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-   SV Talk, Tuning & Tweaking (http://forums.sv650.org/forumdisplay.php?f=111)
-   -   1/4 mile times? (http://forums.sv650.org/showthread.php?t=90430)

sinbad 05-06-07 03:28 PM
Re: 1/4 mile times?
 
Quote:
Originally Posted by Fuzz (Post 1204496)
This is true, and it's because bikes are so much less aerodynamic than a car. (Yes they are!) It has little to do with pure power - consider the power/weight and the power/displacement.

911 Turbo - 480bhp, 1585kg = 0.302 bhp/kg; 3596cc = 133bhp/litre
GSXR1000 - 165bhp, 180kg = 0.917 bhp/kg; 999cc = 165bhp/litre

Bikes aeros are much worse than cars because of us. We might tuck in as much as possible, but them hips, elbows, head, *bottom all add drag. Consider that the bike is also smaller, and therefore hitting less front on "150mph gale" and you can see the wind resistance isn't the problem, but the drag created at the back. Bikes and riders create strong turbulence behind the bike; sports cars are designed to minimise this, and the size of you - other than adding weight - has very little impact.
Bikes are more aerodynamic than a car. How many cars with less than 200bhp can hit 170mph and higher?

the_lone_wolf 05-06-07 03:54 PM
Re: 1/4 mile times?
 
Quote:
Originally Posted by sinbad (Post 1204791)
Bikes are more aerodynamic than a car. How many cars with less than 200bhp can hit 170mph and higher?
high speed is all about drag, as it is proportional to the *cube* of the vehicle speed, ie - to double the top speed of a bike without changing it's aerodynamics you require 8 times the power...

http://www.bgsoflex.com/airdragchart.html
http://www.motorbyte.com/mmm/pages/misc/tularis_22.htm

probably explains it clearest:
http://www.qsl.net/n5mya/aero.html

Quote:
With figures
for both drag and frontal area, it's possible to calculate the coefficient
of drag, which is 0.603 for the 12R and 0.561 for the Hayabusa. The
winner of this wind tunnel shootout is the Suzuki.

...

It's worth remembering, however, that neither of these Cd figures indicate
a particularly impressive degree of streamlining, since even a typical
passenger car has a Cd of less than 0.60 and some models are lower than
0.30. A fully streamlined Bonneville speed-record bike might have a
Cd of 0.10. Such is the nature of streetbikes, where performance derives
mostly from extreme power-to-weight ratios.

sinbad 05-06-07 04:20 PM
Re: 1/4 mile times?
 
Quote:
Originally Posted by the_lone_wolf (Post 1204810)
high speed is all about drag, as it is proportional to the *cube* of the vehicle speed, ie - to double the top speed of a bike without changing it's aerodynamics you require 8 times the power...

http://www.bgsoflex.com/airdragchart.html
http://www.motorbyte.com/mmm/pages/misc/tularis_22.htm

probably explains it clearest:
http://www.qsl.net/n5mya/aero.html
Precisely, so if a bike were as aerodynamic as a car, it would require the same amount of power to hit 200mph. The Cd figure alone isn't of much use, because you need to consider the frontal area. A bike might have a Cd figure of 0.650 and a car have a figure of 0.600, but that just means, simply put, that the car disturbs less of the air that it hits than the bike does, but the car still hits a lot more air.

the_lone_wolf 05-06-07 04:28 PM
Re: 1/4 mile times?
 
Quote:
Originally Posted by sinbad (Post 1204855)
Precisely, so if a bike were as aerodynamic as a car, it would require the same amount of power to hit 200mph. The Cd figure alone isn't of much use, because you need to consider the frontal area. A bike might have a Cd figure of 0.650 and a car have a figure of 0.600, but that just means, simply put, that the car disturbs less of the air that it hits than the bike does, but the car still hits a lot more air.
sorry but the drag coefficient is dependent on the frontal area of the object, so the fact that cars have a greater frontal area is taken into account when their drag coefficients are calculated.
:)

sinbad 05-06-07 04:43 PM
Re: 1/4 mile times?
 
Quote:
Originally Posted by the_lone_wolf (Post 1204867)
sorry but the drag coefficient is dependent on the frontal area of the object, so the fact that cars have a greater frontal area is taken into account when their drag coefficients are calculated.
:)
Sorry back :), I think you're wrong. A flat board at a 90degree angle to the road could have a Cd of 1.1, and so could one of 5 times the size. Which would make more drag?

The value that makes the real difference is CdA, which is the combination of Cd (drag coefficient) and frontal area.

the_lone_wolf 05-06-07 05:12 PM
Re: 1/4 mile times?
 
well you learn something new every day, or more to the point, realise that you don't remember everything you were taught about aerodynamics years ago...

*hangs head in shame*

PAPPACLART 05-06-07 08:45 PM
Re: 1/4 mile times?
 
Quote:
Originally Posted by the_lone_wolf (Post 1204810)
high speed is all about drag, as it is proportional to the *cube* of the vehicle speed, ie - to double the top speed of a bike without changing it's aerodynamics you require 8 times the power...

http://www.bgsoflex.com/airdragchart.html
http://www.motorbyte.com/mmm/pages/misc/tularis_22.htm

probably explains it clearest:
http://www.qsl.net/n5mya/aero.html



CD of a busa doubles with a rider sitting ontop. It takes about 500bhp for a car with with twice as effecient aero's to do 200mph where a bike needs between 180-190bhp at the rear. And Weight has very little to do with top speed whe the speeds get silly. Lots of other variables to consider. rolling resistents, light weight as a negative etc

We were talking about this stuff on tlzone
http://www.tlzone.net/forums/video-s...-yzf-r1-2.html




.

the_lone_wolf 05-06-07 09:19 PM
Re: 1/4 mile times?
 
Quote:
Originally Posted by PAPPACLART (Post 1205083)
CD of a busa doubles with a rider sitting ontop
source?

i'd be amazed if that were truly the case, if you look at a busa from the side there's a space the exact shape of the rider which would cause plenty of turbulence and drag unless someone were sitting on the bike:

http://www.motorcycle.com/mo/mcnuts/chain.htmlhttp://www.suzukicycles.org/photos/G...purple_600.jpg

and with rider filling the gap:

http://www.leesperformance.com/pictures/DSC_0907.2.jpg

sorry, big picture, only side shot i could find of a hayabusa with rider, why would suzuki design a bike that was only good for high speeds without the rider on it?:confused:

PAPPACLART 05-06-07 10:30 PM
Re: 1/4 mile times?
 
Quote:
Originally Posted by the_lone_wolf (Post 1205115)
source?

i'd be amazed if that were truly the case, if you look at a busa from the side there's a space the exact shape of the rider which would cause plenty of turbulence and drag unless someone were sitting on the bike:

http://www.motorcycle.com/mo/mcnuts/chain.htmlhttp://www.suzukicycles.org/photos/G...purple_600.jpg

and with rider filling the gap:

http://www.leesperformance.com/pictures/DSC_0907.2.jpg

sorry, big picture, only side shot i could find of a hayabusa with rider, why would suzuki design a bike that was only good for high speeds without the rider on it?:confused:

As already mentioned it is the dirty air, not to mention the elbows, the feet, the head, the hands and arms creating servere drag. I remeber reading a PB or SB article a good few years ago. CD was around 3.4 but went over 6 once rider was astride. This is the case for Most bikes.

Fuzz 06-06-07 12:23 PM
Re: 1/4 mile times?
 
Quote:
Originally Posted by sinbad (Post 1204791)
Bikes are more aerodynamic than a car. How many cars with less than 200bhp can hit 170mph and higher?
How many bikes weigh 1.5 tonnes? Im sorry but weight has everything to do with it - to do 170mph you have to start from 0. If you don't have the power to accelerate 1500kg to 170mph, you'll never get there unless dropped from a plane.

It's not just the bike you have to think about; do you still perfectly still and rigid while you're onboard? The shape of the car does not alter, the shape of the combined bike/rider does.


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