Help me pick my drive sprockets

[micmac]

I'm currently in the process of the worlds slowest Max IV re-build. It has a Briggs 31 hp Big Block and now I need to figure my gearing. The T-20 has the standered 15 tooth sprocket. What drive sprocket should I consider for all around drivability? I was thinking 30 tooth but would like to get some input on the selection.

Mike

[Bazooo guy]

Do you mean the sprockets on the axles, or the output of the t20?
You may be limited by clearance on the axles.
I would keep them close to the factory size. + or - 2 teeth should be ok.

[Mike]

Mike, check out the last column of this gearing chart if you haven't seen it yet:


It doesn't take into account the CVT ratio, so consider that, but it should give you a close idea of the gearing, RPM, speed, etc. With the 34 tooth that I have on my Max IV, it is geared very low. I feel like even a 16HP motor could turn the Vampire ASX tires I have with ease. I mainly use mine in the mud so I wanted to keep it where it has loads of torque, one reason I kept the 34 tooth. If I plug in a 30 tooth sprocket in that spreadsheet, the speed changes to 34mph (@5500RPM), the chain drive reduction ratio is 2:1 and the final gear ratio is 12.5:1.

I think you could probably go down even further than that with your Big Block. What kind of torque does that motor produce and at what RPM?

[micmac]

I mean on the axles. The machine was originally the low rent 16 hp version which came with 34 tooth pie plates to make up for the low engine hp. Rest have 26 tooth not that it matters.

[micmac]

Thanks Mike that's the kind of input I'm looking for. I plan on keeping the engine governed at 3600 initially. So I'm thinking possibly a 28 tooth sprocket might yield the best of both worlds torque and speed.

[thebuggyman1]

Are you going to move the trans forward, and drop the engine down?
If you are leaving it in the stock position, I'd try the stock gearing to see if you like it. It might give you a better idea of how much to change it.

[whipper-ag]

[micmac]

Are you going to move the trans forward, and drop the engine down?
If you are leaving it in the stock position, I'd try the stock gearing to see if you like it. It might give you a better idea of how much to change it.

No Jim at this point there isn't much stock to speak of as far as the frame goes. I moved the T-20 forward and dropped the engine to the frame. I pretty much copied what whipper did with Godzilla but nowhere near as pretty. Kind of like Bizzaro superman next to the real thing.

[micmac]

Thanks Whipper ill go with the 28 tooth. I'm about a year and a half at this point. It's all Jpswift's fault! Him selling me a darn low price powerful engine causing me to have to reinvent the wheel.

[MAX IV Mark]

Since your in the development stage. I would consider changing the chain from the T20 to the rear axle to a 60 size chain. With my 29hp Kawasaki mine has been stretching too much since new. I know I am a little hard on my machine. I have pulled, plowed, pushed, towed, climbed, slogged and winched to its capacity. Now at just under 150 hours, and it has stretched enough to snap all the teeth off the axle sprocket. Mine came from the factory with a 15 tooth drive sprocket on the T20 and a 34 tooth sprocket on the axle, in 50 oring chain. This is a .441 ratio. I just ordered the parts to go to a 12 tooth T20 to a 27 tooth axle in 630 oring motorcycle chain. This is a .444 ratio. These sprockets have approximately the same diameter as stock, but less teeth because of larger pitch. I was thinking about increasing the ratio for more top end, but I am happy with the low end power my machine has now, and didn't want to decrease it. I may raise the govern up on the engine a few hundred RPM later for more top end. Just something to think about.
MAX IV Mark