Gear Calculator for Multi ratios

damonjackson_spl said:
ok so using the calculator i should aim for 387rpm in the rpm box and then try get the gearing to suit...
Click to expand...

No...The engine RPM should be the maximum that you intend the engine to turn...6,500 or less.

The first parameter at the top is your internal engine reduction of 3:1

The second parameter is from the 11T mounted to the gear reduction to the next sproket in the series...for this example I used 44T...you currently have 22T installed.

The next parameter is the final drive set. I used 20 to 28 at the rear wheel to give 30mph.

I've got to go for now...play with it some and I'll check back in the morning.

Jim
 

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damonjackson_spl said:
i dont understand.. 44/16 is perfect ratio for pedals and it says i only need a rpm of 150 to achieve 30mp/h
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Think about it...44/16 = 1:2.75 ratio. 150 X 2.75 = 412 RPM at the rear wheel. 387, 412...that's pretty close. They may have been figuring in tire slippage, or maybe the tire is slightly under 26". Either way 412 is close enough to 387 to get an idea what's going on.

Jim
 
damonjackson_spl said:
i dont understand.. 44/16 is perfect ratio for pedals and it says i only need a rpm of 150 to achieve 30mp/h
Click to expand...


When pedalling, you want to INCREASE rpm at the wheel because your legs might be pumping 55 rpm.

You have a 2.75 MULTIPLIER factor so 55rpm increases to 150rpm = 30mph.

When motoring, you need to DECREASE rpm at the wheel because the engine might be pumping 6500rpm.

Using a gear calculator in my files, I find that final ratio should be ~16.5-16.78:1.

Then divide by 3(built-in gear reduction box on the engine) = 5.5 to 5.6:1.

This is the additional gearing needed to reach 30mph with 26" wheel at 6500rpm. .wee.
 
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HOWEVER, you make it impossible to reduce gearing because you have a MULTIPLYING factor with your 40/16 chainring/rear sprocket relationship.:-||

In other words, 6500 rpm would have to be reduced to 55rpm at the 40t sprocket. THEN 55rpm would be multiplied 2.75 times at the 16t rear sprocket, which would be 150rpm at the wheel.

In your present setup, your final gear ratio is 2.4:1. At 6500rpm, top speed is 209.5mph.

In other words, your clutch will burn out before the bike moves an inch. :(

If the chainring was 16t and rear sprocket was 44t, then you'd have 11t engine/22t left jackshaft sprocket and 16t right jackshaft sprocket/44t wheel sprocket.

And then your engine would be revving 6500rpm at 30.5mph.

Please reconfirm my calculations; I MIGHT be wrong but I don't think so.
 
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5-7,

I think the information Damon got on his 44/16T chainring set was saying that you need 150RPM at the pedals, which would give 412 at the wheel when figuring in the 1:2.75 overdrive ratio.

I had figured 387RPM at the rear wheel without considering any other variables such as tire slippage, true tire diameter etc. Many 26" tires I have measured with calipers have actually been 25-25-1/2". The, loaded, rolling diameter of the tire can have an effect also; but for this it would be negligable. A drag cars' tires can balloon several inches effectively creating another top end gear ratio. 412RPM at the rear wheel is probably as tested in real life, and more accurate.

The ratio calculator can be used backwards: to show wheel RPM for a given speed and tire diameter. Simply key in a 1:1 ratio for each of the three dialog boxes and the calculator will treat it like the engine is connected directly to the rear wheel at a 1:1 ratio. 1st PIC attached.

Working backwards you can then figure your chain ring gearing and speed. Leave the first 2 dialog boxes at 1:1 and key in the chain ring and rear sprocket sizes. The RPM becomes how fast you must pedal for a given speed. PIC 2 below.

Jim



Jim
 

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Creative, you will not be able to fit a left-side jackshaft sprocket large enough to drop engine rpm from 6500rpm to 150rpm at the right-side jackshaft sprocket..bld.

The 40/16 ratio is good for pedalling but unsuitable for engine rpm reduction. It will INCREASE engine rpm.:-||

On the other hand a 16/40 ratio is unsuitable for pedalling but good for engine rpm reduction. This ratio will REDUCE engine rpm..shft.
 
5-7HEAVEN said:
Creative, you will not be able to fit a left-side jackshaft sprocket large enough to drop engine rpm from 6500rpm to 150rpm at the right-side jackshaft sprocket..bld.

The 40/16 ratio is good for pedalling but unsuitable for engine rpm reduction. It will INCREASE engine rpm.:-||

On the other hand a 16/40 ratio is unsuitable for pedalling but good for engine rpm reduction. This ratio will REDUCE engine rpm..shft.
Click to expand...

The engine has an internal 3:1 ratio reduction which brings the output shaft RPM down to 6500/3 or 2,166RPM. From there he has an 11T sprocket. If it is possible to mount a 44T on the left side the 4:1 reduction would then give 2,166/4 or 541 RPM transfered to the right hand side. At the right hand side; if a 1:1 ratio were used to the rear wheel, (44T at the jackshaft, and 44T at the rear wheel), the top speed would be 42MPH if the engine were powerful enough to do it.

I think I would gear it for a maximum of 25-30MPH based on the 50cc engine. This will require a final right hand side ratio change...i.e. a larger sprocket on the wheel than up front.

This is getting too difficult to explain...I think I'll go back to cobbling something in the shop.laff

Jim
 
ok the way i was told to fill in the gear calc was to enter 20 and 82 in the top 2 spots for the motor

the next 2 are the motor drive sprocket and the left side of the jackshaft

last 2 are the right side of the jackshaft and the rear sprocket

then wheels and 6000 rpm for top speed


not sure if thats what your after....hope this helped

ok i looked at your pics and im not sure thats gunna work

mine is 10t(motor) down to 24t over to 16t back to 22t freewheel.......gives me enuff low end with plenty of top end


that 44t is gunna put you into light speed....lol
 
junkyard said:
ok the way i was told to fill in the gear calc was to enter 20 and 82 in the top 2 spots for the motor

the next 2 are the motor drive sprocket and the left side of the jackshaft

last 2 are the right side of the jackshaft and the rear sprocket

then wheels and 6000 rpm for top speed


not sure if thats what your after....hope this helped

ok i looked at your pics and im not sure thats gunna work

mine is 10t(motor) down to 24t over to 16t back to 22t freewheel.......gives me enuff low end with plenty of top end


that 44t is gunna put you into light speed....lol
Click to expand...

This is right JY...

The Chinese in-frame engines have an internal gear reduction of 4.1:1, 82/20. 82 is the number of teeth on the clutch gear...20 is the number of teeth on the crankshaft gear...it equates to a 4.1:1 ratio.

His has an internal reduction of 3:1, so he has to step down a bit more to end-up with an acceptable rear wheel speed.

Jim
 
Creative Engineering said:
This is right JY...

The Chinese in-frame engines have an internal gear reduction of 4.1:1, 82/20. 82 is the number of teeth on the clutch gear...20 is the number of teeth on the crankshaft gear...it equates to a 4.1:1 ratio.

His has an internal reduction of 3:1, so he has to step down a bit more to end-up with an acceptable rear wheel speed.

Jim
Click to expand...

And that is the factor most people fail to input.....
the First Calculation of the equation is 20/82.
It goes like this:

a.- 20/82
b.- left side jackshaft ratio 10 /?
(engine output sprocket first [usually a 10 tooth])
c.- right side jackshaft ratio to rear wheel sprocket ?/?
d.- True Rear Wheel Diameter , and then desired engine R.P.M.

Jim Sitton (SP?) made a beautiful ratio calculator.
Here it is:
Index of /ratiocalc
'BrettMavriK
 
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