Perfect Gear Ratio?

[Insung]

Hi, I'm planning to build an ebike with a 24" rear wheel, but I'm stuck on what the best gear ratio would be for me. I was told to use a two stage chain drive but I have no clue how it works and how to install it on a bike, so is there a way to make it single stage? I don't know if this helps but I need some torque, and I don't care if it affects my top speed, but not to much torque so I wouldn't be able to keep the front wheel down. Anything helps.

 

[DogDipstick]

What are your off the line tork goals ( Slow bike, with wheelies, or fast bike, soft takeoff, and high top speed?) , and what is the RPM ( speed) you want ( the back wheel) to go? What motro RPMis expected? ( how many volts, what is the kV of the motor,, and whats your bvoltage?

How much " power" will you want to go for? Goal?

 

[DanGT86]

Hi, I'm planning to build an ebike with a 24" rear wheel, but I'm stuck on what the best gear ratio would be for me. I was told to use a two stage chain drive but I have no clue how it works and how to install it on a bike, so is there a way to make it single stage? I don't know if this helps but I need some torque, and I don't care if it affects my top speed, but not to much torque so I wouldn't be able to keep the front wheel down. Anything helps.

Brushless motors have an approximate RPM per volt (called kv) that will determine your RPM based on your battery pack voltage. So if you have already chosen your battery and motor then you just need to pick a gear ratio that gives you the top speed you want.

This is a nice calculator for figuring this out.

The Recumbent Bicycle and Human Powered Vehicle Information Center

Recumbent and Human Powered Vehicle Information Center

recumbents.com

I'm guessing someone told you to use a 2 stage gear reduction because you are dealing with a very high rpm motor and there is not a practical way to get it done with just a simple motor and wheel sprocket. For instance if the max rpm of your wheel needs to be 400rpm and you have a 4000rpm motor then you would need a 10tooth motor sprocket and a 100tooth wheel sprocket. 10 tooth sprockets are loud and wear out fast and 100tooth sprockets are very large. So if you are stuck with those numbers you would use a 2 stage reduction. So you could do something like:
15tooth motor sprocket to a 30tooth jackshaft sprocket for stage one
14 tooth jackshaft sprocket to 70tooth wheel sprocket for stage 2

This would get you 4000rpm X 15 / 30=2000rpm at jackshaft
2000rpm X 14 / 70=400rpm at the wheel

Using multiple stages like that gets you into sprockets that reasonably fit on a bike and are not stressing the chain by forcing it around a very tiny sprocket. Even the numbers I used in this example would be challenging with bicycle chain. These numbers are very reasonable with 219 kart racing chain.

 

[richj8990]

Hi, I'm planning to build an ebike with a 24" rear wheel, but I'm stuck on what the best gear ratio would be for me. I was told to use a two stage chain drive but I have no clue how it works and how to install it on a bike, so is there a way to make it single stage? I don't know if this helps but I need some torque, and I don't care if it affects my top speed, but not to much torque so I wouldn't be able to keep the front wheel down. Anything helps.

First off are you on pavement or offroad. 24" offroad may not be the best idea. So I assume it's pavement. That means a hub drive would be a lot easier to deal with / install for pavement. They have geared hub drives that work just fine and have an 'acceptable' amount of torque. If you are using smaller wheels then you simply use a larger chainring, like 38T middle and 52T big. Who told you to use a 2-stage chain drive on pavement? And why would you want to use a 24" rear wheel? You can get a cheap 27.5 or 29 bike with disk brakes for $300 and then do the conversion. I can pretty much promise a bike like that will not be any worse than a bike that has a 24" rear wheel.

 

[fabieville]

I have a cyclone 24v-72v 3000watt brushless geared motor running at 36v .

I'm currently using a 28T sprocket on the back and the same 28T on the motor. My amps draw on flat terrain is between 28-30 amps. I want to decrease my amps draw on flat terrain to about 20amps max.

What ratio would be best in terms of teeth difference to use. I want to keep the 28T at the motor shaft so what size sprocket should I use at the back? The options at the back are 32,34 and 38.
Which one of these would be best to use at the back to get that 20amps max draw on a flat terrain with good enough torque and a speed on flat terrain at 20-25mph?