Gear ratio help I'm new to this.

[Shax90]

Hello I'm building a bike for the first time. If I'm using 26" tires a predator 212 and a torque converter what would you recommend for a gear ratio? If you need more Info let me know I'll try to give it to you. I know to an extent its personal preference but a good baseline would be great. I heard you can do either lower or higher ratio with a torque converter so I decided to get some help.

 

[JTSpeedDemon]

26" tires?? Are they mountain bike tires per chance?

You want to shoot for at least around an 8:1 gear ratio to keep from burning up the belt with those kind of big tires..

 

[Shax90]

Yes they are I'm scrapping some bikes to make the build cheaper. Do you think that will be a huge problem?

---------- Post added at 11:36 PM ---------- Previous post was at 11:31 PM ----------

26" tires?? Are they mountain bike tires per chance?

You want to shoot for at least around an 8:1 gear ratio to keep from burning up the belt with those kind of big tires..

I have to go pick up the bike still but they look to be 26 once I get it I'll measure to make sure. I also like the look of the bigger bike tires than the mini bike tires is there another size that's still kind of large that would work better? I'm building it to look more like a motor cycle than a mini bike. Kinda like a moped. I also have a centrifugal clutch do you think that would be better for larger tires?

 

[JTSpeedDemon]

Mountain bike tires won't work, just scrap that idea now. They won't hold up to that kind of power, and you'll have a headache matching the bolt circle to a sprocket. If you want a dirt bike look, track down some dirt bike wheels.
With bike tires yo may also run into a "pizza cutter" issue where there's not enough surface area on loose surfaces(like sand) and it just tries to sink in. Minibike tires may look goody to some, but they work, and that's why they look the way they do. Form follows function!

A torque converter will serve you much better than a centrifugal clutch in this application.

 

[Shax90]

Mountain bike tires won't work, just scrap that idea now. They won't hold up to that kind of power, and you'll have a headache matching the bolt circle to a sprocket. If you want a dirt bike look, track down some dirt bike wheels.
With bike tires yo may also run into a "pizza cutter" issue where there's not enough surface area on loose surfaces(like sand) and it just tries to sink in. Minibike tires may look goody to some, but they work, and that's why they look the way they do. Form follows function!

A torque converter will serve you much better than a centrifugal clutch in this application.

Okay if I have the dirt bike wheels do you think I should still do 8:1?

 

[mckutzy]

If this is a bike... With 2 wheels, I'm thinking you'll need a jackshaft, the ratio might be alright..
On my bike I built..
I have a 7:1, with a cent clutch, 24" OD rear tire(that is a car spare tire)

 

[Shax90]

If this is a bike... With 2 wheels, I'm thinking you'll need a jackshaft, the ratio might be alright..
On my bike I built..
I have a 7:1, with a cent clutch, 24" OD rear tire(that is a car spare tire)

I'm a bit confused on how jack shafts work could you explain why this would be a good idea or send me somewhere that could help.

 

[Shax90]

Mountain bike tires won't work, just scrap that idea now. They won't hold up to that kind of power, and you'll have a headache matching the bolt circle to a sprocket. If you want a dirt bike look, track down some dirt bike wheels.
With bike tires yo may also run into a "pizza cutter" issue where there's not enough surface area on loose surfaces(like sand) and it just tries to sink in. Minibike tires may look goody to some, but they work, and that's why they look the way they do. Form follows function!

A torque converter will serve you much better than a centrifugal clutch in this application.

I just found a dirtbike frame with wheels for $60 I'm using for the wheels and forks everything else I'm rebuilding I gotta measure the wheels but they look like 24"

 

[landuse]

Personally, I would shoot for more than 8:1. I would go about 10:1 if you can. If you are using a centrifugal clutch with 12T, that would mean a direct to axle sprocket tooth count of 120T. Obviously this is impractical to get a sprocket that large, so that is why you then use a jackshaft to reach that gearing, but with a whole bunch of smaller gears. You could use a 12T clutch to a 36T JS sprocket. Then a 12T from the other side of the jackshaft to a 36T on the axle. This will give you a (36/12)*(36/12) = 9:1 ratio

Look at Mckutzy's build to see how a jackshaft can be used

http://www.diygokarts.com/vb/showthread.php?t=5461

 

[Shax90]

Personally, I would shoot for more than 8:1. I would go about 10:1 if you can. If you are using a centrifugal clutch with 12T, that would mean a direct to axle sprocket tooth count of 120T. Obviously this is impractical to get a sprocket that large, so that is why you then use a jackshaft to reach that gearing, but with a whole bunch of smaller gears. You could use a 12T clutch to a 36T JS sprocket. Then a 12T from the other side of the jackshaft to a 36T on the axle. This will give you a (36/12)*(36/12) = 9:1 ratio

Look at Mckutzy's build to see how a jackshaft can be used

http://www.diygokarts.com/vb/showthread.php?t=5461

I'm actually planning on using a torque converter would that allow me to reduce the ratio?

 

[mckutzy]

Ok...
First... with the use of the dirt bike the rear sprockets arent going to be the same size that is in the TC. You will need to get appropriate sized sprockets and hubs that mate to your jackshaft dia. That will conform within the ratio desired...
Also itll be needed as the width of the centerline of the rear sprocket is wide as getting better alignment with the motor's weight and TC/clutch sprockets on center, so it is properly ballanced..

Also, a jackshaft will allow you to easier convert to a different ratio when needed, as typically itll be just the one sprocket.....(in your case youll have to think carfully as the dirtbike sprocket is the most different from all of it...)

If not too complicated for you or the wheel.. Id suggest trying to mate a common sprocket to the bike tire...Like a #35 or #40/41 weld on sprocket, around 72t..
You might need to stand-off, or drill the center hole bigger, or even weld/bolt it to the stock one as you wont be using it... .. but however.... I could see this working out about this way...

 

[Shax90]

Ok...
First... with the use of the dirt bike the rear sprockets arent going to be the same size that is in the TC. You will need to get appropriate sized sprockets and hubs that mate to your jackshaft dia. That will conform within the ratio desired...
Also itll be needed as the width of the centerline of the rear sprocket is wide as getting better alignment with the motor's weight and TC/clutch sprockets on center, so it is properly ballanced..

Also, a jackshaft will allow you to easier convert to a different ratio when needed, as typically itll be just the one sprocket.....(in your case youll have to think carfully as the dirtbike sprocket is the most different from all of it...)

If not too complicated for you or the wheel.. Id suggest trying to mate a common sprocket to the bike tire...Like a #35 or #40/41 weld on sprocket, around 72t..
You might need to stand-off, or drill the center hole bigger, or even weld/bolt it to the stock one as you wont be using it... .. but however.... I could see this working out about this way...

Ya that was my plan with putting another sprocket on the dirt bike tire I've worked in a fab shop for a couple years so I trust my welds enough to weld it on there.