Cross sectional area when lowered ?

[PetriK]

Hi,

I am trying to calculate the effect of lowering of a bike as a function that reduces the cross sectional area. The stock bike has the following figures which I have found somewhere:

Cross sectional arera: 6.006 sqft
Co efficient of air drag: 0.561

If I lower a bike for 1" and just take the tyre/wheel width I am calculating about 1hp less required for 200mph - but based on experience I think that the effect of lowering is much higher so I must have a flaw in the thinking.

Any hints ?

EDIT - This is for what I need the info for...

[DarkFalcon]

There are two elements in the equation: Cda and frontal area. The Cda, which is the effective flat frontal area, is determined in wind tunnel tests and I should think that this will change as the bike is lowered.........but I don't know by how much. For a stock Hayabusa with a rider it is 3.37 sq ft.  Actual frontal area is measured and for a stock Hayabusa with a rider is 6.02 sq ft. The coefficient is simply 3.37/6.02 or .56. I think the numerator and denominator will change for a lowered bike, with the numerator perhaps being more significant.

[PetriK]

Thanks - reducing height also the flat frontal area is reduced, I did not know the relation of that to cda - now I get results which more like what I was expecting for... something along the lines of lowering 3" = 5hp @ 200mph.

Its really gearing what I am thinking and need a rough speed estimates for different local weather scenarios. Based on the maths looks like 210-215mph depending on weather conditions is doable with my engine when some nitrous is added. Possibly even more, but then the fuelpump becomes an issue. Interestingly still with those speeds I should be running stock gearing because of power being delivered very well between 10000-11500 due to shorter intake and cam timing and reflashed extended ecu. With this the reflashed ecu and extended limiters could be using 16 in front and still be hitting 200mph



ps. I dont include tire slippage as the tire diameter seems to be increasing during the ride based on my and others experience. We have some piccies of one 217mph ride wheere the front tyre is getting very thin and tall...