around 40degF most days right now and even my 2008 Carolla has been getting like 6-7mpg lower than usual. I can generally pull 38-40 mpg out of that car and ive gotten 31 on the last 2-3 fillups.

Overall I've been having too much fun on the bike to ever ditch it because of a silly thing like gas mileage!

[EenyBear]

Originally Posted by MakarskiJA

EenyBear- I will have to check the plugs and O2 sensor like you have suggested.

Actually, that specific rec was from TwoDear.
The spooky thing is... I was thinking of the lambda sensors and plugs as I wrote my bit but I was over the "too freakin' many words" limit.

I replaced all four sensors in my 2007 Z4M coupe shortly after purchase in 2011 and the difference in performance was night and day.

This stuff can drive you crazy. If there is no surging or lurching and everything else seems smooth... do the basic maintenance and get out and ride.

[MakarskiJA]

Woops, there I go thinking again, I read enough of these posts and they all blend together.

Lambda sensors? Enlighten me

Sorry if I come across stupid sometimes, I'm mechanically inclined, just havent done a lot of engine work so far in life. Ya know the whole age and time for experience thing.

Ive gotten shifting pretty smooth on the bike, took a day to figure that out, but what rpm's seem to be optimum? I read once on here something in the neighborhood of 4-5k? I know when I'm getting near 5k cause the vibrations get noticeably more prominent

[JGard]

I dunno, I can honestly say I've never eclipsed 40mpg on my bike no matter what type of riding I do. Of course, when on the highway, I'm usually not going any slower than 70, so that doesn't help mileage any.

[markjenn]

Originally Posted by MakarskiJA

ckcarr- Every spec sheet I've read on the R1100S has said 48 on average. Perhaps I just have a case of noob. Even the stock bike manual calls out 55mpg at a constant 55mph.

Not sure what "spec sheets" you're talking about that all give the same suspiciously high number. I've probably read every review of the R1100S published and mileage is typically reported to be in the range of 35-42 or so which mirrors about what I get on my bike typically. This is assuming US gallons - you have to watch out for unit problems, especially UK publications with imperial gallons.

A bike that gets 35 mpg in a normal mix of day-to-day riding may very well get 55 mpg at a steady, constant, no-wind, level, no-ethanol, 55 mph. Nothing there is inconsistent. I would try and resolve your speedo/odometer calibration issues - there is no point in worrying about a gas mileage number if you're not sure it is correct.

If your bike has been modified with respect to fueling, all bets are off. Most aftermarket systems try and boost power by running richer.

If you're truly getting 35 mpg more/less overall for a stock bike and your usage includes some urban and/or high speed running, it's probably within the range of normal, maybe slightly low. It should do better if you're dogging it on the highway. I always got 40+ if I was just cruising, but I could also get it in the low-30's pretty easily if I was running 80+ speeds and/or pushing at all.

- Mark

[ckcarr]

I would like to see (again "specific") spec sheets. I have a pretty complete library of r1100s literature from the beginning of the bike.

This is an exercise in chasing ghosts. I'd not suggest starting a futile parts replacement regime.

Here's a math test...

Center column of this page from the October 1998 Motorcyclist magazine, in the middle... "We flogged the R1100S's 4.75 gallon tank down to reserve after 101 miles. Your mileage may vary." Reserve is one gallon per the brochure. Math is 101 miles / 3.75 gallons = 26.93 miles per gallon...

[MakarskiJA]

Check Page 73 of the BMW Service and Technical Booklet in the engine section that comes with the bike. Thats just one such place ive found those numbers. It says 55mpg @ 56mph, 45mpg @ 75mph. My thinking may be flawed that it should be getting better than I am, granted the conditions haven't been optimum.

I believe you as far as what the actual mileage is, doesn't surprise me that its different. I just didn't know how "normal" it was to be like that

[bradzdotcom]

i pour fuel in my bike.
then i ride it.
when it wants more,
i pour more fuel in my bike.


sometimes it gets 31.5235 mpg.
sometimes it gets 49.3234 mpg.
good for it. i don't particularly care.
i just ride it.

if mpg makes you say omg, for the love of god don't go anywhere near craig vetter's fuel challenge events and see what those guys are getting.
don't do it.
it will hurt you.
the pump fuel class winner at last year's vegas to barstow event averaged 125.92 mpg.
his fuel cost for the 225 mile trip was $7.51.

and that's why i just pour fuel in my bike.
then i ride it.

[MakarskiJA]

Well if I wanted super high fuel mileage like that I would have bought something like my stepdad's 650 Kawasaki. I wanted a nice reliable used sport touring bike and that's what I got. I was hoping for mileage better than my car but hey, I'm having fun with it so ill start ignoring it a bit and just feed it.

[twodear]

Lambda = O2 sensor.

But in real life, you're on the verge of thinking too much; that is not conducive to fun riding.

Unless raw fuel is blowing out the exhaust or you suspect holes are being burnt in the pistons, I echo what Bradz so succinctly said.