Know your clutch shaft RPM, rear wheel RPM and max speed!!!

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mech_engineer

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Mar 3, 2014
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The knowledge is the road to the success!!!


I hope this will make faster bicycles... this is a approximation because of the chain.
 
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The_Aleman

The_Aleman

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Jul 31, 2008
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Nice. Many of us just use a small program that's been around the motorized bicycle forums for years, you can get it here: http://jimsitton.net/ratiocalc/

It's quick and doesn't require as much brainpower or paper :D

I uploaded a few pics to demonstrate. From left to right, all assuming 7K engine RPM:

1) Typical 2-stroke kit with 26" wheels

2) Typical 5:1 4G kit with 26" wheels

3) 5:1 4G on SBP shift kit with custom sprockets and a Sturmey Archer 5 speed, in 5th gear
 

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Desert Rat

Desert Rat

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Jul 30, 2012
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The_Aleman said:
Nice. Many of us just use a small program that's been around the motorized bicycle forums for years, you can get it here: http://jimsitton.net/ratiocalc/

It's quick and doesn't require as much brainpower or paper :D

I uploaded a few pics to demonstrate. From left to right, all assuming 7K engine RPM:

1) Typical 2-stroke kit with 26" wheels

2) Typical 5:1 4G kit with 26" wheels

3) 5:1 4G on SBP shift kit with custom sprockets and a Sturmey Archer 5 speed, in 5th gear
Click to expand...
but that doesn't show the rpm for a 26 inch wheel
 
Desert Rat

Desert Rat

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The_Aleman said:
Simple to get that figure. Engine RPM / Drive Ratio = wheel RPM

Picture 1: ~388

Picture 2: ~350

Picture 3: ~475

Those numbers typically don't matter to people who just want to know how fast they'll be going at what engine RPM with what gear ratio.

Wheel RPM typically figures into e-bike building tho.
Click to expand...
my reason for needing to know wheel rpm is for a perm mag motor gen.
so 12 volt at ? rpms.
oh and thanks!
 
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mech_engineer

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to obtain the wheel rpm you need to do the step 1 and 2 of the paper... sorry for the writing quality. but i dont have time to do something nice because i work all day and study at night.
 
max350

max350

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Apr 10, 2010
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Simple formula to calculate the speed !

Motor Drive 4.1:1 = At engine 1000rpm/4.1 = 244rpm at front sprocket, 244rpm / 4.4
= 55.5 rpm x tire circumference 2.05 m = 114.2 m/min/60 = 1.9 m/s x 3,6 at 1000rpm = 6.85 kmh

6.85 x 7000 = 47.8 kmh, 6.85 x 8000 = 54.8 kmh.......... also further

Conversion into mph from kmh x1, 609
4.4 is gearing front and rear sprocket as the sprocket Circumference tires, such as 26inch = 205cm
 
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BarelyAWake

BarelyAWake

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Jul 21, 2009
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All the charts & calculations above aren't for establishing speed, rather they're for optimizing gearing for a speed.

There is a lot more to calculating a "max speed" then RPM, which in fact has little to do with any actual achieved speeds. Gearing will allow you just about any RPM you'd like - but that doesn't mean that RPM will be even remotely effective.

Here's one of many "speed & power" calculators that tries to encompass the real world variables, of which there are many;

http://www.kreuzotter.de/english/espeed.htm

...and let's not forget this devilish detail;

 
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