Home > Kids Scooters > I’m building a kick scooter with 33 cc chainsaw engine and I need the correct gear ratio. ?

Ballin Steve February 24, 2010 at 8:51 pm

The thing is 33cc is not a whole lot but I would go wit a 64 and 18,my scooter had 22 and 72

TXm42 February 24, 2010 at 9:19 pm

Man,,,that’s a crazy High gear ratio.
Like,Ultra Mega Overdrive(from hell)

44×18=2.44 ratio

Assuming 7,000 Rpm,,,,,and actual 10″ tire diameter…

That’s worth 85mph !!
It’ll never do that,,,can’t pull that.
So it’s gonna act like it’s trying to pull tree stumps.
………………………………………..

You are gonna need to target 25~30mph MAX in order to have any acceleration.

7:1 ratio would give you right at 30mph
(about 3X Lower than what ya have now)

8:1 would be about 26mph
9:1 = about 23mph

7:1 would be like a 10T Drive sprkt x 70T Wheel Gear.
8:1 = 9T x 72T,,,or 10 x 80,,or 12T x 96T
9:1,,,,would be ,,,,,,darn near>>
“No Teeth on Front,,,and a REAR Sprkt bigger diameter than tire”.
Allllmost THAT exagerated.

As you can see ,,,to get it Low enough with a single reduction pair becomes Impractical-to-Impossible,real quick.

An intermediate reduction is really best way to go, and virtually Necessary.
Simplest way is via a “jack shaft” set-up

,,,,,,,,,,,,,,,,,,,,,
Using your 18T Drive Sprkt for an example:
Ok,,,coupled straight to the 44T,,,that was a 2.44:1.
Way too high.

But if used with a jackshaft,,,
Your 18T into a 36T would be 2:1 PRIMARY Ratio

Then on the Output of the Jackshaft,,,,
lets say an 11T into your 44T Rear sprkt.
That’s a 4:1 Secondary,,or Final Drive ratio

2:1 Primary x 4:1 Secondary =8:1 Overall

There’s your 8:1,,,good for 25~26 mph with a 10″ Diameter tire and 7,000 Rpm motor

That’s PROBABLY still Too High for a 33cc Motor to be able to pull very strong.

15~20 mph SOUNDS dog slow.
On a Kick scooter,,,,,it AINT.

Generally speaking,,,You’d have Lots more FUN &SCOOT if geared LOWER for 15~20 Top Speed,,,,
rather than fallin’ asleep while waiting for it to pull up to 25~30mph

Whatever—,,,
but with the Jackshaft setup,,,it’s Lots easier and Cheaper to change the Output Drive Gear to gear it Higher/lower.

Gears are about $10 each,,,more/less

So you can better afford to “experiment” in order to find a Overall Ratio that works good for Your Motor AND You.

Dont waste your $$ at this point just to change from 44 to 56T.

Your Thinking is correct,,,and headed in right direction,,,
but in Real-World Terms it’s Sooo far OFF as-is,,,
a switch from 44 to 56 is almost “No Difference”,,,
and not even Close to where ya Need to be—less than Halfway.

Even a 10 x 56 is still only a 5.6:1.
that Calculates out to near 40mph.
Not only would it accell VERY sluggish Still,,,
That kinda speed on a Kick Scooter chassis can be nothing but seriously dangerous.

Ebay has some Jack Shaft Kits—-they are kinda Hi Priced w/ shipping.
You can find them cheaper lots of times Locally,,,or thru Online GoCart /
Mini-bike stores.

Have Fun,,,and be careful on that contraption

Chris AO bundaberg February 24, 2010 at 9:30 pm

i built mine friction drive, i used a 32cc talon straight shaft weed wakker line trimmer wipper snipper brush cutter motor.
on a 12 and a half inch wheel my total reduction 11:1and could do speeds of up to 60km/h 35+m/h at the time my weight was 90kg so that would be what 200lbs. they are now illegal where i live in queensland australia so it now just hangs in the shed.

Garfield February 24, 2010 at 9:49 pm

http://www.gokartracing.org/Calculate.htm

Hope this helps.