Need help getting my ratios correct

[Boz Mon]

I'm not sure if my gearing for my snowbike build is anywhere close to where it needs to be. Heres all of the info that I have that I though would be relevant:

Track drive wheel is 7.5 inches diameter
Track circumference is about 46 inches
The height of the track and wheel is about 9 1/4 inches
The driver gear on the torque converter is 12 tooth
The biggest gear I could fit on the back was a 54 tooth, and its 6.66 inches
This is all with #35 chain.

Can anyone help me make heads or tails of this info? I cannot go any bigger on the rear gear because it would be bigger than the track. I originally thought that the final drive wouldnt matter that much because the torque converter would make up for it on the low end, but now I have no idea.

 

[SAT]

I'm not sure if my gearing for my snowbike build is anywhere close to where it needs to be. Heres all of the info that I have that I though would be relevant:

Track drive wheel is 7.5 inches diameter
Track circumference is about 46 inches
The height of the track and wheel is about 9 1/4 inches
The driver gear on the torque converter is 12 tooth
The biggest gear I could fit on the back was a 54 tooth, and its 6.66 inches
This is all with #35 chain.

Can anyone help me make heads or tails of this info? I cannot go any bigger on the rear gear because it would be bigger than the track. I originally thought that the final drive wouldnt matter that much because the torque converter would make up for it on the low end, but now I have no idea.

I would plug your values into the BMIkarts gear ratio calculator. There’s a guy on FB listing a home-built track bike for sale. Maybe you would benefit from a peek at it. I would think 8:1 would be a good starting point.

 

[Boz Mon]

That gave me a gear ratio of 4.500 with a top speed of 17.xxx. That doesn’t take in account the torque converter. Does that not apply to the equation?

 

[SAT]

That gave me a gear ratio of 4.500 with a top speed of 17.xxx. That doesn’t take in account the torque converter. Does that not apply to the equation?

It does, depending on which TC. Some have a bit of overdrive built into them. It can be remedied with a machined bushing to restrict the driver range of motion. 4.5:1 sounds pretty tall.
Trial and error,maybe? Maybe start a new thread with specific wording to attract more folks attention.
Member jeep2003 has built some machines that overlap yours.

 

[R.E. Wallace]

I'm not sure if my gearing for my snowbike build is anywhere close to where it needs to be. Heres all of the info that I have that I though would be relevant:

Track drive wheel is 7.5 inches diameter
Track circumference is about 46 inches
The height of the track and wheel is about 9 1/4 inches
The driver gear on the torque converter is 12 tooth
The biggest gear I could fit on the back was a 54 tooth, and its 6.66 inches
This is all with #35 chain.

Can anyone help me make heads or tails of this info? I cannot go any bigger on the rear gear because it would be bigger than the track. I originally thought that the final drive wouldnt matter that much because the torque converter would make up for it on the low end, but now I have no idea.

I'm not sure if my gearing for my snowbike build is anywhere close to where it needs to be. Heres all of the info that I have that I though would be relevant:

Track drive wheel is 7.5 inches diameter
Track circumference is about 46 inches
The height of the track and wheel is about 9 1/4 inches
The driver gear on the torque converter is 12 tooth
The biggest gear I could fit on the back was a 54 tooth, and its 6.66 inches
This is all with #35 chain.

Can anyone help me make heads or tails of this info? I cannot go any bigger on the rear gear because it would be bigger than the track. I originally thought that the final drive wouldnt matter that much because the torque converter would make up for it on the low end, but now I have no idea.

Boz,
The Comet torque converters start with a 3:1 ratio (low rpm's) & max out in 1:3 ratio (hi rpm's) if I'm not mistaken. The first number of the ratios are the engine & the last number of the ratios are for the jack-shaft. The Comet series 30 is the same but will add an extra 10% overdrive at Maximum rpm. That's around 3300 - 3600 rpm for the average 4-stroke. Also worth mentioning is that the series 30's are asymmetric, meaning that the belt is steep angled on one side & almost no angle on the other side. If you're running 8HP or more, you'll need to step up to the series 40 setup. Series 20 & 40 are symmetric, meaning that the belt has about a 15 degree angle on both sides. I hope this helps to point you in the right direction. Do you have any pics? Good Luck!

 

[Boz Mon]

My converter has an angle on just 1 side. Like I said before, I can’t get a bigger gear on the drive track so I’m not sure how to get my ratio closer.

 

[R.E. Wallace]

My converter has an angle on just 1 side. Like I said before, I can’t get a bigger gear on the drive track so I’m not sure how to get my ratio closer.

I just posted some pics of the axle drop-plates that I added to gain more clearance for a 60 tooth sprocket. They're posted under the "Trikes" heading on this site.

 

[Boz Mon]

I just posted some pics of the axle drop-plates that I added to gain more clearance for a 60 tooth sprocket. They're posted under the "Trikes" heading on this site.

I see that. I don’t think that would help my application though. My sprocket is literally almost the exact diameter of the drive wheel

 

[R.E. Wallace]

I see that. I don’t think that would help my application though. My sprocket is literally almost the exact diameter of the drive wheel

Maybe you need taller wheels! lol! Just something to think about.

 

[Boz Mon]

I can’t put taller wheels on because the wheels drive the track.
I just ordered a 10t gear that seems like it will work. That will at least gear me down a bit.

 

[R.E. Wallace]

I can’t put taller wheels on because the wheels drive the track.
I just ordered a 10t gear that seems like it will work. That will at least gear me down a bit.

Oh, I didn't know it was a track vehicle! Any pics?

 

[Boz Mon]

Oh, I didn't know it was a track vehicle! Any pics?

i have a build thread in the builds section, all the pics are there

 

[SAT]

L

i have a build thread in the builds section, all the pics are there

Looks like you have enough room for a jackshaft. Maybe it would help on the final engine location. It might allow you to reduce the size of the axle sprocket, could keep it a bit out of harm’s way.
The ratios could be fine-tuned the way you like.
Just a thought

 

[massacre]

You will need to make a jackshaft and run that 54 tooth with like a 10 or 12 tooth attached. then a chain from that 10 or 12 to another 54 tooth?
sounds like you need to gear down

 

[massacre]

If 54 teeth is the biggest you can go, if you can’t get the ratio you want, you will have to run more than one 54 tooth sprocket to achieve the final ratio.

 

[Boz Mon]

So I need to run the torque converter with 2 jackshafts?

 

[massacre]

It appears so.

 

[Boz Mon]

Ok. Well before I fabricate some crazy 2 jackshaft thing, I might just try my 10/54 with he torque converter. What’s the worst that could happen? It just won’t push the machine?

 

[massacre]

Yes you should definitely test it and see how it goes. Maybe it’s fine

 

[jeep2003]

What engine are you using? anything over 5hp i wouldnt worry about that at all. If anything I think youre gearing it too low