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Thread: Why am I getting only 25mpg?

  1. #181
    Alps Adventurer GlobalRider's Avatar
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    Quote Originally Posted by wineguyd View Post
    ...the service agent blew it off telling me that they know better than the amateurs on the forums.
    Well you can tell that inbred that the reason why my everyday cars, my everyday motorcycles, my Porsche and my BMWs have run flawlessly is because I keep them out of shops...since I was 13! And if that does not sit well with some mechanics, well its the name your service industry got somehow.

    But yes, there are a lot of legends in their own mind on forums as well.

  2. #182
    WineGuyD wineguyd's Avatar
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    Quote Originally Posted by GlobalRider View Post
    Well you can tell that inbred that the reason why my everyday cars, my everyday motorcycles, my Porsche and my BMWs have run flawlessly is because I keep them out of shops...since I was 13! And if that does not sit well with some mechanics, well its the name your service industry got somehow.
    So true!
    Purveyor of fine wines & spirits
    Rides a 1996 R1100R

  3. #183
    Registered User roger 04 rt's Avatar
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    Quote Originally Posted by wineguyd View Post
    Thank you all for valuable input over the summer while I sorted out the problems with my bike! As I posted earlier, the problem was created when Bergen BMW's wrench replaced my front brake master cylinder, he over tightened the grub screw on the brake lever thus keeping the calipers from fully releasing. Ironically rxcrider nailed it a while back and on my third visit to Bergen BMW for this issue I even brought a print out of his diagnosis along with the diagram he supplied detailing the grub screw adjustment...the service agent blew it off telling me that they know better than the amateurs on the forums. Since having a local wrench adjust the grub screw and check the calipers I've been through 6 full tanks of gas so far and covering mixed styles of riding and have been getting almost exactly 40mpg after each refill....much better than before but I really want to explore what's holding back the bike from getting closer to 50mpg which many riders get. I'm finally starting to love the bike and the boxer(being a lifetime Jap 4C rider) BUT I HATE THE TURN SIGNAL HORN SETUP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!! I'm going to start a new thread on that one and if any of you R1100 owners have changed the controls then please let me know what you did.
    Glad to hear that you got to the root cause of the poor mileage. At 40 MPG it sounds like you're Around the norm.

    I looked at the reasons our bikes get low-mid 40s in mixed driving: a lot of frontal-area means you're pushing a lot of air aside, high pumping losses at light throttle and a coefficient of drag twice that of a sedan means the gas mileage drops above 60-65 mph. RBRacing.com has a good HP calculator: use 0.77 for drag, 8 sq-ft for frontal area and you're in the ballpark.

  4. #184
    WineGuyD wineguyd's Avatar
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    [QUOTE=a lot of frontal-area means you're pushing a lot of air aside, high pumping losses at light throttle and a coefficient of drag twice that of a sedan means the gas mileage drops above 60-65 mph. RBRacing.com has a good HP calculator: use 0.77 for drag, 8 sq-ft for frontal area and you're in the ballpark.[/QUOTE]

    Does an R1100R have more drag than any other naked bike?
    Purveyor of fine wines & spirits
    Rides a 1996 R1100R

  5. #185
    Registered User roger 04 rt's Avatar
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    Motorcycles fall between 0.6 and 1.0. The less streamlining the higher the drag.

    The two bikes I have estimates for, 1150RT (0.7) and GS (0.77), came from know horsepower, top speeds which I polled for and frontal area which I measured. Using the rb racing calculator, arrived at Cd (drag).

    Here is my measurement: R1150RT Mileage,

    And that of another: Calculations of drag.

    Roughly speaking your best mileage occurs in your highest gear, at a speed where the throttle is opened enough to reduce the pumping losses of the engine, but not at such a high speed the drag is killing your mileage. On my bike that seems to be 55-65 mph.

    A note, at 75 mph+, the drag cuts your mileage significantly and below 40 mph pumping losses do the same. Pumping losses meaning the work the engine has to do to create intake manifold vacuum.

    So enjoy your low 40s, sounds about right to me.

  6. #186
    WineGuyD wineguyd's Avatar
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    [QUOTE=

    Roughly speaking your best mileage occurs in your highest gear, at a speed where the throttle is opened enough to reduce the pumping losses of the engine, but not at such a high speed the drag is killing your mileage. On my bike that seems to be 55-65 mph.

    A note, at 75 mph+, the drag cuts your mileage significantly[/QUOTE]

    My bike came with a stock windscreen that I took off immediately because I wanted the total naked bike look(plus it was noisy) do you think it would make much of an improvement if I put it back on?
    Purveyor of fine wines & spirits
    Rides a 1996 R1100R

  7. #187
    Registered User RINTY's Avatar
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    Glad they got it fixed, WG; I was getting concerned about your shop.
    Rinty

    "When you don't know where you're going, any road will get you there."

  8. #188
    Benchwrenching PGlaves's Avatar
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    So, if I understand correctly, an ill-set grub screw in the master cylinder caused the master cylinder piston not to return fully, so the brakes dragged causing a 30% loss in fuel economy. And nobody noticed that the disk was getting hot? And nobody noticed a lot of brake dust on the wheel? Or rapidly worn pads?

    Amazing!
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://www.bigbend.net/users/glaves

  9. #189
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    Yup, but we know a lot less here than "trained" technicians.

    Early on when I got my 94 RS, back in Oct 94, I read an article by Bob Lentini (I think), that had something to do with adjusting the front brake lever to reduce the "mushy feel" of the brakes. But the article also warned to be careful so as not to cause the brakes to drag.

  10. #190
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    To the questions, I'm sure directed at Roger04rt, does the R have a higher frontal area than any other naked bike, and would putting the windscreen back on help.

    No.
    Impossible to know for certain, probably impossible to measure without instrumentation in a wind tunnel.
    But no.

    Generally a naked bike is "just bad" aerodynamically, and has a deceptive amount of "swept area" because the air goes in and around all the components and the pilot, sweeping across it all, adding drag. Even though an RT, looking at it from the front, appears to occupy more space, exhibiting more "frontal area" than the naked bike, the actual "swept area" is smaller as the air is directed around the lumpy parts more or less.

    I doubt the windscreen has a net effect on the R; it will direct the wind around you, the least aerodynamic part, however it also puts up a big slab of plastic to push through the air. Put it on for your own comfort if you want it.

    As far as fuel consumption or any other measure of efficiency you care to use, even if you had a fairing, not just a windscreen, I wouldn't expect a big difference until the crossover point somewhere around 70mph.

  11. #191
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    "Generally a naked bike is "just bad" aerodynamically, and has a deceptive amount of "swept area" because the air goes in and around all the components and the pilot, sweeping across it all, adding drag."
    If you are built like Jack Riepe, the drag caused by the swept area of the bike is miniscule compared to the inefficient aerodynamic shape of the rider.

  12. #192
    WineGuyD wineguyd's Avatar
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    Quote Originally Posted by RINTY View Post
    Glad they got it fixed, WG; I was getting concerned about your shop.
    It wasn't Bergen BMW that finally figured out the problem and fixed it...they just caused the problems...took a wrench at my local Vespa dealership to fix it. Bergen BMW is a disaster! The reality is that they are first and foremost a Harley dealership, they somehow got the BMW brand and they treat it like the unwanted stepchild.
    Purveyor of fine wines & spirits
    Rides a 1996 R1100R

  13. #193
    WineGuyD wineguyd's Avatar
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    Quote Originally Posted by PGlaves View Post
    So, if I understand correctly, an ill-set grub screw in the master cylinder caused the master cylinder piston not to return fully, so the brakes dragged causing a 30% loss in fuel economy. And nobody noticed that the disk was getting hot? And nobody noticed a lot of brake dust on the wheel? Or rapidly worn pads?

    Amazing!
    Yup, Bergen BMW's service agent got offended when I told him that a member of this forum suggested the grub screw as the culprit. They had me replace the brake lines and when that had no effect they suggested a full front caliper rebuild. At that point I took the bike away from them(and thats when the front right caliper fell off while I was on the highway riding home from them), my mechanic that serviced my Vespa adjusted the grub screw and inspected the calipers and told me they were in perfect working order.
    Purveyor of fine wines & spirits
    Rides a 1996 R1100R

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