Why am I getting only 25mpg?

A (dead) narrow band 02 sensor by itself can't drop mileage to 25 no matter how bad it is. That will be a waste of effort.
Front or rear brake is dragging which ought to be obvious and is a trivial check.
Put the end up, spin the wheel apply the relevant brake hard and let of- after that wheel should still turn easily by hand. If it does, its not the problem.
If it doesn't, you've found it and the right end of the bike

I suspect you drink too much vino- this is a 2 minute job at most to defintively figure out if its brakes and which end and you've been blithering about it for two weeks now...Time to do something useful..

racer7 said:

A (dead) narrow band 02 sensor by itself can't drop mileage to 25 no matter how bad it is. That will be a waste of effort.
Front or rear brake is dragging which ought to be obvious and is a trivial check.
Put the end up, spin the wheel apply the relevant brake hard and let of- after that wheel should still turn easily by hand. If it does, its not the problem.
If it doesn't, you've found it and the right end of the bike

I suspect you drink too much vino- this is a 2 minute job at most to defintively figure out if its brakes and which end and you've been blithering about it for two weeks now...Time to do something useful..

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Wow...my first obnoxious response! You obviously have not be reading all my "blithering".

racer7 said:

I suspect you drink too much vino- this is a 2 minute job at most to defintively figure out if its brakes and which end and you've been blithering about it for two weeks now...Time to do something useful..

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2 minutes huh - same as it would have taken to edit your post before being rude.

I knew this post would be fun........

In my climate, the single greatest affect on fuel economy remains the weather. It can be that simple. Argue that statement. Today, nice easy 45 mpg's and the week before, low 30's. It was a swing of about 15 degrees Celsius and big change in humidity.

You can go ahead and make this as complicated as you want and blame the entire planet but simple things remain pretty clear to me. The basics haven't been gone through, repeatedly and the pre-trips weren't done after the completion of every work scope. I check my bike every day and found the bolts on my center stand loose last week. I know I put them together. Either me bad or "s--t happens".

I'm not complaining about low 30's on a +33C day at just under 150 kmh two up. For giggles, do some math and come up with some of the statements made here.

Bike runs good, it's good, enjoy and ride like you stole it. Bike runs bad, stop, get your flashlight, and give it a good look. Pay attention to every detail including if the valve caps are on the tires.

I have a flashlight tucked in with my first aid stuff and flat tire crap...............next we will do the math on when you get a nail in a tire.

Dieselyoda said:

...

I'm not complaining about low 30's on a +33C day at just under 150 kmh two up. For giggles, do some math and come up with some of the statements made here.

...

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Moving this thread from insulting to boring ...

Did that once while working on the "hit" I might take for running a richer mixture ... R1150RT Fuel Consumption Calculations

It takes about 9 HP to go 55 mph and 44 HP to go 95 mph. That's five times more power to go 1.7 times as fast. So you're going almost twice as many miles in an hour but using 5 times as much HP to do it, but at 45 HP your engine breathes better than at 5 HP so does a better job converting fuel to power. Net net is would be easy to get 1/2 the MPG at 95 as at 55.

Here are some back of the envelope numbers on how mileage can be affected by rpm. Not precise but relatively correct.

Here are three different examples of fuel mileage at 60 mph.
60 mph (estimated 2500 RPM): 58 mpg, 6.2 lbs/hour, 10.4 HP (11% of max), BFSC 0.6=15% lower fuel usage
60 mph (estimated 3000): 50 mpg, 7.3 lbs/hour, 10.4 HP (11% of max), BFSC 0.7
60 mph (estimated 4600): 35 mpg, 10.4 lbs/hour, 10.4 HP (11% of max), BFSC 1.0=42% higher fuel usage

wineguyd,

Just in case this got missed: On a 400 mile freeway trip bringing my new-to-me 1100GS home the bike averaged 41mpg with four of the eight front pistons stuck on hard - so hard that at the end of the ride I couldn't move the bike without the engine. No doubt your brakes needed attention, as they almost all do on these bikes this old, however I doubt seriously if they are the cause of 25mpg. Something else is wrong with your bike.

It's not riding style, gearing, phase of the moon, or anything else - there is something that's wrong and it very likely isn't the brakes alone.

All the best in your attempt to solve the problem. It can be solved, just keep at it.

Bob Johnson

bj333051 said:

No doubt your brakes needed attention, as they almost all do on these bikes this old, however I doubt seriously if they are the cause of 25mpg.

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There is a reason why I change the brake fluid on an annual basis, well at least I used to, but have moved that to every two years.

Same on the car and it sees far harsher conditions, yet 15 years later, the pistons move freely.

So far, no mention to check the codes in the ECM.........................

wineguyd said:

Wow...my first obnoxious response! You obviously have not be reading all my "blithering".

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Perhaps a certain racer should kick back this afternoon with a little vino and chill a bit.

I think the (current) effort on the brakes will not be regretted no matter what else is wrong.
However racer7 is correct that a bad O2 sensor alone should not drop MPG that much - the Motronic will sense the thing isn't working and will leave closed loop. I would still expect high 30's to low 40's in this scenario.

Again, math is involved to prove it, but air resistance increases as to the square of speed - thumb-sighting and arm-waving: above 70mph air resistance will quickly gobble up the engine's power; and anything you can do to streamline the vehicle will help efficiency and performance in general at those speeds. If you're going slower than that there isn't much you can do that makes a huge difference.

In my case, the frontal area of the RT is like a freight train, raising / lowering, bags on / off, makes no difference that I can measure.

I was just real tempted to take some vacation time, run up to NY, and quickly put together a wine-for-work proposition...

Dieselyoda said:

So far, no mention to check the codes in the ECM.........................

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7734 - brakes fell off.


my last flat - which I found in my garage - ended the life of my PR2 rear prematurely.
This was before I got my dumbass-proof mushroom shooter so I tried the gummy worm patches...
I don't know what I ran over but I had 5 separate puncture holes and what looked like woven wire shards or something rattling around inside the tire.
I gave up fixing it, but apparently I had run a couple of hours with those holes the day before.

Update

scott.lambert said:

Perhaps a certain racer should kick back this afternoon with a little vino and chill a bit. I think the (current) effort on the brakes will not be regretted no matter what else is wrong. However racer7 is correct that a bad O2 sensor alone should not drop MPG that much - the Motronic will sense the thing isn't working and will leave closed loop. I would still expect high 30's to low 40's in this scenario.

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I just picked up the bike this morning, the new mechanic found the calipers were in perfect working order and suggested not pulling them apart for a rebuild(I'm holding onto the rebuild kits for the future) He did replace the pads which had life left on them but why not since the calipers were off.

Appears rxcrider nailed it...the grub screw on the newly installed brake master cylinder was overtightened by the wrench at Bergen BMW when they replaced it..backing it off half a turn relieved the pinching brakes. Since the bike was near empty when I gave it to the shop, I also got a jump on checking the mileage but starting a fresh tank today. I'll report on the mileage in about a week.

In the mean time I'm leaning towards replacing the O2 sensor as a precaution, I was going to go with the Bosch universal fit...any pros or cons?

Lastly, my Conti Road Attacks suggest max 42psi, BMW had then at 36psi, any suggestions as to ideal summer inflation for a 200lb guy doing non sport riding?

wineguyd said:

In the mean time I'm leaning towards replacing the O2 sensor as a precaution, I was going to go with the Bosch universal fit...any pros or cons?

Lastly, my Conti Road Attacks suggest max 42psi, BMW had then at 36psi, any suggestions as to ideal summer inflation for a 200lb guy doing non sport riding?

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The O2 sensor runs close to $200 and hardly ever fails - I'd check your mileage again before committing.

At the risk of starting a tire thread...
The tire manufacturer will always recommend running the tire at maximum pressure, whatever that is.
Feel free to do that - it may decrease fuel consumption at lower speeds.
The manufacturer feels that having as little flex and heat buildup as possible will give you the highest (statistical) safety factor.
(Translate this to: you can't sue them for a blowout if you weren't running the thing aired up hard.)
However I find that running the tire that hard does not allow it to flex and makes it wear funny - flat topping.
Any money you save on fuel you're going to spend buying tires (Conti Road Attacks at that!) early with only a strip down the middle worn.
Also increases the tendency to fall into corners - a little more flex will make it feel more stable, and may improve traction by laying down more rubber.

In the owner's manual, and also on a sticker under the seat (on the rear "fender") there should be BMW's recommendation for various loadings.
I don't know if you have the weird 18" rear wheel on that model?
Anyway one up, lightly loaded, go with the minimum pressure that BMW recommends.
You can even run a pound or two softer than that depending on the tire and how it feels to you. I would not recommend that at this time.
The reason I say that is that, like me, it sounds like you ride a bit on the pokey side - that may change in the future, but right now I would say that you're not really going to "warm up the tires" - and the Road Attacks are a really stable compound that doesn't change that much anyway as you ride. They start out pretty sticky but they don't improve much.
36 sounds about right. On the RT the min is 36 front (120/70 17), 41 rear (160/60 18).

scott.lambert said:

The O2 sensor runs close to $200 and hardly ever fails - I'd check your mileage again before committing.

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Thanks for all that valuable insight Scott, I'll play with the pressure you suggested.

Beemerboneyard has the Bosch universal O2 sensor for $75, if my mileage doesn't improve noticeably you don't think replacing the sensor is worth while?

Why are you thinking O2 sensor? You can test it with an old style analog volt/ohm meter.

I wouldn't guess oxygen sensor at this point. I'd make that decision after you check mileage with the brakes repaired.

wineguyd said:

Thanks for all that valuable insight Scott, I'll play with the pressure you suggested.

Beemerboneyard has the Bosch universal O2 sensor for $75, if my mileage doesn't improve noticeably you don't think replacing the sensor is worth while?

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My number came from one of those dealer online fiche searches - at $75 we're back into reasonable R&R range for me.

I swapped out my coil for $60 because it was cheaper than the $300 Hall Effect Sensor plate - even though the coil has an indestructible appearance.
I was right, it was the HES, and now I have a perfectly good spare coil. So it's no big deal.

As Dieselyoda mentioned the motronic error code can be read out and it should tell you or your new mechanic if there is a faulty sensor.
There's the O2 sensor and temperature sensors for air and oil - no their affect would not be cumulative, so this would not explain 25 MPG either, but a failure or disconnect of any one of the three would keep you out of closed loop.
I would definitely do an R&R on a sensor that showed up in the error codes (except for the HES, which always show "bad" if the motor is not turning).
If the sensor does not get reported then you're back on your own again.
I would assume that it is possible to have a sensor that appears to "be there" to the Motronic, but is actually "wrong" so that it is "lying".

Let me know if you need info on how to read and interpret the codes - I don't have it my head but I can find it.

Roger 04 RT said:

Why are you thinking O2 sensor? You can test it with an old style analog volt/ohm meter.

I wouldn't guess oxygen sensor at this point. I'd make that decision after you check mileage with the brakes repaired.

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Ya - wineguyd, do you have a volt/ohm meter? You can use that to read motronic codes as well.

wineguyd said:

Beemerboneyard has the Bosch universal O2 sensor for $75, if my mileage doesn't improve noticeably you don't think replacing the sensor is worth while?

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At your mileage, it would seem unlikely that you have a bad sensor, but then components can fail at any mileage. The sensor in my car has 150K miles.

Already mentioned, high fuel consumption is due to drag (aerodynamic or friction) or excess fuel. Have I missed anything?

You can test your O2 sensor even if you do not have a scope. There are how-to tests on YouTube. These aren't a full test in that without a scope you cannot tell if the sensor is lazy or not. But it is a start.

Roger 04 RT said:

Why are you thinking O2 sensor? You can test it with an old style analog volt/ohm meter

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Because half a dozen respondents to my thread said to check the sensor, I'm not nearly as technically knowledgeable about the bike as all of you guys so I'm trying to listen to all.

scott.lambert said:

Let me know if you need info on how to read and interpret the codes - I don't have it my head but I can find it.

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How does one read the codes? It there some device I need?

wineguyd said:

Because half a dozen respondents to my thread said to check the sensor, I'm not nearly as technically knowledgeable about the bike as all of you guys so I'm trying to listen to all.

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Okay, understood. For now, I recommend setting the O2 question aside and see what mileage you get with the brakes not adding any drag.

Someone will help you find the procedure to read out the error codes but my bet is you won't find any. Anton Largiader has a good site with lots of stuff, have a look at this: http://www.largiader.com/articles/motronic.html

RB