Can someone check my math?

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M

meerkatt

New Member
Nov 4, 2010
15
0
0
oxford
My motor peaks out at 9000rpm
my reduction box is 3:1
my final gearing is 6.5:1 (11/72)
so I make that 19.6:1 overall gearing
my rear tyre is 100/90/18 so circumference is 1.98m (yeah we are metric over here!)

So I get my 9000 reduced to 3000 at the box then 460rpm at the wheel for 911m/minute .... 55km/hour

Question is .... hows my math?

2nd question ... hows my torque gonna be?

All hail the gearing gurus!
 
B

bowljoman

New Member
Aug 7, 2010
370
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0
Wa
you can check that here.

http://www.thebitstream.com/scoot/

Set the crankshaft-to-output-shaft at '3' for 3-to-1.

Set the input and output sprocket at the same tooth-count and select 2nd gear.

From there, figure your tire size in inches and select the engine sprocket and rear tire sprocket tooth-counts.

2nd gear is a one to one ratio at the transmission.
 
M

meerkatt

New Member
Nov 4, 2010
15
0
0
oxford
that calculator cant cope with my sprocket sizes! Halving both sprockets gets me on the chart but I doubt the accuracy of the results.
Anyone else?
 
5

5-7HEAVEN

Well-Known Member
Aug 2, 2008
2,661
240
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meerkatt said:
My motor peaks out at 9000rpm
my reduction box is 3:1
my final gearing is 6.5:1 (11/72)
so I make that 19.6:1 overall gearing
my rear tyre is 100/90/18 so circumference is 1.98m (yeah we are metric over here!)

So I get my 9000 reduced to 3000 at the box then 460rpm at the wheel for 911m/minute .... 55km/hour

Question is .... hows my math?

2nd question ... hows my torque gonna be?

All hail the gearing gurus!
Click to expand...
Try this website, after converting from metric:

Index of /ratiocalc

Your calculations are correct.
 
M

meerkatt

New Member
Nov 4, 2010
15
0
0
oxford
thanks guys
How can I lock that scoot app into 2nd gear?
any idea how my torque will hold up through this gearing?
 
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M

meerkatt

New Member
Nov 4, 2010
15
0
0
oxford
Found this
Gearing Commander: Motorcycle Gear Ratio Calculator for Sprockets RPM Speed Chain
Motorcycle app but easy to use and near infinite variations possible
best of all it confirmed my calculations!

BUT.... I still need someone with a brain to tell me whats gonna happen to my torque?
My understanding is...
torque at motor x gear ratio = torque at wheel
so my 3.5Nm x 19.6 gives me 68.6Nm=50.6lb/ft at the wheel?
is that enough to turn my wheels?
 
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