Gearing ratio and Sprocket blank sources.

JBeasty

JBeasty

#1
#1
So I have a Minico or Zebra miniblike (not sure which) I've been tinkering with on and off for a few years.
It has a Predator 212 that has been moderately upgraded with performance parts. I adapted a Torque converter with a jackshaft mounted 7" driven pulley. My jack-shaft has a 9 tooth sprocket and my rear sprocket is a 37 tooth, which makes the final drive ratio approx 4 to 1. I'm thinking this is way too high. I have 8" rims, and with the tires makes them ~ 15" diameter - further upping my ratio.

I'm thinking I should be shooting for closer to a 6 to 1 ratio (9 front, 54 rear). Or should I go bigger in the rear? Also, I'll have to use a blank sprocket, as this is such an oddball brand. So far I've found this outfit:
Go Kart Galaxy - Sprocket Blanks
Prices seam kinda high, but what do I know. Any thoughts on gearing or sources for sprocket blanks?

Thanks, JB
 
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Raskin

Raskin

#2
#2
Nice bike..looks like that 9t-37t will be about 40mph @ 3600 rpm.not bad if you're happy with the low end..the 54t -28mph.pretty much a wheelie machine coz the tc low end grunt..41 or 42t 35mph is in the middle..those sprocket prices are pretty much normal
 
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JBeasty

JBeasty

#3
#3
Thanks Raskin. Your input will definitely factor into my decision. I think I may be getting higher than 3600 rpm after this latest re-do. Governor is gone and it will have a flat top piston, +0.020 billet rod, billet flywheel, .650 bored carb, CS grind cam, 22# valve springs, cleaned up intake and exhaust ports, and free(er) flowing air filter and exhaust.

I know I don't want it to go much faster than 40 mph though. I wasn't aware the TC gave it that much more grunt - good to know. I'll probably go with your suggestion of 5 to 1(ish).
 
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MB165

MB165

Active Member
#5
#5
the blanks from gokart galaxy are made by Azusa, I don't know if all are but, the ones I have purchased are aluminum
 
JBeasty

JBeasty

#10
#10
Charles S said:
https://www.oldminibikes.com/forum/mini-bike-discussion/152292-mb200-2-arrived-3.html#post1154371
Click to expand...
"A sprocket with an odd number of teeth will offer at least double the service life of a sprocket with even teeth. In simple terms, if a sprocket has an even number of teeth, the same tooth will be engaged by the same rollers on each rotation. This leads to uneven wear on the chain and sprocket and a shortened service life for both components"

Thanks, never even considered that. Wonder if it matters if you have an odd number of teeth on the front sprocket, and an even number on the rear. My little peanut brain tells me as long as one sprocket is odd numbered, you should be good.
 
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Charles S

Charles S

#11
#11
JBeasty said:
Thanks, never even considered that. Wonder if it matters if you have an odd number of teeth on the front sprocket, and an even number on the rear. My little peanut brain tells me as long as one sprocket is odd numbered, you should be good.
Click to expand...
It's because typical drive chains have an even number of links (an exception would be if you were running a half-link). An odd number front sprocket would not alter the chain to rear sprocket relationship (at least that's what I decided the last time I thought about this until the resultant headache caused me to stop). It's not quite as simple as how that article explains it; sprocket size (tooth count) would affect how often a particular link would contact a particular tooth. I'm pretty good at imagining/visualizing things, but this is complicated; I think it would require marking chain links and sprocket teeth and hand rotating the drive to understand what happens. A model, physical or virtual, would be interesting. I'm somewhat skeptical about odd tooth count doubling sprocket life, but I can understand it providing more even wear and thus possibly increasing both sprocket and chain life.
 
JBeasty

JBeasty

#12
#12
Hmmm. Interesting. If it turns out I'm thinking about it too much, I'll go out and mark teeth and links with colored dots. Truth is I doubt I'll ever wear out my chain/sprockets (even or odd). But you never know. I might decide I need to do a mad coast to coast marathon. :smile:
 
Raskin

Raskin

#13
#13
I would think taking the chain loose and moving it a little would change the contact onto different teeth so may help wear some if you're stuck with even number sprockets...disclaimer** no brains were hurt in this exercise..:laugh:
 
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