Lugging at low rpm vs BSFC
 

Good question. It is a term that we all use but can mean many things. On a single cylinder engine the most obvious sign is when the bike is at such a low rpm that it is chugging and bucking. This is the only time when it is extreme enough from a mechanical standpoint that it can do any damage from shaking and loading the parts. Even at these low rpms, you will notice that there is still some useable output from the engine at very slight openings but it quickly changes to bucking if you try to add more throttle. At which point you have to switch to an easier gear to accelerate.
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To a hypermiler, lugging can also mean running too much throttle at too low of an rpm even when you don't feel any chugging. You are using a less efficient part of the engine's power map. Not really gaining any more power with increasing throttle angles. Just wasting gas because you would be more efficient by changing gears to a slightly higher rpm. Engine vacuum can give a rough idea of load vs throttle opening. At low rpm it may only take 20% throttle to go all the way down to 0 inches of vacuum. At the power peak, it might take 90% throttle.
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I have just put a vacuum gauge on my CBR250R but it isn't working right for some reason as it never goes higher than 7 inches and goes right to 0 with any throttle at all. I must have it on a restricted vacuum port that is connected down stream to a slight consumer. A scan gauge such as the MPGuino would be better to find the most efficient throttle and rpm.
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Here is a BSFC map of a four cylinder car engine for example. They read like a topo map. The most efficient range is in the circular peak. Which will be 90-95% load (load not throttle) at an rpm just below the first torque peak.
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There are also different fuel maps involved with fuel injected motorcycles that may be more efficient when using lesser load ranges of 50% because the designers have chosen to help prevent burning the piston at high rpm and load by richening the mixture. I don't know how accurate it is, or have any charts of lesser throttle openings, but I have seen a 100% throttle chart of my bike from a dyno probe that shows it at 16:1 from idle to 4,000 rpm where it changes to 14.7 through the mid range and then all the way to 12:1 at high rpm.
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A real BSFC map of my bike would be nice but there is no dynos in my area. So I guess at least putting a scan gauge on would be a big help.

So you say that BSFC maps can be created from any existing engine? I know the concept and interpretation of those maps, but I've never seen any for my bike (or any bike, to be honest).

It could be put together with multiple runs on a dyno by holding a steady engine vacuum load for each run and then do it again at a higher load and so on from just off closed throttle to 0 inches of vacuum.

I guess this would give you torque curves only unless you also had an injection duration scanner hooked up as well which could be done with the factory scan tool or an MPGuino. The torque curves vs load vs rpm would be almost as helpful as seeing the actual fuel efficiency maps in guiding your riding for best economy.

Well, I have looked for Dyno charts for the F650CS, I finally found one hopefully a bit useful for the GS (same engine, but I don't know which software version was inherited by the single spark CS). It doesn't have multiple runs at different vacuum, but at least go low enough to be relevant for me (many charts begin at 3000+ rpm):

http://i259.photobucket.com/albums/h...650gs_dyno.gif

So it seems the engine still has torque down there, and it works indeed - but, should Teresa pull at 2-2.5k when given some gas, she still makes some pinging noise, so I generally don't go that low (except for a few mistakes). And in 5th she doesn't feel that lively under 3k. To tell the truth, this chart did not help me understand what should I call lugging.

One thing is apparent, torque begins to diminish over 5.5k - but 5.5k is merely there for emergency operation :D

Your BMW has a very flat torque curve which is made for fuel economy. It is hard to say what the best range is. It is all good. 3,000 to 4,000 rpm?

Dunno. Around 3000 feels the smoothest, so it's good for cruising (interesting how this smooth range goes down with lower gears, it's more like 2500-3000 in 4th, and ~2000-2500 in 1st).

When I pulse, I usually go up from this smooth range. 2800->3600-4000 in 5th is a typical thing I do (which means 90-100km/h | 56-64mph pulses) - though if I wanted to break my record and didn't care for running semi-normally I'd probably go down a gear or two to get lower aero drag, and P&G there.

Air drag surely takes over at these speeds: I've experienced that my winter tanks got a bit better when I started to ride in so low temps I couldn't bear the wind anymore and I went down to 4th and slowed to 50-60km/h (31-37mph).

It takes torque to move a vehicle.
This torque fights the weight of the vehicle, the rolling resistance and the drag.

In lower gears, there is a fair multiplicator on the engine torque which is the reduction given by the gearbox.
Usually the reduction of the gearbox is 1 or above in top gear and the bike is geared to be able to hit its rev limiter in top gear or just about.

So basically, the engine is tuned to make full use of those several gears : very low rpm are not taken into account in the flywheel mass, bore to stroke ratio, alternator output, oil pump capacity (we are talking reliability here).

Why ?

Because of the weight !

You could have an engine wich would turn very low rpm hence be super efficient and yet not so useful on a vehicle like a bike.
Truck engine turn low rpm and are quite fuel efficient at the task that is theirs.
But the price they demand in return is weight, they are super heavy.
Their power to weight ratio is lame whereas their capacity to load is excellent (load being what they can carry).

Also, a small rev-range would mean massive gear ratio required (more weight) and stratospherical self braking ability.

My point is why mis-use an engine if you bought to big a one to start with ?

(250 all the way)

The original question was that what counts as lugging (or mis-use, if you like it better). Your note about the engine weight sounds a good food for thought, but I still don't know where is the range of lugging :confused: I still don't know anything better than my empirical approach: when it sounds strange, it's bad :D But, I must admit, I don't have an exact definition for 'strange', not even with one particular bike :D And I still don't know how bad is bad.

There are members at f650.com who even advise not to use this single under 4000 rpm - and I'm very sure they're wrong. If they were right, Teresa wouldn't purr like a healthy kitten after more than a hundred thousand kilometers.

On a side note, they also fear coasting, especially in a turn. They cross themselves when they hear about using the kill switch that's right at their right hand. They fear bikes that aren't faster than anything around them. They seem as superstitious as a sailor to me :D

And please don't blame me for choosing this 650. My original intent was to get a 250, but I just couldn't get a nice, quite new one (it was scary how absent (almost) new 250s were in Hungary in 2008!). My 'plan B' was a CBR125 back then, and if there's such thing as a too small motorcycle, that could have been one in hindsight. Not that I'm in love with speed and acceleration (I simply don't care about them), but because of the tasks Teresa had to do in the 3.5 years since I bought her. Sometimes she was literally used as a freight bike :D What is a small mid-size bike for others (yes, this is the common opinion of a 50hp 650 among many bikers here) may be a heavy duty workhorse for a hypermiler. So I went with "plan C" in the end.

This choice was preceded by a lot of research on my behalf. I wanted to make sure I buy a (n only) vehicle with good fuel economy, and I found that this 650 is basically a 250 in this respect. My later experience that her appetite is very much the same as of our (carbed) Hyosung GV250.

Of course there are better 250s, just have a look at sendler's new CBR (now that he's into the tricks I utilize too, he's steadily well in the 90s with it, even though summer hasn't arrived yet!) - but this is one of the new models that did not exist back then. If I chose a bike now, that would be a worthy candidate, I could even buy it with ABS, which is absolutely worth its price. I'm also very curious about the NC700, which is larger again, but fits my "heavy duty" line (it's also regretfully heavier than Teresa, though). And the fuel injected F650s (now they're called G650s) are still in the picture for the same reason. I've heard about a guy who won an economy run with a new G650GS. With a pillow to help him tuck all the way, but he did 103mpg with his bike, a bit better than my personal best tank (98.9mpgUS).

p.s. I'd still like to have a gray/orange CBR125 (this new design is simply awesome), but we need the money for more important things. If we'll have enough extra to pay for it in cash before the end of the oil age, we'll probably get one...

I read a lot of superstition too. Some old school bikers will argue to the end about how they think you are totally out of control of the bike and are about to crash if you ever coast with the clutch in. Silly! They insist that you MUST engine brake down through every gear every time you come up to a stop light. Rrr, Rrr, Rrr, Rrrrrr! Look at me! I'm so cool!
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Your BMW may be so torquey that the term lugging may not even apply. You could probably just dump the clutch when you take off without even stalling. My CBR250R bucks violently if I try to give it any throttle below 2,500 and high revving bikes like the Ninja250 have no power whatsoever below 4,000. My Ninja doesn't buck as much being a twin but I know that it is in a poor efficiency range when trying to accelerate for a pulse at that rpm. This lack of productivity is also what I call lugging.