End the Aerodynamic argument 12R vs. Busa

[OB_Bob]

Oh well, I thought we might have a black / white argument with knowing the CdA's. Guess Not.
From now on I will ride the Busa naked, shave all hair from myself and curl behind the screen like a cold puppy looking for protection from the wind.

Seriously, I guess we will have to wait for an average of the top speed tests, dynos, 1/4 mi runs, etc. before we know the comparison between stock vs. stock.
Guess I kinda knew this from the beginning anyway.

Bob

[This message has been edited by Bob (edited 18 December 1999).]

 

[OB_ducmanic]

Nice post Mr. Bear,
I didn't know the Frontal Area was based on a flat object of the same size. This
must be hard to compute also. This type of manipulation of un correlated raw data by
marketing departments need to be interpreted with a grain of salt. Unless a person is
going racing- Its not even relevant. An inch narrower at 200+mph is a huge amount.

 

[OB_redelk]

With a waistline that's slowly approaching 37" (5'9" / 215 lbs. - talk about DRAG Cx), I'll be lucky to see 150 mph... and that okay with me.

 

[OB_Bob]

I really do not believe this would affect my decision on either of these bikes, but I keep seeing the topic coming up on CdA.
This can be measured. The rider ultimately determines the drag limitation of the bikes anyway. But everything equal it can be measured.
The HAYABUSA's CdA is slightly less than 0.270. Lowest ever for a Suzuki.
If someone knows what the the number is for the ZX12R, measured during their windtunnel testing, please post it. Then that will be the end of the relatively useless argument.

The 0.270 came right out of a Suzuki tech update-I didn't dream it up.
Bob

[This message has been edited by Bob (edited 18 December 1999).]

 

[OB_Factory]

Bob - You're right, the rider makes the difference.

One of the unique things about the engineering of the Busa is that they designed the bike around the rider in the wind tunnel. Unless Kawi did the same, (I don't believe they did) then the CdA ratio won't compare in a real world situation - with a rider.

 

[OB_BullDog]

What if you are twice as big as the "wind-tunnel-test-guy"?? What is the CdA then!?? =o)

 

[OB_Factory]

I'd say your still better off on the bike that was built around A rider as opposed to the bike that was built around NO rider.

 

[OB_Mr Bear]

CdA numbers are dicey, and can be easily manipulated by advertizing departments to the point where they don't mean much. There was a good article on the subject in the June 99 issue of Cycle World, p. 40. You just need to be careful about getting real facts.

For instance, the aerodynamic argument in favor of the ZX-12 is that its frontal profile is at least an inch narrower than that of the Busa. Since the Cd number is a ratio of wind drag force of the actual machine compared to the drag force produced by a flat surface with the same area as the frontal profile (that area is called CdA), it is an abstract number. But if the Kawasaki has a smaller area, it could still be more slippery than the Busa even with a higher Cd number.

Then the marketing people can always mess with the definition of the number to make it different.

And you are right, that doesn't even touch the difference between riders, which is the most important thing. A skinny little rider who for some reason likes to ride butt-naked will be more aerodynamic than a big fat rider who for some reason likes to wear an open parachute when riding. Sorry...there's all kinds here in So. Cal...that would be an extreme example. But the rider is always the most important factor.

[This message has been edited by Mr Bear (edited 18 December 1999).]

[This message has been edited by Mr Bear (edited 18 December 1999).]

 

[Gixx1300R]

The Busa was tested in the windtunnel with a rider onboard

 

[OB_SlowHand]

One thing that I would put ahead of cd area frontal area and a lot of other things is stability at speed. The Jan. issue of Motorcyclist reports a rumor that the ZX12 has a problem at speed, and that is the reason for the delayed arrival. Only a rumor so far, and may be bogus, but anyone who wants to deal with wobbles or weaves at speeds approaching 200MPH is definitely a nutcase. We do know that the Busa is rock stable at any speed it can attain. I'd do a wait and see on the ZX12.

 

[OB_Mr Bear]

Good point, Slowhand. 200 mph is pushing the limits of technology. Those are top speeds for roadrace bikes; we've never had streetbikes capable of matching top end speeds with the top factory race bikes before. Kawasaki definitely has the capability to make a streetbike that is stable at 200+, but may have had difficulty getting it sorted out on the 12. They wouldn't have released it if they hadn't gotten it sorted out, though.

Tank slappers at 0.3 mach would definitely not be fun. But as much as the original design of the bike, high-speed stability is affected by maintenance and the machine's condition. Tire profile/tread depth, the condition of swingarm pivot bearings & wheel bearings, and most importantly the condition of steering head bearings, all are fairly critical to high-speed stability.

 

[OB_Dirty Pete]

Mr. Bear how can you use the words "stable" and "mach .3" in the same breath?

Anyone who goes that fast on a motorcycle is inherently unstable

BTW I was arrested by your opening phrase "200 mph is pushing the limits of technology." I think that one will go down in history alongside "Man was never meant to fly" and "It is impossible to surpass the speed of sound."

I fully expect the opportunity to go 275 mph on a stock motorcycle before I take a dirt nap (around 2040, lawd willin').

 

[OB_SlowHand]

Mr.Bear, i think you give Kawa., and most mc manufacturers too much credit when you say that they wouldn't have released the bike unsorted. That's like saying that Suzuki wouldn't have released the Busa with a cam chain tensioner and fuel screen problem, or their early TL1000 without the rotary shock and "tank-slapper-happy" steering being sorted.
An earlier post mentioned the ZX12 being wind tunnel tested without a rider. Maybe addition of a rider made it unstable. Or maybe their rider was 5'2" and 125lb, and with a normal-sized American lout aboard it changed everything.
The only law I firmly believe in is Murphy's. Having the capability of building a stable 200mph motorcycle is by no means a guarantee that one will be built. If there is any way for something to get screwed up, it will happen.

 

[OB_Bob]

Mr. Bear--I read the article you referenced--"Aerodynamics 101".

Also posted it on the ZX12R site if anyone wants to read it.

Bob

 

[OB_Bob]

Mr. Bear--I read the article you referenced--"Aerodynamics 101".

Also posted it on the ZX12R site if anyone wants to read it.

Bob