4-stroke sprocket question

phyrstorm · Oct 16, 2012

My first build was a 2-stroke and I was able to get a 27-tooth sprocket and modify it for my engine... Im a pretty light guy: about 140-150~ that being said; The 2-stroke was fine with a 27 tooth sprocket( got it from staton-inc online) in terms of acceleration, hills, and great top speed...

Would a 27-tooth sprocket be alright for my 4-stroke if the 2 stroke performed as it did... Im getting up to about 31mph now with a 44-tooth sprocket. My motor is a stock Stage III Skyhawk HS 49cc...(has metal gears instead of belts for centrifugal clutch area)

xct2

phyrstorm · Oct 16, 2012

26" wheels on my bike------>

laff

MotorBicycleRacing · Oct 16, 2012

phyrstorm said:
My first build was a 2-stroke and I was able to get a 27-tooth sprocket and modify it for my engine... Im a pretty light guy: about 140-150~ that being said; The 2-stroke was fine with a 27 tooth sprocket( got it from staton-inc online) in terms of acceleration, hills, and great top speed...

Would a 27-tooth sprocket be alright for my 4-stroke if the 2 stroke performed as it did... Im getting up to about 31mph now with a 44-tooth sprocket. My motor is a stock Stage III Skyhawk HS 49cc...(has metal gears instead of belts for centrifugal clutch area)

Do you have a pic of your 2 stroke?
What kind of performance mods does it have?
I find it hard to believe that a 27 tooth sprocket worked well on it.
A 36 tooth sprocket would work much better and still give you a
~39 mph top speed.
What is your top speed?

As for your 4 stroke I don't remember what the ratio of the Stage III
gearbox is and what size output sprocket it has.
Do you know?

I really doubt if your ~2 hp HS 49 cc will pull that gearing.

The_Aleman · Oct 16, 2012

The chinagirl 2-stroke has an internal gear reduction of 4.1:1

Looking at my grenaded Stage III, I count 3.7:1 (35 -> 54, 20 -> 48, 11T output)

That equates to a 9.08:1 overall ratio if you use a 27T on your 4-stroke setup. That isn't gonna work well at all. That would mean 60MPH @ a Huasheng's HP peak. The clutch wouldn't fully lock until around 25MPH. I recommend a 44T as that's about the tallest gear you can hit HP peak with on flat ground (37MPH).

Even with a 44T, your clutch aint gonna lock until about 15-16MPH. It's still a rather tall gear, and the Huasheng doesn't have the midrange and peak power that the chinagirl 2-stroke has.

MotorBicycleRacing · Oct 16, 2012

phyrstorm said:
.

Would a 27-tooth sprocket be alright for my 4-stroke if the 2 stroke performed as it did... Im getting up to about 31mph now with a 44-tooth sprocket. My motor is a stock Stage III Skyhawk HS 49cc...(has metal gears instead of belts for centrifugal clutch area)

Thanks Ale for the ratio of the Stage III piece of junk.

Your 44 tooth sprocket on your 4 stroke bike will give you a top speed
of 41 mph at the motors redline of 7800 rpm.

So your bike is only revving out to 5900 rpm now at 31 mph

Going down to 27 teeth would give you a top speed of 67 mph
which you will never come close to pulling.
Just gonna burn your clutch up.

moonerdizzle · Oct 16, 2012

i run a 16-1 setup onmy four stroke, more pedaling till the clutch locks, but shes fine over 15mph, but yea, 27 is too small, i got the 4-1 tbelt tranny with 10 tooth out put and a 40 tooth rear sprocket.

phyrstorm · Oct 18, 2012

Thanks guys for all the good info.. I would post a picture of my 2-stroke ,, but I never took one and it got stolen. When I decided to get a new kit I went for the 4-stroke mainly to avoid having to mix oil into my fuel. I'm alot happier with it as it is quieter and smoother, but im just not going quite as fast as my 2-stroke was( i think i was getting up to around 42mph).
and yea I'm definitely not getting up to the redline on my 4-stroke. I had an air leak and fixed it up but Im still not getting up to 41 with my 44-tooth sprocket( I also was not able to get up to my top speed with the choke fully disengaged... I had to choke it a bit to get up to my perceived redline~ I'd appreciate any good info about this)... I think Ill take apart my carb again and get some gasket sealer in connections.

@ MotorBicycleRacing --> (quoted from The_Aleman earlier in thread) "Looking at my grenaded Stage III, I count 3.7:1 (35 -> 54, 20 -> 48, 11T output)"
i would think these numbers apply to my engine as well...
Would I be ok running a 36 or 40 tooth rear sprocket, I dont mind pedaling a bit to get going and Id like to top out in mid 40mph range if possible and be able to cruise in the 20 and 30mph range.

Thanks again!

MotorBicycleRacing · Oct 19, 2012

phyrstorm said:
@ MotorBicycleRacing --> (quoted from The_Aleman earlier in thread) "Looking at my grenaded Stage III, I count 3.7:1 (35 -> 54, 20 -> 48, 11T output)"
i would think these numbers apply to my engine as well...
Would I be ok running a 36 or 40 tooth rear sprocket, I dont mind pedaling a bit to get going and Id like to top out in mid 40mph range if possible and be able to cruise in the 20 and 30mph range.

Thanks again!

Your motor will not pull less than 44 tooth sprocket and will not
go much over 40 mph as it only has about 2 hp.
If your bike can go 41 mph with a 44 then you could think about using a
smaller rear sprocket.

No matter how much you pedal your gearing won't let you go faster
than 40 mph and your take off will suffer.
If you gear it too high you will actually have a lower top speed and
may burn your clutch up.

The_Aleman · Oct 19, 2012

Yeah, the Huasheng simply makes less power than the chinagirl 2-strokes. 2HP is only going to propel you so fast, no matter what the gearing.

All you can really do is be content with 30MPH cruising or step up to a bigger, more powerful engine. Myself, I've had a stock Huasheng for 2 years and I love it. I used to be able to hit 40-42 on my 66CC 2-strokes with a 34T sprocket, but I'm much more content cruising at 20-29 with the smoother 4-stroke. YMMV of course

moonerdizzle · Oct 28, 2012

The_Aleman said:
Yeah, the Huasheng simply makes less power than the chinagirl 2-strokes. 2HP is only going to propel you so fast, no matter what the gearing.

All you can really do is be content with 30MPH cruising or step up to a bigger, more powerful engine. Myself, I've had a stock Huasheng for 2 years and I love it. I used to be able to hit 40-42 on my 66CC 2-strokes with a 34T sprocket, but I'm much more content cruising at 20-29 with the smoother 4-stroke. YMMV of course

cant beat the sound of a thumper chugging away at 20mph.

phyrstorm · Nov 2, 2012

fixed the air leaks, topped out around 40~41,went from 11 to the 12tooth freewheel with my 44 rear sprocket.. havnt clocked it yet---

http://www.kabamus.com/garage/gears.html ---> gears and speed converter

4stroke HS Skyhawk Stage III; Differential Ratio: 3.7:1
-- Transmission Gear Ratio 44:12= 3.66:1 from 11teeth 4:1

the switch definitely makes 20-30mph easier on the engine rpm, i may get some kind of shift kit for a slower starting gear...

stewpedassle · Dec 13, 2012

i hav 4g 80t solid pulley 12t freewheel drive on 29" genisis astra w 36 tooth works well get about 32-35 on flat i weigh 240

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