What size sprocket to change to?

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GreedyRogue

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Sorry if this has been answered before, I didn't find much using the search.

I have a 80cc grubee motor that came with a 44t rear sprocket. Due to the load I carry with me at all times, I can't climb grades at all.

There are a couple roads that have between 8-12 (I'm guessing) grade on them, How big a sprocket do I have to get to climb those?

Would a 48 be enough or should I go up to a 56? I don't mind the loss in top end speed, In fact I would like to lose about 5-6 mph.

My friend went from a 44 to a 56 and actually gained 1-2 mph, not sure how.
 
The_Aleman

The_Aleman

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Jul 31, 2008
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Each tooth larger or smaller is worth roughly 1MPH. With a 26" wheel and 44T, you're going roughly 26MPH at 6000RPM. So figure you'd do well with a 50T sprocket.

Going from a 44 to a 56 is quite a jump. You'd be turning 6000RPM under 21MPH.
 
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GreedyRogue

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I must be doing better than 6000 rpm then. I have a cns v2 carb I am still trying to get tuned properly, but I have hit 32 mph fully loaded on a flat road more than a few times. I usually average 23-25 but higher speeds are not uncommon.

I was considering either a 48 or a 56 because they are more common sized, and I can get them cheaper. I just want to make sure I can climb the grades that I want to, without having to test multiple sizes. I can afford to only buy 1 sprocket. Just hope I get the right one first.
 
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GreedyRogue

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Either the gear ratio speed rating is wrong or the "each tooth bigger = 1mph slower" is.

With those numbers, a 44t gets 25.7.
Yet a 56 tooth gets 20.2

With the common understanding of sprocket ratio, going from 44 - 56 should lose 12 mph, according to the calc, it only loses 5.5.

Even with those numbers though, it still doesn't answer if I will be able to climb the grades I want. Looks like trial and error is the only way right now.
 
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5-7HEAVEN

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Aug 2, 2008
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Are you pedal-assisting? You should be.

Does your bike have a 7-speed(or more) cassette?

A 56-tooth sprocket STILL might not be the ticket, but pedal-assisting always helps.

My advice? Save your $$ and get a shift kit with the correct sprockets. You'll be able to conquer ANY hill, especially with pedal assist.

Your top speed will also increase immensely.xct2

The best of both worlds, climbing steep hills and top speed.

Save your $$ for the kit. It's worth every penny.dance1
 
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GreedyRogue

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I am pedal assisting, I do have a 7 speed, but a shift kit isn't legal here in Idaho.

I think I'm going to borrow a friends nt carb and see if it does better than this cns v2 I have. I can have a top speed of 20 mph one time and 30+ the next. No consistency at all.

I have a 66cc and my friends 49 cc outruns me by a long shot. Annoys the **** out of me.
 
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5-7HEAVEN

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Do you have an expansion pipe? If not, get one. That is prolly the best performance add-on you can get to beat ur friend's 49cc bike..wee.
 
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GreedyRogue

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I can see how the DL issue can be interpreted 2 ways but there is no way I can interpret this any other way;
"and the moped shall have a power drive system that functions directly or automatically without clutching or shifting by the operator after the drive system is engaged"

To be honest, I'm not even sure if the standard clutch that comes with most kits fits under this definition. Best I have been able to come up with is you only use the clutch to start / stop the engine.

If you put a shift kit on and you only shifted while the engine was off, I think even having the ability to shift would break this part of the statute.
 
DuctTapedGoat

DuctTapedGoat

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Dec 20, 2010
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Well, we know for a fact that we can shift with the bike disengaged - because it says without clutching or shifting by the operator after the drive system is engaged. If it's disengaged, we can regear.

OMFG LOL - what if we just turned off the motor, clutched, shifted and bump started back up?

Bam, legal shift kit.


But seriously, I need to get some definitions figured out as far as what kind of motor this was intended for so we have an idea of what they were thinking of when it was written.
 
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GreedyRogue

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Problem is, all it takes is one cop figuring out we can shift while the motor is running and we get in trouble.

I would rather just skip the shift kit if possible.

I would like to see a stacked rear sprocket system that could be manually changed with a spring loaded tensioner.

Say a 44/50/56/maybe even higher depending on the hills you come across. Then have a spring loaded tensioner that could take the slack even from the smallest without having to change the chain length.
 
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DuctTapedGoat

DuctTapedGoat

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Dec 20, 2010
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Yeah, I know. Like I said, I'm gonna do some research on that one to find out and just call the legislation library again.

Though - if you're looking for hill climbing power, the 44T is really great. With too large a sprocket, you'll hit peak rpm and not very high a load. 2 smokers are great at high rpm and under load, but you take that load off and the high rpm is it's worst enemy.

Maybe consider just getting an expansion chamber? Where I ride often there's a very strong road grade, and the 44T was enough to climb it with a 48cc and a stock exhaust with a shortened stinger. The SBP expansion chamber is awesome in comparison though, I accelerate going up steep hills now.
 
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syates234

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Jun 14, 2011
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I want to make my bike ride smoother. It seems to want to go faster then it really does. I was told to get a smaller sprocket which is what i want to do. Is there any other ways to make my bike dide smoother and has better performance ???
 
DuctTapedGoat

DuctTapedGoat

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Dec 20, 2010
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Hey - what part of Idaho are you from? I'm out in Nampa.

There's a few things you can do - biggest is make sure your motor is mounted straight, make sure you don't have too much or too little chain tension on the motor side, adjust the needle clip/rejet, etc etc.
 
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