Top Speed of Belt Drive Chinese 4 Strokes

Sidewinder Jerry

Well-Known Member
Joined
Mar 14, 2011
Messages
2,256
Your installation is way to complicated and expensive. Long ago, I accomplished the
same result with my RS 35 using a simple $29 5:1 scooter gearbox with a 17T sprocket
driving a 54t sprocket for a 15.88 ratio. It's a double-sided right drive. The setup
drives the rear wheel so it's safe. I designed the motor mount with simple aluminum
and steel angle iron. It has always been very reliable without the use of expensive
staton parts and fun to ride. I'm planning right now beef up my motor mount for the
gx50.
To get 330 lbs up a 30%+ grade hill using 26" Wheels and a RS 35 you'll need a minimum of a 55:1 reduction. Even on level ground pushing 330 lbs on 26" wheels requires a 18.75:1 reduction for a speed of close to 29 mph. For me 15.88:1 would only be a good down hill gear.

Now if you and your bike was a 100 lbs lighter than my bike and me on level ground only then that ratio may have been good for you. However here in Tennessee with only 1.6 hp at a 15.88 reduction you'll blow your engine or at the minimum burn the clutch out trying to climb a 30%+ grade hill.

When you use the system I've setup it then isn't complicated at all.

Red gears
Load pulling, hill climbing
1(1-3)

Yellow gears
Aroundtown general use.
2(3-5)

Green gears
Open road use.
3(5-7)

20210426_173548.jpg


The only time chainrings will be shifted is when either using sprockets (3) or (5). All shifting is done with the left hand.

Next month I'll be modifying the trigger shifter to were the bottom lever will also be up top eliminating the need to reach to the bottom side of the shifter. This will be the shift knob. I also use a tachometer to know exactly when to shift gears.

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Last edited:

Mike St

Active Member
Joined
Jun 16, 2008
Messages
499
You have to understand the engineering beauty of what I did. The ratios can
easily be modified by changing out the drive sprocket on the gearbox. It takes
9,11,14,17,25 tooth sprockets. You can change out the sprockets until you're
satisfied with the performance, and it's 78mm, fits all the motors with 78mm
clutches. That's it in the picture. Thatsdax once used it to mount a motor on the
side and rear but I have it more centered on the bike.
 

Sidewinder Jerry

Well-Known Member
Joined
Mar 14, 2011
Messages
2,256
You have to understand the engineering beauty of what I did. The ratios can
easily be modified by changing out the drive sprocket on the gearbox. It takes
9,11,14,17,25 tooth sprockets. You can change out the sprockets until you're
satisfied with the performance, and it's 78mm, fits all the motors with 78mm
clutches. That's it in the picture. Thatsdax once used it to mount a motor on the
side and rear but I have it more centered on the bike.
Here I'm not trying to take away from what you've done. Your system is fine for flat landers and light to middle weights. However in a mountainous region and being a heavy weight with low hp engines you have to have a wide reduction range.

It takes less than 2 seconds for me to switch to a more efficient ratio for a given terrain. What you might want to consider is doing a shift kit build running your drive system through a 3 or 5 speed IGH????
 

Mike St

Active Member
Joined
Jun 16, 2008
Messages
499
OK, I admit my system may not be the best for hills, but I live in
the Midwest where it's flat as can be. No hills, mountains, just
sweet flat land and endless prairies. I was never interested in
shift kits. They don't appeal to me, but thanks for the suggestion.
 

Sidewinder Jerry

Well-Known Member
Joined
Mar 14, 2011
Messages
2,256
OK, I admit my system may not be the best for hills, but I live in
the Midwest where it's flat as can be. No hills, mountains, just
sweet flat land and endless prairies. I was never interested in
shift kits. They don't appeal to me, but thanks for the suggestion.
I lived in Texas I understand flat, you can see the dust trail from a vehicle 2 miles away lol
 

JerryAssburger

Active Member
Joined
Apr 20, 2017
Messages
155
Jerry, I calculate your theoretical top speed with a 32 T rear sprocket at 33.7 mph.
The problem is at this gearing, your torque will be too low for the power you
have. Definitely, I would boost the power of the motor. The lowest on this
setup should really be no lower than 36T, 41t better. If the engine is
governed, the rpms will be limited. You'd have to purchase the Grubee
ungoverned HS 144 to go higher but it wouldn't fit the belt drive, so
there is no real option to go faster. One more point, the Project Farm
guy is using a 3:1 gearbox, which would give him extremely poor
torque. You're using a 5:1 belt drive.
Since most people are getting 30 - 35 mph out of these things for a top speed, I'd think being geared for 33 mph @ 6800 rpm should be right on the money. I have no appreciable hills to climb where I ride. The torque, or acceleration has been decent, except I can tell there is a lean spot 1/2-full throttle, pointing to the main jet being a little small. Again, this thing is still in the "being babied" mode until I can go back through and make sure it's all buttoned down. To be honest, I've still gotta re-lube the bushing, change out the plug for the NGK I just bought, etc.... Work has been pretty busy (lots of mandatory OT) so I really haven't had the time to tweak this thing.

I PROMISE I will detail the results, ASAP, though.
 

JerryAssburger

Active Member
Joined
Apr 20, 2017
Messages
155
I lived in Texas I understand flat, you can see the dust trail from a vehicle 2 miles away lol
Hehehe! "I understand flat" is an understatement! Good one!

My Uncle lived in Odessa.... the outside pictures he sent always had that absolutely straight horizon line bicecting the background!
 

Mike St

Active Member
Joined
Jun 16, 2008
Messages
499
Ok, you're doing the perfect experiment. Now what you have to do is reem the carb
and put holes in the carb cover. Follow my post how to boost the power so you can
get more low end torque, which you need with a 32 t rear sprocket. This is a great
experiment to see if 32T is suitable. Very interested the result.
 

Will'smotobikes19

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Joined
Apr 9, 2018
Messages
2,152
a speed of close to 29 mph.
That's exactly what I got with a stock gebe kit on a Schwinn mountain bike. around 28-29mph but the thing was pretty lightweight. It just didn't have enough power for hills. I'd rather stay in the 40-49cc range and maybe bigger engines. The bike is long gone now. This was like 3-4 years ago already. Don't get me wrong its a great engine but I'd rather have a larger version of it or put it on a weed wacker. Random people ask me if the huasheng 49cc is a weed wacker engine. Kinda triggers since why would a weed wacker engine have a solid mounting base. To be correct its really a water pump engine.

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