Motorcycle aerodyamics

[shiphteey]

Assuming a small rider on a production based motorcycle w/OEM fairings and windscreen....

... in order of importance and budget...if the following were to be replaced, what order would you guys recommend and why?  I'm thinking

1) Front/upper
2) Tail
3) Front fender
4) side body panels

Thoughts?

A.

[Reverend Hedgash]

I'll have a go at your question even though a driver not a rider.

The problem with aero issues is that it has to be considered a package. Alterations you do up front will change the conditions behind and therefore it is not as simple or generic as to just placing an importance hierarchy.

It is not even as simple as general rules as getting the frontal area down by changing the front as it could then stuff up the flow causing greater drag elsewhere.

One approach would be to compare it to a similar bike which is faster and see where the potential improvements lay and consider their relative importance on issues other than such a complex art as aero.

If you were asking about your ZX-12R then the choice would naturally be the Hayabusa.

The Kawasaki is 45mm shorter in the wheelbase, has a 23.5 degree rake (compared to 24.2) and less trail at 93mm (97) . The Suzuki weighs five kilos more which can help with traction and has a 5mm lower seat so helps with reducing frontal area.

So in there is a batch of potential improvements that can be considered to approach results similar to the Hayabusa prior to comparing the aero body shape.

(Comparison data source: http://www.dropbears.com/m/models/roadtests/zx12r2000.htm and is comparing bikes in first generation form)

The main change the Hayabusa riders seemed to be making early on at Lake Gairdner was getting extra weight on board for extra traction. They had the power but were having trouble getting it all to the ground. I am unsure how much technique had to do with this, but it would seem that this issue would come into play as high on the list of things to resolve...

Hope this has been some help, even if just to start discussion.

Rev. H+

[1212FBGS]

ship
it all starts up front. the drag and turb starts with the front wheel. front fender will help
kr
ps keep the side wings

[landracing]

I really think the answer is without being in a wind tunnel is to take the bike stock ride the hell out of it, then the next year come with a game plan to make small changes and then run it to see if it makes a difference.

Jon

[firemanjim]

Jon and Joe.This is a similar bike to Ronnie S's bike at Gairdiner,right? Ronnie had his bike lowered and we taped all the seams we could find--and his leathers/boots also, he removed the tank cover as it stuck up and out.He picked up about 5 mph--enough to get him over 200 like he wanted.

[hawkwind]

IMHO the most benifit from a 'Cd' point of view  can be made at the rear of the bike ,but due to the RULES it is very difficult to do very much that has not already been tried , attack the problem from the other part of the equation' A ' and make the frontal area as small as possible  
Gary

[stayt`ie]

g`day shiphteey, i`m the ronnie thay mentioned above,,, my zx12 has a frountal area of 4 sq', that is without mirrors and blinkers, and the bottom fairing to ground clerance is 1" (solid rear suspension, about 1" travel in frount), 5" over swingarm, no ballast,  i have a two step drag racing seat , which sits me about half an inch above the fuel tank,,,, take the fuel tank cover off, as this will allow you to tuck your forearms and elbows in approx inch and a half either side, take the damper things off the ends of your handlebars , and move all your controls in as far as possible, i think i trimmed about one inch and a half off either bar by doing that, (cut your grips down so that your hands just fit on), as firemanjim said tape every thing up, the holes where your blinkers go, all the seams, the depressions where the bolts that hold your fairings on, even the ones that hold the ducktail on, and the key hole, the frount mudguard bolts, i even had my alternator cover hole taped over. i went from 199 to 204, that was just by adding tape.... here is a point of interest, i mentioned that i run a two step seat, when sitting on the backed stepped section there is an increase of 22lbs to my rear tyre contact patch, both my 199 and 204 runs were done sitting up there, the one run inbetween those was a 197, where i sat in the normal position,,,,, best of luck  

[Seldom Seen Slim]

A week-and-a-half ago Dave Owen (of the ECTA) went to the wind tunnel in Charlotte with his 223 mph all-motor 'Busa -- and four stock sport bikes.  I don't know for sure, but I believe I heard that Sport Rider (magazine) was going to be there to do an article on the aero characteristics of the stockers and compare 'em to Dave's bike, too.  Dave's a tall guy, and I think I remember hearing that they were hoping to have a "normal" sized person and even a little guy (Lee Sheirts, but he had to cancel at the last minute).  The article won't be in print for a few months, but then you'll have an opportunity to see some aero information taken from a racer's point of view, not the manufacturer's point.

I don't know how many changes they were able to make during the various blows of the tunnel, but there oughta be some solid information there once it's printed.

I know that Dave made a few runs two months ago at Maxton -- with and without the aero hump in the back of his leathers.  He reported GAINING speed with the hump removed, proving that humps might only be bling.

[Seldom Seen Slim]

Kent:

Please ship me one aero front fender for the '00 ZX12R.  Maybe one for the EX250, too, okay?

[Larry Forstall]

Run it without the fairing. Gas record is 188 Fuel 191+ . Eliminates any handicap racing against better faired bikes. FYI Doug Meyer on a stock bodied motor only ZX-12 went 204 a few years ago. Had just over 200 HP. Try ceramic wheel bearings, thin oil, shaved tires, non O-ring chain, etc.  See your Dr. you are about to catch SALT FEVER.   LOL   Good Luck.

[joea]

it may be prudent to take what Dave O and others
find in their windtunnel testing with a grain of salt..............

ie, the hump may be bling for some and helpful for
others..........I would really like to see Dave O's profile

as others may lay out completely different, putting the hump
in a very different presentation to the air..........

Joe

[Seldom Seen Slim]

Yes, I agree, Joe.  Bikes with riders on 'em are way different than a car in a tunnel -- the car doesn't have things that can (much) during a run, so whatever is determined can be fairly easily quantified.  A rider on a bike -- well, hey -- I know that I don't tuck myself in exactly the same position during each run, and that my neck might cramp one way this time vs. what it did last time (and that'd affect any effects from the hump), and so on.  I've got a couple of years' development on my riding position -- seat location, tank shape, helmet positioning.  some day maybe I'll get it to come together all on the same run.

What the time in the tunnel might have accomplished is to identify some of the variables and begin to quantify them.

As for the hump being bling/hump being aero correct -- unh, the squids on the street around here probably don't NEED the hump, but if it helps them get the girl/guy they're hoping to score with -- then the hump was beneficial.  I'm talking about the hump on the back of the leathers, not some other definition of hump, you dirty-minded readers, you.

[PorkPie]

Some interested comments on this issue...

May be some will remember what I wrote before about car/streamliner design.

The rule, that's more important that a car goes properly out of the air (rearend) and less important how he goes into the air (frontend) counts also for a bike.

With a big different:

The drag of a bike is similar like a house....a moving house.

And the house got the better drag........

Alright - I can see now a lot of question marks....

As a example - if you take a block of brick's with the same outside dimensions of a crate of beer (20 bootles) in the windtunnel, you will find out that the brick's got the better aerodynamic with more cross section than the crate (space between the bottles).

The space between the bottles creates turbulences - turbulences means increase of the drag - or in other words - loosing speed.

A motorcycle is similar like the bottles - the open (or semi open) front wheel with the spoke - the front "suspension" fork - the aerodynamic covered engine - which got holes in to give the engine air - for radiator and carburator.....

Somewhere through and around all this "barriers" has the airflow to find there way.

So the frontend has to be cleaned up from barriers - by a motorcycle a clean frontend is more important as by a car - also a car has more length which can be used to smooth the created turbulence on the front.

A great solution is Fireman Jim's front wheel cover - I liked them when I saw the bike the first time at the salt.

The front of the turning wheel is covered, so there is a clean airflow - behind, the air can move clean around the "body", there is no wheel cover from where the airflow has to escape. If he got the front open and the rear of the wheel covered (normal standard wheel cover) the air has to escape forward - against the airflow - and downwards.

Jim's solution eliminate this problem.

But also for the motorcycle it's important that the rearend is clean - so that the air can rip off clean behind the bike.
Without a clean rear end the air collapse behind the bike, creates a vaccum and turbulences - and also it's affect the handling of the bike - the
bike goes not proper straight - feels weak on the rear wheel.

One of the big mistakes I saw over the last years - on this new modern aeropack body parts - Jon Wennerberg, John Noonan and also the Amo brothers using so big rear wheel fender, which goes closed deep down behind the rear wheel.
Under this rear fender the air builds up an air cushion, which likes to go out of this "closed" space - the only chance to escape is downwards, directly into the airflow along the bike and rider - this produces a lot of turbulences.
If the back part of the rear fender got some slots in, the air could escape through this slots and has not to run into above airflow.

In other words, this fender works like a airbrake......

Summary:

A bike has to go clean out of the air, so as a car, but also the frontend has to be free from turbulence creater, due to this that a bike got not the length to smooth the airflow, before the airflow reach the rearend.

This as a short explanation.

See ya

[dirtydave]

good work reverend, sounds like you know your bikes better than me.
Also good feed back guys.
In regard to the hump, I'm sure that i read an article on moto gp discussing the benefits of the hump in the 125cc and 250cc classes, but found that the then 500cc bikes had less corner speed and more grunt that the humps were neither here nor there, but found that the benefits of rider safety increased in protecting them from neck and head injuries in the event of a fall,,they all seam to wear them now anyhow.
2# Rider position is also very important, Carl Foggerty and Pierre Francesco Chili where riding identical Ducati's at Hockenhiem a few years back and Carl was down about 8 kmh on Pierre and complaint to team management that his bike was not as good, he was instructed to sit on the bike further back and get his back flat. which resolved the 8kmh difference in the two bikes..
Might be a good project for FiremanJim while he's spannering at Laguna Seca,

[stayt`ie]

i am not sure that the zx12 aero in the frount is that bad, it is behind the rider that lets them down, one only had too see the mess the rear section of my bike was in, there was salt everywhere, with indications that their was a cyclone happening during the run....

kent, you mention to keep the wings, can you explain why?, i had been thinking of removing them...