How important is a fairing aerodynamically?

[c-m]

I have a ZXR750 - Now I prefer the look of the bike without the lower fairings, but I was just wondering how important they are in terms of aerodynamics?

I know the bely pan fairing on the GPZ500 was a very important aerodynamic piece, there are man stories of high speed weaves and wobbles without it.

Anyway the reason I ask is that I now have a full fairing set for my bike, all be it different colours and was wondering is its worth putting the lower panels on when travelling longer distances like 3000-5000miles.

I presume the weight will reduce fuel economy, but the fairing itself might reduce drag and hence make up for this.

Any thoughts?

[The Artist]

Bikes have the aerodynamics of houses. Just because they are not smooth all along. Even fairings can't make a bike anywhere near as aerodynamic as a car.

Even with fairings, they won't go that much faster.
More handling issues but even those, you will need to do high speeds.

Cue kickstart

[McGee]

[1016]

Good one.... Hope you get a big response 'cos any useful information (on this subject) can only really come from first hand experience, and (as you know) results vary so much from bike to bike. Only generalising here, I would guess sub-50mph additional weight of full fairings would lower MPG but if you were cruising at 80 upwards, then surely you would see a MPG benefit. I think you are the very man for the job of doing back-to-back tests and posting results!

[The Artist]

[chris-red]

Fuel consumption would increase, the amount of weight lost will be negliable compared to the loss of aero dynamics.
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[Pete.]

Guy I know went out on a nitrous GSX1100 and went 164mph, put a fairing on it and went 191mph.

When you're looking for speed, aeros are everything!
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Kickstart]

Hi

Bikes are lousy at aerodynamics. Fairing help, but even a 'busa is pretty dire. It is aerodynamic drag and most of it comes from the back and no bike has even a vaguely clean rear end. The effort goes into the fairings as people think the fairing is important when it is really the back end that is more important.

For comparision my unfaired 1200 Bandit has about 25% more power than my faired Bimota. Through timing lights the Bandit is only a couple of mph faster.

Stability is funny. Might make a massive difference (either way). For a (car) example, the old Ford Sierra had stability problems early on. The fix was a tiny bit of trim sticking out about 1cm at most around the rear side windows.

All the best

Keith
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[Tricolor]

There's a significant difference between a faired and naked bike. However, there's very little difference between a faired and half-faired bike in terms of drag.

The lower half of bikes are aerodynamic disaster areas. Turbulent air coming off the front wheel is the biggest problem. Large cooling surfaces don't help either.
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[c_dug]

[stinkwheel]

This bike has a 50cc engine.
https://www.cybermotorcycle.com/gallery/kreidler/images/Kreidler_Van_Veen.jpg

Aerodynamics make a MASSIVE difference, even at low speeds. Otherwise they wouldn't bother bolting so much plastic to their ultra-lightweight racer.

The difference they make increases exponentially with speed. (friction is directly proportional to speed squared)

My H100 goes 5mph faster if I take one hand off the bars and put it behind my back. That's a 7% increase in top speed.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
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[stinkwheel]

[c_dug]

meh, mines a D and ive never noticed it, i have it all the way up to 110mph and beyond on a pretty much daily basis so long as the weather and traffic allow.

Must just be an uber cool GPZ

c_dug
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[Scotsman37]

Aerodynamics - it keeps the brunt of the wind off you by reducing the drag when at speed and in return you improve the fuel efficiency of the bike. Also, it helps to deflect the rain when also at speed coming at you from the front and especially the when it's cold too.

Plus on the right bike with a smart looking design it just makes the bike look amazing !

[1016]

[Smooth]

From what I remember at uni, in general terms, in order to reduce the 'drag force' the frontal area should be reduced to a minimum, tapered and the rear end of a vehicle should either be vertical or very long and tapered. The typical coupé/hatchback is in-between these and is actually at a disadvantage compared with a like-for-like estate car.

If I remember correctly the Cd of a Transit is lower than that of a typical saloon car, but the frontal area is larger so the force resulting from drag is greater.
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TDM850

[c_dug]

It would be almost impossible to make a vehicle in this shape but im 99% certain the most aerodynamic shape is the shape of a falling water droplet, i.e. large round frontal area and long drawn out rear working its way into a point, like so

c_dug
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[Kickstart]

Hi

Drag makes a difference at low speed, but the difference increases massively with speed. At 40mph a typical unfaired bike will need about 17 lbs of thrust to overcome aerodynamic drag while a 'busa will about 15 lbs of thrust.

To put that in perspective a restricted 6 speed Cagiva Mito in top gear at 40mph has about 41 lbs of thrust (and if using the gears and down in 3rd it would have a 110 lbs of thrust).

While you can improve aerodynamics it tends to add weight, which destroys acceleration. However the weight has very little effect on top speed (a very very marginal effect on rolling resistance). Think this is the basis for the kamm tail designs of cars, as although a full tapering rear is better, once you have started to gently reduce the height at the back you have gained most of the advantages. After that you are adding weight and length for a diminishing return. This is why coupes are shaped like that.

As I understand it a large vertical rear end is pretty dire for aeodynamics. Just look at how a conventional car shape will generally keep the rear window clear of rain when moving, where an estate will need a rear wiper to clear off all the water droplets sucked round onto it.

Tear drop is pretty perfect, and to an extent used in faired bikes for top speed attempts. Trouble is stability. It will move the centre of pressure far forward , well in front of the driving wheel and centre of gravity. Makes it like trying to throw a dart backwards.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Smooth]

[Kickstart]

[Smooth]

[stinkwheel]

Most of the aerodynamic work on motorcycles is pissing into the wind until they make them with enclosed front wheels and stop putting riders on top of them.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Kickstart]

[1016]

When I talked about research, I meant motorbikes... (as I think did OP) If we are including cars I had better reply when I have more time as although very rusty, a bit of a busman's holiday for me.
Meanwhile, does anyone have a (bike fairing related) practical answer for the layman yet?

[Knacker]

Im sure that once i read about this aerodynamics stuff and they compared a lambo to a VW camper and the camper came out on top ??? How the funk ?
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