79cc gear ratio?

[waynesdata]

Most kits I have seen have the same default gear setup.

Motor Sprocket 11 tooth
Jackshaft Input Sprocket 22 tooth
Jackshaft Output Sprocket 9 tooth
Wheel Sprocket 44 tooth
Tire Height 26“

Is this gear ratio ok?

 

[TheNecromancer13]

Most kits I have seen have the same default gear setup.

Motor Sprocket 11 tooth
Jackshaft Input Sprocket 22 tooth
Jackshaft Output Sprocket 9 tooth
Wheel Sprocket 44 tooth
Tire Height 26“

Is this gear ratio ok?

That gear ratio is about 9.78:1, way too steep for a 79cc predator. You'll burn up your clutch and won't be able to go up hills. I have mine geared at 13.1:1, I weigh 155 lbs, it tops out at 40 mph. I wouldn't recommend buying the kit though, most of the parts are **** and it doesn't include everything you'll need to build the bike. Here's what I do: https://www.instructables.com/id/79cc-Motorized-Bicycle-From-Scratch/

 

[Dan]

Wayne, I misread and messed up the math. Necro is 100% correct. But do love that jackshaft. I can't make one from scratch for that price ($99 as of this post) Really is stout and well finished. I deleted my bad advice so as not to cause confusion.

I just use a larger rear sprocket. 54T gives you 12:1.

9:1 would work but is not fun at take offs. Shudders real bad. I did not burn threw any clutches but am sure I would have eventually and I was using less then 9.78:1 .

What did you decide on doing?

 

[waynesdata]

I do not know yet. I got a frame from gasbike when I ordered wheels. Will need to find out if the four stroke mounting hardware will clear my built in mount.

 

[Flyman]

Necro I have a question about your 13 to one ratio. Your 79cc Predator would have to be turning over 6000 RPM to do 40MPH. Even with the governor
removed I can not see that. The math does not add up.

 

[TheUserMac]

See I saw that kit and their out of stock does anyone know where I can order another I don't mind buying a separate sprocket to correct my gear ratio

 

[Sidewinder Jerry]

Necro I have a question about your 13 to one ratio. Your 79cc Predator would have to be turning over 6000 RPM to do 40MPH. Even with the governor
removed I can not see that. The math does not add up.

In order to get close to 40 mph using 13.1:1 at 6000 rpm you'd also need 29" tires.

(6,000×π×29)÷(13 1×1,056)=39.5151747719

 

[Sidewinder Jerry]

Most kits I have seen have the same default gear setup.

Motor Sprocket 11 tooth
Jackshaft Input Sprocket 22 tooth
Jackshaft Output Sprocket 9 tooth
Wheel Sprocket 44 tooth
Tire Height 26“

Is this gear ratio ok?

The recommended safe rpm for these stock engines is 4000 rpm. With your setup on 26" tires your speed will be 31.6 mph

(4,000×π×26)÷((44÷9×2)×1,056)=31.6431078228

 

[Sidewinder Jerry]

Your ideal setup would be to get a fixed geared IGH for a jackshaft transmission and run 11/36;14/56. This'll give you the following reductions.

1) 17.45:1

2) 13.09:1

3) 9.82:1

Get a tachometer. If at WOT you're going over 4000 rpm shift to a higher gear. If at WOT you drop below 3000 rpm shift to a lower gear

 

[TheUserMac]

Your ideal setup would be to get a fixed geared IGH for a jackshaft transmission and run 11/36;14/56. This'll give you the following reductions.

1) 17.45:1

2) 13.09:1

3) 9.82:1

Get a tachometer. If at WOT you're going over 4000 rpm shift to a higher gear. If at WOT you drop below 3000 rpm shift to a lower gear

Any links so I can cheat the researching process?

 

[Sidewinder Jerry]

Any links so I can cheat the researching process?

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Is it possible

Why not instead of getting a jackshaft to use the shifting gears flip the motor around and not even worry about a jackshaft wouldn't the sprocket be going in the right direction and then you can maybe use a 3speed or better internal hub shifter would that work

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