gearing, sprockets and hub questions

Mini Bike & Go-Kart Parts

#1
Ready to order sprockets for the jimmy gote. 13 hp, with jackshaft and torque converter. Be used for trail riding mostly, not really interested in high speed. If it does 35mph I'll be happy. Needs to be able to carry myself and a couple hundred pounds of elk. I was think of a starting gearing around 7 to 1. That sound reasonable or am too low? What value do I give the TC when figuring ratios? Using number 40 chain. It is my understanding that 40/41/420 sprockets all will use 40 chain, am I correct in that? I see several bolt patterns on wheel sprockets. I am running a 22 11 10" rear tire. are some bolt patterns more common and easier to find then others? My rear axle is a 1" keyed shaft so am looking at go cart hubs. My thinking is the larger 4" pattern should be stronger but didn't want to dedicate myself to some odd sprocket that will be a pain to replace later.
 
#2
Jim, do you have the Jack Shaft gearing calculator? If not, let me know. For the Comet TC, the ratio is from zero to 90% over drive. 7:1 might not quite get you to 35MPH, but is fine for a ratio target- with your tire OD being the driving factor.

The way you asked the chain fitment question, the answer is yes. 40,41, and 420 fit a 41 sprocket. A 40 sprocket will not accept a 41 chain however. I cant answer the bolt pattern question.

PM me your mailing address if you want, as I have two 40" lengths of 40 and 420 chain I will never use.
 
#3
Jim, do you have the Jack Shaft gearing calculator? If not, let me know. For the Comet TC, the ratio is from zero to 90% over drive. 7:1 might not quite get you to 35MPH, but is fine for a ratio target- with your tire OD being the driving factor.

The way you asked the chain fitment question, the answer is yes. 40,41, and 420 fit a 41 sprocket. A 40 sprocket will not accept a 41 chain however. I cant answer the bolt pattern question.

PM me your mailing address if you want, as I have two 40" lengths of 40 and 420 chain I will never use.
thanks for the reply. Yes I got the jackshaft calculator thingy, I just wasn't sure if I should use the TC at start up ratio, or at WOT, or ignore and pretend it was a 1 to 1. I may just take you up on the chain! Thanks again Jim
 
#4
For me, it's all about K.I.S.S. So I'd opt for mentally computing 1:1 during the design phase, and allow myself some engineering options on the JS to move up or down a tooth. From what I gather, using a TAV assembly instead of separate driver/driven to a JS causes some degree of limitation on options. Never used a TAV, just from reading here.
 
#5
For me, it's all about K.I.S.S. So I'd opt for mentally computing 1:1 during the design phase, and allow myself some engineering options on the JS to move up or down a tooth. From what I gather, using a TAV assembly instead of separate driver/driven to a JS causes some degree of limitation on options. Never used a TAV, just from reading here.
I am running the driven pulley on a jackshaft for clearance issues. If I use their backing plate I either have to hang it down under the frame or cut off 1/2 of the cylinder. So from that jackshaft to another jackshaft, to the wheel. So I should be able to switch enough sprocket sizes to get where I need. Even thought of two different sprockets side by side on the secondary shaft, both slightly off center so I have a high and low. Kind of like the early Honda CT90's or the 185 Suzuki from the 70's. Sprockets are cheap, I'm just hoping for a starting point. Also didn't want wheel sprocket being so big it hits rocks. Hopefully this weekend it will be a roller. Then gearing, controls, etc, then strip it down, sand and paint. Then cuss because I scratched the hell out of it putting parts back on. Then go flog it in the woods.(if the fire restrictions lift)
 

CarPlayLB

Well-Known Member
#6
The sprockets for #40/41/420 are kind of limited. I like that you have the 1" rear axle though! As long as the axle has a 1/4" key way, a hub like this will work
https://www.OldMiniBikes.com/uni-hub-steel-zinc-plated-1-bore-1-4-keyway-plus-hardware-kit.html

and the matching 60 tooth sprocket here
https://www.OldMiniBikes.com/sprock...-6-holes-5_25-bolt-circle-p5245-60-tooth.html

That is the largest tooth count, off the shelf, sprocket available for the bigger chain. A 10 tooth gear on the jackshaft will give you a 6:1 ratio.
https://www.OldMiniBikes.com/-40-41-420-chain-10-tooth.html
An 8 tooth sprocket is here for a 7.5:1 ratio
https://www.OldMiniBikes.com/-40-41-420-chain-8-tooth-with-keystock.html

or a 9 tooth for a 6.67:1 ratio
https://www.OldMiniBikes.com/-40-41-420-chain-9-tooth-1.html
 
#7
Great timing. I'm setting up my first fattie right now.
I have 60/10 sprockets, Comet 30
El Burro with 21" tire.
Tec HM100
I was hoping for 40MPH@4k and that sounds like it should be good.
 

SAS289

Well-Known Member
#8
Great timing. I'm setting up my first fattie right now.
I have 60/10 sprockets, Comet 30
El Burro with 21" tire.
Tec HM100
I was hoping for 40MPH@4k and that sounds like it should be good.
Too me this is one of the most interesting topics. How did you figure your RPM at top speed with a TAV?

We already know the OD function of the TAV will/can restrict the engines maximum RPM capability due to gearing. My question is, is it possible to target a max RPM you would like to run at top speed, then gear to that? It would be nice to get close from the get go so you wouldn't have to keep changing the gearing.

I could care less about the top speed number. The max RPM number is more important for what I want to do. Or not do with the engine.

Say I want to run out of engine at 4700 RPM with a TAV. How do I gear to that with 19 inch tires?
 
#9
Too me this is one of the most interesting topics. How did you figure your RPM at top speed with a TAV?

We already know the OD function of the TAV will/can restrict the engines maximum RPM capability due to gearing. My question is, is it possible to target a max RPM you would like to run at top speed, then gear to that? It would be nice to get close from the get go so you wouldn't have to keep changing the gearing.

I could care less about the top speed number. The max RPM number is more important for what I want to do. Or not do with the engine.

Say I want to run out of engine at 4700 RPM with a TAV. How do I gear to that with 19 inch tires?
WAG, mostly. I used the ratio/speed calculator, and entered my rear sprocket at .9 of actual, 54 vs 60, to adjust for the OD function of the 6" driven. Mine is a standard Comet, not the TAV setup, so I have a little adjustment in C/C distance to play with as well. I'm used to the sled clutches, exponentially more tuneable than these. I'll hook up a tach, set the phone for GPS, mark the sheaves to check belt travel. Maybe even mount the cam/phone to view clutch for a little run down the block, top end, trailing and adding throttle, to see if I can get it feeling and working how I'd like.


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And, if yours hits .9 OD, you'd add 10% on the rear to 66t,
 
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#12
I think it is a guess, tho with more experience and money spent, the guess gets better. Horse power enters into it. Just because it works on paper, doesn't mean the motor has the hp to drive the gears. Add weight, altitude, etc and it's a guess, or a starting point. For me I really don't care about top end. I want the bike to haul, me, maybe a hunting buddy, and our gear and or deer or elk. Speed isn't much of an issue. But having said that, I don't want to be a rolling road block if I have to go down the road a ways. I am not sure I would look good as a hood ornament.
 

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