Motorcycles and fuel economy: the good, the bad and the ugly

I've been looking at a few posts on reeky and ukrm about fuel economy
recently. I was wondering whether one can point to bikes which are
particularly fuel-efficient.

OK, OK, bike engines are astonishingly efficient in themselves, and I
know from experience that if one rides a modern superbike at gentle
(say 80mph max) speeds, you can eke out an astonishing mpg figure.
Quite a few Kawasakis seem to manage this trick. In fact, even the old
air-cooled ones did it, too.

And the Harley (and BMW airhead) fraternity have often trumpeted
amazing fuel consumption figures, omitting to acknowledge that at
60mph or below, anything will sip fuel. At Chimay, I encountered a
Brit with the same model of Triumph Trophy 1200 as mine, who claimed
50mpg-plus. As the Trophy Twelve was one of the most fuel-inefficient
bikes of all time (rivalled my Kawasaki H1 triple sometimes), I
concluded he never exceeded 55mph. So it's not just a Harley/Beemer
phenomenon.

And yes, low-powered singles are easy on fuel, but then they don't go
very fast, do they?

It's easy to identify the thirsty bikes - most two-strokes, including
any Kawasaki triple, Trophy Twelves, Honda CBR1000s seemed to be a bit
iffy, Bandit 12s, later model detoxed BMW airheads, Suzuki TL1000S,
Honda's Firestorm and Varadero.... but it's not so easy to pinpoint
the opposite. BMW's F800 seems to be amazingly frugal, and my own
K1100LT is surprisingly good. I remember the fuel-injected Moto Guzzi
Calfironia as being a fuel-sipper, too.

Any other candidates? And what sort of car engine tech might help?
Diesels, obviously. Anything else? Engines not tuned to perform at
their best at 10,000rpm and above?

 

http://www.spritmonitor.de/en/overview/6-BMW/1043-F_800.html?powerunit=2
4.53 l/100km averaged by 53 users. That's only 0.4 more than my 250 scooter.

http://www.spritmonitor.de/en/overview/6-BMW/807-K_1100.html?powerunit=2
5.35 l/100km by 30 assorted flavours of K1100. Certainly good.

My personal best was 3.3l/100km cruising at legal speeds on a GPZ500S

 

I got > 50mpg from the Busa when I took it to Derbyshire a while back

 

He did say "at 60mph or below, anything will sip fuel"

 

The Tenere is pretty good with a mixture of 80mph motorway cruising
and 'as fast as I can go' commuting between home and Luton (20 miles)
seeing it return about 60mpg. It did return somewhere approaching
70mpg when I was riding it at a nice steady 65mph but that was so
fucking boring I've never done it since.

The 250 mile tank range is probably the best reason to use it for the
commute rather than using the 10R and riding like an even bigger twat.

 

You should be ashamed of yourself.

 

My old Sprint ST 955i was pretty frugal even when abused (I mean an easy
190+ miles unless really hammered up the French autoroutes when it was
still good for 170+ miles). However as I dont know the tank capacity
that may not be helpful information...

 

That's a nifty site. Is there any way of getting it to display in
miles per (US or Imperial) gallon, or just it does do litres per 100km?

 

In communiqué

Ah. I was going to nominate Morini V twins (the old ones). 80 mpg easily
attained allegedly.

In the case of Morini, Heron Heads perhaps.
--
+-------------------------------------------------------------------+
| Pete Fisher at Home: |
| Voxan Roadster Yamaha WR250Z/Supermoto "Old Gimmer's Hillclimber" |
| Gilera GFR * 2 Moto Morini 2C/375 Morini 350 "Forgotten Error" |
+-------------------------------------------------------------------+

 

They were good, the old ones, weren't they? Or the 350s were - I think
the 500s lost a bit.

IO remember roadtests of the late 1970s crediting the MV Agusta 850
America with something like 55-60mpg....

 

My Quota used to reliably return about 55mpg until I had to drop the
compression ratio. Doesn't even make 50 now.

Lower revs always help simply by reducing mechanical friction. It also
reduces the proportion of the crank rotation where fuel is actually
burning: the engine runs closer to the theoretical isochoric
combustion of a true Otto cycle, but I'm not sure if that's a good
thing or not. I think I read somewhere that it can cause problems.

Engine tech: goood combustion chamber design; well mixed air & fuel;
enough but not too much turbulence in the combustion chamber;
stratified charge (GDI, for example); maybe VVT if you want
performance and economy; Turbos help Diesel economy at least. If
nothing else they *might* allow petrol engine combustion chambers to
be sized for optimum efficiency: too small and there's heat loss to
the walls; too big and you have slow combustion and (I think) other
problems; maybe increased risk of pre-ignition.

An engine that's running at a high volumetric efficiency through a
greater part of its operating life might be more efficient: petrol
engines generally cruise at part throttle, so there are pumping losses
at the throttle plate and the peak compression pressures are lower.
The easiest way to achieve this is to use a low-power engine and run
it harder.

 

"TOG@Toil" <> escribió en el mensaje de
noticias

That's a nifty site. Is there any way of getting it to display in

I knew sir would appreciate.

miles per (US or Imperial) gallon, or just it does do litres per 100km?

http://www.eforecourt.com/l_100km_mpg_convert.htm

Shamelessly stealing the formula (from the page source code), you can
convert between from both units by simply dividing a constant by the input
fuel economy "x"-

US liquid gallon
answer = (235.2146 / x);

Imperial gallon
answer = (282.481 / x);

Which seems ok, as the conversion factor is 100*(litres in a
gallon)/(kilometers in a mile), and using 4.5 and 1.6 is near those two
contants.

 

My NT700V is delivering a bit over 53 MPG (US Gallons) so far, and
that includes both around-town stop-and-go chores and freeway cruising
at 85+.

Not awe-inspiring, mind you, but not bad at all for an
enthusiastically-ridden 475 pound bike that pushes a lot of air
around.

 

That's claimed to make quite a difference to recent VW "FSI" engines.
It's direct injection, which in itslef allows for better control of
the charge, and the stratified nature allows only the middle of the
cyclinder to be fueled when in low-load situations, with a much wider
spray, and more of it of course, under high koad/hogh throttle.

Certainly seems to work, letting me average about 28mpg (Imperial, of
course, == 23 US, 10 l/100km) out of the 300bhp VR6 in mine. And
although I'm often trying for economy by leaving it in high gear, I
don't exactly hang about.

 

The GS500 does rather well on fuel, 70mpg is achieveable easily by
keeping the revs down and riding like a wuss.
Give any engine a dose of wellie and it will drink. One simple bit
of physics, friction is proportional to the square of velocity so
keeping the revs down is good.
Another thing to look at is bhp/litre, which is achieved by having
a hotter camshaft. Increased valve overlap means more unburnt fuel.

 

Point of clarification... Bandit 1200s are notoriously shit, but the
Bandit 1250 is much much better. Mine returned 180 miles to an 18 litre
tank on motorway runs cruising at 80. Someone else can do the mpg sums.

 

My RS sits at around 50-55 mpg unless I *really* cane it when it drops to
the mid 40s. I did see 60 mpg once when I was on a run back from Derbyshire
last year but I was bimbling at close to legal speeds all the way (yawn).

 

Mine was quite good on a run. High forties at a steady 90-100.

Blackbird was shocking round town, but not bad at all in its preferred
environment.

CB1300 is particularly frugal - 40mpg in town, where the B'bird would
return 28. >50mpg on a cross-country jaunt is a walk in the park.

Wing is less frugal since I got the clutch fixed.

 

Oh, and on its first Chimay run, the CBX used as much fuel as darsy's
400 Four, and sweller's Guzzi 850.

Combined.

 

I must've got a Friday afternooner then. I don't think I've ever had more
than 37mpg out of mine.