It's the specific output (BHP / litre) that is the killer. Thirty years ago, Japanese bikes were routinely giving 100+ BHP per litre, and it's now nearer 200bhp per litre for the sportsbikes.
To achieve this, you've got to get more combustible mixture in the cylinders = more fuel used.
But a modern 1 litre bike is much more economical at speed than a 70s superbike.
The old "grey porridge" sub-350cc British single cylinder machines from AJS, Matchless, Ariel etc, which were the bread & butter of biking in the 50s and 60s, were lucky to produce 20bhp and would quite happily give 80-odd to the gallon.
Mind you, they had a top whack of 75mph if you were lucky.
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Air resistance is pretty stiff too at over 80mph on a naked bike.
I once rode mine back to Yorkshire, from Koblenz in one trip. Holding it above 80 in an upright, (swept back bars,) riding position wearing an old waxed cotton Belstaff suit really took it out of you, with the air pressure.
Re-jetted and with a Dunstall megaphone, that could get down to 45mpg.
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very true, "traditional" machines hang you out in the breeze, I reckon the max. cruising speed on these bikes is about 80mph as above that it doesn't have stretch your neck & shoulder muscles.
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I agree. It reminds me of a mate who sustained 140 mph on a Kawasaki ZRX1100 for about 20 minutes in Germany once. His neck muscles took a week to recover.
Big naked bikes make a lot of sense for recreational purposes though. You get the massive acceleration of a big bore bike, but with an automatic reminder in the form of windblast and eventual pain to keep the overall speeds sensible. You can't do a ton + on a naked bike without at least being aware you're doing it.
At the other end of the spectrum, you have the big sports tourers like the Honda Blackbird and Kawasaki ZZR1100/1200 which will whisk you to a ton in about 7 seconds, and disguise the speed so well, you have no idea without looking at the speedo. These are the real license losers in my opinion, not necessarily the out and out sportsbikes. A brief ride on a Blackbird once saw me doing speeds I've never got close to in a car, and in total comfort.
In terms of the OP's question on economy, I think it was Bike magazine who managed to empty the entire contents of a ZZR1400 test bike's fuel tank on the German autobahn in about 25 minutes! That said, they'd covered about 85 miles!
Cheers
DP
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Thanks for the replies all, interesting.
"The old "grey porridge" sub-350cc British single cylinder machines from AJS, Matchless, Ariel etc, which were the bread & butter of biking in the 50s and 60s"
It dates me I know - but those are the bikes I knew and lusted after! (Not the Ariel!) - and not forgetting the Triumph Tiger Cub!
Edited by PhilW on 23/06/2008 at 19:24
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The GS gives the best of both worlds - an armchair riding position and the (almost) perfect screen take away enough wind blast - believe me his big ugly monster can cruise, quite happily, at the ton with no effort and still returning decent fuel usage. We had one motorway blast from Namur to Brugge for the last night, it was effortless - this linked to excellently surfaced roads in Belgium and very good lane discipline - one memorable moment when our little group, strung out like pearls on a necklace, cruising along at 85 were overtaken by a brace of British registered megabikes (all 08 reg) at well over a 100mph, the lead rider pulled a lengthy wheelie (whilst fully loaded) as he passed. Respect - total respect.
Edited by Pugugly on 23/06/2008 at 19:36
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nowadays there is the Kawasaki 650 diesel which gives 96 miles to the U.S. gallon at 55 mph.:
tinyurl.com/4bek3o
and I read of a dutch diesel V-twin a couple of years ago which looked promising both in terms of power and performance - lightweight, too. There must have been a problem because the story went silent.
Motorcycles have very poor coefficients of drag, even with fairings, whereas cars are getting very good.
My theory on why engines have evolved as they have is down to insurance and registration laws that penalize displacement. If motor vehicles were taxed based on horsepower at the wheels, I think you would see relatively light and under stressed but large displacement engines running at low revs, since the way to gain the all-important performance advantage with a horsepower rather than displacement limit is to provide a wide torque band. This is also a formula for good specific fuel consumption figures.
With displacement limitations multiple pistons and high revs bring performance gains at the expense of efficiency.
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"The old "grey porridge" sub-350cc British single cylinder machines from AJS Matchless Ariel etc which were the bread & butter of biking in the 50s and 60s" It dates me I know - but those are the bikes I knew and lusted after! (Not the Ariel!)
What Ariel? Colt (wasn't that 200cc?)? Can't be an Arrow or similar, which was generally a 250, and a spankin' good semi-unit design to boot.... Oh I remember that AW- had one o' they there timed at 132 through the speed trap at S-! Mind you, it had "special" alloy cylinders with Nikosil bores, and had been dealt with in other ways, but the crank was standard, if somewhat "padded", and it had a 5-speed 'box (needed more han this for use), and.... but I digress.
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Ariel NH was a 350 single OHV. I had one, until it mysteriously wore its cams out when I was away from Uni.
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My Honda X11 (1137cc) produces 136BHP, has a top speed of 160mph, pulls 0 to 60 in under 3 seconds. On top of that I get 45mpg. Nice!
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"The old "grey porridge" sub-350cc British single cylinder machines from AJS, Matchless, Ariel etc, which were the bread & butter of biking in the 50s and 60s, were lucky to produce 20bhp and would quite happily give 80-odd to the gallon.
Mind you, they had a top whack of 75mph if you were lucky. "
Absolutely right for my BSA B31 350cc, to start with. Eventually, after much swopping of parts for Gold Star items, GP carb, 8.8 to 1 compression ratio, port polishing, etc, it would do the ton, downwind and flat on the tank; it needed a new speedo head to go with the added rev counter - very sporting - and a McCandless proprietary rear frame to keep the back wheel on the road. It then did 40 mpg, so not much has changed.
(it would have been cheaper in the end, with more status, just to get a GS in the first place but I never had that much cash in one go!)
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Sounds nice though, Tomo :)
A friend had a 441 Shooting Star 'power egg' single which looked gorgeous but was a pig to own & run. One thing we did learn is that Brit singles are just as finicky in set up of carb & timing as any highly-strung Japanese 2 stroke ....
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