Top Speed Calculations

[Northman]

OK, here's the best info I can find - I hope it's accurate.

Primary reduction: 1.571

6th Gear Ratio: 1.042

Final Drive (stock): 2.647

Which, gives you a crankshaft : rear wheel ratio of 4.33:1

Changing the gearing to 18/45 yields a ratio of 4.09

Going down 2 on the back as well yields 3.91:1

Rear tire diameter (according to Dunlop) is 24.96" = 78.37" circumference

Plugging all of this into the computer & calculating theoretical top speed in 6th gear, at 11K rpm.............

Stock gearing: 188.4mph

18/45 gearing: 199.5mph

18/43 gearing: 208.8mph

Considering this, I'm going to run the 18/45 combo at first. If I manage to eclipse 11K in 6th gear, and smack the limiter, I'll probably go one down in the back for starters, then two, etc. until it won't pull any faster.

I guess it will all depend on how easily it does it, too........ :razz:

[Redbird]

Damn, I was close with my off the top of my head guess :grin:

[Furbird]

Sweet. I have the exact gears (18/43) sitting in the garage right now. Time to go school the new R1's, 1000RR's, and GSXR1000's that claim they can go 200. Might have to roll away from a few Busas for you boys as well :twisted:

[aptyp]

How realistic is it when you figure in wind resistance? I understand that there is some kind of a wall you hit where no matter how much power you have it just won't let you accellerate.

[Pete in PA]

So North what exactly are you doing to your XX :?: :?:

You'll need a lot of power to get the last 10 mph to 200. The factor of three of aerodynamics.

If it wasn't for air resistence a CB125 could go 200.

[Northman]

The V&M Blackbirds were pushing 180RWHP, and would break 200mph.

Mine should go faster than that........... :twisted:

[Northman]

OK, now that I thought about it........

I'm not saying if you guys go out and make gearing changes, your bike will do 200mph. I'm just calculating theoretical top speed (mechanical) for a given ratio.

If you've got enough hp to push it, then that is the approx speed you're doing with those gearing choices.

I needed to make these calculations for my own reasons, but thought I'd share...... :grin:

[aptyp]

I remember hearing that with a busa you need 186 hp to break 200mph figuring in the wind drag, anyone done the same kind of research with the XX?

[Northman]

The V&M Blackbirds were pushing 180RWHP, and would break 200mph.

Mine should go faster than that........... :twisted:

Re-read the above post............

[Motobeagle]

I needed to make these calculations for my own reasons, but thought I'd share......

Based on my thrust to weight ratio, and my optimal drive angle, I should be ripping my wife in two, while causing massive abdominal damage. :shock:

Fact is,

I'm barely passing the labia, while causing massive marital damage. :???:

Good luck on your quest buddy. :wink:

[pai]

its not that difficult to hit 200 on the speedo guys. i hav hit mine countless times n hav gone beyond as many times. i would like to share with all of u.

jus read everythin in km/h. try it!

[bartonmd]

North,

That calculation is with your rear wheel going 200mph, but I was always told that there is about 8-10% rear-wheel slip at high speeds. Are you taking that into account?

[carl]

How realistic is it when you figure in wind resistance?  I understand that there is some kind of a wall you hit where no matter how much power you have it just won't let you accellerate.

every vehicle has a "wall." this is when road load forces (namely aerodynamic drag) become equal to the accelerative force exerted by your rear tire on the road surface.

if you know the torque curve of the bike via a dyno ("at the wheels"), then it's just a matter of dividing the torque values by the moment arm (radius of the rear tire)...this will give you your accelerative force.

if you know the aerodynamic properties of the bike (Cd and A), you can then determine the aerodynamic drag at various speeds.

then, it's just a matter of finding the point at which the aero drag overcomes your accelerative force.

*the below taken from "Fundamentals of Vehicle Dynamics" by Gillespie. This was the class text for my Automotive Engineering class in college.

Da=(1/2)*rho*V^2*Cd*A

where:

Da=aerodynamic drag

rho=air density

V=velocity

Cd=aerodynamic drag coefficient

A=frontal area of the vehicle

rho=0.00236*(Pr/29.92)*(519/(460+Tr))

where:

Pr=atmospheric pressure in inches of mercury

Tr=air temperature in degrees Fahrenheit

*at standard conditions (59 degrees F and 29.92 inches of Hg), rho is simply 0.076 lb/ft^3...divide by gravity (32.2 ft/sec^2) for mass density and get 0.00236 lb*sec^2/ft^4

PS - if someone would be so kind as to post the Cd and A for the XX, i'll run the calcs and post graphs and whatnot.

[blackbd1]

i have just read some very poor physics above

for starters: at 200 the 8-10% difference isn't do to tire slip, it is due to inaccuracy in your speedo

this is why they use timing gates to measure speeds at the flats and not mechanical speedos

so your indicated 200 was actually a more true 180 (assuming 10%)

my 00 XX is a true 142 mph at an indicated 155 mph (@ 9.2%)

secondly, the factor of three business

aerodynamic drag increases as the square of the velocity of travel

so if your speed doubles, the drag increase by a factor of 4!

the bottom line is the relation between hp and velocity (including drag) is that your hp required goes as the 3rd power of the velocity (factor of three is actually a 3rd power thing)

meaning if you want to double your velocity, any velocity, you need 2 to the 3rd power (8 times) the horse.

so, if it takes 30 hp to travel 100 mph, it will take 240 hp to travel 200 mph

to do a specific example, if the busa requires 186 hp to do 200 mph,

provided that its gearing will permit it, it will require 200.301 hp to do 205 mph.

thats 14.3 more horse to gain 5 mph at that speed.

you would need 15.0 more horse yet to make it to 210 (215.318 hp)

FRICTION IS SUCH A DRAG!!!!

my 2 cents

[Hobicus]

Based on my thrust to weight ratio, and my optimal drive angle, I should be ripping my wife in two, while causing massive abdominal damage

Nearly spit soda all over my keyboard.

I believe that it's not just the size of the piston, but the stroke length that determines displacement.

[matey_peeps]

How realistic is it when you figure in wind resistance?  I understand that there is some kind of a wall you hit where no matter how much power you have it just won't let you accellerate.

every vehicle has a "wall." this is when road load forces (namely aerodynamic drag) become equal to the accelerative force exerted by your rear tire on the road surface.

if you know the torque curve of the bike via a dyno ("at the wheels"), then it's just a matter of dividing the torque values by the moment arm (radius of the rear tire)...this will give you your accelerative force.

if you know the aerodynamic properties of the bike (Cd and A), you can then determine the aerodynamic drag at various speeds.

then, it's just a matter of finding the point at which the aero drag overcomes your accelerative force.

*the below taken from "Fundamentals of Vehicle Dynamics" by Gillespie. This was the class text for my Automotive Engineering class in college.

Da=(1/2)*rho*V^2*Cd*A

where:

Da=aerodynamic drag

rho=air density

V=velocity

Cd=aerodynamic drag coefficient

A=frontal area of the vehicle

rho=0.00236*(Pr/29.92)*(519/(460+Tr))

where:

Pr=atmospheric pressure in inches of mercury

Tr=air temperature in degrees Fahrenheit

*at standard conditions (59 degrees F and 29.92 inches of Hg), rho is simply 0.076 lb/ft^3...divide by gravity (32.2 ft/sec^2) for mass density and get 0.00236 lb*sec^2/ft^4

PS - if someone would be so kind as to post the Cd and A for the XX, i'll run the calcs and post graphs and whatnot.

STOP! MY HEAD HURTS!

[blackbd1]

to northman

a while back i made an excel spreadsheet of the gearing setup per my XX and my buddies busa. your information and mine are exactly the same.

i am actually wanting to drop a tooth on the front, i would rather be a little quicker (my preference)

i was wondering, if i dropped the tooth and it changed my top end by 10%, would that correct my speedo?? if it is read from the tranny it will.

am i correct in thinking this??

[Northman]

Yeah, what Joe said..... :grin:

The factory speedo reads about 8% low. Lowering the gearing adds another 7% (approx) for about a 15% error on the low side.

Adding a tooth on the front sprocket should correct the speedo close enough.

My point was to calculate my speed based on my tach, not my speedo.