New Engine!!! Need help about chain drive

[duivendyk]

this 1000 figure is conservative,if hills are not a problem you could go to 750 and a 30:1 reduction.20mph corresponds to 270 rpm at the wheel (26").So at that speed your engine speed would be around 8k rpm,You could try 25 at 20mph you would have 6750 rpm.Take you pick.

 

[brendonv]

Well i just found out my engine is 31cc not 25cc lol, i got a manual of the internet and it has everything in it, how to clean it and other info like.
Stroke: 31.75mm ( 1.25 in. )
Displacement: 31cc ( 1.9 cu. in. )
Idle speed RPM: 2800-3600rpm
Operating RPM: 7000-8200rpm

It tells me how to tune the carby and clean everything, its really good.

Hope this info works.

 

[brendonv]

Can i do just a straight chain drive say, a 10T on the motor to a 55T on the wheel? According to the gear ratio calculator i would go pretty fast. Why do i have to do a 2 way reduction, atm im thinking ill just do friction drive again.

 

[duivendyk]

Yes you would go pretty fast,in theory at least,but you would never get there you would run out of torque (driving force) at some low speed.The engine torque at the wheel is multiplied by the reduction ratio,so in your case would be increased just 5,5 times and the the engine rpm would go up to that speed when this equalled the rolling resistance,at IDLE speed you would be doing over 50 km/hr.You need a 15-20 overall reduction.That's about what the friction drive would do for you.

 

[brendonv]

so your saying if i go from a 10T on the motor to a 20T then on to a 10T to a 40T on the wheel that should work well?

 

[duivendyk]

No, that works out to 20/10 * 40/10=8 ,you need 2-3 times as much, like 10 to 40 followed by another 10 to 40, giving a 16 overall reduction.If you live in the flats you could get away with that.Still pretty tall gearing in my estimation,around 4000 rpm at 30 km/hr (26" wheel)

 

[duivendyk]

For your further enlightenment I'll give you a handy formula(don't get all scared it's not all that bad).Here goes:
S= 0.12 * rpm/ R , S, road speed (km/hr), rpm (rev/min),
R is overall reduction.Lets try 4000 rpm, 16 reduction, we get: S= 0.12*4000/16 = 30 km/hr,take 5000 and 20 ,you get
S= 30.You see it's easy

 

[brendonv]

So if i have a little hills what reduction should i do? 10 to 40 to 10 to 60?

 

[duivendyk]

Probably something like that (if you can find it),depending on what you call "little" ,less than 5%?.( for every 10 m you go up 0.5 m),or a just a short hill, just what do you mean.Be more specific.

 

[brendonv]

i have say a 20 degree incline for about 300m.