RFL

[cros]

On listening to the banter `interesting` as my R1100RS will only average 33 mpg on a buzzing around situation! `Ride up north, A1 route, 38/40 mpg averaging 75/85 mph.

[bikesnbones]

On listening to the banter `interesting` as my R1100RS will only average 33 mpg on a buzzing around situation! `Ride up north, A1 route, 38/40 mpg averaging 75/85 mph.

If it's any comfort, I have a same generation engine R1200C that gives me 40mpg in the buzzin around situation and 45 on a run (50 if I keep to 60mph)
My 12S beats it hands down, averaging 55mpg day to day, and 57 on a 70/80mph constant speed run, and it get's ridden hard compared to my old Cruiser.

[Corvus]

Don't forget the effect of aerodynmaics.
Any bike, no matter how well faired, is an aerodynamic nightmare.
Stick a rider on board, and the problem is doubled.
Of course this only excuses low mpg at constant motorway speeds.
Not in town.

Exactly.

I had this discussion with a non-biking friend some time ago, who was asking what the performance of my Blackbird was like against modern supercars. I stated that on acceleration, it would take a very serious car to even get anywhere close to it from a *rolling start up to 140mph or so. I then explained its power/weight ratio and the peformance potential hits home (ie 145-150bhp at the wheel pushing 220kg or so) ie 650+bhp/tonne.

However, its top speed is nothing like what one would imagine it should be, bearing in mind the power to weight. There are many cars going a fair bit quicker, on a much lower power-weight.

Said friend was slightly baffled at this but it's simple - as BnB said, bikes' aerodynamics are pretty dreadful. Above 100mph, a huge amount of the engine's oomph is taken just to battle against the drag of the air. Cars win back very convincingly.

*I say a rolling start as cars are a darn sight easier to get off the line with their traction/launch controls etc.

This is an interesting debate and I think there are many aspects to it. But as far as power to weight ratio is concerned my understanding is that this really counts on acceleration. The actual weight starts to have less bearing on top speed as long as there is enough time to allow the vehicle to reach the potential based on power versus aero drag. Yes, weight will increase rolling friction and generally weight goes with bulk, so aero drag would suffer accordingly.

So, basically, what I'm suggesting is that two bikes with identical aero drag and available power, but one weighing 30 kg more, would reach very similar top speed in the same ambient conditions. The heavier one would need longer to get there and the extra rolling friction would knock a bit off the top speed.

In a nutshell, if you want top speed and are prepared to wait longer to get there, look at the power and the drag coefficient. Obviously, in the real world the power to weight ratio is of far more relevance.

Does that sound reasonable?

[Corvus]

So, if we're chasing mpg and always travel at the speed limit, what would the best motorcycle for the job be?

I'd suggest two categories. One including motorways/ fast dual carriageways and one excluding those roads.

If we were designing it, heaven forbid, what cc, no cyls, etc would we use?

[Corvus]

How much do motorcycles vary, across the spectrum, with regard to drag coefficient?

[conkerman]

From awful to shit I imagine.

Don't think they are ever published anywhere.

[Gromit]

From awful to shit I imagine.

Don't think they are ever published anywhere.

Indeed - and there are so many variables (ie size of rider, clothing etc) that it'd be hard to evaluate.

[Corvus]

From awful to shit I imagine.

Don't think they are ever published anywhere.

Well, at least we have a scale!

[Corvus]

From awful to shit I imagine.

Don't think they are ever published anywhere.

Indeed - and there are so many variables (ie size of rider, clothing etc) that it'd be hard to evaluate.

True. Although if those factors are relevant to any great degree then there must be some (considerable) differences in actual values on conkerman's scale.

[Corvus]

How does an average bike plus rider compare to an average car, with regard to drag coefficient?

[McBoxer]

Indeed - and there are so many variables (ie size of rider, clothing etc) that it'd be hard to evaluate.

+1 on that. The only thing the manufacturers could measure with any degree of consistency is the bike without rider, and those figures would be meaningless as soon as a fat pork pie eating Scotsman got within 6 feet of it

[Corvus]

Indeed - and there are so many variables (ie size of rider, clothing etc) that it'd be hard to evaluate.

+1 on that. The only thing the manufacturers could measure with any degree of consistency is the bike without rider, and those figures would be meaningless as soon as a fat pork pie eating Scotsman got within 6 feet of it

True, to a point. One could always design the bike with bodywork to cater for the worst case. To a point.

I personally hate fairings, but that's not the point here.

Or have industry standards. eg: 6 foot rider weighing 13 stones sat with knees on tank, etc. or whatever other figures you like.

[conkerman]

Or just not bother and save a load of cash

The only reason I can see this changing is if someone wants to have a big marketing push on aero like Audi did in the 80's.

But according to the market research, that's not what we want. So we don't get it.

[McBoxer]

Indeed - and there are so many variables (ie size of rider, clothing etc) that it'd be hard to evaluate.

+1 on that. The only thing the manufacturers could measure with any degree of consistency is the bike without rider, and those figures would be meaningless as soon as a fat pork pie eating Scotsman got within 6 feet of it

True, to a point. One could always design the bike with bodywork to cater for the worst case. To a point.

I personally hate fairings, but that's not the point here.

Or have industry standards. eg: 6 foot rider weighing 13 stones sat with knees on tank, etc. or whatever other figures you like.

Good points. I guess I was thinking more of naked bikes - and it would take bodywork larger than Texas to fair in some riders (myself included!), but the industry standard could work. maybe some kind of crash test dummy?

[Corvus]

+1 on that. The only thing the manufacturers could measure with any degree of consistency is the bike without rider, and those figures would be meaningless as soon as a fat pork pie eating Scotsman got within 6 feet of it

True, to a point. One could always design the bike with bodywork to cater for the worst case. To a point.

I personally hate fairings, but that's not the point here.

Or have industry standards. eg: 6 foot rider weighing 13 stones sat with knees on tank, etc. or whatever other figures you like.

Good points. I guess I was thinking more of naked bikes - and it would take bodywork larger than Texas to fair in some riders (myself included!), but the industry standard could work. maybe some kind of crash test dummy?

Dummy?

How much they paying?

I think conkerman is right (again. Grr). I'm glad too. Perish the thought of all bikes looking the same, chasing the same aero target. Urgh. I just wondered to what degree aero figures with bikes and is therefore likely (or not) to figure in the inevitable chase for better mpg.